Abstract
ObjectiveThe difference between positive and negative outcomes is important in trial‐and‐error decision‐making processes and affects corticospinal excitability. This study investigated corticospinal excitability during the performance of trial‐and‐error decision‐making tasks with varying competing behavioral outcomes.MethodsEach trial began with one of five colored circles presented as a cue. Each color represented a different reward probability, ranging from 10% to 90%. The subjects were instructed to decide whether to perform wrist flexion in response to the cue. Two seconds after the presentation of the cue, a reward stimulus (picture of a coin) or penalty stimulus (mauve circle) was randomly presented to the subject. If the picture of a coin appeared, the subjects received the coin after the experiment if they had performed wrist flexion, but not if they had not performed wrist flexion. If a mauve circle appeared, a coin was deducted from the total reward if the subjects had performed wrist flexion, but not if they had not performed wrist flexion. One second after the reward or penalty stimulus, transcranial magnetic stimulation was delivered to the primary motor cortex at the midpoint between the centers of gravity of the flexor carpi radialis (agonist) and extensor carpi radialis (antagonist) muscles.ResultsCumulative wrist flexions were positively correlated with reward probabilities. Motor evoked potential (MEP) amplitudes in agonist muscles were significantly higher when wrist flexion incurred a penalty than when it incurred a reward, but there was no difference in the MEP amplitudes of antagonist muscles.ConclusionPositive and negative behavioral outcomes differentially altered behavior and corticospinal excitability, and unexpected penalties had a stronger effect on corticospinal excitability for agonist muscles.
Highlights
In everyday life, people usually learn from positive and negative behavioral outcomes to reinforce rewarded behaviors and avoid nonrewarded behaviors (Herzfeld, Vaswani, Marko, & Shadmehr, 2014; Klein et al, 2007)
Our results showed that (a) cumulative wrist flexions increased with greater reward probabilities; (b) behaviors fluctuated randomly for most reward probabilities; (c) agonist flexor carpi radialis (FCR) Motor evoked potential (MEP) amplitudes were increased in trials where wrist flexion incurred a penalty, but antagonist extensor carpi radialis (ECR) MEP amplitudes were not; and (d) MEP amplitudes in the agonist and antagonist muscles did not change in trials without wrist flexion regardless of the outcome
Crosstalk between agonist and antagonist muscles might be present in surface EMG, we found that negative outcomes increased agonist FCR MEP amplitudes but did not affect antagonist ECR MEP amplitudes, a difference that might exceed any present crosstalk
Summary
People usually learn from positive and negative behavioral outcomes to reinforce rewarded behaviors and avoid nonrewarded behaviors (Herzfeld, Vaswani, Marko, & Shadmehr, 2014; Klein et al, 2007). Behavioral learning is often described as a trial-and- error decision-making process involving interacting social, economic, psychological, and neurophysiological aspects The impact of positive and negative outcomes has been explored at the corticospinal and behavioral levels
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