Preattentive dysfunction in patients with bipolar disorder as revealed by the pitch‐mismatch negativity: a magnetoencephalography ( MEG ) study

Objectives Mismatch negativity ( MMN ) and its magnetic counterpart ( MMN m) are thought to reflect an automatic process that detects a difference between an incoming stimulus and the sensory memory trace of preceding stimuli. In patients with schizophrenia, an attenuation of the MMN / MMN m amplitude has been repeatedly reported. Heschl's gyrus ( HG ) is one of the major generators of MMN and the functional alteration of HG has been reported in patients with bipolar disorder. The present study investigated the pitch‐ MMN m in patients with bipolar disorder using whole‐head 306‐ch magnetoencephalography ( MEG ). Methods Twenty‐two patients and 22 healthy controls participated in this study. Subjects were presented with two types of auditory stimulus sequences. One consisted of 1,000 Hz standards (probability = 90%) and 1,200 Hz deviants (probability = 10%), and the other consisted of 1,000 Hz standards (90%) and 1,200 Hz deviants (10%). These two tasks were each performed twice. Event‐related brain responses to standard tones were subtracted from responses to deviant tones. Results Patients with bipolar disorder showed a significant bilateral reduction in magnetic global field power ( mGFP ) amplitudes (p = 0.02) and dipole moments of the MMNm (p = 0.04) compared with healthy controls. Patients with admission experience showed significantly reduced mGFP amplitudes of MMNm compared with patients without admission experience (p = 0.004). Additionally, patients with more severe manic symptoms had smaller mGFP amplitudes of MMNm (ρ = −0.50, p = 0.05). Conclusions The results of this study suggest that patients with bipolar disorder may exhibit preattentive auditory dysfunction indexed by reduced pitch‐ MMN m responses. Pitch‐ MMN m could be a potential trait marker reflecting the global severity of bipolar disorder.