Sensory enrichment after peripheral nerve injury restores cortical, not thalamic, receptive field organization

Sensory perception can be severely degraded after peripheral injuries that disrupt the functional organization of the sensory maps in somatosensory co rtex, even after nerve regeneration has occurred. Rehabilitation involving sensory retraining can improve perceptual function, presumably through plas ticity mechanisms in the somatosensory processing network. However, virtual ly nothing is known about the effects of rehabilitation strategies on brain organization, or where the effects are mediated. In this study, five macaq ue monkeys received months of enriched sensory experience after median nerv e cut and repair early in life. Subsequently, the sensory representation of the hand in primary somatosensory cortex was mapped using multiunit microe lectrodes. Additionally, the primary somatosensory relay in the thalamus, t he ventroposterior nucleus, was studied to determine whether the effects of the enrichment were initiated subcortically or cortically. Age-matched con trols included six monkeys with no sensory manipulation after median nerve cut and regeneration, and one monkey that had restricted sensory experience after the injury. The most substantial effect of the sensory environment w as on receptive field sizes in cortical area 3b. Significantly greater prop ortions of cortical receptive fields in the enriched monkeys were small and well localized compared to the controls, which showed higher proportions o f abnormally large or disorganized fields. The refinements in receptive fie ld size and extent in somatosensory cortex likely provide better resolution in the sensory map and may explain the improved functional outcomes after rehabilitation in humans.