Neurophysiological studies of sensory gating in mania: comparison with schizophrenia.

The action of central nervous system mechanisms involved in sensory gating was assessed in acutely psychotic manic patients. An early positive component of the auditory average evoked response, recorded at the vertex 50 msec after a click stimulus, was studied. Stimuli were delivered at 10-sec intervals to establish a base-line response. Sensory gating mechanisms were then tested using a conditioning-testing paradigm to assess the change in response to a second stimulus following the first at either 0.5-, 1.0- or 2.0-sec intervals. A similar paradigm had been used previously to assess deficits in this function in acute and chronic schizophrenics. We found a deficit in sensory gating in acutely manic patients. similar to that found in schizophrenics, although the variability in response was more marked in the manic patients. We followed these patients during their treatment on lithium carbonate and found a return of these neuronal functions towards normal values which corresponded to their clinical improvement. A series of stable euthymic bipolar patients were found to have responses indistinguishable from normal controls. The data suggest that deficits in neuronal gating functions, similar to those found in schizophrenia, can be seen during acute mania but these deficits return to normal as the acute psychosis abates.