Responses of the human motor system to observing actions across species: A transcranial magnetic stimulation study

The role of primary motor cortex in manual inhibition of return: A transcranial magnetic stimulation study

Inhibition of return (IOR) is a behavioural phenomenon characterised by longer response times (RTs) to stimuli presented at previously cued versus uncued locations. The neural mechanisms underlying IOR effects are not fully understood. Previous neurophysiological studies have identified a role of frontoparietal areas including posterior parietal cortex (PPC) in the generation of IOR, but the contribution of primary motor cortex (M1) has not been directly tested. The present study investigated the effects of single-pulse transcranial magnetic stimulation (TMS) over M1 on manual IOR in a key-press task where peripheral (left or right) targets followed a cue at the same or opposite location at different SOAs (100/300/600/1000 ms). In Experiment 1, TMS was applied over right M1 on a randomized 50% of trials. In Experiment 2, active or sham stimulation was provided in separate blocks. In the absence of TMS (non-TMS trials in Experiment 1 and sham trials in Experiment 2), evidence of IOR was observed in RTs at longer SOAs. In both experiments, IOR effects differed between TMS and non-TMS/sham conditions, but the effects of TMS were greater and statistically significant in Experiment 1 where TMS and non-TMS trials were randomly interspersed. The magnitude of motor-evoked potentials was not altered by the cue-target relationship in either experiment. These findings do not support a key role of M1 in the mechanisms of IOR but suggest the need for further research to elucidate the role of the motor system in manual IOR effects.

"The clothes (and the face) make the Starman": Facial and clothing features shape self-other matching processes between human observers and a cartoon character

Anthropomorphization occurs when human characteristics are attributed to nonhuman animals or objects. One process that could facilitate the anthropomorphization of nonhuman animals may be a self-other body-part matching mechanism wherein the body of the nonhuman animal is conceptually mapped to the human observer's representation of their body. The present study was designed to determine if specific features could facilitate body-part matching between the cartoon of a nonhuman animal and human observers. Participants responded to targets presented on the cartoon of a starfish. In No Structure conditions, dots and curved lines were distributed evenly within the starfish. In Face conditions, two dots and one curved line represented eyes and a mouth of a "face". In Clothes conditions, dots and lines represented a shirt and pants. Body-part matching emerged when the image had a face or clothing, but did not emerge in No Structure conditions. These studies provide unique evidence that the anthropomorphization of a nonhuman cartoon may be facilitated by human-like internal features on the image.

What modulates the Mirror Neuron System during action observation?: Multiple factors involving the action, the actor, the observer, the relationship between actor and observer, and the context

Seeing an agent perform an action typically triggers a motor simulation of that action in the observer's Mirror Neuron System (MNS). Over the past few years, it has become increasingly clear that during action observation the patterns and strengths of responses in the MNS are modulated by multiple factors. The first aim of this paper is therefore to provide the most comprehensive survey to date of these factors. To that end, 22 distinct factors are described, broken down into the following sets: six involving the action; two involving the actor; nine involving the observer; four involving the relationship between actor and observer; and one involving the context. The second aim is to consider the implications of these findings for four prominent theoretical models of the MNS: the Direct Matching Model; the Predictive Coding Model; the Value-Driven Model; and the Associative Model. These assessments suggest that although each model is supported by a wide range of findings, each one is also challenged by other findings and relatively unaffected by still others. Hence, there is now a pressing need for a richer, more inclusive model that is better able to account for all of the modulatory factors that have been identified so far.

The influence of intrapersonal sensorimotor experiences on the corticospinal responses during action-observation

The coupling of perception and action has been strongly indicated by evidence that the observation of an action primes a response in the observer. It has been proposed that these primed responses may be inhibited when the observer is able to more closely distinguish between self- and other-generated actions - the greater the distinction, then the greater the inhibition of the primed response. This self-other distinction is shown to be enhanced following a period of visual feedback of self-generated action. The present study was designed to examine how sensorimotor experiences pertaining to self-generated action affect primed responses from observed actions. Single-pulse transcranial magnetic stimulation was used to investigate corticospinal activity elicited during the observation of index- and little-finger actions before and after training (self-generated action). For sensorimotor training, participants executed finger movements with or without visual feedback of their own movement. Results showed that the increases in muscle-specific corticospinal activity elicited from action-observation persisted after training without visual feedback, but did not emerge following training with visual feedback. This inhibition in corticospinal activity during action-observation following training with vision could have resulted from the refining of internal models of self-generated action, which then led to a greater distinction between "self" and "other" actions.

Theory of Animal Mind: Human Nature or Experimental Artefact?

Are animals capable of empathy, problem-solving, or even self-recognition? Much research is dedicated to answering these questions and yet few studies have considered how humans form beliefs about animal minds. Evidence suggests that our mentalising of animals is a natural consequence of Theory of Mind (ToM) capabilities. However, where beliefs regarding animal mind have been investigated, there has been slow progress in establishing the mechanism underpinning how this is achieved. Here, we consider what conclusions can be drawn regarding how people theorise about animal minds and the different conceptual and methodological issues that might limit the accuracy of conclusions currently drawn from this work. We suggest a new empirical framework for better capturing the human theory of animal mind, which in turn has significant political and social implications.