Neuronal firing rate, inter-neuron correlation and synchrony in area MT are correlated with directional choices during stimulus and reward expectation

Sensation, memories, and predictions contribute to choices in everyday life, and their relative impact should change with task constraints. To investigate how the impact from sensory cortex on decision making varies with task constraints we trained macaque monkeys in a direction discrimination task where they could maximize reward by waiting for sensory visual information early in a trial, while focusing on memory and reward prediction as a trial progressed. The task constraints caused animals to indicate decisions in complete absence of visual motion stimuli (stimulus independent decisions), as 25% of the trials were 'no stimulus' trials. On 'no stimulus' trials reward delivery depended on the current decision in relation to the decision history. Stimulus independent decisions occurred during an epoch when a stimulus could in principle have been presented, or afterwards when stimuli could not occur anymore. Stimulus independent decisions were significantly different during these two periods. Reward exploitation was more efficient late in the trial, but it was not associated with systematic activity changes in directionally selective neurons in area MT. Conversely, systematic changes of neuronal activity and firing rate correlation in directionally selective middle temporal area (MT) neurons were restricted to a short time period before early decisions. Changing task constraints in the course of a single trial thus determines how neurons in sensory areas contribute to decision making.