Epigenetic properties and identification of an imprint mark in the Nesp-Gnasxl domain of the mouse Gnas imprinted locus

The Gnas locus in the mouse is imprinted with a complex arrangement of alternative transcripts defined by promoters with different patterns of monoallelic expression. The Gnas transcript is subject to tissue-specific imprinted expression, Nesp is expressed only from the maternal allele, and Gnasxl is expressed only from the paternal allele. The mechanisms controlling these expression patterns are not known. To identify potential imprinting regulatory regions, particularly for the reciprocally expressed Nesp and Gnasxl promoters, we examined epigenetic properties of the locus in gametes, embryonic stem cells, and fetal and adult tissues. The Nesp and Gnasxl promoter regions are contained in extensive CpG islands with methylation of the paternal allele at Nesp and the maternal allele at Gnasxl. Parental allele-specific DNase I-hypersensitive sites were found at these regions, which correlate with hypomethylation rather than actual expression status. A germ line methylation mark was identified covering the promoters for Gnasxl and the antisense transcript Nespas. Prominent DNase I-hypersensitive sites present on paternal alleles in embryonic stem cells are contained within this mark. This is the second gametic mark identified at Gnas and suggests that the Nesp and Gnasxl promoters are under separate control from the Gnas promoter. We propose models to account for the regulation of imprinting at the locus.

Neurophysical modeling of brain dynamics

A recent neurophysical model of brain electrical activity is outlined and applied to EEG phenomena. It incorporates single-neuron physiology and the large-scale anatomy of corticocortical and corticothalamic pathways, including synaptic strengths, dendritic propagation, nonlinear firing responses, and axonal conduction. Small perturbations from steady states account for observed EEGs as functions of arousal. Evoked response potentials (ERPs), correlation, and coherence functions are also reproduced. Feedback via thalamic nuclei is critical in determining the forms of these quantities, the transition between sleep and waking, and stability against seizures. Many disorders correspond to significant changes in EEGs, which can potentially be quantified in terms of the underlying physiology using this theory. In the nonlinear regime, limit cycles are often seen, including a regime in which they have the characteristic petit mal 3 Hz spike-and-wave form.

Simulated electrocortical activity at microscopic, mesoscopic, and global scales

Simulation of electrocortical activity requires (a) determination of the most crucial features to be modelled, (b) specification of state equations with parameters that can be determined against independent measurements, and (c) explanation of electrical events in the brain at several scales. We report our attempts to address these problems, and show that mutually consistent explanations, and simulation of experimental data can be achieved for cortical gamma activity, synchronous oscillation, and the main features of the EEG power spectrum including the cerebral rhythms and evoked potentials. These simulations include consideration of dendritic and synaptic dynamics, AMPA, NMDA, and GABA receptors, and intracortical and cortical/subcortical interactions. We speculate on the way in which Hebbian learning and intrinsic reinforcement processes might complement the brain dynamics thus explained, to produce elementary cognitive operations.

Conserved methylation imprints in the human and mouse GRB10 genes with divergent allelic expression suggests differential reading of the same mark

Grb10/GRB10 encodes a cytoplasmic adapter protein which modulates coupling of a number of cell surface receptor tyrosine kinases with specific signalling pathways. Mouse Grb10 is an imprinted gene with maternal-specific expression. In contrast, human GRB10 is expressed biallelically in most tissues, except for maternal-specific expression of one isoform in muscle and paternal expression in fetal brain. Owing to its location in 7p11.2-p12, GRB10 has been considered a candidate gene for the imprinted growth disorder, the Silver-Russell syndrome (SRS), but its predominantly biallelic expression argues against involvement in the syndrome. To investigate the discrepant imprinting between mouse and human, we compared the sequence organization of their upstream regions, and examined their allelic methylation patterns and the splice variant organization of the mouse locus. Contrary to expectation, we detected both maternal and paternal expression of mouse Grb10. Expression of the paternal allele arises from a different promoter region than the maternal and, as in human, is restricted to the brain. The upstream regions are well conserved, especially the presence of two CpG islands. Surprisingly, both genes have a similar imprinted methylation pattern, the second CpG island is a differentially methylated region (DMR) with maternal methylation in both species. Analysis of 24 SRS patients did not reveal methylation anomalies in the DMR. In the mouse this DMR is a gametic methylation mark. Our results suggest that the difference in imprinted expression in mouse and human is not due to acquisition of an imprint mark but in differences in the reading of this mark.

Blood aspiration syndrome as a cause of respiratory distress in the newborn infant

Early-onset respiratory distress and a radiographic appearance of an aspiration syndrome occurred in three neonates who had not passed meconium before delivery. In each case there was evidence of inhalation of blood, associated with very high plasma protein concentration in lung fluid. Blood aspiration syndrome is a distinct diagnostic entity that can result in significant respiratory distress in the neonate.

Target and non-target ERP disturbances in first episode vs. chronic schizophrenia

OBJECTIVES

Event-related potential (ERP) abnormalities to target stimuli are reliably found in schizophrenia. However, as people with schizophrenia are thought to have difficulty discerning the relevance of incoming sensory stimuli it is also important to examine ERPs to non-targets. To differentiate between potential trait markers of the disease and deficits that might be associated with the consequence of illness chronicity, this study investigated ERPs to both target and non-target stimuli in groups of people with either first episode or chronic schizophrenia (CSz).

METHODS

Using an auditory oddball paradigm, ERPs to target, non-target before target (Nt before) and non-target after target (Nt after) stimuli were analysed for 40 patients with CSz, 40 patients with first episode schizophrenia (FESz) and two groups of normal controls matched for age and sex with their patient counterparts.

RESULTS

The FESz group showed the same pattern of amplitude disturbance as the CSz group to both targets (reduced N100, N200, P300 and increased P200) and non-targets (reduced N100) compared to controls. Both CSz and FESz groups also failed to show the changes to the P200-N200 component between targets and non-target stimuli that was exhibited by controls (smaller earlier P200 to targets vs. increased delayed P200 to non-targets) or the reduction in N100 amplitude of ERPs to the Nt after stimuli compared with ERPs to the Nt before stimuli. Previous literature has focussed on the sensitivity of P300 deficits in classifying persons into schizophrenia and non-schizophrenia groups. This study demonstrated improved accuracy in the classification of patients with schizophrenia from controls using discriminant analysis of target and non-target N100 and P200 components.

CONCLUSIONS

The results suggest that ERP disturbances are evident at the time of first referral to mental health services and may be a potential trait (rather than secondary effect) of the illness. It is important to include both target and non-target stimuli processing, and their interrelationship in future research.

ERPs associated with and without an "orienting reflex" in patients with schizophrenia

In this study, we measured traditional late components of the Event Related Potential (ERP: N 100, P 200, N 200 and P 300) in a conventional auditory oddball paradigm, but additionally and simultaneously assessed electrodermal "orienting reflexes (ORs)" in 40 patients with schizophrenia and 40 age and gender matched normal controls. The single epoch ERPs that did and did not evoke an OR, were sub-averaged separately. The control subjects (but not the patient group), revealed delayed P 300 latency in the ERP sub-averages without ORs (ERP-OR), compared with ERP sub-averages with ORs (ERP+OR). Between-group analysis showed reduced N 100, N 200 and P 300 amplitudes (as well as delayed P 300 latency) in the ERP+OR sub-average in patients with schizophrenia. In the ERP-OR sub-average, the patient group also had smaller N 100, N 200 and P 300 amplitudes, but larger P 200 amplitude (compared with normal controls). This study shows the potential to tease out physiologically based OR sub-processes, by simultaneous acquisition and analysis of ERPs and autonomic electrodermal activity. Such ERP sub-averages (based on autonomic responses) highlight that multiple processes overlap across the trial, and their delineation may elucidate more specific patterns of disturbance in schizophrenia, than traditional averaged measures.

Crystal structure of PBP2x from a highly penicillin-resistant Streptococcus pneumoniae clinical isolate: a mosaic framework containing 83 mutations

Penicillin-binding proteins (PBPs) are the main targets for beta-lactam antibiotics, such as penicillins and cephalosporins, in a wide range of bacterial species. In some Gram-positive strains, the surge of resistance to treatment with beta-lactams is primarily the result of the proliferation of mosaic PBP-encoding genes, which encode novel proteins by recombination. PBP2x is a primary resistance determinant in Streptococcus pneumoniae, and its modification is an essential step in the development of high level beta-lactam resistance. To understand such a resistance mechanism at an atomic level, we have solved the x-ray crystal structure of PBP2x from a highly penicillin-resistant clinical isolate of S. pneumoniae, Sp328, which harbors 83 mutations in the soluble region. In the proximity of the Sp328 PBP2x* active site, the Thr(338) --> Ala mutation weakens the local hydrogen bonding network, thus abrogating the stabilization of a crucial buried water molecule. In addition, the Ser(389) --> Leu and Asn(514) --> His mutations produce a destabilizing effect that generates an "open" active site. It has been suggested that peptidoglycan substrates for beta-lactam-resistant PBPs contain a large amount of abnormal, branched peptides, whereas sensitive strains tend to catalyze cross-linking of linear forms. Thus, in vivo, an "open" active site could facilitate the recognition of distinct, branched physiological substrates.

Toward an integrated continuum model of cerebral dynamics: the cerebral rhythms, synchronous oscillation and cortical stability

Continuum models of cerebral cortex with parameters derived from physiological data, provide explanations of the cerebral rhythms, synchronous oscillation, and autonomous cortical activity in the gamma frequency range, and suggest possible mechanisms for dynamic self-organization in the brain. Dispersion relations and derivations of power spectral response for the models, show that a low frequency resonant mode and associated travelling wave solutions of the models' equations of state can account for the predominant 1/f spectral content of the electroencephalogram (EEG). Large scale activity in the alpha, beta, and gamma bands, is accounted for by thalamocortical interaction, under regulation by diffuse cortical excitation. System impulse responses can be used to model Event-Related Potentials. Further classes of local resonance may be generated by rapid negative feedbacks at active synapses. Activity in the gamma band around 40 Hz, associated with large amplitude oscillations of pulse density, appears at higher levels of cortical activation, and is unstable unless compensated by synaptic feedbacks. Control of cortical stability by synaptic feedbacks offers a partial account of the regulation of autonomous activity within the cortex. Synchronous oscillation occurs between concurrently excited cortical sites, and can be explained by analysis of wave motion radiating from each of the co-active sites. These models are suitable for the introduction of learning rules-most notably the coherent infomax rule.

Arousal dissociates amygdala and hippocampal fear responses: evidence from simultaneous fMRI and skin conductance recording

The experience and appraisal of threat is essential to human and animal survival. Lesion evidence suggests that the subjective experience of fear relies upon amygdala-medial frontal activity (as well as autonomic arousal), whereas the factual context of threat stimuli depends upon hippocampal-lateral frontal activity. This amygdala-hippocampus dissociation has not previously been demonstrated in vivo. To explore this differentiation, we employed functional magnetic resonance imaging (fMRI) and simultaneous skin conductance response (SCR) measures of phasic arousal, while subjects viewed fearful versus neutral faces. fMRI activity was subaveraged according to whether or not the subject evoked an arousal SCR to each discrete face stimulus. The fMRI-with arousal and fMRI-without arousal data provided a distinct differentiation of amygdala and hippocampal networks. Amygdala-medial frontal activity was observed only with SCRs, whereas hippocampus-lateral frontal activity occurred only in the absence of SCRs. The findings provide direct evidence for a dissociation between human amygdala and hippocampus networks in the visceral experience versus declarative fact processing of fear.

Integrative psychophysiology

This paper attempts to provide an overview of the current status and some possible future directions of 'Integrative Psychophysiology'. Exemplar integrations are offered for: (i) the theory of some of the more cited models of the brain as a system; (ii) a numerical simulation of brain dynamics (highlighting the plausibility of exploring mechanisms at the whole brain scale); and (iii) an empirical profile of disturbances in patients with schizophrenia (reflecting a prototypical disorder of overall brain instability and suboptimal integrative information processing). These 'integrative' dimensions provide a frame of reference for considering interrelationships among brain dynamics and behaviour, in health and disease.

Alcohol and marijuana: effects on epilepsy and use by patients with epilepsy

We review the safety of alcohol or marijuana use by patients with epilepsy. Alcohol intake in small amounts (one to two drinks per day) usually does not increase seizure frequency or significantly affect serum levels of antiepileptic drugs (AEDs). Adult patients with epilepsy should therefore be allowed to consume alcohol in limited amounts. However, exceptions may include patients with a history of alcohol or substance abuse, or those with a history of alcohol-related seizures. The most serious risk of seizures in connection with alcohol use is withdrawal. Alcohol withdrawal lowers the seizure threshold, an effect that may be related to alcohol dose, rapidity of withdrawal, and chronicity of exposure. Individuals who chronically abuse alcohol are at significantly increased risk of developing seizures, which can occur during withdrawal or intoxication. Alcohol abuse predisposes to medical and metabolic disorders that can lower the seizure threshold or cause symptoms that mimic seizures. Therefore, in evaluating a seizure in a patient who is inebriated or has abused alcohol, one must carefully investigate to determine the cause. Animal and human research on the effects of marijuana on seizure activity are inconclusive. There are currently insufficient data to determine whether occasional or chronic marijuana use influences seizure frequency. Some evidence suggests that marijuana and its active cannabinoids have antiepileptic effects, but these may be specific to partial or tonic-clonic seizures. In some animal models, marijuana or its constituents can lower the seizure threshold. Preliminary, uncontrolled clinical studies suggest that cannabidiol may have antiepileptic effects in humans. Marijuana use can transiently impair short-term memory, and like alcohol use, may increase noncompliance with AEDs. Marijuana use or withdrawal could potentially trigger seizures in susceptible patients.

Single-event-related potential analysis by means of fragmentary decomposition

A recently developed fragmentary decomposition method is employed to analyse single-trial event-related potentials (ERPs), thereby extending the traditional method of averaging. Using a conventional auditory oddball paradigm with 40 target stimuli, single-trial ERPs in 40 normal subjects were analysed for midline scalp (Fz, Cz and Pz) recording sites. The normalization effect, reported in our previous study of eye blink EMGs and proposed to be a characteristic property of a wide class of non-stationary physiological processes, was found to apply to these single-trial ERPs. Fragmentary decomposition of single-trial ERPs may be regarded as re-statement of the normalization effect. This allows both pre-stimulus EEGs and post-stimulus ERPs to be regarded as overlapping generic mass potentials (GMPs), with a characteristic Gaussian amplitude spectrum. On theoretical and empirical grounds we uniquely deduce a model GMP using an introduced d" function, and physically support it by the resting and transient conditions. The model takes into account the shape of the component, which suggests a simple relationship between the peak latency and the time of the component onset. Given that GMPs may be manipulated and sorted out, we present principles of the fragmentary synthesis, i.e. probabilistic ERP reconstructions on the basis of individual and ensemble properties of its identified components. Summarizing the component quantification in the form of the dynamic model provides for the first time the opportunity to quantify all significant components in single-trial ERPs. This method of single-trial analysis opens up new possibilities of exploring the dynamical ERP changes within a recording trial, particularly in late component "cognitive" paradigms.

An integration of 40 Hz Gamma and phasic arousal: novelty and routinization processing in schizophrenia

OBJECTIVES

Frontal and lateralized schizophrenia disturbances were examined in terms of arousal-modulated changes in 40 Hz Gamma activity.

METHODS

Forty patients with schizophrenia and 40 age- and gender-matched controls were studied in a conventional auditory ERP oddball paradigm. We investigated sub-averaged Gamma activity based upon a simultaneous measure of electrodemal skin conductance response (phasic arousal) to differentiate novelty (large responses) from routinization (small or no responses). Both early Gamma (Gamma 1) and later induced Gamma (Gamma 2) activities were examined.

RESULTS

Patients with schizophrenia (compared with controls) had significantly reduced Gamma 1 amplitude in the right hemisphere for novelty processing and delayed Gamma 2 latency in the left hemisphere for both novelty and routinization. Overall, reduced Gamma 1 amplitude in patients with schizophrenia was also evident.

CONCLUSIONS

These findings indicate that the normal laterality of Gamma activity is specifically disturbed in schizophrenia in response to novel, but not routine (familiar) stimuli. The distinct pattern of findings suggests a dysregulation of activation across left and right hemispheres during initial attention and preparatory phases of information processing, in particular, in patients with schizophrenia.

Application of the comet and micronucleus assays to butterfish (Pholis gunnellus) erythrocytes from the Firth of Forth, Scotland

This report describes an investigation of genotoxic effects in an inter-tidal fish species sampled along a pollution gradient in the Firth of Forth, Scotland, UK. The comet assay is an electrophoretic technique for measuring DNA breakage in nuclei from individual cells and has only recently been applied to field investigations of genotoxicity. The measurement of nuclear anomalies (NA), such as the presence of micronuclei (MN) and 'lobes', has been successfully utilised in many field studies of genotoxic effects of contaminated sediments. These two techniques were applied to nucleated red blood cells (RBC) from the butterfish, Pholis gunnellus. The comet assay was adapted and validated for use in this species. Fish were sampled from the inner Firth of Forth, which has a legacy of industrial contamination and the outer Firth of Forth which is comparatively clean. The analysis of DNA strand breakage using this technique did not reveal any significant differences between animals sampled from inner and outer zones of the Firth. In contrast, MN and NA frequencies were elevated in the inner polluted zone of the Firth compared to the outer zone. This study suggests: (1) there are genotoxic effects associated with contaminants in the inner Firth of Forth, and (2) the comet assay may not be a suitable genotoxicity biomarker in fish.

Crystal structure of UDP-N-acetylmuramoyl-L-alanyl-D-glutamate: meso-diaminopimelate ligase from Escherichia coli

UDP-N-acetylmuramoyl-l-alanyl-d-glutamate:meso-diaminopimelate ligase is a cytoplasmic enzyme that catalyzes the addition of meso-diaminopimelic acid to nucleotide precursor UDP-N-acetylmuramoyl-l-alanyl-d-glutamate in the biosynthesis of bacterial cell-wall peptidoglycan. The crystal structure of the Escherichia coli enzyme in the presence of the final product of the enzymatic reaction, UDP-MurNAc-l-Ala-gamma-d-Glu-meso-A(2)pm, has been solved to 2.0 A resolution. Phase information was obtained by multiwavelength anomalous dispersion using the K shell edge of selenium. The protein consists of three domains, two of which have a topology reminiscent of the equivalent domain found in the already established three-dimensional structure of the UDP-N-acetylmuramoyl-l-alanine: D-glutamate-ligase (MurD) ligase, which catalyzes the immediate previous step of incorporation of d-glutamic acid in the biosynthesis of the peptidoglycan precursor. The refined model reveals the binding site for UDP-MurNAc-l-Ala-gamma-d-Glu-meso-A(2)pm, and comparison with the six known MurD structures allowed the identification of residues involved in the enzymatic mechanism. Interestingly, during refinement, an excess of electron density was observed, leading to the conclusion that, as in MurD, a carbamylated lysine residue is present in the active site. In addition, the structural determinant responsible for the selection of the amino acid to be added to the nucleotide precursor was identified.

The modulation of late component event related potentials by pre-stimulus EEG theta activity in ADHD

Electroencephalography (EEG) and Event Related Potentials (ERPs) studies in ADHD have generally been studied separately. This study examined these measures simultaneously in 54 adolescent unmedicated ADHD males and age and gender matched normal controls during an auditory oddball paradigm. Compared with controls, ADHD patients showed increased pre-stimulus EEG Theta activity and post-stimulus reduced N200 amplitude, increased P200 amplitude and delayed N200 and P300 latencies evoked to target stimuli. Moreover, Theta activity was negatively correlated with N200 amplitude and positively correlated with P200, N200 and P300 latency in ADHD. There were no correlations in the control group. Pre-stimulus preparatory state increases in Theta activity in ADHD may underlie some of the reported disturbances in information processing reflected in ADHD.

The topography of quantified electroencephalography in three syndromes of schizophrenia

This study investigated the association between quantified electroencephalography (qEEG) and three psychopathological syndromes, derived by a factor analysis of the symptom profile of a group of 40 subjects diagnosed with schizophrenia. An initial comparison with aged and sex matched normal controls showed an overall increase in slow wave activity in subjects with schizophrenia. The symptomatology of the subjects with schizophrenia was then factor analysed into three psychopathological syndromes that closely resembled Liddle's (1987b) original delineation. Correlations were undertaken between the three syndrome scores and qEEG. The "psychomotor poverty" factor was associated with increased beta activity most marked posteriorly and increased delta activity (accounted for by the effects of medication). The "disorganisation" factor was associated with widespread negative correlations in the alpha and beta bands and the "reality distortion" factor was associated positively with left anterior alpha activity. These distinct patterns of qEEG that clearly differentiate between the three syndromes, may contribute towards elucidating the underlying pathophysiological processes in schizophrenia. The results support the use of symptom based syndromes in reducing the diversity of findings in schizophrenia.

Sex differences, gamma activity and schizophrenia

This study explores the possibility that the more favourable clinical prognosis in females with schizophrenia may be associated with their greater network interconnectedness, which is possibly reflected in enhanced "Gamma" (40 Hz) electrical brain activity. An auditory "oddball" task was administered to 35 patients with schizophrenia and 35 age and sex matched controls (25 males and 10 females). Peak Gamma amplitude (from a time series of Gamma activity averaged for 40 target stimuli, as well as the immediately preceding 40 background tones) was examined across 19 sites. Peak Gamma activity occurred 250 to 450 ms in targets and 350 to 550 ms in backgrounds. Multiple within and between group MANOVAs were undertaken analysing both Peak Gamma amplitude (microvolts) and latency (milliseconds). Within-group, the control males showed a pattern of earlier Gamma latency in the right compared with the left hemisphere (F(1, 33)=3.70, p<.06), while control females exhibited delayed latency frontally compared with the posterior region (F(1, 33)=6.25, p<.04). This male lateralization finding and the anterior/posterior gradient in females is consistent with Goldberg's model. The patient group however, failed to show this male lateralized and female frontal-posterior pattern of Gamma activity, suggesting suboptimal network integration in the patient group, in both males and females.

Event-related potentials to threat-related faces in schizophrenia

Specialised network disturbances such as abnormalities in processing faces, may be associated with functional disturbances of interpersonal communication in schizophrenia. This study focused on the temporal dimension, investigating facial processing deficits in patients with schizophrenia (and non-patient controls) in a passive event-related potential (ERP) paradigm. ERPs invoked to an angry and neutral face stimulus were recorded in 27 patients with schizophrenia and 27 age and sex matched normal controls. Patients with schizophrenia showed a significant generalised delay, and diminished P200 amplitude (primarily frontal) for both stimuli-with more widespread regions of disturbance associated with the angry face. Normal controls, on the other hand, showed relatively reduced posterior P200 amplitude for angry compared to neutral faces, and a lateralised pattern of engagement in response to both stimuli. These findings indicate suboptimal processing of neutral faces in patients with schizophrenia, further exacerbated for affect laden angry faces.

Heme ligation and conformational plasticity in the isolated c domain of cytochrome cd1 nitrite reductase

The heme ligation in the isolated c domain of Paracoccus pantotrophus cytochrome cd(1) nitrite reductase has been characterized in both oxidation states in solution by NMR spectroscopy. In the reduced form, the heme ligands are His69-Met106, and the tertiary structure around the c heme is similar to that found in reduced crystals of intact cytochrome cd1 nitrite reductase. In the oxidized state, however, the structure of the isolated c domain is different from the structure seen in oxidized crystals of intact cytochrome cd1, where the c heme ligands are His69-His17. An equilibrium mixture of heme ligands is present in isolated oxidized c domain. Two-dimensional exchange NMR spectroscopy shows that the dominant species has His69-Met106 ligation, similar to reduced c domains. This form is in equilibrium with a high-spin form in which Met106 has left the heme iron. Melting studies show that the midpoint of unfolding of the isolated c domain is 320.9 +/- 1.2 K in the oxidized and 357.7 +/- 0.6 K in the reduced form. The thermally denatured forms are high-spin in both oxidation states. The results reveal how redox changes modulate conformational plasticity around the c heme and show the first key steps in the mechanism that lead to ligand switching in the holoenzyme. This process is not solely a function of the properties of the c domain. The role of the d1 heme in guiding His17 to the c heme in the oxidized holoenzyme is discussed.

Syndromes of schizophrenia and smooth-pursuit eye movement dysfunction

There have been a number of studies on smooth pursuit eye movement (SPEM) dysfunction in schizophrenia. However, the association between SPEM dysfunction and particular clinical symptoms remains unclear. We examined SPEM dysfunction in relation to schizophrenic symptoms using both the positive/negative dichotomy and the three-syndrome model. Subjects included 78 patients with schizophrenia and 60 healthy control subjects. SPEM performance was indexed by root mean square error. Symptom profiles were assessed using the Positive and Negative Syndrome Scale (PANSS), and the three-primary syndromes were identified by factor analysis of PANSS ratings (Psychomotor poverty: deficit negative symptoms; Disorganization: defined primarily by thought disorder; and Reality distortion: hallucinations and delusions). Compared with controls, the schizophrenia group showed significant impairment in global SPEM function. The three-syndrome approach produced more specific findings than the dichotomous model. Of the three syndromes, only the Disorganization dimension showed a significant association with increased global SPEM dysfunction. The specificity of SPEM dysfunction to Disorganization was verified in comparisons among schizophrenia subgroups and the control group. By contrast, the general domains of positive and negative symptoms were both found to be modestly associated with SPEM dysfunction. The separation of positive and negative symptoms that contribute to Disorganization from those that define Reality Distortion and Psychomotor Poverty has revealed significant new associations between SPEM and schizophrenic symptoms. These findings are interpreted in light of the proposal that the Disorganization syndrome is the central form of pathology in schizophrenia.

Prediction of electroencephalographic spectra from neurophysiology

A recent neurophysical model of propagation of electrical waves in the cortex is extended to include a physiologically motivated subcortical feedback loop via the thalamus. The electroencephalographic spectrum when the system is driven by white noise is then calculated analytically in terms of physiological parameters, including the effects of filtering of signals by the cerebrospinal fluid, skull, and scalp. The spectral power at low frequencies is found to vary as f(-1) when awake and f(-3) when asleep, with a breakpoint to a steeper power-law tail at frequencies above about 20 Hz in both cases; the f(-1) range concurs with recent magnetoencephalographic observations of such a regime. Parameter sensitivities are explored, enabling a model with fewer free parameters to be proposed, and showing that spectra predicted for physiologically reasonable parameter values strongly resemble those observed in the laboratory. Alpha and beta peaks seen near 10 Hz and twice that frequency, respectively, in the relaxed wakeful state are generated via subcortical feedback in this model, thereby leading to predictions of their frequencies in terms of physiological parameters, and of correlations in their occurrence. Subcortical feedback is also predicted to be responsible for production of anticorrelated peaks in deep sleep states that correspond to the occurrence of theta rhythm at around half the alpha frequency and sleep spindles at 3/2 times the alpha frequency. An additional positively correlated waking peak near three times the alpha frequency is also predicted and tentatively observed, as are two new types of sleep spindle near 5/2 and 7/2 times the alpha frequency, and anticorrelated with alpha. These results provide a theoretical basis for the conventional division of EEG spectra into frequency bands, but imply that the exact bounds of these bands depend on the individual. Three types of potential instability are found: one at zero frequency, another in the theta band at around half the alpha frequency, and a third at the alpha frequency itself.

Late component ERPs are associated with three syndromes in schizophrenia

Previous studies have revealed various abnormalities in late-component ERP amplitude and latency in schizophrenia, considered as a diagnostic category. The aim of this study was to investigate the within-sample associations between late-component ERPs and three primary syndromes of schizophrenia Reality Distortion, Psychomotor Poverty and Disorganisation. Subjects included 40 schizophrenics and 40 age and sex matched nonpsychiatric controls. Auditory ERPs (N100, N200, P200, P300) were elicited using an auditory oddball paradigm. Between-group analyses of target data showed reduced N100, N200 and P300 amplitude, increased P200 amplitude and delayed N200 latency in schizophrenics compared to controls. For non-target data, schizophrenics showed similarly reduced N100 amplitude and delayed N200 latency. Within-group analyses of target data showed that the three syndromes (determined by principal component analysis of PANSS ratings) were differentiated by ERP latency, but not amplitude (Disorganisation delayed left hemisphere P200 and P300 latency; Reality Distortion earlier global, midline and left hemisphere N200 latency; Psychomotor Poverty delayed posterior N100 latency). Notably, only Disorganisation showed a divergent pattern of associations with non-target ERP data: reduced P200 amplitude and delayed N100 latency.