Charalabos Papageorgiou

Design and implementation of an SVM-based computer classification system for discriminating depressive patients from healthy controls using the P600 component of ERP signals

A computer-based classification system has been designed capable of distinguishing patients with depression from normal controls by event-related potential (ERP) signals using the P600 component. Clinical material comprised 25 patients with depression and an equal number of gender and aged-matched healthy controls. All subjects were evaluated by a computerized version of the digit span Wechsler test. EEG activity was recorded and digitized from 15 scalp electrodes (leads). Seventeen features related to the shape of the waveform were generated and were employed in the design of an optimum support vector machine (SVM) classifier at each lead. The outcomes of those SVM classifiers were selected by a majority-vote engine (MVE), which assigned each subject to either the normal or depressive classes. MVE classification accuracy was 94% when using all leads and 92% or 82% when using only the right or left scalp leads, respectively. These findings support the hypothesis that depression is associated with dysfunction of right hemisphere mechanisms mediating the processing of information that assigns a specific response to a specific stimulus, as those mechanisms are reflected by the P600 component of ERPs. Our method may aid the further understanding of the neurophysiology underlying depression, due to its potentiality to integrate theories of depression and psychophysiology.

Associations of the Expanded Disability Status Scale with anxiety and depression in multiple sclerosis outpatients

Objectives – We evaluated cross‐sectionally the associations of depression and anxiety with age, sex, duration of illness, educational level, degree of disability and treatment with interferon‐β in outpatients with relapsing–remitting multiple sclerosis (RRMS) during a clinically stable phase of their illness.

Towards functional noninvasive imaging of excitable tissues inside the human body using focused microwave radiometry

Focused microwave radiometry, aiming mainly in clinical applications at measuring temperature distributions inside the human body, may provide the capability of detecting electrical conductivity variations at microwave frequencies of excitable cell clusters, such as in the case of brain tissues. A novel microwave radiometric system, including an ellipsoidal conductive wall cavity, which provides the required beamforming and focusing, is developed for the imaging of biological tissues via contactless measurements. The measurement is realized by placing the human head in the region of the first focus and collecting the radiation converged at the second by an almost isotropic dipole antenna connected to a sensitive radiometer operating at 3.5 GHz. In order to compute the focusing properties of the ellipsoidal reflector, an accurate electromagnetic numerical analysis is developed using a semianalytical method. The experimental part of this study focuses on measurements of activation of the primary somatosensory (SI) brain area, elicited during the application of the cold pressor test, a standard experimental condition inducing pain. Analysis of the measured data from 16 healthy subjects suggests that this methodology may be able to pick up activation of the SI during the pain conditions as compared with the nonpainful control conditions. Future research is needed in order to elucidate all the interacting factors involved in the interpretation of the presented results. Finally, potential limitations to the generalization of our results and strategies to improve the systems response are discussed.

Do Obsessive-Compulsive Patients and Abstinent Heroin Addicts Share a Common Psychophysiological Mechanism?

Background/Aim: Working memory (WM) and attentional deficits have been implicated in the pathophysiology of both obsessive-compulsive disorder (OCD) and opioid addiction. The P300 component of event-related potentials (ERPs) is considered as an index of on-line updating of WM and/or attentional operations involved in this function. The present study aimed at comparing the P300 elicited during a WM test in patients with prolonged heroin abstinence, those with OCD and healthy controls, in order to demonstrate possibly common underlying psychophysiological mechanisms. Methods: The P300 component was evaluated during the anticipatory period of a WM test in 20 patients characterized by a past history of opioid dependence (6 months abstinence), in 18 OCD patients, and 20 healthy subjects matched for age, sex and educational level. Results: The two patient groups showed a considerable reduction of the P300 amplitudes, located at the right frontal area as compared with healthy controls. The abstinent heroin addicts exhibited a significantly lower P300 amplitude at central frontal areas and a significantly higher P300 amplitude at the left occipital region relative to the other two groups. Furthermore, the abstinent group showed a notable delay of P300 latency relative to controls and OCD patients at the right occipital region. Moreover, the OCD patients manifested a significant prolongation of P300 located at the central prefrontal area, relative to addicts and healthy controls. Conclusions: These findings point to considerable WM and/or attentional deficits in the long-term abstinent syndrome of heroin misuse and OCD associated with distributed and prefrontal cortical circuits, respectively. Furthermore, the present findings suggest that both OCD and long-term abstinent heroin addicts may share a common impairment of WM and/or attention involving or affecting the right prefrontal areas.

Acute mobile phone effects on pre-attentive operation

There is a debate whether electromagnetic field (EMF) emitted by mobile phones (MP) have an effect on cognitive functions. Since the auditory P50 component of event-related potentials (ERPs) reflects pre-attentive processing and working memory (WM) operation, the present study was designed to investigate whether the exposure to MP-EMF affects the patterns of the P50 component of ERPs elicited during a WM test. The P50 elicited during a WM task and evoked by two warning stimuli low and high frequency (500 and 3000 Hz) has been assessed in 19 normal subjects (10 women and 9 men) both without and with exposure to a 900 MHz signal, emitted by a dipole antenna placed near the subjects. Results showed that the presence of MP-EMFs induced statistically significant increase in the amplitude of P50 evoked by the low frequency stimuli, at Fp1 and O1 electrode leads as compared to themselves without MP-EMF exposure. In contrast the exposure to MP-EMFs revealed statistically significant decrease of the amplitude of P50 evoked by the high frequency stimuli, at Fp1 electrode lead as compared to themselves without MP-EMF exposure. These findings provide evidence that the MP-EMF emitted by mobile phone affect pre-attentive information processing as it is reflected in P50 evoked potential. The basis of such an effect is unclear, although several possibilities exist and call for potential directions of future research.

Gender related differences on the EEG during a simulated mobile phone signal.

The present study investigated the gender-related influence of electromagnetic fields (EMF), similar to that emitted by mobile phones, on brain activity. Ten women and nine men performed a short memory task (Wechsler test), both without (baseline) and with exposure to a 900 MHz signal. The EEG energy of the total waveform and the &agr;, &bgr;, &dgr; and &thgr; rhythms were calculated from the recordings of 15 scalp electrodes. Baseline EEG energy of males was greater than that of females, while exposure to EMF decreased EEG energy of males and increased that of females. Memory performance was invariant to EMF exposure and gender influences. These findings indicate that EMF may exert a gender-related nfluence on brain activity.

Abnormal P600 in heroin addicts with prolonged abstinence elicited during a working memory test.

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.

GHQ‐28 as an aid to detect mental disorders in neurological inpatients

Lykouras L, Adrachta D, Kalfakis N, Oulis P, Voulgari A, Christodoulou GN, Papageorgiou C, Stefanis C. GHQ‐28 as an aid to detect mental disorders in neurological inpatients. Acta Psychiatr Scand 1996: 93: 212–216.

Psychophysiological evidence for altered information processing in delusional misidentification syndromes

Recent research provides evidence that delusional misidentification syndromes (DMS) are associated with cognitive deficits. However, the underlying mechanisms of these deficits are not known. Since the P300 component of event-related potentials (ERPs) is related to fundamental aspects of working memory (WM), the present study is focused on P300 elicited during a WM test in DMS patients, as compared to those of healthy controls. Nine patients with DMS and 11 healthy controls, matched for age, sex and educational level were tested with a computerized version of the digit span test of the Wechsler batteries. Auditory ERPs were measured during the anticipatory period of the test. DMS patients showed significant reductions in P300 amplitude at the right frontal region compared to healthy controls. P300 latency in the central midline brain region was significantly prolonged in the DMS group. Each of these measures classified correctly 90% of the two groups. Moreover, the memory performance of the patient group was significantly lower, relatively to healthy controls. These findings provide evidence supporting the suggestion that DMS is associated with psychophysiological alterations occurring at the right frontal region, which mediates automatic processes, as well as with an irregular allocation of attentional resources, involving the interhemispheric circuitry, possibly due to gray matter degeneration. Finally, present work points to a need for further research investigating the characteristics, causes, course and treatment of severe cognitive deficits associated with DMS.

Abnormal P600 in obsessive-compulsive disorder. A comparison with healthy controls

Recently, the P600 component of the event-related potential (ERP), a waveform that is thought to be generated and/or modulated by the anterior cingulate gyrus and basal ganglia has been considered as an index of second pass-parsing processes of information processing, having much in common with working memory (WM) operation. Moreover, dysfunction of these brain structures as well as WM deficits have been implicated in the pathophysiology of obsessive-compulsive disorder (OCD). The present study is focused on P600 elicited during a WM test in OCD patients compared with healthy controls. Twenty drug-free OCD patients and an equal number of normal subjects matched for age, sex and educational level were studied via a computerized version of the Wechsler digit span test. Auditory P600 was measured during the anticipatory period of this test. The patient group, as compared with healthy controls, showed significantly enhanced amplitudes of P600 at the right temporoparietal area and prolonged latencies at the right parietal region. Moreover, the memory performance of patients was significantly impaired. These findings may indicate that OCD patients manifest abnormal aspects of second pass-parsing processes of information processing as they are reflected by P600 amplitudes and latencies.