Whole-head MEG data were acquired during the standard paired-click paradigm in 20 bipolar I disorder patients and 20 healthy controls. The M50 and the M100 responses were investigated, and dipole source localizations were also investigated. Sensory gating were determined by measuring the strength of the M50 and the M100 response to the second click divided by that of the first click (S2/S1).
In every subject, M50 and M100 dipolar sources localized to the left and right posterior portion of superior temporal gyrus (STG). Bipolar I disorder patients showed bilateral gating deficits in M50 and M100. The bilateral M50 S2 source strengths were significantly higher in the bipolar I disorder group compared to the control group.
The sample size was relatively small. More studies with larger sample sizes are warranted. Bipolar subjects were taking a wide range of medications that could not be readily controlled for.
These findings suggest that bipolar I disorder patients have auditory gating deficits at both pre-attentive and early attentive levels, which might be related to STG structural abnormality.