Exploring the temporal nature of hemodynamic responses of cortical motor areas using functional MRI

Objective: To use functional MRI (fMRI) to study grouped patterns of cerebral activation and the course of hemodynamic responses during performance of two activation tasks (paradigms) using a hand-held joystick to perform movements in a repetitively fixed direction and movements in freely selected random directions. Background: Evidence from lesion, electrophysiologic, and functional imaging studies implicates prefrontal and mesial frontal cortex in motor preparation and primary motor cortex in motor execution. fMRI can be used to study cerebral activation and has practical advantages over other methods of functional neuroimaging. Methods: We acquired 100 multislice T2* -weighted data sets from five healthy volunteers during performance of each paradigm using conventional fMRI. For each paradigm, rest and movement epochs were alternated every 30 seconds. After coregistration and spatial normalization, we combined the data for group studies. We used statistical parametric mapping to compare the early (first 15 seconds) components of the movement epochs with rest as well as the late (last 15 seconds) components of the movement epochs with rest. Results: During the early phase of both paradigms, significant activation was present in rostral and caudal mesial premotor cortex. Right prefrontal cortex was significantly activated during the early component of freely selected joystick movements. Activation of rostral supplementary motor area was maintained during the late component of freely selected movements but decreased during repetitively fixed movements. In contrast, significant activation in contralateral sensorimotor cortex was maintained during both early and late components of both paradigms. Conclusions: fMRI can detect cortical activation. The temporal resolution of fMRI also allows adaptation of blood oxygenation level-dependent (BOLD) contrast signal to be detected in association cortex. However, the level of BOLD contrast signal in primary motor cortex remained significantly elevated throughout task performance.