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

Abstract

Sensory perception can be severely degraded after peripheral injuries that disrupt the functional organization of the sensory maps in somatosensory cortex, even after nerve regeneration has occurred. Rehabilitation involving sensory retraining can improve perceptual function, presumably through plasticity mechanisms in the somatosensory processing network. However, virtually nothing is known about the effects of rehabilitation strategies on brain organization, or where the effects are mediated. In this study, five macaque monkeys received months of enriched sensory experience after median nerve cut and repair early in life. Subsequently, the sensory representation of the hand in primary somatosensory cortex was mapped using multiunit microelectrodes. Additionally, the primary somatosensory relay in the thalamus, the ventroposterior nucleus, was studied to determine whether the effects of the enrichment were initiated subcortically or cortically. Age-matched controls 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 was on receptive field sizes in cortical area 3b. Significantly greater proportions of cortical receptive fields in the enriched monkeys were small and well localized compared to the controls, which showed higher proportions of abnormally large or disorganized fields. The refinements in receptive field 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.

Role of distorted body image in pain

“…Perhaps this increased excitability enhances cortical reorganization processes in S1 and M1, as it is observed in experimentally induced increased excitability [57]. Data from animal studies suggest underlying reorganization processes are likely due to cortical rather than subcortical mechanisms [58], which suggests that the increased cortical excitability found in pain patients [59,60] may help drive cortical reorganization. This finding might explain the rapid normalization of S1 organization when pain is eliminated [61].…”

The auditory acclimatization effect in sensorineural hearing-impaired listeners: Evidence for functional plasticity

“…They found that amputation-induced cortical reorganization was reversed following hand transplantation (Giraux et al, 2001). In animals, the enriched sensory experience of macaque monkeys after median nerve sectioning and repair caused reWnements in receptive Weld size at the somatosensory cortical level (Florence et al, 2001). In the auditory system, few data are available in humans.…”

Effect of Facial Sensory Re-training on Sensory Thresholds

“…Re-training alters central nervous system organization so that the most functionally useful information can be extracted from the impoverished and disordered nerve signals (Florence et al, 2001;Lundborg, 2003). The aim of such re-training has been to improve patients' manual dexterity and use of the hand, to increase tactile awareness, and to lessen the objectionable impressions of hypoesthesic (numbness), paresthesic (tingling), and dysesthesic (uncomfortable or painful) sensations.…”