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Our data demonstrate major effects of vagus nerve stimulation on both daytime alertness (which is improved) and nocturnal rapid eye movement sleep (which is reduced). These effects could be interpreted as the result of a destabilizing action of vagus nerve stimulation on neural structures regulating sleep-wake and rapid eye movement/non-rapid eye movement sleep cycles. Lower intensity vagus nerve stimulation seems only to improve alertness; higher intensity vagus nerve stimulation seems able to exert an adjunctive rapid eye movement sleep-attenuating effect.

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Oscillatory mass responses centered at about 20-35 Hz or 100-120 Hz occur (after contrast or luminance visual stimulation, respectively) in the retina and cortex of animals and man and are recorded by electrical or magnetic methods. These oscillatory events reflect stimulus-related uni/multicellular oscillations of the firing rate/membrane potential and result from synchronization of neuronal assemblies selectively responding to the stimulus characteristics. Methodological problems in the study of these events derive from the contiguity in frequency between the ERG or VEP and the oscillatory responses and from the need to reliably define oscillatory events in time and frequency. Two methods (time-frequency analysis by matching pursuit and locking index) have been implemented to approach this issue. Theory and application are reviewed.