There is considerable evidence that passive observation of graspable objects can induce a preparatory motor response to act towards that object. However, there is conflicting evidence regarding the automaticity of this response. We used motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation, in combination with an attentional blink (AB) paradigm, to investigate the excitability of the motor cortex in response to visual presentations of pictures of graspable and non-graspable objects. After an initial non-graspable object, a graspable or non-graspable object was briefly presented at either a short (167ms) or long (583ms) SOA. MEPs were induced by applying TMS to the hand area representation of the motor cortex 250ms following onset of the second target object. We observed larger amplitude MEPs for graspable compared to non-graspable objects when these stimuli occurred at the short SOA (i.e., during the AB period). Furthermore, when short SOA trials were separated into correct and incorrect responses, the difference in MEPs was only present for objects that had been correctly identified. These findings suggest that enhanced motor excitability for graspable objects is only elicited when the objects are consciously identified. Intriguingly, this motor enhancement for graspable objects was not present when the second target was presented at a long SOA (outside the time window of the AB). This finding may reflect cortical inhibition due to the preparation of a motor response made with the opposite hand.

The stop signal task models response inhibition by pitting two independent processes against each other (go vs. stop processes). The main dependent variable is Stop Signal Reaction Time (SSRT), an estimate of the latency of the inhibitory process which has been shown to be increased in numerous clinical groups. However, SSRT estimation is fraught with numerous difficulties, such as the inability to predict the occurrence of and to control for trials on which the inhibitory process fails to trigger (i.e, trigger failure, TF). In this study, we use Bayesian parameter estimation to quantify TF and investigate the behavioural and ERP factors that account for variability in TF. We estimated TFs and the entire SSRT distribution simultaneously, independent of one another. This study included 182 participants (56% female; mean age 21 years). The addition of TFs in the model decreased SSRTs, thereby reducing overall variance. We found evidence that reduced attentional load accounted for some variance in TFs. Furthermore, moderate relationships were found between error-related ERPs and TF suggesting that conscious appraisal of errors influenced occurrence of TFs. However, behaviourally, there was no evidence of post-error response adjustment relating to any model parameters. Finally, oscillatory power following an erroneous response was weakly related to reduced SSRT and lower TF rates. These novel relationships between brain activity, behavioural measures, and model parameters of TF and SSRT will form a reference for future studies utilising estimates of TF to investigate inhibitory ability.

Previous research has shown that people experience a sense of reward as a result of exercising choice over a decision. This study aimed to examine brain activity prior to the decision point to see if unique neural networks were active in the formation of a free choice. Participants were required to select one of three alternate doors in a virtual corridor environment during functional MRI. In the Instructed condition, participants were told which door to choose whereas in the Free condition, they could choose freely between two valid options. A multivariate Partial Least Squares analysis revealed distinct neural networks for each of the conditions. During Instructed trials, there was greater activation of frontal regions including the medial frontal gyrus and the anterior cingulate cortex, which suggests that participants relied on task-set rules to make their choices. During Free choice trials, broad activation of frontoparietal and salience networks was evident, indicative of the use of a priority map generated by salient stimuli and current goals to drive behaviour. These results suggest that while instructed choices utilise a rule-based decision-making strategy, free choices engage networks that serve to evaluate the most salient option available. This salience-driven processing may prime the system to incorporate feedback, resulting in a greater sense of reward. Ongoing analysis aims to detail how these networks emerge over time leading up to the decision.

Background: Social interaction requires interrelated action perception and motor control processes. Human mirror system research has focused on congruent observed and executed actions, relating mirroring to automatic imitation and stimulus-response compatibility (SRC) effects. However, many real-life situations require responses that differ from observed actions. We aimed to investigate how mirrored action-representations are modulated to allow for task-relevant incongruent responses, over mere incidental incompatibility.
Methods: In a concurrent action observation/execution fMRI task, participants either: 1) preformed a predefined action, incidentally matching or mismatching an irrelevant action-stimulus; or 2) responded relative to the stimulus, intentionally copying it or executing the opposite action. Thus, neural substrates for imitation versus counter-imitation were measured, controlling for incidental SRC effects.
Results: Incidental stimulus-response mapping was dissociated from intentional imitation and counter-imitation, highlighting the differential engagement of control networks for counter-imitation. Regions of the action observation network including the medial temporal gyrus and occipital regions were more active in imitation compared to counter-imitation. In contrast, a frontal network was engaged during counter-imitation, including the insula and anterior cingulate cortex. These regions are implicated in executive control processes such as conflict detection and response selection/inhibition.
Conclusions: Our results suggest that intentionally opposing observed actions involves greater engagement of frontal executive control processes, perhaps to counter-act more automatic mirroring processes. Such task-dependent, top-down modulation of mirroring has been largely overlooked. In future work, we will employ dynamic causal modelling (DCM) to explore the interactions between these regions, in particular during the down-regulation of action mirroring during counter-imitation.