Cortical Reorganization of Early Somatosensory Processing in Hemiparetic Stroke

Abstract

The cortical motor system can be reorganized following a stroke, with increased recruitment of the contralesional hemisphere. However, it is unknown whether a similar hemispheric shift occurs in the somatosensory system to adapt to this motor change, and whether this is related to movement impairments. This proof-of-concept study assessed somatosensory evoked potentials (SEPs), P50 and N100, in hemiparetic stroke participants and age-matched controls using high-density electroencephalograph (EEG) recordings during tactile finger stimulation. The laterality index was calculated to determine the hemispheric dominance of the SEP and re-confirmed with source localization. The study found that latencies of P50 and N100 were significantly delayed in stroke brains when stimulating the paretic hand. The amplitude of P50 in the contralateral (to stimulated hand) hemisphere was negatively correlated with the Fügl–Meyer upper extremity motor score in stroke. Bilateral cortical responses were detected in stroke, while only contralateral cortical responses were shown in controls, resulting in a significant difference in the laterality index. These results suggested that somatosensory reorganization after stroke involves increased recruitment of ipsilateral cortical regions, especially for the N100 SEP component. This reorganization delays the latency of somatosensory processing after a stroke. This research provided new insights related to the somatosensory reorganization after stroke, which could enrich future hypothesis-driven therapeutic rehabilitation strategies from a sensory or sensory-motor perspective.

EEG Responses to Upper Limb Pinprick Stimulation in Acute and Early Subacute Motor and Sensorimotor Stroke

“…Given the sensory nature of pinprick, this was to be expected (2). However, not in agreement with previous research, the reduced amplitudes of somatosensory evoked potentials were not significantly correlated to the motor clinical score (14). This could be due the different sensory stimuli be applied to the upper limb, as previous work used median nerve stimulation, which involves different ascending sensory pathways and corticospinal projections compared to pinprick, leading to a decreased contribution to the motor impairment (44).…”

“…When combined with somatosensory evoked potentials (SEPs), EEG can provide information on the integrity of the central nervous system's motor and somatosensory pathways. Notably, the absence of SEPs indicates poor upper limb recovery (14)(15)(16).…”

Comparison of Immediate Neuromodulatory Effects between Focal Vibratory and Electrical Sensory Stimulations after Stroke

“…In contrast, the αERD over the contralesional hemisphere remained after stroke ( Figure 7 C, stroke group, and Figure 8 A), but the αERD over the ipsilesional hemisphere was significantly weakened ( Figure 8 B). This observation agreed with previous findings that the reorganization of somatosensory neurocircuits after stroke involves cortical recruitment concentrated in contralesional cortical regions, i.e., contralesional compensation [ 67 , 68 ]. Furthermore, αERD peaks shifted to the contralesional parietal–occipital area in the stroke group ( Figure 8 A), which revealed that the contralesional somatosensory association cortex and visual cortex outside the S1 were involved in the sensory process poststroke [ 23 , 69 ].…”

Identifying biomarkers related to motor function in chronic stroke: A fNIRS and TMS study

“…This suggests that the contralesional hemisphere may compensate for the loss of the ipsilesional hemisphere by reshaping neuronal circuits and establishing new sensory processing pathways. Interestingly, a recent study by Williamson et al 43 . reported a hemispheric shift in sensory processing after stroke, with bilateral activation of S1 in response to tactile stimulation of the paretic hand in stroke patients, while healthy controls showed only contralateral S1 activation.…”

“…42 This suggests that the contralesional hemisphere may compensate for the loss of the ipsilesional hemisphere by reshaping neuronal circuits and establishing new sensory processing pathways. Interestingly, a recent study by Williamson et al 43 reported a hemispheric shift in sensory processing after stroke, with bilateral activation of S1 in response to tactile stimulation of the paretic hand in stroke patients, while healthy controls showed only contralateral S1 activation. This finding is consistent with our results, indicating a higher degree of reliance on the contralesional hemisphere for sensory processing in severely impaired patients compared to those with mild to moderate impairment.…”