Specific changes in somatosensory evoked magnetic fields during recovery from sensorimotor stroke

We studied recovery-induced changes in the responsiveness of the primary so matosensory cortex in stroke patients with sensory and/or motor symptoms. S omatosensory evoked magnetic fields, in response to median nerve stimulatio n, were recorded in 14 patients with their first symptomatic unilateral str oke 1 to 15 days from the first symptoms and again 2 to 3 months later. Neu ronal activity at the contralateral primary somatosensory cortex was modele d with equivalent current dipoles at the peak latencies of the first two co rtical deflections at about 20 msec (Nlm) and at 28 to 91 msec (Plm). Twent y-three age-matched healthy volunteers, 9 of whom were tested also in seria l recordings, served as control subjects. At follow-up, 6 patients showed a significant increase of Plm amplitude, whereas Nlm increased only in 1. Cl inical improvement of two-point discrimination ability, but not of other ba sic somatosensory skills, was significantly correlated with the increase of Plm. We conclude that the recovery of discriminative touch after stroke is paralleled by the growth of the Plm somatosensory evoked magnetic field de flection, and we propose that this may reflect reestablishment of lateral i nhibitory functions at the primary somatosensory cortex.