Brain sensorimotor hand area organization and functionality in acute stroke: insights from MEG

A 'snapshot' of the acute phase following a cerebral stroke is fundamental to understand the brain's adaptation potential, which plays a key role in clinical recovery. In the present study, the characteristics of the spontaneous cerebral activity of the rolandic region and the evoked response following the stimulation of the median nerve have been studied trough magnetoencephalographic (MEG) recordings in 32 patients admitted to neurological ward for first-ever acute ischaemic stroke involving upper limb and hand. Both in affected (AH) and un-affected hemispheres (UH) spontaneous activity evaluation was performed by analysis of total power and spectral properties, individual alpha frequency and spectral entropy. Evoked activity was evaluated by characterization of the cortical sources activated by stimulation of the median nerve, in terms both of absolute values in each hemisphere, and of interhemispheric differences. Interhemispheric waveshapes cross-correlations were also carried out. Neurophisiological findings were correlated with neuroradiological ones and clinical scores. In the acute phase after an ischemic attack, the rest activity showed signs suggesting: a reduction of spectral richness; an increase of the intra-regional neural synchrony; an increase of the lower with respect to the higher frequency powers. Signs of enhanced excitability were present in the AH following a cortical lesion, usually in combination with preserved hand functionality. An enhanced excitability of the UH was paired with larger lesions with cortical involvement; signs compatible with an abnormal transcallosal transmission and intracortical function of inhibitory GABAergic inter-neurons in the AH were found subtending UH enhancement. Spared responsiveness from Brodmann's area (BA) 2 and posterior parietal areas despite an altered response from BA 3b was found in six patients, combined to high hand functionality. Present results in acute phase increase the knowledge of the mechanisms governing brain adaptation/reaction capabilities, for future efforts to establish therapeutic and rehabilitative procedures.