Activation of distinct motor cortex regions during ipsilateral and contralateral finger movements.

Previous studies have shown that unilateral finger movements are normally accompanied by a small activation in ipsilateral motor cortex. The magnitude of this activation has been shown to be altered in a number of conditions, particularly in association with stroke recovery. The site of this activation, however, has received limited attention. To address this question, functional magnetic resonance imaging (MRI) was used to study precentral gyrus activation in six control and three stroke patients during right index finger tapping, then during left index finger tapping. In each hemisphere, the most significantly activated site (P < 0.001 required) was identified during ipsilateral and during contralateral finger tapping. In the motor cortex of each hemisphere, the site activated during use of the ipsilateral hand differed from that found during use of the contralateral hand. Among the 11 control hemispheres showing significant activation during both motor tasks, the site for ipsilateral hand representation (relative to contralateral hand site in the same hemisphere) was significantly shifted ventrally in all 11 hemispheres (mean, 11 mm), laterally in 10/11 hemispheres (mean, 12 mm), and anteriorly in 8/11 hemispheres (mean, 10 mm). In 6 of 11 hemispheres, tapping of the contralateral finger simultaneously activated both the ipsilateral and the contralateral finger sites, suggesting bilateral motor control by the ipsilateral finger site. The sites activated during ipsilateral and contralateral hand movement showed similar differences in the unaffected hemisphere of stroke patients. The region of motor cortex activated during ipsilateral hand movements is spatially distinct from that identified during contralateral hand movements.