Physiological changes in primate somatosensory thalamus induced by deafferentation are dependent on the spinal funiculi that are sectioned and time following injury

The importance of spike bursts in thalamo-cortical processing of sensory information has received an increasing amount of interest over the past several years. Previously it has been reported that short high-frequency spike trains (3-8 action potentials occurring at 67-167 Hz), or spike bursts, are increased in both human and non-human primate thalamus following deafferentation. Here we examine the effects of lesion of the ventral spinal quadrant alone versus combined lesion of the ventral and dorsal spinal quadrants on the evoked and spontaneous spike trains in thalamic neurons. A total of 1175 neurons were sampled from 13 animals, three intact, six with ventral quadrant lesions (three with prolonged survival and three with short-term survival after spinal lesion) and four with combined ventral and dorsal quadrant lesions. Detailed analysis was conducted on 256 of these neurons, which revealed that thalamic neurons of animals with ventral quadrant lesions had elevated burst and non-burst spike rates while neurons from animals with combined ventral-dorsal lesions showed two types of change. Neurons in the forelimb areas showed increased bursts without a change in non-burst activity, while neurons in lateral VPL without receptive fields showed very low non-burst activity, but high burst spike rates. The magnitude of the effects produced by ventral-lateral spinal lesions was more pronounced in the short-term survival animals than in the long-term survival animals. These results show that the effects of deafferentation on the physiological properties of thalamic neurons are dependent on the afferent tract or tracts that are lesioned and the time after lesion.