A transcranial magnetic stimulation study on response activation and selection in spatial conflict

Action-rule-based cognitive control enables efficient execution of stimulus-response conflict tasks: a model validation of Simon task performance

Introduction

The human brain can flexibly modify behavioral rules to optimize task performance (speed and accuracy) by minimizing cognitive load. To show this flexibility, we propose an action-rule-based cognitive control (ARC) model. The ARC model was based on a stochastic framework consistent with an active inference of the free energy principle, combined with schematic brain network systems regulated by the dorsal anterior cingulate cortex (dACC), to develop several hypotheses for demonstrating the validity of the ARC model.

Methods

A step-motion Simon task was developed involving congruence or incongruence between important symbolic information (illustration of a foot labeled "L" or "R," where "L" requests left and "R" requests right foot movement) and irrelevant spatial information (whether the illustration is actually of a left or right foot). We made predictions for behavioral and brain responses to testify to the theoretical predictions.

Results

Task responses combined with event-related deep-brain activity (ER-DBA) measures demonstrated a key contribution of the dACC in this process and provided evidence for the main prediction that the dACC could reduce the Shannon surprise term in the free energy formula by internally reversing the irrelevant rapid anticipatory postural adaptation. We also found sequential effects with modulated dip depths of ER-DBA waveforms that support the prediction that repeated stimuli with the same congruency can promote remodeling of the internal model through the information gain term while counterbalancing the surprise term.

Discussion

Overall, our results were consistent with experimental predictions, which may support the validity of the ARC model. The sequential effect accompanied by dip modulation of ER-DBA waveforms suggests that cognitive cost is saved while maintaining cognitive performance in accordance with the framework of the ARC based on 1-bit congruency-dependent selective control.

Two Distinct Systems Represent Contralateral and Ipsilateral Sensorimotor Processes in the Human Premotor Cortex: A Dense TMS Mapping Study

Animal brains contain behaviorally committed representations of the surrounding world, which integrate sensory and motor information. In primates, sensorimotor mechanisms reside in part in the premotor cortex (PM), where sensorimotor neurons are topographically clustered according to functional specialization. Detailed functional cartography of the human PM is still under investigation. We explored the topographic distribution of spatially dependent sensorimotor functions in healthy volunteers performing left or right, hand or foot, responses to visual cues presented in the left or right hemispace, thus combining independently stimulus side, effector side, and effector type. Event-related transcranial magnetic stimulation was applied to single spots of a dense grid of 10 points on the participants' left hemiscalp, covering the whole PM. Results showed: (1) spatially segregated hand and foot representations, (2) focal representations of contralateral cues and movements in the dorsal PM, and (3) distributed representations of ipsilateral cues and movements in the ventral and dorso-medial PM. The present novel causal information indicates that (1) the human PM is somatotopically organized and (2) the left PM contains sensory-motor representations of both hemispaces and of both hemibodies, but the hemispace and hemibody contralateral to the PM are mapped on a distinct, nonoverlapping cortical region compared to the ipsilateral ones.

The neurocognitive underpinnings of the Simon effect: An integrative review of current research

For as long as half a century the Simon task - in which participants respond to a nonspatial stimulus feature while ignoring its position - has represented a very popular tool to study a variety of cognitive functions, such as attention, cognitive control, and response preparation processes. In particular, the task generates two theoretically interesting effects: the Simon effect proper and the sequential modulations of this effect. In the present study, we review the main theoretical explanations of both kinds of effects and the available neuroscientific studies that investigated the neural underpinnings of the cognitive processes underlying the Simon effect proper and its sequential modulation using electroencephalogram (EEG) and event-related brain potentials (ERP), transcranial magnetic stimulation (TMS), and functional magnetic resonance imaging (fMRI). Then, we relate the neurophysiological findings to the main theoretical accounts and evaluate their validity and empirical plausibility, including general implications related to processing interference and cognitive control. Overall, neurophysiological research supports claims that stimulus location triggers the creation of a spatial code, which activates a spatially compatible response that, in incompatible conditions, interferes with the response based on the task instructions. Integration of stimulus-response features plays a major role in the occurrence of the Simon effect (which is manifested in the selection of the response) and its modulation by sequential congruency effects. Additional neural mechanisms are involved in supporting the correct and inhibiting the incorrect response.

Tracking the Time Course of Top-Down Contextual Effects on Motor Responses during Action Comprehension

Context plays a key role in coding high-level components of others' behavior, including the goal and the intention of an observed action. However, little is known about its possible role in shaping lower levels of action processing, such as simulating action kinematics and muscular activity. Furthermore, there is no evidence regarding the time course and the neural mechanisms subserving this modulation. To address these issues, we combined single-pulse transcranial magnetic stimulation and motor-evoked potentials while healthy humans watched videos of everyday actions embedded in congruent, incongruent, or ambiguous contexts. Video endings were occluded from view and participants had to predict action unfolding. Transcranial magnetic stimulation was delivered at 80, 240, and 400 ms after action onset. An earlier selective facilitation of motor resonance occurring at 240 ms was observed for actions embedded in congruent contexts, compared with those occurring in incongruent and ambiguous ones. Later on, at 400 ms, a selective inhibition of motor resonance was found for actions embedded in incongruent contexts, compared with those taking place in congruent and ambiguous ones. No modulations were observed at 80 ms. Together, these findings indicate that motor resonance can be modulated by contextual information with different timings, depending on the (in)congruency between the different levels of action representation. Furthermore, the different time course of these effects suggests that they stem from partially independent mechanisms, with the early facilitation directly involving M1, and the later inhibition recruiting high-level structures outside the motor system.

SIGNIFICANCE STATEMENT

Previous studies indicate that, when we observe other people's actions, the context in which actions take place influences intention understanding. However, little is known about the precise mechanisms involved in the contextual modulation of action representation (i.e., inhibition vs facilitation) and how they unfold in time. The present study sheds light on these aspects. Specifically, we show an early top-down facilitation (at ∼240 ms) and a later inhibition (at ∼400 ms) of motor resonance in response to actions observed in congruent and incongruent contexts, respectively.