Behavioural correlates of age-related differences in movement representation

In the past few years, several functional MRI (fMRI) studies have revealed pronounced aging effects on cortical activation patterns during a variety of cognitive or perceptual tasks. It has been suggested that increased task-related activation in old subjects may signal beneficial compensatory activity to counteract structural and neurochemical changes associated with the normal aging process.

Under the assumption that incremental movement rates are associated with an increased functional demand on the motor system we used fMRI to investigate the behavioural significance of additionally recruited brain regions in a group of healthy, old subjects (mean age 66yrs.) compared with a group of young (mean age 23yrs.) subjects during motor activation. The performance of acoustically paced movements of the right index finger at six different frequencies (2.0, 2.5, 3.0, 4.0, 5.0 and 6.0Hz) was identical in both groups. Across all subjects and frequencies a typical pattern of activation was observed, which mainly included the contralateral sensorimotor cortex (SMC), the parietal cortex, the ipsilateral cerebellum and supplementary motor areas (SMA). In addition to these regions older subjects also demonstrated significant brain activation within the ipsilateral SMC and premotor cortex. The magnitude of the hemodynamic response increased linearly with the frequency of the finger tapping task at the level of the SMA and left SMC in both groups, whereas the magnitude of the hemodynamic response did not change with increasing movement rate in those regions showing significant overactivation in the elderly subjects.

In contrast to previous findings during perceptual and cognitive paradigms these results do not support the notion that additionally activated brain structures within the motor system of old subjects necessarily reflect a purposeful response to compensate for the neurobiological changes of aging.