Lateralization and adaptation of a continuously variable behavior following lesions of a reticulospinal command neuron.

This study utilizes digitized cinematic data and lesions of individual Mauthner (M-) cells, large medial reticulospinal command neurons, to examine their role in goldfish C-starts elicited by displacement stimuli. Our results show a major difference in response lateralization in animals with only one M-cell compared to those with both cells intact, or both cells absent. Animals with one M-cell responded by turning to the side opposite the remaining M-cell in 94% of the trials, whereas those with both M-cells intact or both cells absent responded with equal probability to both sides. When the M-cells were absent, the responses were on the average 4 ms longer in latency. This difference may confer a behaviorally significant advantage to the M-cell in blocking other networks that can trigger C-starts. Nevertheless, with the exception of latency, the central program producing the escape behavior adapts automatically to the absence of both M-cells: animals with bilateral M-cell lesions continued to produce the full spectrum of kinematic performance levels seen in intact animals.