Showing papers by "Patrick D. Wall published in 1978"

Reorganisation of spinal cord sensory map after peripheral nerve injury

Abstract: IT has generally been assumed that the connections of spinal cord cells are laid down during development and then remain stable throughout adult life. However, it has been shown that dorsal horn cells can be excited in a novel fashion by afferents over distant intact dorsal roots if section of nearby dorsal roots results in the degeneration of the afferent sensory fibres which normally activate the cells1. Here we show that this plasticity of afferent connection can be provoked by section of peripheral nerves where there is no gross anatomical change of the central terminals of the sectioned fibres and yet the cells on which the cut nerves end begin to respond to the nearest intact nerves.

Properties of two unmyelinated fibre tracts of the central nervous system: lateral Lissauer tract, and parallel fibres of the cerebellum.

Abstract: 1. Monoplar tungsten micro-electrodes were used to stimulate and platinun plated tungsten micro-electrodes to record from single, unmyelinated cerebellar parallel fibres and lateral Lissauer tract axons in cats. 2. Stimulation of the lateral Lissauer tract resulted in the activation of a narrow, longitudinal 'beam', much as on the cerebellar surface. 3. Following impulse conduction, parallel and Lissauer tract fibres showed a supernormal conduction velocity (up to 25% increase) and increased excitability (up to 40% increase). No subnormality was encountered following supernormality. Some Lissauer tract fibres had prolonged relative refractory periods and no supernormal periods. 4. Chronaxies ranged from 155 to 380 microseconds. 5. Single fibres exhibited a remarkable increase in conduction velocity (up to 18% and excitability (up to 40%) following a single subthreshold stimulus. The duration of this effect (up to 20 msec) was much longer than expected from membrane time constant estimates.