Time-dependent impact of urgency on corticospinal excitability during action selection
(2018) 28th Annual Meeting of the Society for the Neural Control of Movement — Location: Santa Fe
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- Abstract
- Action selection involves a tight balance between the competing demands of decision speed and accuracy. Recent work suggests that this balance is adjusted by an urgency signal that operates as a modulator of neural gain, boosting activity in motor areas when speed is of essence and reducing it when the focus is on accuracy. Importantly, the level of urgency changes during action selection, typically increasing as time passes. Here, we investigated the impact of varying the pattern of this time-dependent increase in urgency on corticospinal excitability in humans by applying transcranial magnetic stimulation (TMS) over the primary motor cortex. Subjects performed a modified version of the tokens task (Thura and Cisek, 2014, Neuron). In each trial, 15 tokens jumped one-by-one every 200 ms from a central circle to one of two lateral target circles; participants had to guess which of those targets would ultimately receive the majority of the tokens, and to report their decision before the final token jump on a key-board with either the left or right index finger. Importantly, in two separate blocks, we manipulated the within-trial increase in urgency, by providing different penalties for incorrect responses as a function of time. In one block type, the cost of making an error was lower for fast decisions than for slow ones, producing a context where urgency was initially high and increased only marginally during the course of action selection (UrgeEarly block). In contrast, in the other block type, the penalty was higher for fast decisions than for slow ones. Hence, here urgency was initially low but then increased drastically later on (UrgeLate block). TMS was exploited to elicit motor evoked potentials (MEPs) at different timings during the decision process (i.e., either early or late in the trial) in a right hand muscle when it was either selected for the forthcoming response (right index response), or non-selected (left index response). MEP amplitudes provided us with a muscle-specific assay of corticospinal excitability at the time of the stimulation. Our results indicate that varying the temporal pattern of urgency alters corticospinal excitability during action selection. As such, when elicited early on, MEPs were more facilitated in the UrgeEarly than in the UrgeLate block, regardless of whether the target muscle ended up being selected or non-selected. Conversely, when elicited later on, MEPs showed more suppression in the UrgeLate compared to the UrgeEarly block, specifically when the target muscle was not selected. Hence, whereas urgency globally amplified the facilitation of corticospinal excitability at early stages of action selection, it selectively boosted inhibitory changes occurring at a later time in the non-selected effector.
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Derosiere, G., Thura, D., Cisek, P., & Duque, J. (2018). Time-dependent impact of urgency on corticospinal excitability during action selection. 28th Annual Meeting of the Society for the Neural Control of Movement, Santa Fe. https://hdl.handle.net/2078.5/122278