The large study from Nuevo and colleagues is very thought provoking. There was substantial between-site variation in response to various psychosis-screening items. Assuming that endorsement of these items is a mix of: 1) "true" psychotic-like experiences, 2) "true" responses that are understandable from the perspective of local cultures and beliefs, and 3) innocent misinterpretations of the questions, why is there such marked variation? For example, why do 46 percent of respondents from Nepal endorse at least one psychotic-like experience and a third report auditory hallucinations?

It seems self-evident that populations with strong religious and/or cultural beliefs related to psychotic-like experiences might endorse psychosis-screening items more readily (type 2 in the above list). But could it be feasible that these same populations might also “kindle” psychotic experiences in vulnerable people? This notion is pure speculation, but we should remain mindful that dopaminergic pathways related to psychosis are vulnerable to the process of endogenous sensitization (  Read more

The large study from Nuevo and colleagues is very thought provoking. There was substantial between-site variation in response to various psychosis-screening items. Assuming that endorsement of these items is a mix of: 1) "true" psychotic-like experiences, 2) "true" responses that are understandable from the perspective of local cultures and beliefs, and 3) innocent misinterpretations of the questions, why is there such marked variation? For example, why do 46 percent of respondents from Nepal endorse at least one psychotic-like experience and a third report auditory hallucinations?

It seems self-evident that populations with strong religious and/or cultural beliefs related to psychotic-like experiences might endorse psychosis-screening items more readily (type 2 in the above list). But could it be feasible that these same populations might also “kindle” psychotic experiences in vulnerable people? This notion is pure speculation, but we should remain mindful that dopaminergic pathways related to psychosis are vulnerable to the process of endogenous sensitization (Laruelle, 2000).

What does it mean to be a member of a cultural group that is more “prone” to psychotic-like experiences? Tanya Luhrmann, an anthropologist based at Stanford University, has examined individuals attending evangelical churches who “hear” the voice of God during prayer (Luhrmann et al., 2010). The vignettes suggest that some individuals reported more “hearing the voice of God” after improving their prayer skills. Practice makes perfect, but could it also kindle pathways related to schizophrenia?

Regardless of the underlying mechanisms, understanding variations in these symptoms is a fascinating topic worthy of more multidisciplinary research.

References:

Laruelle M. The role of endogenous sensitization in the pathophysiology of schizophrenia: implications from recent brain imaging studies. Brain Res Brain Res Rev. 2000;31(2-3):371-84. Abstract

Luhrmann TM, Nusbaum H, Thisted R. The absorption hypothesis: learning to hear God in evangelical Christianity. American Anthropologist. 2010;112 (1):66-78.

It seems to me that there may be two different patterns that show up in these large epidemiological studies: the psychotic continuum and phenomena associated with absorption. Absorption is basically a capacity for/interest in being caught up in your imagination. It is associated with hypnotizability and dissociation, but not identical to them (Tellegen and Atkinson, 1974).

In my own work on evangelical Christianity, I identify a pattern in which people report hallucination-like phenomena that are rare, brief, and not distressing (as opposed to the pattern associated with psychotic disorder, in which the hallucinations are often frequent, extended, and distressing). Those who report hearing God’s voice audibly or seeing the wing of an angel are also more likely to score highly on the Tellegen absorption scale (Luhrmann et al., 2010). This relationship between unusual experiences and absorption also shows up in a significant relationship between absorption and the Posey-Loesch hearing voices scale when these scales are given to...  Read more

It seems to me that there may be two different patterns that show up in these large epidemiological studies: the psychotic continuum and phenomena associated with absorption. Absorption is basically a capacity for/interest in being caught up in your imagination. It is associated with hypnotizability and dissociation, but not identical to them (Tellegen and Atkinson, 1974).

In my own work on evangelical Christianity, I identify a pattern in which people report hallucination-like phenomena that are rare, brief, and not distressing (as opposed to the pattern associated with psychotic disorder, in which the hallucinations are often frequent, extended, and distressing). Those who report hearing God’s voice audibly or seeing the wing of an angel are also more likely to score highly on the Tellegen absorption scale (Luhrmann et al., 2010). This relationship between unusual experiences and absorption also shows up in a significant relationship between absorption and the Posey-Loesch hearing voices scale when these scales are given to undergraduates. Among undergraduates, the rates for hallucination-like phenomena are also consistently far higher than the Nuevo paper reports, perhaps because neither the absorption scale nor the Posey-Loesch scale seems to probe for pathology (Luhrmann, forthcoming).

I am not the only one to have found a significant association between unusual sensory experiences and absorption. Aleman and Laroi (2008) report that a handful of other researchers have also found significant correlations between hallucination scales and the absorption scale. As a result of this work, I think that there may be different pathways to hallucination-like phenomena—some pathological, others less so.

Yet, I also wonder whether there is indeed something like “priming” psychosis, as John suggested. This would arise if there were some looseness in the relationship between psychosis and dissociation, which there appears to be. At least that's the way I interpret some of the phenomena that Romme and Escher (1993) report. If there is some kind of loose relationship, it would suggest that someone could have an absorption/dissociation response to trauma that would look psychotic; it might also suggest that an intensely absorbing negative imaginative experience (being pursued by demons, e.g.) might contribute to a vulnerable person exhibiting more psychotic-like symptoms.

How would we begin to pull this apart?

References:

Aleman A, Laroi F. Hallucinations: The science of idiosyncratic perception. Washington, DC: American Psychological Association, 2008.

Luhrmann TM. When God speaks back. New York: Knopf, forthcoming.

Luhrmann TM, Nusbaum H, Thisted R. The absorption hypothesis: learning to hear God in evangelical Christianity. American Anthropologist. 2010;112 (1):66-78.

Romme M, Escher S. Accepting voices. London: Mind, 1993.

Tellegen A, Atkinson G. Openness to absorbing and self-altering experiences (“absorption”): a trait related to hypnotic susceptibility. J Abnorm Psychol. 1974;83(3):268-77. Abstract

This beautifully written piece serves to excite interest in the fascinating epidemiology of schizophrenia. In our search for the “missing heritability” of schizophrenia, we don’t have to look too far for clues. There are many contained in this piece. It just requires some Sherlock Holmes-type deductive reasoning to put them all together now!

The realization that psychotic symptoms (or psychotic-like experiences) can be used as a proxy for schizophrenia risk has opened up new vistas for exploration (Kelleher and Cannon, 2010). For instance, the paper by Nuevo and colleagues will provide a fertile ground for testing ecological hypotheses on the etiology of schizophrenia—such as examining cross-national vitamin D levels (McGrath et al.) or fish oil consumption. Geneticists have yet to appreciate the potential value of studying such symptoms. Ian Kelleher, Jack Jenner, and I have argued in a recent editorial that the non-clinical psychosis phenotype provides us with a population in which to test hypotheses about the...  Read more

This beautifully written piece serves to excite interest in the fascinating epidemiology of schizophrenia. In our search for the “missing heritability” of schizophrenia, we don’t have to look too far for clues. There are many contained in this piece. It just requires some Sherlock Holmes-type deductive reasoning to put them all together now!

The realization that psychotic symptoms (or psychotic-like experiences) can be used as a proxy for schizophrenia risk has opened up new vistas for exploration (Kelleher and Cannon, 2010). For instance, the paper by Nuevo and colleagues will provide a fertile ground for testing ecological hypotheses on the etiology of schizophrenia—such as examining cross-national vitamin D levels (McGrath et al.) or fish oil consumption. Geneticists have yet to appreciate the potential value of studying such symptoms. Ian Kelleher, Jack Jenner, and I have argued in a recent editorial that the non-clinical psychosis phenotype provides us with a population in which to test hypotheses about the evolutionary benefit of psychosis genes (Kelleher et al., 2010; see also Nesse, 2004). This non-clinical psychosis phenotype gives rise to the possibility of moving beyond just-so stories into the realm of testable hypotheses.

References:

Kelleher I, Cannon M. Psychotic-like experiences in the general population: characterizing a high-risk group for psychosis. Psychol Med. 2010 May 19:1-6. Abstract

Kelleher I, Jenner JA, Cannon M. Psychotic symptoms in the general population - an evolutionary perspective. Br J Psychiatry. 2010 Sep;197(3):167-9.

Nesse RM. Cliff-edged fitness functions and the persistence of schizophrenia. Behav Brain Sci. 2004;27:862-3.

With interest, I read Victoria Wilcox's summary of some thought-provoking papers published this year. It seems that schizophrenia, like cancer, has many different causes. I would like to point out that three of the studies (Zammit et al., 2010; Wicks et al., 2010; Schofield et al., 2010) support the idea that social defeat and/or social exclusion increase risk. The paper by Zammit et al. showed this in an elegant way: being different from the mainstream, no matter on what account, increased the subject's risk. The next step is to show that social exclusion has an impact on an individual's dopamine function. My group is examining this in young adults with an acquired hearing impairment, using SPECT.

References:

Zammit S, Lewis G, Rasbash J, Dalman C, Gustafsson J-E, Allebeck P. Individuals, schools, and neighborhood: a multilevel longitudinal study of variation in incidence of psychotic disorders. Arch Gen Psychiatry. 2010 Sep;67(9):914-22. Abstract

Wicks S, Hjern A, Dalman C. Social risk or genetic liability for psychosis? A study of children born in Sweden and reared by adoptive parents. Am J Psychiatry. 2010 Oct;167(10):1240-6. Epub 2010 Aug 4. Abstract

Schofield P, Ashworth M, Jones R. Ethnic isolation and psychosis: re-examining the ethnic density effect. Psychol Med. 2010 Sep 22:1-7. Abstract

View all comments by Jean-Paul Selten

I have been collecting diverse references for environmental risk factors in schizophrenia at Schizophrenia Risk Factors. These include many prenatal influences due to maternal infection, usually with some sort of virus, or immune activation with fever. Several animal studies have shown that infection or immune activation in mice can produce schizophrenia-like symptoms in the offspring. Toxoplasmosis has often been cited as a risk factor in adulthood.

Many of the genes implicated in schizophrenia are also involved in the life cycles of these pathogens, and interactions between genes and risk factors can together contribute to endophenotypes; for example, MICB and Herpes simplex infection have single and combined effects on grey matter volume in the prefrontal cortex.

Over 600 genes have been associated with schizophrenia. When these were pumped through a Kegg pathway analysis, the usual suspects (neuregulin, dopamine, and glutamate pathways, among others) figure highly in the   Read more

I have been collecting diverse references for environmental risk factors in schizophrenia at Schizophrenia Risk Factors. These include many prenatal influences due to maternal infection, usually with some sort of virus, or immune activation with fever. Several animal studies have shown that infection or immune activation in mice can produce schizophrenia-like symptoms in the offspring. Toxoplasmosis has often been cited as a risk factor in adulthood.

Many of the genes implicated in schizophrenia are also involved in the life cycles of these pathogens, and interactions between genes and risk factors can together contribute to endophenotypes; for example, MICB and Herpes simplex infection have single and combined effects on grey matter volume in the prefrontal cortex.

Over 600 genes have been associated with schizophrenia. When these were pumped through a Kegg pathway analysis, the usual suspects (neuregulin, dopamine, and glutamate pathways, among others) figure highly in the list of pathways. Immune-related pathways are also highly represented, as are many pathogen entry pathways, including that for toxoplasmosis, which heads the list. Some of the more exotic pathways, for example, Chaga’s disease, should be considered as generic, as well as specific.

These Kegg-generated data suggest that there are strong relationships between genes and risk factors. Perhaps stratification of GWAS data in relation to infection could take this into account.

References:

Bortolato M, Godar SC. Animal models of virus-induced neurobehavioral sequelae: recent advances, methodological issues, and future prospects. Interdiscip Perspect Infect Dis . 2010 Jan 1 ; 2010():380456. Abstract

Carter CJ. Schizophrenia susceptibility genes directly implicated in the life cycles of pathogens: cytomegalovirus, influenza, herpes simplex, rubella, and Toxoplasma gondii. Schizophr Bull . 2009 Nov 1 ; 35(6):1163-82. Abstract

Fatemi SH, Emamian ES, Kist D, Sidwell RW, Nakajima K, Akhter P, Shier A, Sheikh S, Bailey K. Defective corticogenesis and reduction in Reelin immunoreactivity in cortex and hippocampus of prenatally infected neonatal mice. Mol Psychiatry . 1999 Mar 1 ; 4(2):145-54. Abstract

Fatemi SH, Pearce DA, Brooks AI, Sidwell RW. Prenatal viral infection in mouse causes differential expression of genes in brains of mouse progeny: a potential animal model for schizophrenia and autism. Synapse . 2005 Aug 1 ; 57(2):91-9. Abstractx

Ozawa K, Hashimoto K, Kishimoto T, Shimizu E, Ishikura H, Iyo M. Immune activation during pregnancy in mice leads to dopaminergic hyperfunction and cognitive impairment in the offspring: a neurodevelopmental animal model of schizophrenia. Biol Psychiatry . 2006 Mar 15 ; 59(6):546-54. Abstract

Prasad KM, Bamne MN, Shirts BH, Goradia D, Mannali V, Pancholi KM, Xue B, McClain L, Yolken RH, Keshavan MS, Nimgaonkar VL. Grey matter changes associated with host genetic variation and exposure to Herpes Simplex Virus 1 (HSV1) in first episode schizophrenia. Schizophr Res . 2010 May 1 ; 118(1-3):232-9. Abstract

Yolken RH, Torrey EF. Are some cases of psychosis caused by microbial agents? A review of the evidence. Mol Psychiatry . 2008 May 1 ; 13(5):470-9. Abstract

Zuckerman L, Weiner I. Maternal immune activation leads to behavioral and pharmacological changes in the adult offspring. J Psychiatr Res . 2005 May 1 ; 39(3):311-23. Abstract

Questions on the different rates of occurrence of the schizophrenia spectrum of brain disorders between northern (developed) and southern underdeveloped countries, between urban and rural, as well as the birth order within the family of those suffering from schizophrenia are important ones.

However, when thinking about family exposure to environmental factors, I think that there is much to learn from social science. Say that a 1970s family moved from the country to the city just at the time when the birth control pill had been developed and began to be widely available in urban industrialized areas: Estrogen levels on the early formulations of the "pill" were too high, causing women to search for other legal birth control methods which they could tolerate more easily. About the only other things that doctors could offer women back then were the highly touted IUDs.

Say also that a woman tried the birth control pill but, because her taking of the pill was spotty, she became pregnant with her first child. After delivering their first children, many 1970s women then...  Read more

Questions on the different rates of occurrence of the schizophrenia spectrum of brain disorders between northern (developed) and southern underdeveloped countries, between urban and rural, as well as the birth order within the family of those suffering from schizophrenia are important ones.

However, when thinking about family exposure to environmental factors, I think that there is much to learn from social science. Say that a 1970s family moved from the country to the city just at the time when the birth control pill had been developed and began to be widely available in urban industrialized areas: Estrogen levels on the early formulations of the "pill" were too high, causing women to search for other legal birth control methods which they could tolerate more easily. About the only other things that doctors could offer women back then were the highly touted IUDs.

Say also that a woman tried the birth control pill but, because her taking of the pill was spotty, she became pregnant with her first child. After delivering their first children, many 1970s women then turned to IUDs, which did not cause bloating or the other nasty physical side effects of the pill. What IUDs did have was a hidden wicking string. Those strings were ladders for infection moving into the uterus. So when thinking of environmental factors at the level of the family, one has to ask broad-spectrum socioeconomic questions about what families were actually up against in the 1970s.

Birth control methods could also add insight into why schizophrenia was identified in the late 1800s, a time when women were moving into paid labor outside the home. It had been common knowledge since ancient times that any foreign object inserted into the uterus (IUD) would interfere with pregnancy. Working women had to limit the number of children they had. There was information-sharing among female coworkers.

Think about the implications of IUD use in Catholic countries such as Ireland, which has a high rate of schizophrenia. Catholic mothers of schizophrenics would be loath to discuss birth control methods used prior to or during the birth of a child born with schizophrenia. Moreover, during the Dalkon Shield scandal and IUD birth defect lawsuits of the 1970s and 1980s, the schizophrenias did not get any coverage because children born with these disorders hadn't reached the age of onset yet.

I am a parent of a second-born adult daughter suffering from schizophrenia. Families, especially mothers, do not want to go back to the days when it was said that bad mothering caused schizophrenia. Yet, we who carried these children to term have to ask ourselves what was different going into and throughout these pregnancies?

Skilled researchers need to formulate and ask probing questions about what the mother was exposed to prior to and during these pregnancies.

This excellent review confirms the previous meta-analysis by Henquet et al. (2005) and as such does not add anything new. The importance lies in the UK context: previously the Lancet has been mostly skeptical with regard to this issue. The fact that the leading UK medical journal now also allows these findings to see daylight is a significant event and helps stimulate further funding for the effort that several groups worldwide have started working on over the last five years: the search for the mechanism explaining the link.

View all comments by Jim van Os

It is reassuring to see that the results of the latest meta-analysis (Moore et al., 2007) are consistent with previous meta-analyses, and that the various meta-analyses are broadly consistent with the now much-tortured primary data. Despite the meta-analysis fatigue, the results are too important to ignore.

When thinking about the impact of cannabis on schizophrenia frequency measures, it is important to remember that cannabis use may translate to an increase in the prevalence of active psychosis via two mechanisms. The data suggest that as the prevalence of cannabis use increases in a population, the incidence of schizophrenia should also increase (Hickman et al., 2007). Furthermore, in those with established schizophrenia, cannabis use is associated with poorer outcomes (i.e., reduced remission rates). Thus, from a modeling perspective, increased cannabis use could lead to an increase in the prevalence of active psychosis via two mechanisms (i.e., increased “inflow” and...  Read more

It is reassuring to see that the results of the latest meta-analysis (Moore et al., 2007) are consistent with previous meta-analyses, and that the various meta-analyses are broadly consistent with the now much-tortured primary data. Despite the meta-analysis fatigue, the results are too important to ignore.

When thinking about the impact of cannabis on schizophrenia frequency measures, it is important to remember that cannabis use may translate to an increase in the prevalence of active psychosis via two mechanisms. The data suggest that as the prevalence of cannabis use increases in a population, the incidence of schizophrenia should also increase (Hickman et al., 2007). Furthermore, in those with established schizophrenia, cannabis use is associated with poorer outcomes (i.e., reduced remission rates). Thus, from a modeling perspective, increased cannabis use could lead to an increase in the prevalence of active psychosis via two mechanisms (i.e., increased “inflow” and decreased “outflow”) (McGrath and Saha, 2007).

The prevalence of active psychosis in the community may be “under the influence” of cannabis from more than one perspective.

References:

Moore THM, Zammit S, Lingford-Hughes A, Barnes TRE, Jones PB, Burke M, Lewis G. Cannabis use and risk of psychotic or affective mental health outcomes: A systematic review. Lancet. 2007 July 28; 370:319-328. Abstract

McGrath J, Saha S. Thought experiments on the incidence and prevalence of schizophrenia “under the influence” of cannabis. Addictions 2007 Apr;102(4):514-5. Abstract

Hickman M, Vickerman P, Macleod J, Kirkbride J, Jones PB. Cannabis and schizophrenia: model projections of the impact of the rise in cannabis use on historical and future trends in schizophrenia in England and Wales. Addiction. 2007 Apr;102(4):597-606. Abstract

The recent meta-analysis in the Lancet (Moore et al., 2007) regarding cannabis use and psychotic or affective mental health outcomes is, indeed, a necessary contribution. It is the first systematic review restricted to longitudinal studies of cannabis use and mental health outcomes. For this addition to the contours of the literature, Zammit and colleagues are to be commended.

We may be more optimistic than the authors, however, about the potential for future longitudinal studies to shed further light on the question of causality, and perhaps more cautious about the present state of the evidence. Given the public health and policy implications, we propose a concerted effort to complete observational studies that are designed to rule out the main alternative explanations for the association (e.g., genetic or social factors that independently influence both cannabis use and psychosis). The Swedish conscript study (Zammit et al., 2002) is a fine example of one such study. We should...  Read more

The recent meta-analysis in the Lancet (Moore et al., 2007) regarding cannabis use and psychotic or affective mental health outcomes is, indeed, a necessary contribution. It is the first systematic review restricted to longitudinal studies of cannabis use and mental health outcomes. For this addition to the contours of the literature, Zammit and colleagues are to be commended.

We may be more optimistic than the authors, however, about the potential for future longitudinal studies to shed further light on the question of causality, and perhaps more cautious about the present state of the evidence. Given the public health and policy implications, we propose a concerted effort to complete observational studies that are designed to rule out the main alternative explanations for the association (e.g., genetic or social factors that independently influence both cannabis use and psychosis). The Swedish conscript study (Zammit et al., 2002) is a fine example of one such study. We should also be considering natural experiments and designs based on instrumental variables enabled by in order to complement this work. For instance, we might capitalize on situations created by policy changes that affect the availability—and therefore use—of cannabis in order to examine the impact on the development of psychosis. Whether at the individual or the population level, both creativity and rigor are required.

References:

Moore TH, Zammit S, Lingford-Hughes A, Barnes TR, Jones PB, Burke M, Lewis G. Cannabis use and risk of psychotic or affective mental health outcomes: a systematic review. Lancet. 2007 Jul 28;370(9584): 319-28. Abstract

Zammit S, Allebeck P, Andreasson S, Lundberg I, Lewis G. Self reported cannabis use as a risk factor for schizophrenia in Swedish conscripts of 1969: historical cohort study. BMJ. 2002 Nov 23;325 (7374):1199. Abstract

Current interest in cannabis and the onset of psychosis is laudable. The Lancet paper no doubt establishes a causal link based upon what has been known in the literature (Raphael et al., 2005; Roberts et al., 2007; Rey et al., 2004; Wittchen et al., 2007). The authors need to be congratulated for taking extreme care to incorporate most of the studies and also for making conclusions with a sense of skepticism. That is where further questions arise.

1. Cannabis is used only in certain cultures and known to be involved in a maximum 50 percent of cases of psychosis, schizophrenia, and schizophreniform psychosis (Gregg et al., 2007). In that sense, are there two different phenotypes of schizophrenia, a) where exposure to cannabis is necessarily a factor and b) where a different set of potentiating or precipitating factors work, not cannabis?

2. Even if we focus only on the first...  Read more

Current interest in cannabis and the onset of psychosis is laudable. The Lancet paper no doubt establishes a causal link based upon what has been known in the literature (Raphael et al., 2005; Roberts et al., 2007; Rey et al., 2004; Wittchen et al., 2007). The authors need to be congratulated for taking extreme care to incorporate most of the studies and also for making conclusions with a sense of skepticism. That is where further questions arise.

1. Cannabis is used only in certain cultures and known to be involved in a maximum 50 percent of cases of psychosis, schizophrenia, and schizophreniform psychosis (Gregg et al., 2007). In that sense, are there two different phenotypes of schizophrenia, a) where exposure to cannabis is necessarily a factor and b) where a different set of potentiating or precipitating factors work, not cannabis?

2. Even if we focus only on the first possibility, there are few unanswered questions such as, what are the concurrent clinical conditions along with cannabis abuse? Do these patients have cognitive dysfunction? Is that reflective of broader brain mechanism changes?

3. There seems to be no reliable biological explanation as to why exposure to cannabis should precipitate psychosis. Cannabis is one of the most commonly used illicit drugs. Its active compound “cannabidols” has 64 active isomers, each having differing effects on health and behavior. There is strong support for a link between cannabis and development—exacerbation of psychosis as well as other mental health conditions (e.g., anxiety, depression). Further research is needed to determine the underlying neurochemical processes and their possible contributions to etiology, as well as the social factors that contribute to the increasing use of cannabis by young people.

4. There is a theory that preexisting cognitive dysfunction is a core feature of schizophrenia. Accepting this, there are no studies to show “causal relationship” between cannabis and cognitive dysfunction.

The current levels of information and understanding, though collected over last 25-30 years of research, are far from adequate to establish any direct relationship except “mere association.” It is hoped that more precise biological, imaging, and neuropsychological studies would be able to throw fresh light on this important area of research.

Acute cannabis administration can induce memory impairments, sometimes persisting months following abstinence. There is no evidence that residual effects on cognition remain after years of abstinence. The scarce literature on neuroimaging, mainly done in non-psychotic populations, shows little evidence that cannabis has effects on brain anatomy. Acute effects of cannabis include increases of cerebral blood flow, whereas long-term effects of cannabis include attenuation of cerebral blood flow. In animals Δ9-tetrahydrocannabinol enhances dopaminergic neurotransmission in brain regions known to be implicated in psychosis. Studies in humans show that genetic vulnerability may add to increased risk of developing psychosis and cognitive impairments following cannabis consumption. Δ9-tetrahydrocannabinol induces psychotic-like states and memory impairments in healthy volunteers (Linszen et al., 2007).

On the basis of six studies, it is concluded that there was insufficient evidence to prove conclusively that long-term cannabis use causes or does not cause residual abnormalities. The results of several reviews were also inconclusive as to whether cannabis use during adolescence may have a lasting effect on cognitive functioning and brain structure. However, it could not rule out that a) certain cognitive and cerebral abnormalities existed in patients before cannabis use began and b) that patients were suffering from subacute effects of cannabis (Weeda et al., 2006).

Continued cannabis use by persons with schizophrenia predicts a small increase in psychotic symptom severity but not vice versa (Degenhardt et al., 2007). Currently, there is a lot of interest in cannabis use as a risk factor for the development of schizophrenia. Cognitive dysfunction associated with long-term or heavy cannabis use is similar in many respects to the cognitive endophenotypes that have been proposed as vulnerability markers of schizophrenia. In this situation, we need to examine the similarities between these in the context of the neurobiology underlying cognitive dysfunction, particularly implicating the endogenous cannabinoid system, which plays a significant role in attention, learning, and memory, and in general, inhibitory regulatory mechanisms in the brain. Closer examination of the cognitive deficits associated with specific parameters of cannabis use and interactions with neurodevelopmental stages and neural substrates will better inform our understanding of the nature of the association between cannabis use and psychosis. The theoretical and clinical significance of further research in this field is enhancing our understanding of underlying pathophysiology and improving the provision of treatments for substance use and mental illness (Solowij et al., 2007). Many studies now show a robust and consistent association between cannabis consumption and the ulterior development of psychosis. Furthermore, our better understanding of cannabis biology allows the proposal of a plausible hypothetical model, based notably on possible interactions between cannabis and dopaminergic neurotransmission (Jockers-Scherubl, 2006). Do they suffer from other disorders, which are underlying or may be causal or comorbid, and do these comorbid conditions also have neurocognitive changes, e.g., psychosis, ADHD, LD, Tourette disorder, and other movement disorders, or depression? Is there an interrelationship among these factors to cause abuse and degree of cannabis consumption?

References:

Raphael B, Wooding S, Stevens G, Connor J. Comorbidity: cannabis and complexity. J Psychiatr Pract. 2005 May; 11(3): 161-7.

Roberts RE, Roberts CR, Xing Y. Comorbidity of substance use disorders and other psychiatric disorders among adolescents: Evidence from an epidemiologic survey. Drug Alcohol Depend. 2007 Apr;88 Suppl 1:S4-13. Epub 2007 Feb 1. Abstract

Rey JM, Martin A, Krabman P. Is the party over? Cannabis and juvenile psychiatric disorder: the past 10 years. J Am Acad Child Adolesc Psychiatry. 2004 Oct; 43(10): 1194-205. Abstract

Wittchen HU, Frohlich C, Behrendt S. Cannabis use and cannabis use disorders and their relationship to mental disorders: A 10-year prospective-longitudinal community study in adolescents. Drug Alcohol Depend. 2007 Apr;88 Suppl 1:S60-70. Epub 2007 Jan 25. Abstract

Gregg L, Barrowclough C, Haddock G. Reasons for increased substance use in psychosis. Clin Psychol Rev. 2007 May;27(4):494-510. Epub 2007 Jan 19. Abstract

Linszen D, van Amelsvoort T. Cannabis and psychosis: an update on course and biological plausible mechanisms. Curr Opin Psychiatry. 2007 Mar; 20(2): 116-20. Abstract

Weeda MR, Peters BD, De Haan L, Linszen DH. Residual neuropsychological, structural and functional brain abnormalities after long-term cannabis use] Tijdschr Psychiatr. 2006; 48(3): 185-93. Abstract

Degenhardt L, Tennant C, Gilmour S, Schofield D, Nash L, Hall W,McKay D. The temporal dynamics of relationships between cannabis, psychosis and depression among young adults with psychotic disorders: findings from a 10-month prospective study. Psychol Med. 2007 Feb 9; 1-8.

Solowij N, Michie PT. Cannabis and cognitive dysfunction: parallels with endophenotypes of schizophrenia? J Psychiatry Neurosci. 2007 Jan; 32(1): 30-52. Abstract

Jockers-Scherubl MC. [Schizophrenia and cannabis consumption: epidemiology and clinical symptoms] Prax Kinderpsychol Kinderpsychiatr. 2006; 55(7): 533-43. Abstract

Curtis L, Rey-Bellet P, Merlo MC. [Cannabis and psychosis] Rev Med Suisse. 2006 Sep 20; 2(79): 2099-100, 2102-3.

Costentin J. [Neurobiology of cannabis--recent data enlightening driving disturbances] Ann Pharm Fr. 2006 May; 64(3): 148-59. Abstract

Tracking down the agent(s) responsible for the elusive “migrant” effect in schizophrenia bears similarities with the clever plot twists in a well-crafted crime novel. The new study by Jeremy Coid and coworkers makes substantial headway toward narrowing down the list of suspects, with the spotlight increasingly focused on ethnicity. The current venture has a number of outstanding strengths: large sample size, robust denominator data, and stringent methods of case ascertainment, including leakage analysis. The choice of venue of East London, an area characterized by socioeconomic deprivation, is a strategic advantage, in that the effect of ethnicity can be teased out from socioeconomic disadvantage. The findings indicate that ethnicity had a stronger effect on risk magnitude than did generational status (i.e., place of birth). Black Caribbeans were the only ethnic group where generational status “mattered,” an effect that the authors attribute to differences in the age structures of the underlying populations at risk.

How best to interpret these results, and where do...  Read more

The findings from Lederbogen et al. are very thought provoking. The dissociation between the fMRI correlates of current versus early life urbanicity is unexpected. The authors have replicated their finding in an independent sample, reducing the chance that the finding was a type 1 error.

It is heartening to see important clues from epidemiology influencing fMRI research design. With respect to schizophrenia, the findings provide much-needed clues to the neurobiological correlates of urban birth (Pedersen and Mortensen, 2001; Pedersen and Mortensen, 2006; Pedersen and Mortensen, 2006). Somewhat to the embarrassment of the epidemiology research community, the link between urban birth and risk of schizophrenia has been an area of research where the strength of the empirical evidence has been much stronger than hypotheses proposed to explain the findings (McGrath and Scott, 2006;   Read more

The findings from Lederbogen et al. are very thought provoking. The dissociation between the fMRI correlates of current versus early life urbanicity is unexpected. The authors have replicated their finding in an independent sample, reducing the chance that the finding was a type 1 error.

It is heartening to see important clues from epidemiology influencing fMRI research design. With respect to schizophrenia, the findings provide much-needed clues to the neurobiological correlates of urban birth (Pedersen and Mortensen, 2001; Pedersen and Mortensen, 2006; Pedersen and Mortensen, 2006). Somewhat to the embarrassment of the epidemiology research community, the link between urban birth and risk of schizophrenia has been an area of research where the strength of the empirical evidence has been much stronger than hypotheses proposed to explain the findings (McGrath and Scott, 2006; March et al., 2008). The new findings should trigger more focused research exploring the fMRI correlates in urban- versus rural-born individuals with schizophrenia.

References:

March D, Hatch SL, Morgan C, Kirkbride JB, Bresnahan M, Fearon P, Susser E. Psychosis and place. Epidemiol Rev . 2008 Jan 1 ; 30():84-100. Abstract

McGrath J, Scott J. Urban birth and risk of schizophrenia: a worrying example of epidemiology where the data are stronger than the hypotheses. Epidemiol Psichiatr Soc . 2006 Oct-Dec ; 15(4):243-6. Abstract

Pedersen CB, Mortensen PB. Evidence of a dose-response relationship between urbanicity during upbringing and schizophrenia risk. Arch Gen Psychiatry . 2001 Nov 1 ; 58(11):1039-46. Abstract

Pedersen CB, Mortensen PB. Are the cause(s) responsible for urban-rural differences in schizophrenia risk rooted in families or in individuals? Am J Epidemiol . 2006 Jun 1 ; 163(11):971-8. Abstract

Pedersen CB, Mortensen PB. Urbanization and traffic related exposures as risk factors for schizophrenia. BMC Psychiatry . 2006 Jan 1 ; 6():2. Abstract

The study by Lederbogen et al. linking neural processes to epidemiology opens up an exciting avenue of inquiry, It suggests that exposure to urban upbringing could modify brain activity. Whether that could lead to schizophrenia per se remains to be seen.

Still, one might want to keep in mind that there is no evidence that urban-rural differences in schizophrenia risk are causally related to individual exposure. Pedersen and Mortensen (2006) showed that the association between urban upbringing and the development of schizophrenia is attributable both to familial-level factors as well as individual-level factors. Thus, the link between urbanicity and schizophrenia may be mediated by genetic factors, and if so, the social stressors shown by Lederbogen may in turn be related to those same genes.

Although it might be tempting to speculate whether Lederbogen’s findings have implications for migrant research, the “migrant effect” does not seem neatly explained by urban birth/upbringing. To the contrary, our findings show that the...  Read more

The study by Lederbogen et al. linking neural processes to epidemiology opens up an exciting avenue of inquiry, It suggests that exposure to urban upbringing could modify brain activity. Whether that could lead to schizophrenia per se remains to be seen.

Still, one might want to keep in mind that there is no evidence that urban-rural differences in schizophrenia risk are causally related to individual exposure. Pedersen and Mortensen (2006) showed that the association between urban upbringing and the development of schizophrenia is attributable both to familial-level factors as well as individual-level factors. Thus, the link between urbanicity and schizophrenia may be mediated by genetic factors, and if so, the social stressors shown by Lederbogen may in turn be related to those same genes.

Although it might be tempting to speculate whether Lederbogen’s findings have implications for migrant research, the “migrant effect” does not seem neatly explained by urban birth/upbringing. To the contrary, our findings show that the dose-response relationship between urbanization and schizophrenia (Pedersen and Mortensen, 2001) could be replicated only among persons born in Denmark whose parents had both been born in Denmark, and not in second-generation immigrants (Cantor-Graae and Pederson, 2007). Second-generation immigrants had an increased risk of developing schizophrenia independently of urban birth/upbringing (Cantor-Graae and Pedersen, 2007).

References:

Pedersen CB, Mortensen PB. Are the cause(s) responsible for urban-rural differences in schizophrenia risk rooted in families or in individuals? Am J Epidemiol. 2006; 163:971-8. Abstract

Pedersen CB, Mortensen PB. Evidence of a dose-response relationship between urbanicity during upbringing and schizophrenia risk. Arch Gen Psychiatry. 2001; 58:1039-46. Abstract

Cantor-Graae E, Pedersen CB. Risk of schizophrenia in second-generation immigrants: a Danish population-based cohort study. Psychol Med. 2007; 37:485-94. Abstract

There is increasing evidence that favors the prenatal beginning of schizophrenia (Gourion et al., 2004; Cannon and Murray, 1998; Wintour et al., 2006). This evidence points toward intrauterine environmental factors that act specifically during the second pregnancy trimester, producing direct damage of the brain of the fetus. The currently available technology doesn't allow us to observe what is happening at the cellular level, since the human brain is not available for direct analysis in that stage of life. Most of the techniques that have accumulated evidence of prenatal cerebral damage have been of low resolution and by means of indirect methods. It is necessary to have a technique with high resolution that allows for obtaining the necessary information on the brain of the fetus and of the environmental factors that surround him or her.

In 1977, we began direct research of the brain with schizophrenia with electron microscopic techniques, using the brains of deceased adult...  Read more

There is increasing evidence that favors the prenatal beginning of schizophrenia (Gourion et al., 2004; Cannon and Murray, 1998; Wintour et al., 2006). This evidence points toward intrauterine environmental factors that act specifically during the second pregnancy trimester, producing direct damage of the brain of the fetus. The currently available technology doesn't allow us to observe what is happening at the cellular level, since the human brain is not available for direct analysis in that stage of life. Most of the techniques that have accumulated evidence of prenatal cerebral damage have been of low resolution and by means of indirect methods. It is necessary to have a technique with high resolution that allows for obtaining the necessary information on the brain of the fetus and of the environmental factors that surround him or her.

In 1977, we began direct research of the brain with schizophrenia with electron microscopic techniques, using the brains of deceased adult schizophrenic patients, animals experimentally inoculated with cerebrospinal fluid from schizophrenic patients, and fetuses of schizophrenic mothers. The obtained results guide toward a viral etiology of the illness, specifically by herpes simplex hominis type 1 virus (Mesa-Castillo, 2001; Mesa-Castillo, 2011). Later results of other authors using other techniques and research designs relate damage of the brain to the direct action of a virus or indirect immunologic damage (Fruntes and Limosin, 2008; Brown et al., 2004; Shi et al., 2005). The objective of our research was not only to study the brain of the fetus, but also the environment that surrounds him or her; thus, we studied both the brain of the fetus and the placenta during the second trimester of schizophrenic mothers whose pregnancies were interrupted for medical indications.

References:

Gourion D, Gourevitch R, Leprovost JB, Olie H loo JP, Krebs MO. Neurodevelopmental hypothesis in schizophrenia. Encephale 2004; 30: 109-118. Abstract

Cannon M, Murray MR. Neonatal origins of schizophrenia. Arch Dis Child 1998; 78: 1-3. Abstract

Wintour EM, Owens AJ. Early Life Origins of Health and Disease. Auckland, New Zealand: Eurekah.com and Springer Science + Business Media; 2006.

Mesa-Castillo S. An ultrastructural study of the temporal lobe and peripheral blood in schizophrenic patients. Rev Neurol. 2001; 33: 619-23. Abstract

Mesa-Castillo S. Direct evidence of herpes simples hominis type I virus in the temporal lobe of schizophrenic patients, their offspring and experimental animals. Boletín de esquizofrenia y otras psicosis. 2011.

Fruntes V, Limosin F. Schizophrenia and viral infection during neurodevelopment: A pathogenesis model? Med Sci Monit 2008; 14: 71-77. Abstract

Brown AS, Begg MD, Gravenstein S, Schaefer CA, Wyatt RJ. Serologic evidence of prenatal influenza in the etiology of schizophrenia. Arch Gen Psychiatry 2004; 61: 774-780. Abstract

Shi L, Tu N, Patterson PH. (2005): Maternal influenza infection is likely to alter fetal brain development indirectly: The virus is not detected in the fetus. Int J Dev Neurosci 23: 299-305. Abstract

Mannheim, Germany, has long played a pivotal role in unearthing links between the environment and schizophrenia (Hafner et al., 1969). Using administrative incidence data from Mannheim in 1965, Hafner and colleagues were amongst the first groups to independently verify Faris and Dunham’s seminal work from Chicago in the 1920s, which showed that hospitalized admission rates of schizophrenia were higher in progressively more urban areas of the city (Faris and Dunham, 1939). Now, almost 50 years later, Mannheim’s historical pedigree in this area looks set to endure, following the publication of the landmark study by Lederbogen et al. in Nature, which reported for the first time associations of urban living and upbringing with increased brain activity amongst healthy volunteers in two brain regions involved in determining environmental threat and processing stress responses.

Tantalizingly, their work bridges epidemiology and neuroscience, and provides some of the first empirical data to directly implicate functional neural alterations in stress processing associated with...  Read more

Mannheim, Germany, has long played a pivotal role in unearthing links between the environment and schizophrenia (Hafner et al., 1969). Using administrative incidence data from Mannheim in 1965, Hafner and colleagues were amongst the first groups to independently verify Faris and Dunham’s seminal work from Chicago in the 1920s, which showed that hospitalized admission rates of schizophrenia were higher in progressively more urban areas of the city (Faris and Dunham, 1939). Now, almost 50 years later, Mannheim’s historical pedigree in this area looks set to endure, following the publication of the landmark study by Lederbogen et al. in Nature, which reported for the first time associations of urban living and upbringing with increased brain activity amongst healthy volunteers in two brain regions involved in determining environmental threat and processing stress responses.

Tantalizingly, their work bridges epidemiology and neuroscience, and provides some of the first empirical data to directly implicate functional neural alterations in stress processing associated with living in urban environments. One important step will now be to discover whether such neural changes (following exposure to urban environments) are associated with clinical phenotypes, such as schizophrenia. This would support long-speculated paradigms of social stress (Selten and Cantor-Graae, 2005) as an important mechanism in a causal pathway between the environment and psychosis, although alternative environmental exposures in urban areas, including viral hypotheses and vitamin D, should not yet be excluded.

The work by Lederbogen et al. opens many avenues for possible study, including replication of their findings in clinical samples (via case-control designs) and using population-based rather than convenience samples. One of the greatest challenges in the social epidemiology of psychiatric disorders is to identify the specific suite of factors that underpin associations between the urban environment and the risk of clinical disorder. While Lederbogen et al. did not provide specific enlightenment on what these factors might be, their work also informs this search, because it suggests that focusing on factors likely to induce (or protect against) social stress would be potentially fruitful. To this end, their work should pave the way for mimetic studies, in both non-clinical and clinical populations, to investigate neural processing in relation to candidate social risk factors for psychiatric illness that were implicated in previous epidemiological studies (Cantor-Graae and Selten, 2005; March et al., 2008). These candidates may include migration or minority group membership (Coid et al., 2008), childhood traumas and other major life events (Kendler et al., 1992; Morgan et al., 2007), neighborhood socioeconomic deprivation (Croudace et al., 2000), income inequality (Boydell et al., 2004), and both individual-level social networks and neighborhood-level social cohesion and ethnic density (Kirkbride et al., 2008); some of these factors may also mitigate the effects of social stress.

The interface between social epidemiology and social neuroscience will also potentially provide new avenues by which to develop public health interventions. Presently, universal prevention strategies that focus on community-based interventions to prevent mental illness are not readily viable (Kirkbride et al., 2010), given both the absolute rarity of psychotic disorder and the relative ubiquity of broadly defined exposures such as urban living (many people live in urban environments, but only a handful of them will ever develop a psychotic illness). However, social neuroscience breakthroughs like those reported here may increase the viability of community-based public health initiatives by making it possible to move the focus of the intervention from preventing the clinical phenotype to preventing the abnormal neural changes associated with social-stress processing. Importantly, such strategies must also consider the possible benefits of enhanced social-stress processing in urban environments, which might be an important adaptation to more threatening environments. Because social stress may be associated with a range of neuropsychiatric and somatic disorders, public health strategies that target reductions in social stress rather than any single disorder may lead to significant improvements in population health across a range of morbidities. Such strategies, if justifiable, may also be cost effective, since a single intervention may prevent a range of disorders.

References:

Hafner H, Reimann H, Immich H, Martini H. Inzidenz seelischer Erkrankungen in Mannheim 1965. Soc Psychiatr. 1969;4:127-35.

Faris REL, Dunham HW. Mental disorders in urban areas. Chicago: University of Chicago Press; 1939.

Selten JP, Cantor-Graae E. Social defeat: risk factor for schizophrenia? Br J Psychiatry. 2005 August 1;187(2):101-2. Abstract

Cantor-Graae E, Selten J-P. Schizophrenia and Migration: A Meta-Analysis and Review. Am J Psychiatry. 2005 January 1;162(1):12-24. Abstract

March D, Hatch SL, Morgan C, Kirkbride JB, Bresnahan M, Fearon P, Susser E. Psychosis and Place. Epidemiol Rev. 2008;30:84-100. Abstract

Coid JW, Kirkbride JB, Barker D, Cowden F, Stamps R, Yang M, Jones PB. Raised incidence rates of all psychoses among migrant groups: findings from the East London first episode psychosis study. Arch Gen Psychiatry. 2008;65(11):1250-8. Abstract

Kendler KS, Neale MC, Kessler RC, Heath AC, Eaves LJ. Childhood parental loss and adult psychopathology in women. A twin study perspective. Arch Gen Psychiatry. 1992 Feb;49(2):109-16. Abstract

Morgan C, Kirkbride JB, Leff J, Craig T, Hutchinson G, McKenzie K, Morgan K, Dazzan P, Doody GA, Jones P, Murray R, Fearon P. Parental separation, loss and psychosis in different ethnic groups: a case-control study. Psychol Med. 2007;37(4):495-503. Abstract

Croudace TJ, Kayne R, Jones PB, Harrison GL. Non-linear relationship between an index of social deprivation, psychiatric admission prevalence and the incidence of psychosis. Psychol Med. 2000 Jan;30(1):177-85. Abstract

Boydell J, van Os J, McKenzie K, Murray RM. The association of inequality with the incidence of schizophrenia--an ecological study. Soc Psychiatry Psychiatr Epidemiol. 2004 Aug;39(8):597-9. Abstract

Kirkbride J, Boydell J, Ploubidis G, Morgan C, Dazzan P, McKenzie K, Murray RM, Jones PB. Testing the association between the incidence of schizophrenia and social capital in an urban area. Psychol Med. 2008;38(8):1083-94. Abstract

Kirkbride JB, Coid JW, Morgan C, Fearon P, Dazzan P, Yang M, Lloyd T, Harrison GL, Murray RM, Jones PB. Translating the epidemiology of psychosis into public mental health: evidence, challenges and future prospects. J Public Ment Health. 2010;9(2):4-14. Abstract

This publication is interesting and important, as it is one of the first efforts to connect epidemiological findings to neuroscience. Both fields of research have made great progress over the last decades, but results were limited because epidemiologists and neuroscientists rarely joined forces.

Several risk factors that implicate preconceptional, prenatal, or early childhood exposures have been consistently related to schizophrenia in epidemiological studies, including paternal age at conception, early prenatal famine, urban birth, childhood trauma, and migration (Van Os et al., 2010). While some of these associations are likely to be causal, the mechanisms by which they are linked to schizophrenia are still largely unknown. A next phase of studies is required, the methods and measures of which link social environment to psychosis, brain function, and genes. The study by Lederbogen and colleagues is a fine example of such an innovative research design. Their findings are consistent with hypotheses of social stress mediating...  Read more

This publication is interesting and important, as it is one of the first efforts to connect epidemiological findings to neuroscience. Both fields of research have made great progress over the last decades, but results were limited because epidemiologists and neuroscientists rarely joined forces.

Several risk factors that implicate preconceptional, prenatal, or early childhood exposures have been consistently related to schizophrenia in epidemiological studies, including paternal age at conception, early prenatal famine, urban birth, childhood trauma, and migration (Van Os et al., 2010). While some of these associations are likely to be causal, the mechanisms by which they are linked to schizophrenia are still largely unknown. A next phase of studies is required, the methods and measures of which link social environment to psychosis, brain function, and genes. The study by Lederbogen and colleagues is a fine example of such an innovative research design. Their findings are consistent with hypotheses of social stress mediating the relationship between environmental factors and schizophrenia. It stimulates further research in this direction.

Two key issues need to be addressed. First, measures of social pathways should be refined (March et al., 2008). Which aspects of the daily social environment contribute to the onset of psychotic symptoms, how do these symptoms develop, and which individual characteristics moderate this outcome? It is extremely difficult to investigate daily social environments, because they are highly complex, cannot be controlled, are never exactly the same, and are strongly influenced by the individual’s behavior. Arguably, the only way to test mechanisms of psychotic responses to the social environment, and the moderators thereof, is to randomize individuals to controlled experimental social risk environments. Virtual reality (VR) technology, that is, substituting sense data from the natural world with sense data about an imaginary world that change in response to the user’s actions in an interactive three-dimensional virtual world, offers the possibility to do so. Freeman pioneered VR in psychosis research, investigating safety and feasibility (Fornells-Ambrojo et al., 2008; Freeman, 2008); however, there are no studies investigating mechanisms of risk environments. Our group recently found in a small pilot study that virtual environments with high population density or low ethnic density appear to elicit more physiological and subjective stress, as well as higher level of paranoia towards avatars (Brinkman et al., 2011). Larger studies and more experiments are needed.

Second, how are early social experiences translated to brain dysfunction? Another recent development has been in the field of epigenetics. Epigenetic mechanisms may mediate the effects of environmental risk factors, as the epigenetic status of the genome can be modified in response to the environment during embryonic growth, and probably also in the early years of life (Heijmans et al., 2009). Preliminary evidence suggests that epigenetic differences may be related to schizophrenia (Mill et al., 2008), but these epigenetic studies have not yet included environmental exposures. Epidemiologic studies may be a tool to detect epigenetic mechanisms in schizophrenia. Environmental exposures such as prenatal famine or migration may be used, as these exposures have been related to schizophrenia, can be measured with sufficient precision, offer homogeneously exposed populations for study, and had plausible biological pathways suggested for them (Veling et al. Environmental studies as a tool for detecting epigenetic mechanisms in schizophrenia. In: Petronis A, Mill J, editors. Epigenetics and Human Health: Brain, Behavior and Epigenetics. Heidelberg: Springer; 2011). Comparing the epigenome of exposed and unexposed schizophrenia cases and controls may help us to understand how gene expression affects disease risk.

As far fetched and futuristic as these research designs perhaps may seem, the publication of Lederbogen and colleagues shows that novel approaches can be very fruitful. If we improve interdisciplinary collaboration and use new technology, we may advance from associations to understanding in etiologic schizophrenia research.

References:

Van Os J, Kenis G, Rutten BPF. The environment and schizophrenia. Nature. 2010;468:203-12. Abstract

March D, Hatch SL, Morgan C, Kirkbride JB, Bresnahan M, Fearon P, et al. Psychosis and place. Epidemiological Reviews. 2008;30:84-100. Abstract

Fornells-Ambrojo M, Barker C, Swapp D, Slater M, Antley A, Freeman D. Virtual Reality and persecutory delusions: safety and feasibility. Schizophrenia Research. 2008;104:228-36. Abstract

Freeman D. Studying and treating schizophrenia using Virtual Reality: a new paradigm. Schizophrenia Bulletin. 2008;34:605-10. Abstract

Brinkman WP, Veling W, Dorrestijn E, Sandino G, Vakili V, Van der Gaag M. Virtual reality to study responses to social environmental stressors in individuals with and without psychosis. Studies in Health Technology and Informatics. 2011;167:86-91. Abstract

Heijmans BT, Tobi EW, Lumey LH, Slagboom PE. The epigenome; archive of the prenatal environment. Epigenetics. 2009;4:526-31. Abstract

Mill J, Tang T, Kaminsky Z, Khare T, Yazdanpanah S, Bouchard L, et al. Epigenomic profiling reveals DNA-methylation changes associated with major psychosis. American Journal of Human Genetics. 2008;82:696-711. Abstract

Veling W, Lumey LH, Heijmans BT, Susser E. Environmental studies as a tool for detecting epigenetic mechanisms in schizophrenia. In: Petronis A, Mill J, editors. Epigenetics and Human Health: Brain, Behavior and Epigenetics. Heidelberg: Springer; 2011.

The paper by Lederbogen and colleagues represents a critical step in elucidating the mechanisms underlying the consistent association between urban upbringing and adult schizophrenia. As John McGrath rightly points out, the urbanicity findings have long been in search of hypotheses. We understand little about what the effects of place on psychosis might actually be (March et al., 2008). What it is about place that matters for neurodevelopment and for schizophrenia in particular can be greatly enriched by a translational approach linking epidemiological findings to clinical and experimental science (Weissman et al., 2011), which will in turn help us formulate and refine our hypotheses about why place matters. Lederbogen and colleagues have opened the door in Mannheim. Where we go from here will require creativity, persistence, and collaboration.

References:

March D, Hatch SL, Morgan C, Kirkbride JB, Bresnahan M, Fearon P, Susser E. Psychosis and place. Epidemiol Rev . 2008 Jan 1 ; 30:84-100. Abstract

Weissman MM, Brown AS, Talati A. Translational epidemiology in psychiatry: linking population to clinical and basic sciences. Arch Gen Psychiatry . 2011 Jun 1 ; 68(6):600-8. Abstract

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