Modulation of intracortical circuits in primary motor cortex during automatic action tendencies

Humans display automatic action tendencies toward emotional stimuli, showing faster automatic behavior (i.e., approaching a positive stimulus and avoiding a negative stimulus) than regulated behavior (i.e., avoiding a positive stimulus and approaching a negative stimulus). Previous studies have shown that the primary motor cortex is involved in the processing of automatic actions, with higher motor evoked potential amplitudes during automatic behavior elicited by single-pulse transcranial magnetic stimulation. However, it is unknown how intracortical circuits are involved with automatic action tendencies. Here, we measured short-interval intracortical inhibition and intracortical facilitation within the primary motor cortex by using paired-pulse transcranial magnetic stimulation protocols during a manikin task, which has been widely used to explore approaching and avoiding behavior. Results showed that intracortical facilitation was stronger during automatic behavior than during regulated behavior. Moreover, there was a significant negative correlation between reaction times and intracortical facilitation effect during automatic behavior: individuals with short reaction times had stronger faciliatory activity, as shown by higher intracortical facilitation. By contrast, no significant difference was found for short-interval intracortical inhibition between automatic behavior and regulated behavior. The results indicated that the intracortical facilitation circuit, mediated by excitatory glutamatergic neurons, in the primary motor cortex, plays an important role in mediating automatic action tendencies. This finding further supports the link between emotional perception and the action system.

Repeated response execution and inhibition alter subjective preferences but do not affect automatic approach and avoidance tendencies toward an object

Background

Repeated action or inaction toward objects changes preferences for those objects. However, it remains unclear whether such training activates approach-avoidance motivation toward the objects, which leads to actual behavior. We conducted a pre-registered online experiment to examine whether approach and avoidance tendencies were affected by the experience of having executed or withheld a button-press response to a stimulus.

Methods

Participants (N = 236) performed a Go/NoGo task in which they were asked to repeatedly execute a response to a picture of a mug (i.e., Go-primed stimulus) and suppress a response to another picture of a mug (i.e., NoGo-primed stimulus). They then received one of two manikin tasks, which were implicit association tests designed to assess approach-avoidance tendencies. One manikin task measured the reaction times of moving a manikin toward or away from the Go-primed stimulus and the other picture of a mug (i.e., unprimed stimulus). The other manikin task measured the reaction times of moving a manikin toward or away from the NoGo-primed stimulus and the unprimed stimulus. The participants then rated their preference for the Go-primed, NoGo-primed, and unprimed items.

Results

The Go-primed item was evaluated as more highly preferable than the unprimed item in the Go condition, while the NoGo-primed item was evaluated as less preferable than the unprimed item in the NoGo condition. In contrast, the mean approach/avoidance reaction times in the manikin task showed no difference between the Go-primed and unprimed stimuli or between the NoGo-primed and unprimed stimuli.

Conclusion

When participants repeatedly responded or inhibited their responses to an object, their explicit preference for the object increased or decreased, respectively. However, the effect did not occur in approach-avoidance behaviors toward the object.

Effect of health warning labels on motivation towards energy-dense snack foods: Two experimental studies

Health warning labels (HWLs) show promise in reducing motivation towards energy-dense snack foods. Understanding the underlying mechanisms could optimise their effectiveness. In two experimental studies in general population samples (Study 1 n = 90; Study 2 n = 1382), we compared the effects of HWLs and irrelevant aversive labels (IALs) on implicit (approach) motivation towards unhealthy snacks, using an approach-avoidance task (Study 1), and a manikin task (Study 2). We also assessed explicit motivation towards unhealthy snacks using food selection tasks. We examined whether labelling effects on motivation arose from the creation of outcome-dependent associations between the food and its health consequences or from simple, non-specific aversive associations. Both label types reduced motivation towards snack foods but only when the label was physically present. HWLs and IALs showed similar effects on implicit motivation, although HWLs reduced explicit motivation more than IALs. Thus, aversive HWLs appear to act both through low level associative mechanisms affecting implicit motivation, and by additionally emphasizing explicit causal links to health outcomes thereby affecting explicitly motivated choice behaviours.

Involvement of the primary motor cortex in the early processing stage of the affective stimulus-response compatibility effect in a manikin task

Compatible (positive approaching and negative avoiding) and incompatible (positive avoiding and negative approaching) behavior are of great significance for biological adaptation and survival. Previous research has found that reaction times of compatible behavior are shorter than the incompatible behavior, which is termed the stimulus-response compatibility (SRC) effect. However, the underlying neurophysiological mechanisms of the SRC effect applied to affective stimuli is still unclear. Here, we investigated preparatory activities in both the left and right primary motor cortex (M1) before the execution of an approaching-avoiding behavior using the right index finger in a manikin task based on self-identity. The results showed significantly shorter reaction times for compatible than incompatible behavior. Most importantly, motor-evoked potential (MEP) amplitudes from left M1 stimulation were significantly higher during compatible behavior than incompatible behavior at 150 and 200 ms after stimulus presentation, whereas the reversed was observed for right M1 stimulation with lower MEP amplitude in compatible compared to incompatible behavior at 150 ms. The current findings revealed the compatibility effect at both behavioral and neurophysiological levels, indicating that the affective SRC effect occurs early in the motor cortices during stimulus processing, and MEP modulation at this early processing stage could be a physiological marker of the affective SRC effect.

Expecting the good: Symbolic valence signals provoke action biases and undermine goal-directed behavior

Positive and negative events are known to trigger opposing action tendencies (approach vs. avoidance). Recently, we found that advance monetary incentive cues can override such valence-action biases. In the present study we tested whether symbolic emotional valence cues can lead to similar adjustments and facilitate performance regardless of the required action. To this end, we performed three closely related experiments in which valence prospect (positive vs. neutral; indicated by stimulus color) and action requirements (approach vs. avoid; indicated by stimulus shape) were manipulated in a trial-to-trial fashion. Orthogonal to this, valence prospect was either embedded in the cue or target stimulus in discrete blocks (cue-valence vs. target-valence blocks). Actual valence was presented in the form of emotional face stimuli after response execution, which mirrors monetary incentive manipulations. In two of the experiments, we observed a positive-approach bias in form of performance benefit for positive versus neutral valence trials, which was exclusive for approach actions. Although numerically more pronounced in target-valence blocks, the bias was not significantly diminished in cue- versus target-valence blocks. This opposes our prediction that emotional valence cues can diminish such biases and instead highlights the robustness of inherent mappings between emotional valence and action tendencies - even if this goes against the task goal.