We investigated the role of ipsilateral ascending pathways in the neural coupling underlying cooperative hand movements of stroke subjects. Ipsi- and contralateral somatosensory evoked potentials (SSEP) were recorded following ulnar nerve stimulation during cooperative and non-cooperative hand movements. The amplitude ratio, that is, ipsilateral divided by contralateral amplitude, was highest during the cooperative task when the affected arm was stimulated, reflecting an enhanced afferent volley to the unaffected hemisphere. The presence of ipsilateral SSEP from the paretic arm was closely related with the patients’ hand function. This shows for the first time a laterality in ascending pathways after unilateral stroke and implies an involvement of the unaffected hemisphere in the control of paretic hand movements.
Cooperative hand movements, defined as movements where the action of one hand is supported by counteraction of the other one (e.g., opening a bottle), are required in activities of daily living (ADL). These object-oriented movements are controlled by a task-specific neural coupling[1-3] which differs from that of neural networks underlying the control of non-cooperative bimanual tasks[4-11]. These bimanual separate hand movements, in contrast to cooperative hand movements studied here, do not use the neural coupling mechanism in movement control. The neural coupling is reflected in the appearance of electromyographic (EMG) reflex responses in activated forearm muscles of both sides following unilateral stimulation of ulnar nerve and activation of bilateral secondary somatosensory (S2) cortical areas in fMRI recordings. These observations indicate that each hemisphere is task-specifically involved in the control of both hands during cooperative movements. The neural coupling underlying cooperative hand movements might be achieved by an involvement of ipsilateral pathways.
In stroke subjects, the neural coupling mechanism is preserved from the unaffected to the paretic side but defective from the affected side due to an impaired processing of afferent input. For a better understanding of the compensatory role of the ipsilateral, unaffected hemisphere in movement control it is important to explore the function of ascending pathways in cooperative tasks. It is hypothesized that the strength of ipsilateral afference from the affected forearm to the unaffected hemisphere is reflected in ipsilateral somatosensory evoked potentials (SSEPs). This would indicate an involvement of the unaffected hemisphere in the control of the paretic arm/hand during cooperative movements and might determine outcome of hand function.
Continue —> Neural coupling of cooperative hand movements after stroke: role of ipsilateral afference – Schrafl-Altermatt – 2016 – Annals of Clinical and Translational Neurology – Wiley Online Library