“…animals are motivated to optimize their reward rate…they must find the best speed-accuracy trade-off (SAT) for both their decisions and their movements, and to adjust it to the current context.”

“…during natural behavior, animals are faced with a dynamic and continuously changing environment; and in such conditions, gradual accumulation of evidence is too sluggish to quickly respond to stimulus changes…activity in both regions combines rapid estimates of evidence with a growing “urgency signal” related to elapsed time…the urgency signal effectively controls the dropping accuracy criterion…the same urgency signal that energizes the decision also appears to influence the vigor of the selected action..when decisions are hasty, the urgency signal will increase the baseline and gain of both decision- and movement-related neural activity in the motor system….The manner in which monkeys reduced the duration of movements was complex and idiosyncratic…Reward rate is a major factor motivating animal behavior and to optimize it, animals must adjust…during both decision-making and movement execution. At the neural level, this could be accomplished through a variety of mechanisms, including changing the neural firing threshold for initiating movement, the baseline activity before evidence processing, or the gain with which evidence is processed…”In other words, despite the significant differences between tasks (static vs changing evidence, instructed vs volitional SAT adjustment), despite the different regions from which neural activity is recorded (frontal vs parietal, skeletal vs oculomotor systems), and despite the differences in the theoretical frameworks used to interpret the data, a consistent theme emerging from all studies of SAT is that it involves adjusting the baseline and gain of neural processing.”

“If an urgency signal controls the SAT, then what is its source? Previous work implicates the striatum which projects to PMd and M1 through the globus pallidus and dorsomedial thalamus. Furthermore, there is compelling evidence that pallidal output regulates movement vigor …we hypothesize that for deciding and acting may be controlled by a shared urgency/vigor signal that originates in the basal ganglia and controls both the gain of PMd/M1 decision-related cells as well as the premovement burst of cells that influence movement velocity. This leads to the prediction that, while monkeys perform the tokens task, neural activity in the globus pallidus will exhibit patterns resembling our hypothetical urgency signal. . Namely, it will not be directionally tuned during deliberation but will be related to elapsing time and will change when monkeys switch between a hasty versus a conservative decision policy..”

Modulation of Premotor and Primary Motor Cortical Activity during Volitional Adjustments of Speed-Accuracy Trade-Offs

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