Decision-related activity and movement selection in primate visual cortex

Fluctuations in the activity of sensory neurons often predict perceptual
decisions. This connection can be quantified with a metric called choice
probability (CP), and there has been a longstanding debate about whether
CP reflects a causal influence on decisions, or an echo of decision-making
activity elsewhere in the brain. Here we show that CP can actually reflect
a third variable, namely the movement used to indicate the decision. In a
standard visual motion discrimination task, neurons in the middle temporal
(MT) area of the primate visual cortex responded more strongly during
trials in which the animals executed a saccade toward their receptive
fields, and less strongly for saccades directed away from the receptive
fields. The resulting trial-to-trial variability accounted for much of the
CP observed across the neuronal population, and it arose through training.
The learned association between MT activity and oculomotor selection was
causal, as pharmacological inactivation of MT neurons biased behavioral
responses away from the corresponding receptive field locations. These
results demonstrate that training on a task with fixed sensorimotor
contingencies introduces movement-related activity in sensory brain
regions, and that this plasticity can shape the neural circuitry of
perceptual decision-making.