Event-Related Potentials (ERPs) provide non-invasive measurements of the electrical activity on the scalp that are linked to the presentation of stimuli and events. Brain mapping techniques are able to provide evidence for the solution of debatable issues in cognitive science. In this paper, a two-step signal classification approach is proposed, extending the use of the Low Resolution Brain Electrical Tomography (LORETA) inversion technique. The first step concerns the feature extraction module, which is based on the combination of the Multivariate Autoregressive model with the Simulated Annealing technique. The classification module, as the second step of the methodology, is implemented by means of an Artificial Neural Network (ANN) trained with the back- propagation algorithm under "leave-one-out cross- validation". The ANN is a multi-layer perceptron, the architecture of which, is selected after a detailed search. The proposed methodology has been applied for the classification of first episode schizophrenic patients and normal controls using as input signals the intracranial current sources obtained by the inversion of ERPs using the LORETA technique. Results by implementing the proposed methodology provide classification rates of up to 93.1%. Finally, the proposed methodology may be used for the design of more robust classifiers based on the head-surface measured potentials as well as on the intracranial source locations, which directly relate to cognitive mechanisms. Keywords—Multivariate Autoregression (MVAR), Simulated Annealing (SA), Classification, Cross-validation, LORETA

RATIONALE:Attentional deficits have been implicated in the pathophysiology of auditory hallucinations in schizophrenia. Since the latency of the P300 component of event-related potentials (ERPs) is considered to be a sensitive measure of stimulus classification speed, while its amplitude-a measure of attentional resource allocation when memory updating is engaged, the present study focuses on the comparison of P300 between healthy subjects and schizophrenic patients experiencing auditory hallucinations and treated with clozapine and olanzapine. METHODS:The auditory P300 was assessed during the anticipatory period of a short memory test, in 16 male hallucinated schizophrenic patients and 13 male normal subjects matched for age and educational level. The patients were reexamined under identical conditions when their hallucinations had resolved following treatment with clozapine (8 patients) and olanzapine (8 patients). RESULTS:The patients with hallucinations exhibited significantly reduced P300 amplitude at leads Fp1, F3, (C3-T5)/2, F4, Cz and Fz, when compared to the normal controls and at leads Fp1, F3, F4, (C4-T6)/2, C4, P4, Cz and Fz when compared to themselves during the remission phase. However logistic regression models revealed that the most important leads, differentiating the patient group before treatment either with the healthy controls, or with itself after treatment, were that at the left temporoparietal and at the left prefrontal area. Memory performance of the patient group, even after treatment and in spite of its significant improvement, remained significantly less than that of healthy controls. both antipsychotic agents had similar effects on the p300 amplitude and memory performance. CONCLUSIONS:These findings indicate that auditory hallucinations in schizophrenia manifest abnormal aspects of attention, mediated by a distributed network involving or affecting the left temporoparietal and left prefrontal area. Additionally, the present study points to an improvement of attentional function in schizophrenic patients experiencing auditory hallucinations, both in the clozapine group but also in the olanzapine group.

Background: Recently it has been shown that the second-pass parsing process of information processing, as indexed by the P600 component of event-related potentials (ERPs), elicited during a working memory (WM) test, is impaired in first episode schizophrenic (FES) patients. Objective: The purpose of this study is to develop a decision support system – based on artificial neural networks (ANN) technology – for the classification of patients experiencing FES compared to healthy controls,

The P600 component of event-related potentials, believed to be generated by anterior cingulate gyrus and basal ganglia, is considered as an index of aspects of second-pass parsing processes of information processing, having much in common with working memory (WM) systems. Moreover, dysfunction of these brain structures as well as WM deficits have been implicated in the pathophysiology of opioid addicts. The present study is focused on P600 elicited during a WM test in twenty heroin addicts with prolonged abstinence compared with an equal number of healthy controls. The results showed significantly prolonged latencies at right hemisphere, specifically at Fp2 abduction. Moreover, memory performance of patients did not differ from that of normal controls. These findings may indicate that abstinent heroin addicts manifest abnormal aspects of second-pass parsing processes as are reflected by the P600 latencies, elicited during a WM test. Additionally, the P600 might serve as a valuable investigative tool for a more comprehensive understanding of the neurobiological substrate of drug abuse.

Deficits of working memory (WM) are recognized as an important pathological feature in schizophrenia. Since the P600 component of event related potentials has been hypothesized that represents aspects of second-pass parsing processes of information processing, and is related to WM, the present study focuses on P600 elicited during a WM test in drug-naive first-episode schizophrenics (FES) compared to healthy controls. We examined 16 drug-naive first-episode schizophrenic patients and 23 healthy controls matched for age and sex. Compared with controls schizophrenic patients showed reduced P600 amplitude on left temporoparietal region and increased P600 amplitude on left occipital region. With regard to the latency, the patients exhibited significantly prolongation on right temporoparietal region. The obtained pattern of differences classified correctly 89.20% of patients. Memory performance of patients was also significantly impaired relative to controls. Our results suggest that second-pass parsing process of information processing, as indexed by P600, elicited during a WM test, is impaired in FES. Moreover, these findings lend support to the view that the auditory WM in schizophrenia involves or affects a circuitry including temporoparietal and occipital brain areas.