The IMAGEN study: reinforcement-related behaviour in normal brain function and psychopathology

A fundamental function of the brain is to evaluate the emotional and motivational significance of stimuli and to adapt behaviour accordingly. The IMAGEN study is the first multicentre genetic-neuroimaging study aimed at identifying the genetic and neurobiological basis of individual variability in impulsivity, reinforcer sensitivity and emotional reactivity, and determining their predictive value for the development of frequent psychiatric disorders. Comprehensive behavioural and neuropsychological characterization, functional and structural neuroimaging and genome-wide association analyses of 2000 14-year-old adolescents are combined with functional genetics in animal and human models. Results will be validated in 1000 adolescents from the Canadian Saguenay Youth Study. The sample will be followed up longitudinally at the age of 16 years to investigate the predictive value of genetics and intermediate phenotypes for the development of frequent psychiatric disorders. This review describes the strategies the IMAGEN consortium used to meet the challenges posed by large-scale multicentre imaging-genomics investigations. We provide detailed methods and Standard Operating Procedures that we hope will be helpful for the design of future studies. These include standardization of the clinical, psychometric and neuroimaging-acquisition protocols, development of a central database for efficient analyses of large multimodal data sets and new analytic approaches to large-scale genetic neuroimaging analyses.

Altered awareness of action in schizophrenia: a specific deficit in predicting action consequences

Patients suffering from schizophrenia may report unusual experiences of their own actions. They may either feel that external forces are controlling their actions or even their thoughts, or they may feel in control of events that in fact are not caused by their actions. Most theories link these disturbances in the sense of agency to deficits in motor prediction, resulting in a mismatch between predicted and actual sensory feedback at a central comparator mechanism. Such theories therefore can account for situations in which the sense of agency is reduced. However, other experiments as well as clinical observations show an enhanced rather than reduced sense of agency in schizophrenic patients. Here, we distinguish between a predictive and a retrospective mechanism where both contribute to the experience of agency, and show that schizophrenia is associated with a specific impairment to the predictive component. We measured subjective time estimates of self-initiated voluntary action (a key press) that were followed by a sensory effect (a tone). When the voluntary actions had a high probability of causing tones, healthy volunteers showed a predictive shift of the perceptual estimate of the action towards the tone, even on occasional trials where the tone was omitted. No such shift occurred in the absence of the tone on blocks when tones were less frequent. The predictive component of action awareness was calculated as the difference between time estimates on 'action only' trials from blocks with lower and higher tone probabilities. Schizophrenic patients lacked this predictive component of action awareness, showing a shift on 'action only' trials, regardless of the probability of the tone. Importantly, the schizophrenic deficit in predicting the relation between action and effect was strongly correlated with severity of positive psychotic symptoms, specifically delusions and hallucinations. Furthermore, the patients showed an exaggerated retrospective binding between action and tone, shifting the perceived time of action whenever the tone occurred, relative to when it did not occur. Our quantitative, implicit measures show how basic sensory and motor experience may be altered in acute psychosis. The enhanced sense of agency in schizophrenia reflects reliance on retrospection, rather than prediction, to associate actions with external events. The failure to predict the effects of one's own actions may underlie the blurring and confusion in the relationship between the self and the world that characterizes acute psychosis.

Association of a variant in the muscarinic acetylcholine receptor 2 gene (CHRM2) with nicotine addiction

Genetic factors contribute to the overall risk of developing nicotine addiction, which is the major cause of preventable deaths in western countries. However, knowledge regarding specific polymorphisms influencing smoking phenotypes remains scarce. In the present study we provide evidence that a common single nucleotide polymorphism (SNP) in the 5' untranslated region of CHRM2, the gene coding for the muscarinic acetylcholine receptor 2 is associated with nicotine addiction. CHRM2 was defined as a candidate gene for nicotine addiction based on previous evidence that linked variations in CHRM2 to alcohol and drug dependence. A total of more than 5,500 subjects representative of the German population were genotyped and assessed regarding their smoking habits. The impact of three SNPs in CHRM2 on smoking behavior/nicotine addiction was investigated using logistic regression models or a quasi-Poisson regression model, respectively. We found the T allele of SNP rs324650 to be associated with an increased risk of smoking/nicotine dependence according to three different models, the recessive models of regular or heavy smokers vs. never-smokers (odds ratio 1.17 in both analyses) and according to the Fagerström index of nicotine addiction. In the analysis stratified by gender this association was only found in females. Our data provide further evidence that variations in CHRM2 may be associated with the genetic risk of addiction in general or with certain personality traits that predispose to the development of addiction. Alternatively, variations in CHRM2 could modulate presynaptic auto-regulation in cholinergic systems and may thereby affect an individual's response to nicotine more specifically.

Gender-dependent association of a functional NGF polymorphism with anxiety-related personality traits

INTRODUCTION

Nerve growth factor (NGF) has been shown to be involved in anxiety behaviour and the expression of conditioned fear in mice.

METHODS

We have tested a total of 337 (age: 39.2 +/- 14.6 years) unrelated subjects of German descent (166 males; 171 females) who were carefully screened for psychiatric health. The self-ratable State-Trait Anxiety Inventory, which enables anxiety to be quantified as a comparatively stable personality trait was applied and a recently described non-synonymous NGF SNP (rs6330,c.104C > T,p.Ala35Val) was examined.

RESULTS

In the trait-related anxiety score, a significant gender-dependent effect of the genotype was observed (F=4.580, df=2, p=0.011) with higher levels of trait anxiety in females with C/C genotype when compared to females with T/T and C/T genotypes and an opposite effect in males.

DISCUSSION

Our findings support the hypothesis that anxiety relates to a genetic variation of NGF and that genes modulate behaviour in a gender-dependent manner. Since anxiety and attention deficit hyperactivity disorder are related to NGF, the present results may represent a common biological link for the gender-specific occurrence and comorbidity of the diseases.

Acute prefrontal cortex transcranial magnetic stimulation in healthy volunteers: no effects on brain-derived neurotrophic factor (BDNF) concentrations in serum

BACKGROUND

Transcranial magnetic stimulation (TMS) of the dorsolateral prefrontal cortex is a brain stimulation technique widely used to treat depression. BDNF serum concentrations have been shown to be decreased in patients with major depressive disorder and can be upregulated by several antidepressive treatment strategies including repetitive TMS.

METHODS

In this study we were interested whether acute TMS evolves effects on serum BDNF concentrations in 42 healthy volunteers.

RESULTS

Mean BDNF serum concentration in 19 male and 23 female volunteers was 10.70+/-3.6 ng/ml (n=42) at baseline, and 10.76+/-3.9 ng/ml (n=42) after TMS treatment. BDNF serum levels did not change after acute TMS (n=42, Z=-0.44, p=0.965). BDNF serum concentrations at baseline did not differ between male (n=19, 10.05+/-2.6 ng/ml) and female (n=23, 11.25+/-4.27 ng/ml) participants of the study (n=42, Z=-0.91, p=0.363).

CONCLUSIONS

Our result suggests that TMS does not change BDNF serum concentrations immediately in healthy human volunteers.

Functional Cortical Effects of Novel Allelic Variants of the Serotonin Transporter Gene-linked Polymorphic Region (5-HTTLPR) in Humans

INTRODUCTION

Genetic variations of the serotonin transporter-linked polymorphic region (5-HTTLPR) have been implicated in the pathogenesis of several psychiatric disorders. Recent evidence indicates that the biallelic polymorphic region (S and L allele) contains additional variations affecting the mRNA expression.

METHODS

According to recent preclinical and clinical studies, the loudness dependence of auditory evoked potentials (LD) was investigated as surrogate parameter for the central serotonergic activity in 185 healthy subjects subdivided according to newly identified 5-HTTLPR genotypes.

RESULTS

Individuals homozygous for the L (A) allele showed the lowest LD of all genotypes suggesting a high serotonergic neurotransmission. The other observed genotypes (L (A)/L (G), S/L (A), S/L (G), S/S) had an LD which was similar to each other but higher compared to the L (A)/L (A) genotype.

DISCUSSION

The data provide a rationale to subdivide the L allele of the 5-HTTLPR into L (A) and L (G) alleles in terms of their serotonin activity as indicated by the LD. The present IN VIVO measurements provide a basis for grouping the L (G) and S alleles for further investigations.

Gender-dependent association of the functional catechol-O-methyltransferase Val158Met genotype with sensation seeking personality trait

The gene encoding cathechol-O-methyltransferase (COMT) contains a common functional missense polymorphism (Val158Met) that regulates dopamine in an allele-dependent manner. A pivotal role of dopamine neurotransmission in the prefrontal cortex has been implicated in drug-seeking behavior and related personality traits, such as sensation seeking, with some evidence for a gender-specific association. Here, we tested the hypothesis that the COMT Val158Met polymorphism modulates the personality dimension, sensation seeking, in a gender-dependent manner. Study sample included 214 male (age 38.1+/-12.6 years) and 218 female (age 36.1+/-13.6 years) healthy volunteers, who were assessed with Zuckerman's sensation-seeking scale and genotyped for the Val158Met polymorphism (dbSNP:rs4680). Univariate analysis of variance showed that the sensation seeking score was significantly affected by a COMT genotype x gender interaction (F=5.330, df=2, p=0.005). The Val158Met polymorphism was associated with the sensation seeking personality trait in women only. The highest scores in the sensation-seeking scale and in three of the four subscales were observed in female subjects with the Val/Val genotype relative to women carrying the Met allele. Our results suggest that high COMT enzyme activity associated with the Val allele predisposes to high sensation seeking scores in female subjects and add to increasing evidence for a gender specific role of COMT in normal and dysfunctional behavior.

Correlation between serum brain-derived neurotrophic factor level and an in vivo marker of cortical integrity

BACKGROUND

Brain-derived neurotrophic factor (BDNF) signaling at synapses improves synaptic strengthening associated with learning and memory. In the present study we hypothesized that serum BDNF concentration is associated with in vivo level of cerebral N-acetylaspartate (NAA), a well established marker of neuronal integrity.

METHODS

In 36 healthy subjects BDNF serum concentration and absolute concentration of NAA together with other metabolites were measured by proton magnetic resonance spectroscopy (1H-MRS) in regions with high BDNF levels (anterior cingulate cortex [ACC], left hippocampus). Relationship between BDNF concentration and brain metabolites was studied in linear regression analysis with BDNF concentration as dependent variable and metabolite concentrations, age, and gender as predictor variables.

RESULTS

The BDNF serum concentrations were positively associated with the concentrations of NAA (T = 2.193, p = .037) and total choline (T = 1.997, p = .055; trend) but not total creatine or glutamate in the ACC. No significant association was observed between BDNF serum concentration and absolute metabolite concentrations in the hippocampus.

CONCLUSIONS

The preliminary data might indicate that BDNF serum concentration reflects some aspects of neuronal plasticity as indicated by its association with NAA level in the cerebral cortex. The results would be in line with the notion that BDNF plays a central role in the regulation of neuronal survival and differentiation in the human brain.

Regional cerebral glutamate concentrations and chronic tobacco consumption

INTRODUCTION

Increasing evidence indicates a crucial role of glutamate in the brain reward system and nicotine addiction. Because the pertinent models involve frontal and hippocampal glutamatergic projections, our goal was to investigate cerebral glutamate concentrations in healthy subjects with different smoking behavior.

METHODS

Glutamate was measured with proton magnetic resonance spectroscopy at 3 tesla in the left hippocampus and anterior cingulate cortex (ACC) in 13 chronic tobacco smokers, 9 former smokers, and 16 never-smokers using a dedicated quantification method.

RESULTS

Glutamate concentrations did not differ between groups in either voxel ( F=1.151, DF=2, P=0.340). No significant correlations between glutamate concentrations and age of smoking onset, daily cigarette consumption, or lifetime exposure to tobacco smoke (pack-years) were observed.

CONCLUSION

Our findings do not support a crucial role of cingulate or hippocampal glutamate concentration in chronic tobacco consumption. Besides group differences potentially gone unnoticed due to the limited sample size, however, these results cannot rule out dysfunctional glutamatergic neurotransmission or glutamate dysfunctions in other brain regions of smokers.

P300 is enhanced in responders to vagus nerve stimulation for treatment of major depressive disorder

BACKGROUND

Vagus nerve stimulation (VNS) is a new therapy option for treatment of otherwise therapy-refractory major depressive disorder. However, the mechanism of central nervous action is poorly understood. Electroencephalographic (EEG) studies may be of interest since chronic peripheral current application to the vagus nerve may exert lasting neurophysiologically detectable effects on central electrical activity. In an exploratory study, we investigated the effects of VNS on auditory event-related potentials (ERP).

METHODS

Thirteen depressive patients (mean Hamilton depression score (HAMD) at baseline=24.2) receiving VNS were investigated prior to implantation and 10 weeks after standard cycling VNS. Stimulation intensity was 0.94+/-0.46 mA, pulse width 0.250 mus, and frequency 20 Hz. 1 h prior to follow-up investigation, VNS was turned off. Auditory ERP were elicited using a standard auditory oddball paradigm and were recorded with 29-channel EEG.

RESULTS

Post VNS, grand averages of the auditory ERP did not show significant differences as compared to baseline recording. However, differential effects were found when separating ERP of responders (N=5, mean HAMD post VNS=8.8) and non-responders (N=8, mean HAMD post VNS=22.4). In VNS responders only, P300 at midline electrodes Fz and Cz was significantly increased and correlated with HAMD scores.

CONCLUSION

Auditory ERP seem to provide a useful tool for investigating VNS-induced changes concerning information processing in major depressive disorder. In our sample, enhancement of P300 distinguished VNS responders from non-responders 10 weeks after therapy onset. Our findings may be relevant for the understanding of both neurophysiological mechanism of action of VNS and pathophysiology of depression.

Self-reported empathic abilities in schizophrenia

BACKGROUND

Increasing evidence indicates impairments of empathic abilities in schizophrenia that may impact outcome and course of the disease. While there is consensus on the presence of deficits in 'theory of mind' in this disorder, i.e. cognitive aspects of mental state attribution, the ability to infer emotional experiences of others, i.e. affective empathy, has not been investigated so far.

METHODS

We assessed multiple dimensions of empathy in 45 schizophrenic patients and 45 healthy controls, matched for age and gender, with a self-rating instrument, the Interpersonal Reactivity Index (IRI). To control for modulating effects of cognitive deficits, a neuropsychological test battery was employed.

RESULTS

Schizophrenic patients showed significantly lower scores in cognitive empathy ('perspective taking': F=12.176, df=1, p=0.001) but more self-related aversive feelings in response to the distress of others ('personal distress: F=16.477, df=1, p<0.001). Self-ratings of affective empathy, i.e. concern for others, did not differ between groups. Results in the domains of empathy were not explained by symptoms or neurocognition as revealed by regression analysis. However, lower scores in 'perspective taking' were found with advancing duration of illness (r=-0.453, p=0.002).

CONCLUSIONS

Results indicate reductions of cognitive empathy but relatively preserved emotional empathic abilities in schizophrenia. Although previous studies observed deficits in emotion perception and expression, our findings support the concept of differentially disturbed abilities in cognitive and emotional empathy in schizophrenia.

Motor cortex excitability after vagus nerve stimulation in major depression

Recent data suggest that inhibitory pathways may be involved in the pathophysiology of depression and in the mode of action of some antidepressant interventions. The aim of the present study was to test whether vagus nerve stimulation (VNS) can affect motor cortex excitability. Measures of motor cortical excitability were probed by using single-pulse and paired-pulse transcranial magnetic stimulation at baseline, after 10 weeks of left VNS, and additionally, in an on-off paradigm in 10 patients with treatment-resistant unipolar depression. Ten weeks of VNS was associated with a selective and pronounced increase in intracortical inhibition, whereas no changes occurred in the on-off paradigm. These results suggest that VNS is capable of changing motor cortical excitability in patients with depression.

Association between cerebral glutamate and human behaviour: the sensation seeking personality trait

INTRODUCTION

Brain imaging studies have linked the anterior cingulate cortex (ACC) to motivation, drive, and personality traits like novelty and sensation seeking. Animal studies have shown glutamatergic neurotransmission to be important in ACC function as well as motivated behaviour. However, the role of glutamate in related personality traits like sensation seeking has not been investigated in humans.

METHODS

The associations between sensation seeking personality scores and absolute glutamate concentrations in the ACC and the hippocampal region measured by 3-Tesla proton magnetic resonance spectroscopy (1H-MRS) were investigated.

RESULTS

ACC glutamate concentration was negatively correlated with the sensation seeking sum score and the experience seeking subscore. A weak negative correlation was also observed between the hippocampal glutamate and the sensation seeking sum score. The reexamination of the glutamate concentration after 4 weeks revealed a similar relationship with sensation seeking.

DISCUSSION

Although preliminary, the results are in line with the key role of the ACC for motivation and executive control and with the impact of glutamate on novelty related behaviour observed in animal experiments. The role of the hippocampus for novelty processing is discussed. Glutamate measurement with 1H-MRS may facilitate the understanding of biological underpinnings of personality traits and psychiatric diseases associated with dysfunctions in motivation and drive.

COMT genotype predicts BOLD signal and noise characteristics in prefrontal circuits

OBJECTIVE

Prefrontal dopamine (DA) is catabolized by the COMT (catechol-O-methyltransferase) enzyme. Literature suggests that the Val/Met single nucleotide polymorphism (SNP) in the COMT gene predicts executive cognition in humans with Val carriers showing poorer performance due to less available synaptic DA. Recent fMRI studies are thought to agree with these studies having demonstrated prefrontal hyperactivation during n-back and attention-requiring tasks. This was interpreted as "less efficient" processing due to impaired signal-to-noise ratio (SNR) of neuronal activity. However, electrophysiological studies of neuronal SNR in primates and humans imply that prefrontal cortex should show a diminished prefrontal BOLD response in Val carriers. In the present study, we addressed the question of whether the prefrontal SNR of the BOLD response is decreased in Val carriers using a visual oddball task and an approach to analysis of fMRI data that maximizes noise characterization.

METHODS

We investigated N=17 homozygous Met carriers compared with N=24 Val carriers matched for age, sex, education, IQ, reaction time (variability) and head motion. Event-related fMRI was conducted presenting 160 visual stimuli (40 targets, checkerboard reversal). Subjects had to respond as quickly as possible to targets by button press. In the fMRI GLM [y(t)=beta*x(t)+c+e(t)] analysis, voxel-by-voxel 'activation' [y(t)] as well as residual noise variance [e(t)=sigma2] were calculated using a conservative full-width half maximum (FWHM=6 mm).

RESULTS

As compared to Val carriers, we observed a stronger and more extended BOLD responses in homozygous Met carriers in left supplementary motor area (SMA) extending to ACC and dorsolateral prefrontal cortex. Vice versa, increased levels of noise were seen in Val carriers surrounding the peak activation maximum.

DISCUSSION

In line with our expectations from prior electrophysiological studies, we observed a diminished BOLD response and increased noise in Val carriers. This suggests that the DA stabilizes cortical microcircuits by sharpening the signal and suppressing surrounding noise.

Hippocampal glutamate concentration predicts cerebral theta oscillations during cognitive processing

RATIONALE

Brain waves reflect collective behavior of neurons and provide insight into distributed network processing. Frontal and hippocampal theta oscillations (4-7 Hz) were linked to cognitive tasks and animal studies have suggested an involvement of glutamatergic neurotransmission in integrative frontal-hippocampal processing. Human evidence for such relationships is lacking.

METHODS

Here, we studied the associations between glutamate concentrations in the hippocampal region, measured by a 3-T proton magnetic resonance spectroscopy (1H-MRS), and EEG theta activity during an auditory target detection paradigm.

RESULTS

A robust relationship between hippocampal glutamate and frontal theta activity during stimulus processing was found. Moreover, frontal theta oscillations were related to response speed.

CONCLUSION

The results suggest a functional coupling between the frontal cortex and hippocampal region during stimulus processing and support the idea of the hippocampus as a neural rhythm generator driven by glutamatergic neurotransmission. These preliminary data show, for the first time, a relationship between in vivo measured glutamate and basic cerebral information processing in humans.

Brain-derived neurotrophic factor serum concentrations in depressive patients during vagus nerve stimulation and repetitive transcranial magnetic stimulation

BACKGROUND

Vagus nerve stimulation (VNS) and repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex are brain stimulation techniques used as therapeutic interventions in major depression.

METHODS

In this study, we report the impact of these stimulation techniques on serum concentrations of brain-derived neurotrophic factor (BDNF) in treatment-resistant patients with a diagnosis of major depression.

RESULTS

We found no changes of BDNF serum concentrations and no association of neurotrophin concentrations in serum with clinical parameters in our sample.

CONCLUSION

Our preliminary results suggest that brain stimulation techniques-in contrast to several antidepressant medications-do not change BDNF serum concentrations.

Interictal slow-wave focus in left medial temporal lobe during bilateral electroconvulsive therapy

The interictal state between two electroconvulsive therapy (ECT) sessions is clinically characterised by possible cognitive adverse effects like mild amnestic syndrome. ECT-induced amnestic deficits can persist for several weeks after ECT. Electrophysiologically, slowing of brain electrical activity in the interictal state has often been reported. Especially, for bilateral ECT a correlation between enhanced left frontotemporal theta activity and retrograde amnesia has been demonstrated. This study focuses on the topographic distribution of cortical slow-wave oscillations during the interictal state of a bilateral ECT cycle. Twelve patients with major depression have been investigated with 32-channel resting EEG 24 h after the 6th ECT session. As controls, 8 major depressive patients were investigated prior to antidepressive treatment. The generating sources of slow-wave activity are estimated within the theta frequency band with low-resolution brain electromagnetic tomography. Source analysis revealed a distinct pattern of theta activity in the depth of the left temporal lobe (fusiform and parahippocampal gyri, Brodmann areas 37 and 36, respectively; p< 0.05) during the interictal state. This finding suggests a dysfunction of the left medial temporal lobe memory system during the interictal state of a bilateral ECT cycle. It will further be discussed whether it is possible to obtain information about activity of deep brain structures like the hippocampal formation from scalp-recorded signals.

Combination of Multimodal Imaging and Molecular Genetic Information to Investigate Complex Psychiatric Disorders

Multimodal imaging, the combination of several brain imaging techniques in one subject, provides a wealth of parameters and favours the interpretation of complex models in schizophrenia research. Moreover, new imaging tools allow the investigation of distinct neurotransmitter systems and their modulation by pharmacological intervention. An important feature of multimodal imaging is the possibility to characterize the activation dependencies of different neurotransmitters and provide the experimental tool to test system models of brain function and dysfunction. The combination of measurement techniques with high temporal resolution (e. g. MEG, EEG) and high spatial resolution (e. g. fMRI) facilitate the understanding of local and global systems as well as time characteristics. Moreover, the association of imaging parameters with genetic variations of neurotransmitter systems allows the investigation of neurotransmitter activity and its role in the pathophysiology of schizophrenia. To overcome the limitations of standard statistical methods, new approaches in machine learning have to be adapted to handle multiple parameters obtained from brain imaging and genetic measurements.

Confirmation of association between the Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene and bipolar I disorder

Recent studies have indicated that the brain-derived neurotrophic factor (BDNF) gene is involved in the etiology of bipolar disorder (BPD). Two family-based association studies showed that the Val allele of the functional polymorphism Val66Met in the BDNF gene is associated with BPD; however, others could not confirm the results. Here we performed a replication study in an independent sample and tested the hypothesis that the Val66 allele in the BDNF gene confers susceptibility to bipolar I disorder (BPI). Six hundred twenty-one patients with BPI and 998 control subjects were genotyped for the Val66Met polymorphism. All cases and controls were of European descent. All BPI patients had a positive family history of affective disorder. The frequency of the Val allele was significantly increased in BPI patient when compared to controls (chi2 = 4.8; df = 1; P = 0.028; two-sided; OR = 1.22; 95% CI: 1.02-1.47). Results confirm previous findings and suggest that the Val allele increases risk for BPI in patients of European descent. Further studies are necessary to elucidate the involvement of the BDNF gene in the pathophysiology of BPD.

Serotonergic Effects of Smoking are Independent from the Human Serotonin Transporter Gene Promoter Polymorphism: Evidence from Auditory Cortical Stimulus Processing

BACKGROUND

Cigarette smoking has been associated with mood enhancing properties and modulating effects on serotonin activity. The loudness dependence (LD) of the auditory-evoked N1/P2-component has been related to serotonergic neurotransmission, i. e. the allelic variants in the promoter of the 5-hydroxytryptamine-transporter (5-HTT) gene (SCL6A4). Moreover, smoking behavior has been associated to the 5-HTT-genotype. It was hypothesized that cigarette smoking modulates the LD and this effect was expected to interact with the 5-HTT-genotype.

METHODS

5-HTT-genotype and LD were determined in 63 healthy smokers and 114 nonsmokers.

RESULTS

LD was significantly affected by smoking status (p = 0.008) and 5-HTT-genotype (p = 0.045) but not by smoking*genotype-interaction or daily cigarette consumption. Current smokers exhibited a significantly weaker LD compared to nonsmokers. 5-HTT-genotype showed no significant effect on smoking behavior.

DISCUSSION

The results indicate a higher serotonergic activity in smokers as compared to nonsmokers independent of 5-HTT-genotype. Since former smokers and never smokers showed similar LDs, the serotonin enhancing effect of smoking seems to be a characteristic state, which may contribute to the maintenance of smoking behavior.

The neural basis of the P300 potential. Focus on the time-course of the underlying cortical generators

The locations and time-courses of the neural generators of the event-related P300 potential have been well described using intracranial recordings. However, this invasive method is not adequate for usage in healthy volunteers or psychiatric patients and not all brain regions can be covered well with this approach. With functional MRI, a non-invasive method with high spatial resolution, most of these locations could be found again. However, the time-course of these activations can only be roughly determined with this method, even if an event-related fMRI design has been chosen. Therefore, we have now tried to analyse the time-course of the activations using EEG data providing a better time resolution. We have used Low Resolution Electromagnetic Tomography (LORETA) in the analysis of P300 data (27 electrodes) of healthy volunteers (n = 50) in the time frame 230-480 ms and found mainly the same activations that have been described using intracranial recordings or fMRI, i. e. the inferior parietal lobe/temporo-parietal junction (TPJ), the supplementary motor cortex (SMA) and the anterior cingulate cortex (ACC), the superior temporal gyrus (STG), the insula and the dorsolateral prefrontal cortex. In these selected regions, an analysis of the activation time-courses has been performed.

Loudness Dependence of Primary Auditory-Cortex-Evoked Activity as Predictor of Therapeutic Outcome to Prophylactic Lithium Treatment in Affective Disorders - A Retrospective Study

INTRODUCTION

Lithium has been found to be very effective in prophylactic treatment of affective disorders. However, approximately one-third of patients do not respond to this treatment, which does not become apparent until after a year or more of treatment. Therefore, predictors are needed to avoid a long and unsuccessful therapy with risk of severe side effects. Since lithium acts as a serotonin agonist in prophylactic treatment, a predictor of being able to identify patients with low serotonergic activity, who may be responders to lithium, is promising. To determine whether the loudness dependence (LDAEP) of primary, but not of secondary, auditory-cortex-evoked activity, which is inversely related to central serotonergic neurotransmission, could be such a predictor, responders and non-responders to prophylactic lithium treatment were compared.

METHODS

Thirty patients with uni- and bipolar affective disorders, who have taken a prophylactic lithium medication continuously for at least 3 years, were included in the study. Patients were classified as responders if they had no hospitalization within the past 3 years. Dipole source analysis allowing us to separate evoked activity of the primary and secondary auditory cortex was used.

RESULTS

The LDAEP of the primary, but not of the secondary, auditory cortex was significantly stronger in the responders to the lithium treatment than in the non-responders, implicating low serotonergic function in these patients.

DISCUSSION

This finding, which is in line with previous studies, suggests that loudness dependence of primary auditory-cortex-evoked activity could be a clinically relevant predictor of prophylactic treatment with lithium in affective disorders.

Superior temporal gyrus and P300 in schizophrenia: a combined ERP/structural magnetic resonance imaging investigation

Decrement of the auditory P300 component of the event-related potentials (ERP) is a robust finding in schizophrenic patients and seems to be most pronounced in the left temporal region. Structural MRI studies support the hypothesis that regional structural brain differences in this patient group include reduced volume in temporal lobe structures. The aim of the presented study was to investigate the possible gray matter volume reductions in the left posterior superior temporal gyrus (STG) and the P300 reduction and left <right topographic asymmetry in schizophrenic patients. Therefore, in 50 male schizophrenic patients and 50 age- and educational level-matched male controls, auditory ERPs and structural MRI measurements of the gray matter volume of the STG were assessed. In the group of patients, the psychopathological symptom of thought disorder was correlated with the electrode site T3 and underlying gray matter of the left posterior superior temporal gyrus. The subgroup of patients with pronounced negative symptoms was analyzed with respect to ERP and structural MRI measurements. Our data revealed no evidence for a reduction of P300 amplitude or left STG gray matter volume in schizophrenic patients. However, the higher amount of thought disorders was related to a small T3 amplitude. No associations between the electrophysiological and structural measurements could be detected. There were also no significant reductions of ERP and MRI measurements within the subgroup of patients with pronounced negative symptoms.

Abnormalities of Inhibitory Neuronal Mechanisms in the Motor Cortex of Patients with Schizophrenia

BACKGROUND

Focal transcranial magnetic stimulation (TMS) of the motor cortex was used to study two cortically activated inhibitory neuronal mechanisms that suppress ongoing tonic voluntary electromyographic activity in contralateral (postexcitatory inhibition [PI]) and ipsilateral (transcallosal inhibition [TI]) hand muscles. The PI follows the corticospinally mediated excitatory motor response (MEP) and is influenced by dopaminergic neurotransmission. TI reflects transcallosally mediated inhibition of the contralateral motor cortex, leading to motor inhibition in muscles ipsilateral to stimulation. PI and TI were studied to explore whether dopaminergic neurotransmission or interhemispheric transfers are altered in schizophrenia.

METHODS

TMS was performed in 16 patients with this disease and in 16 healthy control subjects. Surface electromyographic activity was recorded bilaterally from the first dorsal interosseous muscle during a sustained strong isometric contraction.

RESULTS

When compared with the findings in healthy subjects, patients with schizophrenia had a significantly longer PI and TI. The changes of the PI support the notion of an overactivity of the central dopaminergic system in schizophrenia.

CONCLUSION

The prolonged TI suggests an abnormal activation of interhemispheric connections between the motor cortices and may be related to previously reported pathology of the corpus callosum in schizophrenic patients.