Activity in somatosensory cortices during stroke recovery

Abstract

The aim of the thesis was to examine how activity in somatosensory cortex changes during stroke recovery by analysing previously-recorded magnetoencephalographic (MEG) responses to tactile pneumatic stimulation and passive movement of the right and left index fingers. The measurements were made for 23 stroke patients with upper limb paresis at acute phase, one month and 12 months after stroke. To our knowledge, this is the first follow-up study to research somatosensory evoked responses to passive movement in several stroke patients.

The activity in somatosensory cortices evoked by both tactile and passive stimuli increased significantly from the acute phase to 12 months post-stroke in both affected and unaffected hemispheres. In addition, the activity was stronger in patients than in healthy control subjects at 12 months after the stroke symptoms in both hemispheres. In healthy subjects, the SEF-response amplitudes are approximately equal in two hemispheres whereas the patients had weaker responses to tactile stimuli in the affected (AH) than the unaffected hemisphere (UH) at one month after the stroke. In contrast to tactile stimuli, no significant differences between the contralateral affected and unaffected hemispheres in the passive movement were observed. However, both tactile and passive stimuli elicited enhanced activity in the ipsilateral unaffected hemisphere with respect to the impaired hand stimulation during the whole follow-up year.

In conclusion, the results confirmed that a stroke changes both proprioceptive and tactile information processing and a unilateral stroke affects both hemispheres. Moreover, the results indicate that the activity changes during one-year follow-up, which refers that neural changes occur within first three months but can continue significantly up to 12 months. Enhanced activity in the healthy hemisphere may be associated with incomplete functional recovery.