Increased cortical inhibition in depression: a prolonged silent period with transcranial magnetic stimulation (TMS)

Background. Motor slowing in depression may be associated with a relative d opaminergic (DA) deficit. Bradykinesia in Parkinson's syndrome is associate d with an abnormally short silent period (SP) using transcranial magnetic s timulation (TMS). We hypothesized that depression would also be associated with a short SP. Methods. Sixteen patients with DSM-IV depression and 19 matched controls pa rticipated. SPs were elicited by exercising the contralateral abductor poli cis brevis (APB) during TMS. Results. The SP was significantly increased in the patient group. No correl ation was found between SP and depression score. Conclusion. A long SP suggests increased motor cortical inhibition in depre ssion. This finding is inconsistent with the hypothesis of behavioural moto r slowing in depression being associated with Parkinsonian-like mechanisms including the dopaminergic deficit. There is a need for studies incorporati ng larger patient groups to investigate potential correlations between SP a nd depression indices.