Jeremy Hogeveen

Resonating with Others: The Effects of Self-Construal Type on Motor Cortical Output

“Self-construal” refers to how individuals view and make meaning of the self, and at least two subtypes have been identified. Interdependent self-construal is a view of the self that includes relationships with others, and independent self-construal is a view of the self that does not include relations with others. It has been suggested that priming these two types of self-construal affects the cognitive processing style that an individual adopts, especially with regard to context sensitivity. Specifically, an interdependent self-construal is thought to promote attention to others and social context to a greater degree than an independent self-construal. To investigate this assertion, we elicited motor-evoked potentials with transcranial magnetic stimulation during an action observation task in which human participants were presented with either interdependent or independent self-construal prime words. Priming interdependent self-construal increased motor cortical output whereas priming independent self-construal did not, compared with a no-priming baseline condition. These effects, likely mediated by changes in the mirror system, essentially tune the individual to, or shield the individual from, social input. Interestingly, the pattern of these self-construal-induced changes in the motor system corroborates with previously observed self-construal effects on overt behavioral mimicry in social settings, and as such, our results provide strong evidence that motor resonance likely mediates nonconscious mimicry in social settings. Finally, these self-construal effects may lead to the development of interventions for disorders of deficient or excessive social influence, like certain autism spectrum and compulsive imitative disorders.

Social Interaction Enhances Motor Resonance for Observed Human Actions

Understanding the neural basis of social behavior has become an important goal for cognitive neuroscience and a key aim is to link neural processes observed in the laboratory to more naturalistic social behaviors in real-world contexts. Although it is accepted that mirror mechanisms contribute to the occurrence of motor resonance (MR) and are common to action execution, observation, and imitation, questions remain about mirror (and MR) involvement in real social behavior and in processing nonhuman actions. To determine whether social interaction primes the MR system, groups of participants engaged or did not engage in a social interaction before observing human or robotic actions. During observation, MR was assessed via motor-evoked potentials elicited with transcranial magnetic stimulation. Compared with participants who did not engage in a prior social interaction, participants who engaged in the social interaction showed a significant increase in MR for human actions. In contrast, social interaction did not increase MR for robot actions. Thus, naturalistic social interaction and laboratory action observation tasks appear to involve common MR mechanisms, and recent experience tunes the system to particular agent types.

Automatic imitation is automatic, but less so for narcissists

Imitation is a fundamentally important human capability and has been the topic of considerable research in the behavioural sciences. One paradigm for investigating the basic nature of imitation is the “automatic imitation” paradigm. In this paradigm, participants are symbolically cued to make a particular response, whilst being incidentally exposed to a congruent or incongruent motor action performed by another person. The robust finding is that when the incidental action is incongruent with the cued action, participants are slower to respond than when it is congruent. Despite the name given to this paradigm, the extent to which the imitative tendency involved is actually automatic remains unclear. Here, we manipulated the probability of congruent and incongruent trials within blocks to assess the effects of expectation on the imitative process. In addition, we determined whether an individual difference variable related to how people process others’ behaviour—narcissism—affected the automaticity of imitation. Our results confirm that imitation as observed in this paradigm is robust in the face of expectation. However, the degree to which expectation modulates automatic imitation was enhanced for individuals who scored higher on a narcissism inventory. Together, these results suggest that imitation in the automatic imitation paradigm is indeed largely automatic, but that individual differences in narcissism can change the extent to which imitative behaviour manifests.

Incidental action observation modulates muscle activity

Similar circuits in the brain are engaged during the performance and observation of identical actions. Such engagement manifests in priming effects, where observation of an action leads to faster production of that action and slower production of an action involving a different movement of the same effector (e.g. observed finger flexion vs. produced finger extension), or a completely different effector (e.g. observed hand action vs. produced leg action). Here, we asked whether priming occurs for actions involving identical muscle groups where the degree of muscle contraction in observed actions was the same or different to that underlying an instructed response and whether patterns of muscle activation were also affected. Participants held an unseen rubber ball between their forefinger and thumb and responded to colour cues instructing a hard or a soft squeeze, whilst EMG activity from the first dorsal interosseous and the abductor pollicis brevis was recorded. The colour cues were superimposed on videos depicting a hard or soft squeeze of an identical rubber ball. Thus, there were two congruent (observe hard, produce hard; observe soft, produce soft) and two incongruent (observe hard, produce soft; observe soft, produce hard) conditions. Results showed that reaction time was slowed and EMG activity was modulated in the direction of the difference between observed and instructed squeezing movements. Hence, neural circuits underlying action observation are sensitive not only to differences in the actual muscle groups underlying observed actions but also to different extents of activation of the same muscle groups.

Automatic imitation is reduced in narcissists.

Narcissism is a personality trait that has been extensively studied in normal populations. Individuals high on subclinical narcissism tend to display an excessive self-focus and reduced concern for others. Does their disregard of others have roots in low-level processes of social perception? We investigated whether narcissism is related to the automatic imitation of observed actions. In the automatic imitation task, participants make cued actions in the presence of action videos displaying congruent or incongruent actions. The difference in response times and accuracy between congruent and incongruent trials (i.e., the interference effect) is a behavioral index of motor resonance in the brain-a process whereby observed actions activate matching motor representations in the observer. We found narcissism to be negatively related to interference in the automatic imitation task, such that high narcissism is associated with reduced imitation. Thus, levels of narcissism predict differences in the tendency to automatically resonate with others, and the pattern of data we observe suggests that a key difference is that high narcissists possess an improved ability to suppress automatic imitation when such imitation would be detrimental to task performance. To the extent that motor resonance is a product of a human mirror system, our data constitute evidence for a link between narcissistic tendencies and mirror system functioning.

Social Mimicry Enhances Mu-Suppression During Action Observation

During social interactions, there is a tendency for people to mimic the gestures and mannerisms of others, which increases liking and rapport. Psychologists have extensively studied the antecedents and consequences of mimicry at the social level, but the neural basis of this behavior remains unclear. Many researchers have speculated that mimicry is related to activity in the human mirror system (HMS), a network of parietofrontal regions that are involved in both action execution and observation. However, activity of the HMS during reciprocal social interactions involving mimicry has not been demonstrated. Here, we took an electroencephalographic (EEG) index of mirror activity-mu-suppression during action observation-in a pretest/post-test design with 1 of 3 intervening treatments: 1) social interaction in which the participant was mimicked, 2) social interaction without mimicry, or 3) an innocuous computer task, not involving another human agent. The change in mu-suppression from pre- to post-test varied as a function of the intervening treatment, with participants who had been mimicked showing an increase in mu-suppression during the post-treatment action observation session. We propose that this specific modulation of HMS activity as a function of mimicry constitutes the first direct evidence for mirror system involvement in real social mimicry.

Altogether now: Activating interdependent self-construal induces hypermotor resonance.

Nonconscious mimicry (NCM) has been widely studied but the mechanisms underlying it remain unspecified. One possibility is that NCM is mediated by motor resonance (MR). If so, factors that moderate NCM may affect MR. Priming interdependent self-construal (InterSC) increases NCM. We measured MR in a cued-response task using electromyography (EMG) while participants squeezed a rubber ball hard or softly in response to colored words. Words were superimposed on videos depicting hard or soft squeezes. Words primed InterSC or independent self-construal (IndSC). When observed squeezes were incongruent with word color, reaction time (RT) slowed and EMG activity was modulated. These effects were greater for InterSC primes than IndSC primes. Participants who failed to notice any difference in the actions in the videos also showed the effect. Activating InterSC causes MR processes to become hypersensitive to observed actions, even in the absence of awareness of what the action was.

The controlled imitation task: a new paradigm for studying self-other control

In the automatic imitation task (AIT) participants make a cued response during simultaneous exposure to a congruent or incongruent action made by another agent. Participants are slower to make the cued response on incongruent trials, which is thought to reflect conflict between the motor representation activated by the cue and the motor representation activated by the observed action. On incongruent trials, good performance requires the capacity to suppress the imitative action, in favor of producing the cued response. Here, we introduce a new experimental paradigm that complements the AIT, and is therefore a useful task for studying the control of self and other activated representations. In what we term the “Controlled Imitation Task (CIT)”, participants are cued to make an action, but on 50% of trials, within 100 ms of this cue, an on-screen hand makes a congruent or incongruent action. If the onscreen hand moves, the participant must suppress the cued response, and instead imitate the observed action as quickly and accurately as possible. In direct contrast to the AIT, the CIT requires suppression of a self-activated motor representation, and prioritization of an imitative response. In experiment 1, we report a robust pattern of interference effects in the CIT, such that participants are slower to make the imitative response on incongruent compared to congruent trials. In experiment 2, we replicate this effect while including a non-imitative spatial-cue control condition to show that the effect is particularly robust for imitative response tendencies per se. Owing to the essentially opposite control requirements of the CIT versus the AIT (i.e., suppression of self-activated motor representations instead of suppression of other-activated motor representations), we propose that this new task is a potentially informative complementary paradigm to the AIT that can be used in studies of self-other control processes.

TMS-induced neural noise in sensory cortex interferes with short-term memory storage in prefrontal cortex

In a previous study, Harris et al. (2002) found disruption of vibrotactile short-term memory after applying single-pulse transcranial magnetic stimulation (TMS) to primary somatosensory cortex (SI) early in the maintenance period, and suggested that this demonstrated a role for SI in vibrotactile memory storage. While such a role is compatible with recent suggestions that sensory cortex is the storage substrate for working memory, it stands in contrast to a relatively large body of evidence from human EEG and single-cell recording in primates that instead points to prefrontal cortex as the storage substrate for vibrotactile memory. In the present study, we use computational methods to demonstrate how Harris et al.s results can be reproduced by TMS-induced activity in sensory cortex and subsequent feedforward interference with memory traces stored in prefrontal cortex, thereby reconciling discordant findings in the tactile memory literature.

Simulating stimulus- and TMS-induced interference in short-term memory using a model of prefrontal cortex

Scalar short-term memory (STM) tasks are those in which the to-be-remembered property of a stimulus can be represented as a scalar quantity – for example, the frequency of a tactile vibration or an auditory pure tone, or the duration or amplitude of a stimulus. Scalar STM tasks have been studied extensively using single-cell methods [1-3], and have proven to be useful model systems for examining behavioural aspects of short-term memory [4-6] and developing computational models [7-10]. In two studies [11,12], we applied a model of prefrontal cortex [9] to experimental datasets [5,13]. In Study 1, we simulated the effects of presenting an irrelevant (distractor) stimulus to experimental subjects during the maintenance period of a vibrotactile scalar STM task by assuming the stimulus was encoded into memory, intruding into the PFC memory store. We were able to replicate previous experimental results [5], and our results also suggested that distractors were only encoded into memory on approximately 50% of trials, consistent with experimental indications that activity in sensory cortex may be inhibited during memory maintenance in order to protect the contents of memory against interference [6,14]. In Study 2, we simulated a previous vibrotactile scalar STM study in which TMS was applied to somatosensory cortex during the maintenance period of the memory task, resulting in decreased performance [13]. We were able to replicate experimental results by assuming that TMS produced increased, noisy neural activity in sensory cortex, which then degraded the contents of the PFC memory store through feedforward interference.