NEURONAL-ACTIVITY IN RAT RED NUCLEUS DURING FORELIMB REACH-TO-GRASP MOVEMENTS

The activity of 259 task-related red nucleus neurons was recorded usin g chronic electrophysiological methods in free moving rats. Modulation s in activity were analysed in relation to onset (first detected wrist movement) and end (arrival of the paw over the food) of a reach-to-gr asp movement. Excitatory peaks were found to begin before, during and after the reach, but there were clear peaks in the distribution of ons et times after reach-onset and before reach-end, reflecting the fact t hat one third of all peaks began specifically during the reach, althou gh this occupied only a small fraction of the analysis time. Both exci tations and inhibitions showed a strong tendency to end in close tempo ral association with reach-end. Analysis of excitatory modulation ampl itudes showed that the largest peaks were formed when data was aligned to reach-end, and that these largest peaks nearly all began during th e reach and ended precisely at the time the paw would have been about to grasp the food: The spread of neural activation onset times through out the course of the complex reach-to-grasp movement is consistent wi th a relationship of individual neurons in the rat red nucleus with mo vements of all parts of the forelimb, as would be expected if all limb muscle groups are represented in the nucleus. On the other hand the d isproportionate number of modulations that occur during the reach and their strong alignment with time of reach-end suggests there is a bias in red nucleus function towards the control of distal motions associa ted with accurate grasp, consistent with the result of recent lesion s tudies. This provides indirect evidence that functionally the rat red nucleus may be organized in a similar way to that of monkeys, in which an important role in control of accurate distal movements is well est ablished. The possibility is discussed that red nucleus offers a timin g signal for co-ordination of movements across joints, in particular t he precise distal-proximal binding normally seen in accurate reach-to- grasp movements. (C) 1998 IBRO. Published by Elsevier Science Ltd.