The effects of behavioral tasks on optic flow responses of MST neurons

Several lines of evidence support a role for the Medial Superior Temporal (MST) area of extrastriate visual cortex in navigation behavior. MST cells have large receptive fields and are responsive to full field optic flow stimuli that an observer sees as he moves through the environment. Neurons in MST respond to real movement and pursuit eye movements and combine these responses with optic flow selectivity to maintain a stable representation of heading. The behavioral relevance of visual stimuli has been found to modulate responses in several areas within the ventral ("what") and dorsal ("where") streams of extrastriate visual cortex.;I recorded 415 neurons from two rhesus monkeys trained to perform four memory guided saccade tasks in which optic flow was either behaviorally relevant or irrelevant. I have shown that individual MST cells are modulated by the behavioral relevance of optic flow. Responses in the flow-relevant condition were typically enhanced, although suppressive responses were also observed. Neuronal modulation was often by a multiplicative gain effect across all optic flow stimuli, although examples of effects on FOE tuning were also observed. In the flow-irrelevant task, the monkey had to remember the location or identity of a cue that was presented before the optic flow. Behavioral relevance effects were observed whether or not this cue contained spatial information. The degree of behavioral relevance modulation increased in a manner consistent with an effect of greater task difficulty. More significant effects were observed when the task was made more difficult by including an additional flow field before the relevant flow.;In a diverse set of behavioral tasks, MST neurons showed a range of effects on FOE tuning curves when behavior was guided by optic flow. These results suggest that behavioral modulation of neuronal responses may play an important role in sensory motor integration. Enhanced responses of MST neurons could send a stronger signal to motor control centers when the encoded optic flow must be used to guide behavior.