Directional tuning of cortical neurons for the case of bimanual movements.
Although the majority of our upper-limb movements are performed with two arms, only a few neurophysiological studies have addressed neuronal mechanisms of bimanual motor control. In particular, little is known about directional tuning of cortical neurons during bimanual motor tasks. This contrasts with the vast literature on the same topic for unimanual movements. Georgopoulos and his colleagues pioneered the description of neuronal mechanisms of unimanual movements in terms of directional tuning curves, where firing rate of a neuron is expressed as a function of reach angle for center-out movements. According to Georgopoulos, individual neurons in the motor cortex are broadly tuned to movement direction, with the firing rate reaching a maximum value for the direction called preferred. This tuning pattern is well approximated by a cosine curve. No such description has been developed for bimanual movements. The main objective of the project is to address this gap in knowledge. For this purpose, an analysis will be presented of neuronal recordings performed in rhesus monkeys trained to perform bimanual tasks. Multiple linear regression fitting methods will be used to describe the dependency of neuronal rates on the movement directions of two arms, comparing the results obtained with each method. Neuronal tuning for unimanual movements (performed with either the left or right arm) will also be compared with the tuning for bimanual movements, testing whether bimanual tuning could be derived from the tuning for each arm tested separately, or if it is principally different from the dependencies for unimanual movements. The results from this work will eventually lead to improved neural decoding algorithms that could be utilized in brain-machine interfaces.