N2 and P3b components of the event-related potential in students at risk for psychosis.

The N2 and P3b components of event-related potentials (ERPs) were studied in students who were identified as being at high risk for psychosis on the basis of their scores on the Chapman Psychosis Proneness Scales (PPS). The Magical Ideation subscale (MIS), the Perceptual Aberration subscale (PABS), and the Social Anhedonia subscale (SAS) were administered to 2,022 undergraduate university students. To determine if there were any relationships between these psychometric instruments and electrophysiological measures, 40 high-risk students were compared with 40 age- and gender-matched control students using auditory ERPs obtained from three midline electrodes (Fz, Cz, Pz) in a standard oddball paradigm. N2 (rare stimuli) and N2b latencies were significantly longer in the high-risk than in the control subjects, and the high-risk group also evidenced significantly smaller amplitude of the P3b component. No significant correlations between scores on the PPS or its three subscales and the amplitudes or latencies of the P3b or N200 component were found. These findings suggest that the N2 and P3b ERP components might serve as trait markers for psychosis and that individuals psychometrically identified as being at high risk for psychosis have deficits in the maintenance of attention and in decision-making.

Regional correlations between the EEG and oxygen metabolism in dementia of Alzheimer's type.

To determine the relationship between EEG slowing and cerebral hypometabolism in dementia, 10 patients with dementia of Alzheimer's type (DAT) were evaluated with quantitative topographic EEG and positron emission tomography (PET). Power in each 1-Hz frequency band from 2-20 Hz, power ratio index, and normalised PET data from corresponding cortical sites were compared to data obtained from 20 normal volunteers. PET revealed significant parieto-temporal hypometabolism, and topographic EEG mapping and power spectrum analysis revealed a slowing of the background EEG that was most pronounced in the parietal-temporal areas. Correlation analysis between EEG power spectrum data and CMRO2 revealed significant negative correlations for frequencies below 8 Hz and significant positive correlations above 8 Hz in the parieto-temporal regions, which have previously been identified as the areas most severely affected by pathological changes associated with DAT. Correlation coefficients plotted as functions of frequency illustrated the relationships between EEG changes and reduced CMRO2, supporting previous views that EEG slowing in DAT may be related to hypometabolism in cortical regions most affected by the disease.

Laterality of mental imagery generation and operation: tests with brain-damaged patients and normal adults.

The relationships between hemispheric function and components of the imagery process were examined in patients with unilateral right and left brain damage and in intact adult subjects. In the image generation condition, subjects were required to mentally generate Katakana letters corresponding to Hiragana letters displayed on a CRT. The results for the intact adults suggested a left hemisphere superiority, but the unilaterally brain-damaged subjects showed no hemispheric difference in this task. In the imagery operation task (transformation or lateral translation), subjects were asked to find a genuine Kanji among distractors (pseudo-Kanji) that were constructed from two Kanji radicals (themselves real Kanji) that were either displayed in reverse order or shifted apart. The results for both intact adults and patients with unilateral brain damage suggest the superiority of the right hemisphere.