Decisions are expedited through multiple neural adjustments spanning the sensorimotor hierarchy

Abstract

When decision makers prioritize speed over accuracy, neural activity is elevated in brain circuits involved in preparing actions. Such "urgency" signal components, defined by their independence from sensory evidence, are observed even before evidence is presented and can grow dynamically during decision formation. Is urgency applied globally, or are there adjustments of a distinct nature applied at different processing levels? Using a novel multi-level recording paradigm, we show that dynamic urgency impacting cortical action-preparation signals is echoed downstream in electromyographic indices of muscle activation, but does not directly influence upstream cortical levels. A motor-independent representation of cumulative evidence reached lower pre-response levels under conditions of greater motor-level urgency, paralleling a decline in choice accuracy. At the sensory level itself, we find a boost in differential evidence, which is correlated with changes in pupil size and acts to alleviate, rather than contribute to, the overall accuracy cost under speed pressure.. CC-BY-NC 4.0 International license It is made available under a (which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/203141 doi: bioRxiv preprint first posted online Oct. 14, 2017; 3 When situations call for it, animals can prioritize speed over accuracy in their sensoryguided actions. Prominent computational models suggest that sensorimotor decisions are made by drawing sequential samples from noisy evidence representations and integrating them up to an action-triggering threshold 1,2 . In this framework speed can be emphasized at the expense of accuracy by lowering this threshold, which in the models may be constant or collapsing (i.e., narrowing) over the timeframe of the decision 3,4 .Neural circuits involved in preparing decision-reporting actions have been found to implement such adjustments in the form of "urgency" signal components, which nonselectively elevate activity towards action thresholds. A "static" component of urgency has been widely observed in raised baseline activity before evidence presentation 5-8 , and recent work has further revealed a "dynamic" component that grows over the course of a decision, effectively implementing a collapsing bound [8][9][10][11] . A key defining property of urgency is that it is generated purely from knowledge of time constraints and/or elapsed time itself, and it contributes to neural buildup activity alongside, but strictly independent of, the influence of sensory evidence 12 . This means that any speed benefits of urgency necessarily incur a cost to choice accuracy. Thus far, urgency components have been identified only in neural circuits involved in preparing actions. Recent work has implicated diffusely-projecting neuromodulatory systems in the generation of urgency 11,13 , suggesting that it may, in fact, act globally, i.e., at all levels of the sensor...