38. Motor programming deficits in depression: support for a dopaminergic mechanism

Abstract

Several investigators have reported parallels between motor and cognitive slowing in patients with major depression (MD). Such a relationship between depression and motor function suggests the possibility of a shared neuropathologic mechanism. This mechanism has remained elusive largely because depression may involve any of several neurotransmitters. While others have shown that MD and parkinsonism share a number of features, especially in the motor domain, previous technologies have not delineated the cognitive from neuromotor aspects of the motor impairment in MD. The aim of the present study was to examine motor programming in MD patients using a measure adopted from studies of parkinsonian bradykinesia. There is a general consensus that parkinsonian bradykinesia stems from an inability to modify, or scale, velocity during movement. In the present study, we hypothesized that a substantial proportion of MD patients would exhibit deficits in velocity scaling. Our measure of velocity scaling quantifies the extent to which a subject programs or scales movement velocity in anticipation of increasing target distance. We studied 54 patients who met DSM-IV criteria for major depression and 26 age and gender comparable healthy comparison subjects. All MD patients were unmedicated at the time of testing. An instrumental measure of wrist movement was developed to quantify several aspects of movement including reaction time (RT), peak velocity (PV), and velocity scaling (VS). Subjects were instructed to flex their wrist when a target box appeared on the computer screen and to reach the target as quickly and as accurately as possible. Results indicated that MD patients exhibited significantly (p < 0.001) longer mean RT (477 ms) than comparison subjects (391 ms). There was a trend (p = 0.07) for MD patients to have lower scores on the VS measure (2.68 deg/sec/deg) compared with comparison subjects (3.33 d/s/d). 53.7% of the MD patients had VS scores lower than the 95th percentile of the comparison subjects. These findings suggest that MD patients as a group exhibit delayed reaction times. Nevertheless, a significant proportion of MD patients also exhibit disturbances in the programming of movement velocity reflective of a putative dopaminergic disturbance, similar to that seen in parkinsonism.