Cortical map remodeling in the intact hemisphere and functional recovery after focal lesion to the primary somatosensory cortex

After injury to the primary somatosensory cortex (S1), most studies have focused on perilesional remodeling and its role in functional recovery. In contrast, alterations within the contralesional cortex remain poorly understood, even though the interhemispheric communication is disrupted by the lesion. Using electrophysiological mapping, we investigated in rats the time-course of cutaneous map remodeling in the intact hemisphere following unilateral focal damage to the forepaw area in S1 along with behavioral assessment of sensorimotor deficits. Cortical maps showed a representational dedifferentiation inducing a degradation of the somatotopic organization, starting immediately after the lesion and worsening until the end of the 14th day post-injury. These changes were underpinned by a dramatic enlargement of cutaneous receptive fields accompanied by an increase in neuronal sensitivity. Strong impairment of tactile sensitivity and sensorimotor adjustments was shown for the forepaw contralateral to the injured hemisphere, that gradually abated from the 2nd to the 7th week. Interestingly, deficits of fine sensorimotor adjustments were also observed in the “non-paretic” forepaw. They were less pronounced than in the “paretic” limb but evolved with a similar time course of recovery. A substantial restoration of somatotopic organization occurred gradually, in parallel with the functional recovery. Immediate post-lesion effects suggest an altered interhemispheric interplay and highlight the critical role of hemispheric cross influences in maintaining fine somatotopic organization of cutaneous maps in each hemisphere. S1 map normalization in intact cortex paralleling functional recovery may reflect compensatory mechanisms reorganizing interhemispheric communication and shaping cortical neurons' responses.