Neurophysiological findings in patients with bipolar disorder.

The present article reviews findings from measuring evoked and event-related responses, neural oscillation and synchronization, and near-infrared spectroscopy (NIRS) studies in patients with bipolar disorder. Studies of evoked responses have indicated that the P50 suppression deficits may be related to the generation of psychosis and may constitute an endophenotype of bipolar disorder patients with psychotic features. The N100 may be intact in patients with bipolar disorder, and the N100 might be a biological index to distinguish bipolar disorder and schizophrenia. In studies of event-related responses, bipolar disorder patients appear to exhibit P300 abnormalities to some extent. In addition, some bipolar disorder patients may have preattentive dysfunction, indexed by abnormal mismatch negativities. Recent studies of neural oscillations suggest that bipolar disorder may be characterized by deficits in the auditory steady-state response. Moreover, bipolar patients may have altered gamma band responses, as well as abnormal beta and alpha activities perhaps related to deficits of fronto-temporal-parietal functional connectivity. NIRS studies of bipolar disorder have indicated hypofrontality during a verbal fluency task, and altered NIRS responses compared with those of patients with major depressive disorder or healthy subjects. In future studies, these techniques may be used to elucidate the neurophysiological abnormalities in patients with bipolar disorder. Moreover, neurophysiological approaches may reveal appropriate biological indices to distinguish bipolar disorder and schizophrenia, aiding the development of more effective medication at the early stages of illness.