PRIMARY MOTOR AND SENSORY CORTEX ACTIVATION DURING MOTOR-PERFORMANCE AND MOTOR IMAGERY - A FUNCTIONAL MAGNETIC-RESONANCE-IMAGING STUDY

The intensity and spatial distribution of functional activation in the left precentral and postcentral gyri during actual motor performance (MP) and mental representation [motor imagery (MI)] of self-paced fing er-to-thumb opposition movements of the dominant hand were investigate d in fourteen right-handed volunteers by functional magnetic resonance imaging (fMRI) techniques. Significant increases in mean normalized f MRI signal intensities over values obtained during the control (visual imagery) tasks were found in a region including the anterior bank and crown of the central sulcus, the presumed site of the primary motor c ortex, during both MP (mean percentage increase, 2.1%) and MI (0.8%). In the anterior portion of the precentral gyrus and the postcentral gy rus, mean functional activity levels were also increased during both c onditions (MP, 1.7 and 1.2%; MI, 0.6 and 0.4%, respectively). To locat e activated foci during MI, MP, or both conditions, the time course of the signal intensities of pixels lying in the precentral or postcentr al gyrus was plotted against single-step or double-step waveforms, whe re the steps of the waveform corresponded to different tasks. Pixels s ignificantly (r > 0.7) activated during both MP and MI were identified in each region in the majority of subjects; percentage increases in s ignal intensity during MI were on average 30% as great as increases du ring MP. The pixels activated during both MP and MI appear to represen t a large fraction of the whole population-activated during MP. These results support the hypothesis that MI and MP involve overlapping neur al networks in perirolandic cortical areas.