Objective: It has recently been hypothesized that synaptic plasticity may play an important role in the pathophysiology and treatment of bipolar disorders. In this study, we aimed to induce and assess plastic modifications of evoked responses in the visual system of healthy controls. In addition, we aimed to examine whether this form of plasticity is altered in patients with bipolar II disorder (BD-II).
Methods: Recordings of visually evoked potentials (VEPs) in healthy controls and BD-II patients. Clinical information was obtained using standardized questionnaires and interviews.
Results: In healthy controls, a 10-minute modulation phase using checkerboard reversals (2 Hz) resulted in significant plasticity of the VEP. The P1 and N1 peak as well as the P1-N1 peak-to-peak amplitude were all significantly increased, of which we found the P1-N1 peak-to-peak amplitude to be the most robust measure of the effect. In BD-II patients, no significant plasticity of the VEP was found. Comparing the healthy controls and patients, we found a significant group difference in the P1-N1 peak-to-peak plasticity. We found no significant correlations when exploring possible relationships between P1-N1 peak-to-peak plasticity and clinical variables in the patient group.
Conclusions: These findings suggest that plasticity of the VEP is an accessible and robust method for assessing neocortical plasticity in the intact human brain. The current evidence supports the notion that VEP plasticity reflects a form of neocortical plasticity closely related to long-term potentiation. Patients with BD-II had impaired neocortical plasticity relative to healthy controls. Future studies should longitudinally assess plasticity of the VEP in BD-II before and after treatment.