There is more to decisions than meets the eye: Cortical motor activity and previous motor responses predict sensorimotor decisions

Abstract

Abstract Human behavior is largely guided by sensory information about our environment. The process of transforming sensory evidence into appropriate behavior is called sensorimotor decision making. Despite the many advances in uncovering its neural basis, it remains unclear which role cortical motor areas play in the functional architecture enabling sensorimotor decision making. Specifically, it is unknown whether cortical motor areas actually contribute to the decision making process, e.g. by casting a vote on the response alternatives, or whether they alternatively simply produce the behavior selected elsewhere. To investigate the involvement of cortical motor areas in sensorimotor decision making, we conducted two experiments in which human participants made choices about motion in visual stimuli and reported the choice with one of two manual responses, i.e. button presses with the left or the right index finger. Using magnetoencephalography to measure neural activity during decision making, in the first experiment we showed that activity in sensorimotor areas was predictive of upcoming choices several seconds before the button press and even before stimulus presentation. In part, this activity could be linked to the neural aftermath of the previous trial’s choice report, which shifted a measure of cortical activity in sensorimotor areas towards the previously unchosen response alternative in the current trial. This previously unknown tendency to alternate between hands when reporting sensorimotor decisions was significant and varied in size with the size of the neural aftermath of the previous button press over sensorimotor areas across several independent statistics. The results show that beyond the current stimulus, i.e. beyond what meets the eye, other factors like the previous motor act may influence response selection in sensorimotor decision making. Additionally, the results suggest that this is driven by the neural aftermath of previous responses in cortical motor areas. More generally, this suggest that neural fluctuations in cortical motor areas can influence response selection in sensorimotor decision making. This means that cortical motor areas may be more than an output stage in sensorimotor decision making. Consistent with this interpretation, we showed that response alternation in sensorimotor decision making can be manipulated in a directed fashion through instructed and non-choice-related simple button 12 | Abstract presses in an independent group of participants in our second study. This result establishes that previous motor acts can influence response selection in sensorimotor decision making, independent of whether they are choice-related or simply instructed. Given this generalization beyond choice-driven button presses, the results of the second experiment are consistent with the interpretation that response alternation is at least partly driven by neural correlates of previous motor acts. In summary, our results suggest that neural fluctuations in cortical motor areas can influence response selection in sensorimotor decision making, in turn suggesting that motor areas may be more than an output stage of the brain during sensorimotor decision making.