Auditory steady state response in bipolar disorder: relation to clinical state, cognitive performance, medication status, and substance disorders

Objectives: Abnormalities in auditory steady state response (ASSR) at gamma range frequencies have been found in bipolar disorder, but the relationship of these neurophysiological disturbances to clinical factors has not been well characterized. We therefore evaluated the ASSR in bipolar disorder and examined its sensitivity to clinical symptoms, cognitive function, and pharmacological treatment. Methods: A total of 68 patients with bipolar disorder and 77 control participants were evaluated. Click trains presented at 20, 30, 40, and 50 Hz evoked ASSRs. Mean trial power (MTP) and phase locking factor (PLF) measured response magnitude and phase synchronization of the ASSR at each stimulation frequency. Clinical state, pharmacological treatment, and neuropsychological performance were assessed, and their respective relationships with ASSR measures were evaluated. Results: Patients with bipolar disorder showed reduced MTP and PLF compared to control participants. Bipolar disorder patients taking psychotropic medications had decreased PLF relative to patients withdrawn from medications. Control participants performed better on neuropsychological tests than bipolar disorder patients; however, test scores did not correlate with ASSR measures. Conclusions: Deficits in the generation and maintenance of ASSR are present in bipolar disorder, implicating disturbances in auditory pathways. ASSR may be sensitive to medication status. Other clinical features, including mood state, psychotic features, cognitive performance, smoking, or history of substance use disorder, were unrelated to MTP or PLF.