Studies have suggested that consciousness is encoded discretely in time and synchronously in space of the brain. The present study was to model the alpha EEG as a brain clock to carry out the functions and to test whether the quality and rate of the oscillation could predict behavioral timing. Results showed that the alpha peak frequency was correlated with the conflict reaction time, and the selectivity was associated with the simple reaction time. These findings are consistent with previous reports and support the hypothesis that alpha EEG represents excitability cycles and may serves as a brain clock for spatial synchronization.

No abstract

Event-related potentials of the brain are enhanced when stimulation is synchronized with diastolic phases of cerebral or cephalic pulse pressure waves. A cerebral vascular event has been found to be temporally consistent with the event-related potential. Averaged evoked vascular responses were measured with bioimpedance techniques from the brain and the arm. Changes in brain blood volume occurred 150 to 250 milliseconds after stimulation synchronized with diastolic but not systolic phases of the cerebral pulse pressure wave. The time course of this phenomenon defies the usually accepted characteristics of metabolic activity. The evoked vascular response may be a neurally mediated event in anticipation of altered metabolic demand, and it offers the possibility of measurement in real time.

These results indicate that examiner-assisted, computerized administration is equivalent to traditional, paper-based administration, and shows significantly greater test-retest reliability.

Auditory event-related potentials (ERPs) to pure tones and performance on a measure of item recognition were compared in 20 controls, 14 alcoholics, 20 depressed and 21 schizophrenic patients. Compared with normal controls, P2 and N2 were delayed and of diminished amplitude in the psychopathological groups. Increased amplitude of P1 in alcoholics, diminished N1 in depressed patients, increased latencies of N1 in schizophrenics and N2 in alcoholics were pathology-specific. Unusual patterns of response in the item recognition test (elevated intercept and flattened slope) and its relationship with ERPs distinguished the diagnostic groups from the controls. Support for the preferential involvement of the left hemisphere in schizophrenia and of the right hemisphere in depression was found. Disinhibition of CNS activity in the response of alcoholics (increased P1 and delayed P3) was indicated. The findings suggested that discriminant analysis of auditory ERPs to simple, pure tones, in conjunction with psychometric data significantly differentiated pathologic groups from each other and from controls.