Ipsilateral activation of the unaffected motor cortex in patients with hemiparetic stroke

Background and purpose: Recent research has shown that following stroke patients can display ipsilateral activity reflecting a functional link between the undamaged hemisphere and the affected upper limb on the same side of the body. In the present study the capacity for ipsilateral activation is documented during recovery by using transcranial magnetic stimulation (TMS) and transcranial Doppler (TCD). Methods: Fourteen patients affected by hemispheric stroke were examined with TMS and TCD within 48 h of onset, and again 6 months later. Neurological signs were scored with reference to the NIHSS, and patients executed a thumb to finger opposition task so as to further estimate the motor deficit. Twenty healthy volunteers represented the control population. Results: (1) Both TMS and TCD yielded homogeneous results showing ipsilateral activity between affected hands and undamaged hemispheres. On stimulating the motor cortex 3 cm anterior and 3 cm lateral to Cz, a scalp site remote from the primary motor area, ipsilateral motor evoked potentials (iMEPs) from hand muscles were found in recovered patients. (2) In 8 controls iMEPs with smaller amplitudes than patients could be obtained by stimulating only the left hemisphere. (3) TCD revealed increased blood flow velocity in the ipsilateral MCA by activating the recovering hand (10.5±3.3%; P<0.001). Conclusion: TMS reveals a specific area in the motor cortex from which ipsilateral MEPs can be elicited and both TMS and TCD indicate that an ipsilateral corticospinal tract can be accessible in some adult controls or becomes unmasked after cerebral damage.