A Swedish study published as a research letter in this week’s issue of THE LANCET concludes that the return of sensory control in the hand after nerve damage in the arm is an age-related learning process involving the central nervous system, and is similar to the processes involved in language acquisition.
One of the challenges in reconstructive surgery is to ensure that hand sensibility (tactile gnosis), the ability to identify shapes and textures, is regained after nerve repair. After surgical repair of a nerve, axons may regenerate. But because of misdirection during regrowth, most of the fibres reinnervate incorrect areas in the hand. As a result there is a functional remodelling of the projectional areas of the fingers and the hand in the brain cortex.
Göran Lundborg and Birgitta Rosén from Malmö University Hospital, Sweden, assessed tactile gnosis in 54 patients (average age 32 years, ranging from 4 to 72 years) after repair of transected median or ulnar nerves at the wrist. The investigators found that there was a well-defined critical period for sensory relearning of tactile gnosis after nerve repair. They observed an optimum capacity below age 5-10 years followed by a rapid decline, which levelled out after puberty. Their findings correlated closely with previously published data on critical periods for secondary language acquisition by Chinese and Korean immigrants arriving in the USA; they conclude that recovery of functional sensibility after nerve repair is based on a learning process.
Göran Lundborg comments: "We have defined a critical age period for regaining functional sensibility after nerve repair, ending in the late teen ages. The critical period is closely associated with a corresponding critical period for language acquisition, indicating a strong learning component, also in acquisition of functional sensibility. Future principles for improving the outcome from nerve repair during adolescence should therefore focus on development of improved training programmes for enhanced sensory relearning, in which the capacity for functional remodelling, which characterises the adult brain, is worked on."
Contact: Dr Göran Lundborg, Department of Hand Surgery, Malmö University Hospital, SE-205 02 Malmö, Sweden; T) 46-40-331725 or 331000; F) 46-40-928855; E) goran.lundborg@hand.mas.lu.se
Journal
The Lancet