Neuronal activity in the primate supplementary motor area and the primary motor cortex in relation to spatio-temporal bimanual coordination.

Single neuronal activity was recorded from the supplementary motor area (SMA-proper and pre-SMA) and primary motor cortex (M1) in two Macaca fascicularis trained to perform a delayed conditional sequence of coordinated bimanual pull and grasp movements. The behavioural paradigm was designed to distinguish neuronal activity associated with bimanual coordination from that related to a comparable motor sequence but executed unimanually (left or right arm only). The bimanual and unimanual trials were instructed in a random order by a visual cue. Following the cue, there was a waiting period until presentation of a "go-signal", signalling the monkey to perform the instructed movement. A total of 143 task-related neurons were recorded from the SMA (SMA-proper, 62; pre-SMA, 81). Most SMA units (87%) were active in both unimanual contralateral and unimanual ipsilateral trials (bilateral neurons), whereas 9% of units were active only in unimanual contralateral trials and 3% were active only in unimanual ipsilateral trials. Forty-eight per cent of SMA task-related units were classified as bimanual, defined as neurons in which the activity observed in bimanual trials could not be predicted from that associated with unimanual trials when comparing the same events related to the same arm. For direct comparison, 527 neurons were recorded from M1 in the same monkeys performing the same tasks. The comparison showed that M1 contains significantly less bilateral neurons (75%) than the SMA, whereas the reverse was observed for contralateral neurons (22% in M1). The proportion of M1 bimanual cells (53%) was not statistically different from that observed in the SMA. The results suggest that both the SMA and M1 may contribute to the control of sequential bimanual coordinated movements. Interlimb coordination may then take place in a distributed network including at least the SMA and M1, but the contribution of other cortical and subcortical areas such as cingulate motor cortex and basal ganglia remains to be investigated.

Single unit activity in the inferior colliculus of the rat elicited by electrical stimulation of the cochlea.

The activity of single neurons (n = 182) of the central nucleus of the inferior colliculus (CIC) of the rat was recorded in response to unilateral electrical stimulation of the left cochlea and/or acoustical stimulation of the right ear. The probability of response to both modes of stimulation was comparable (90 per cent for contralateral and 60 per cent for ipsilateral presentation). Response patterns consisted predominantly of onset excitations. Response latencies to electrical stimuli ranged from 3 to 21 ms, with an average value of 9.7 ms (SD = 3.5 ms) in the ipsilateral CIC and 6.6 ms (SD = 3.4 ms) in the contralateral CIC. With respect to binaural inputs, the majority of units were excited by stimulation of either ear (EE; about 60 per cent) while about one third were influenced by one ear only (EO). Units excited by one ear and inhibited by the other (EI) were rare. The main difference between the present implanted rats and normal animals was the virtual absence here of inhibitory effects for both types of stimuli when they were delivered to the ipsilateral ear (very few EI units).