Enhanced Sensory Relearning (ESR) after nerve repair

Projekt: Forskning



The refined sensibility of the human hand includes several modalities such as tactile gnosis (the ability to recognize and appreciate shapes and textures) and protective sensibility aiming at avoiding injuries to the hand. Hand sensibility is also important to make possible adjustments of the motor function of the hand, based on a feedback system. Sensory functions of the hand are essential also for the body image.

Sensory functions of the glabrous skin of the hand and fingers are based on receptors responding to static pressure (such as Merkel's end organs) and receptors responding to dynamic, vibrotactile stimuli (such as Meissner's end organ and Pacini's corpuscles). Hand sensibility may be impaired or may be lacking in advanced neuropathies, in major nerve injuries and in injury to the spinal cord or brain. Hand prostheses used by amputees lack sensibility.

Sensory relearning following nerve repair

Transection of a major nerve trunk in the upper extremity represents an acute de-afferentiation and induces immediately substantial cortical reorganisations. The de-afferentiation results in an immediate silent area – a “black hole” in the contralateral somatosensory cortex followed by expansion of adjacent cortical areas. In this way the cortical hand representation may disappear and will remain so until reinnervation of the hand begins. During this time-period, which we prefer to call phase one , there is no sensation in the hand and cortex remains functionally reorganised. With beginning reinnervation of the hand ( phase two ) axons are reinnervating nervous pathways of the hand, although in a disorganised pattern because of the unavoidable axonal misdirection which always takes place at the repair site. As a result, the hand representation is again established, however, now in a completely disbursed and mosaic-like pattern “the hand speaks a new language to the brain, and the adult brain can not understand the new pattern of sensory inflow associated with touch”. In current sensory re-educational programs the patient trains to touch and recognise familiar patterns and items under guidance of vision. In this way the brain is reprogrammed to cope with the new situation. However, in adult patients the outcome is usually disappointing with no or little recovery of discriminative functions of the hand.

The current sensory re-educational programs have not changed over the last 25 years in spite of a dramatic development in the fields of neuroscience and cognitive science. Our aim is to use evolving neuroscientific concepts to improve current sensory re-educational programs in order to enhance sensory recovery after nerve repair. Specific strategies are needed in phase one and phase two respectively.

Phase one
Early after nerve repair our aim is to activate and maintain the cortical hand representation. This can be done in several ways: 1) by imaging active hand movements without really performing such movements; 2) by observing hand movements performed by other individuals (Rizzolatti 20XX); 3) by reading or listening to “action words” related to hand activities In addition, we are trying new principles based on audiotactile and audiovisual cortical interactions. Using the Sensor Glove System we are demonstrating that the friction sound, elicited by touch of textures and surfaces, activates not only auditory areas but also somatosensory areas of the brain. In a multicentre, prospective randomised study on median and ulnar nerve injuries we have demonstrated that the use of the Sensor Glove System postoperatively significantly improves and enhances the recovery of functional sensibility in the hand. We are also exploring possibilities to activate and maintain the hand cortical representation by observing hands being touched. Using fMRI technique we have demonstrated that observing hands being touched activates not only visual cortical areas but also somatosensory areas in brain cortex.

Phase two
We explore new principles to enhance the effects of sensory training in phase two. We are specially interested in brain plasticity mechanisms, focusing at the capability of cortical areas to expand when adjacent cortical areas are de-afferentiated by peripheral anaesthesia (see above: Hand and brain - fMRI studies). In healthy individuals we have demonstrated that cutaneous anaesthesia of the forearm results in rapid improvement in sensory functions of the hand with respect to pressure perception (SW filaments) as well as tactile discrimination (two-point discrimination). We have recently reported that also in nerve injured patients with repaired median or ulnar nerves, the effects of sensory training can be substantially enhanced by repeated de-afferentiation of the forearm by the anaesthetic cream EMLA containing lidocain and prilocain. We are presently exploring the optimal pattern and time dynamics of such selective de-afferentiation to achieve a long-term effect on sensory recovery (Rosén et al., 2003; Lundborg, 2004).
Gällande start-/slutdatum2010/01/01 → …

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