Sensorimotor gating in manic and mixed episode bipolar disorder

OBJECTIVES: Few studies have examined acoustic startle sensorimotor gating in bipolar disorder (BPD) despite the fact that patients with BPD have exhibited inhibitory dysfunctions on a variety of early information processing tasks. The present study aimed to expand the current literature through the investigation of electromyographic (EMG) measures of acoustic startle prepulse inhibition (PPI) in manic and mixed episode BPD. METHODS: Fourteen manic and 21 mixed episode BPD patients were compared to 32 healthy controls on acoustic startle measures of PPI using a 120-ms lead interval. RESULTS: Prepulse inhibition did not significantly differ across diagnostic groups (manic, mixed, control), and the presence of psychosis in the patient sample was not significantly related to PPI levels. With respect to startle response characteristics, patients in the mixed phase of the disorder showed prolonged prepulsed startle latency and attenuated responses to both probe-alone and prepulsed probes, though no differences in startle habituation were found across diagnostic groups. CONCLUSIONS: Although PPI deficits were not observed in either BPD sub-group, attenuated probe-alone and prepulsed startle magnitudes and reduced prepulse-induced latency facilitation in the mixed episode group is consistent with evidence that the mixed phase of BPD is associated with a more severe clinical outlook than other stages of the disorder. The absence of attenuated PPI in the patient sample may be due to the low incidence of psychosis in the BPD groups, though further studies are required to systematically assess the effects of symptom factors and clinical phase on sensorimotor gating in BPD.