Photographs of Actions: What Makes Them Special Cues to Social Perception

I have reviewed studies on neural responses to pictured actions in the action observation network (AON) and the cognitive functions of these responses. Based on this review, I have analyzed the specific representational characteristics of action photographs. There has been consensus that AON responses provide viewers with knowledge of observed or pictured actions, but there has been controversy about the properties of this knowledge. Is this knowledge causally provided by AON activities or is it dependent on conceptual processing? What elements of actions does it refer to, and how generalized or specific is it? The answers to these questions have come from studies that used transcranial magnetic stimulation (TMS) to stimulate motor or somatosensory cortices. In conjunction with electromyography (EMG), TMS allows researchers to examine changes of the excitability in the corticospinal tract and muscles of people viewing pictured actions. The timing of these changes and muscle specificity enable inferences to be drawn about the cognitive products of processing pictured actions in the AON. Based on a review of studies using TMS and other neuroscience methods, I have proposed a novel hypothetical account that describes the characteristics of action photographs that make them effective cues to social perception. This account includes predictions that can be tested experimentally.

Cerebral hemodynamic response during a live action-observation and action-execution task: A fNIRS study

Although many studies have examined the location of the action observation network (AON) in human adults, the shared neural correlates of action-observation and action-execution are still unclear partially due to lack of ecologically valid neuroimaging measures. In this study, we aim to demonstrate the feasibility of using functional near infrared spectroscopy (fNIRS) to measure the neural correlates of action-observation and action execution regions during a live task. Thirty adults reached for objects or observed an experimenter reaching for objects while their cerebral hemodynamic responses including oxy-hemoglobin (HbO) and deoxy-hemoglobin (HbR) were recorded in the sensorimotor and parietal regions. Our results indicated that the parietal regions, including bilateral superior parietal lobule (SPL), bilateral inferior parietal lobule (IPL), right supra-marginal region (SMG) and right angular gyrus (AG) share neural activity during action-observation and action-execution. Our findings confirm the applicability of fNIRS for the study of the AON and lay the foundation for future work with developmental and clinical populations.

Largely shared neural codes for biological and nonbiological observed movements but not for executed actions in monkey premotor areas

The neural processing of others' observed actions recruits a large network of brain regions (the action observation network, AON), in which frontal motor areas are thought to play a crucial role. Since the discovery of mirror neurons (MNs) in the ventral premotor cortex, it has been assumed that their activation was conditional upon the presentation of biological rather than nonbiological motion stimuli, supporting a form of direct visuomotor matching. Nonetheless, nonbiological observed movements have rarely been used as control stimuli to evaluate visual specificity, thereby leaving the issue of similarity among neural codes for executed actions and biological or nonbiological observed movements unresolved. Here, we addressed this issue by recording from two nodes of the AON that are attracting increasing interest, namely the ventro-rostral part of the dorsal premotor area F2 and the mesial pre-supplementary motor area F6 of macaques while they 1) executed a reaching-grasping task, 2) observed an experimenter performing the task, and 3) observed a nonbiological effector moving in the same context. Our findings revealed stronger neuronal responses to the observation of biological than nonbiological movement, but biological and nonbiological visual stimuli produced highly similar neural dynamics and relied on largely shared neural codes, which in turn remarkably differed from those associated with executed actions. These results indicate that, in highly familiar contexts, visuo-motor remapping processes in premotor areas hosting MNs are more complex and flexible than predicted by a direct visuomotor matching hypothesis.

Subjective understanding of actions and emotions involves the interplay of the semantic and action observation networks in the brain

How we subjectively generate an understanding of other people's bodily actions and emotions is not well understood. In this 7T fMRI study, we examined the representational geometry of bodily action- and emotion-understanding by mapping individual subjective reports with word embeddings, besides using conventional univariate/multivariate analyses with predefined categories. Dimensionality reduction revealed that the representations for perceived action and emotion were high dimensional, each correlated to but were not reducible to the predefined action and emotion categories. With searchlight representational similarity analysis, we found the left middle superior temporal sulcus and left dorsal premotor cortex corresponded to the subjective action and emotion representations. Furthermore using task-residual functional connectivity and hierarchical clustering, we found that areas in the action observation network and the semantic/default-mode network were functionally connected to these two seed regions and showed similar representations. Our study provides direct evidence that both networks were concurrently involved in subjective action and emotion understanding.

Top-Down Attention Guidance Shapes Action Encoding in the pSTS

The posterior superior temporal sulcus (pSTS) is a brain region characterized by perceptual representations of human body actions that promote the understanding of observed behavior. Increasingly, action observation is recognized as being strongly shaped by the expectations of the observer (Kilner 2011; Koster-Hale and Saxe 2013; Patel et al. 2019). Therefore, to characterize top-down influences on action observation, we evaluated the statistical structure of multivariate activation patterns from the action observation network (AON) while observers attended to the different dimensions of action vignettes (the action kinematics, goal, or identity of avatars jumping or crouching). Decoding accuracy varied as a function of attention instruction in the right pSTS and left inferior frontal cortex (IFC), with the right pSTS classifying actions most accurately when observers attended to the action kinematics and the left IFC classifying most accurately when observed attended to the actor’s goal. Functional connectivity also increased between the right pSTS and right IFC when observers attended to the actions portrayed in the vignettes. Our findings are evidence that the attentive state of the viewer modulates sensory representations in the pSTS, consistent with proposals that the pSTS occupies an interstitial zone mediating top-down context and bottom-up perceptual cues during action observation.

Characterizing the Action-Observation Network Through Functional Near-Infrared Spectroscopy: A Review

Functional near-infrared spectroscopy (fNIRS) is a neuroimaging technique that has undergone tremendous growth over the last decade due to methodological advantages over other measures of brain activation. The action-observation network (AON), a system of brain structures proposed to have “mirroring” abilities (e.g., active when an individual completes an action or when they observe another complete that action), has been studied in humans through neural measures such as fMRI and electroencephalogram (EEG); however, limitations of these methods are problematic for AON paradigms. For this reason, fNIRS is proposed as a solution to investigating the AON in humans. The present review article briefly summarizes previous neural findings in the AON and examines the state of AON research using fNIRS in adults. A total of 14 fNIRS articles are discussed, paying particular attention to methodological choices and considerations while summarizing the general findings to aid in developing better protocols to study the AON through fNIRS. Additionally, future directions of this work are discussed, specifically in relation to researching AON development and potential multimodal imaging applications.

Impacts of Transcranial Direct Current Stimulation on the Action Observation Network and Sports Anticipation Task

Effective anticipation skills in sporting cognition have been shown to facilitate expertise in sports. Transcranial direct current stimulation (tDCS) has shown to improve motor and cognitive functioning. Therefore, this study aimed to determine the assistive effects of tDCS on the action observer network in both novice and expert gamers during an occlusion task, as well as the related electroencephalographic spectral power response. Twenty-three novice and 23 expert video gamers received either sham or active tDCS with a right parietal anode and left frontal cathode. Only experts demonstrated a significant improvement in predicting ball direction for the overall and early occlusions after tDCS. Spectral power results revealed significant changes in theta, high-gamma, and delta frequencies. The findings indicate that tDCS was able to modulate anticipatory behavior and cortical activity in experts compared with novice participants, suggesting a facilitatory role for tDCS to improve anticipatory effects and assist as a neurocognitive training technique.

Gamma frequencies as a predictor for the accomplishment of a motor task guided through the action observation network

BACKGROUND: Action observation describes a concept where the subsequent motor behavior of an individual can be modulated though observing an action. This occurs through the activation of neurons in the action observation network, acting on a variety of motor learning processes. This network has been proven highly useful in the rehabilitation of patients with acquired brain injury, placing “action observation” as one of the most effective techniques for motor recovery in physical neurorehabilitation. OBJECTIVE: The aim of this paper is to define an EEG marker for motor learning, guided through observation. METHODS: Healthy subjects (n = 41) participated voluntarily for this research. They were asked to repeat an unknown motor behavior, immediately after observing a video. During the observation, EEG raw signals where collected with a portable EEG and the results were later compared with success and fail on repeating the motor procedure. The comparison was then analyzed with the Mann-Whitney U test for non-parametrical data, with a confidence interval of 95%. RESULTS: A significant relation between motor performance and neural activity was found for Alpha (p = 0,0149) and Gamma (0,0005) oscillatory patterns. CONCLUSION: Gamma oscillations with frequencies between 41 and 49,75 Hz, seem to be an adequate EEG marker for motor performance guided through the action observation network. The technology used for this paper is easy to use, low-cost and presents valid measurements for the recommended oscillatory frequencies, implying a possible use on rehabilitation, by collecting data in real-time during therapeutic interventions and assessments.

Implicit visual sensitivity towards slim versus overweight bodies modulates motor resonance in the primary motor cortex: A tDCS study

Motor resonance (MR) can be influenced by individual differences and similarity in the physical appearance between the actor and observer. Recently, we reported that action simulation is modulated by an implicit visual sensitivity towards normal-weight compared with overweight bodies. Furthermore, recent research has suggested the existence of an action observation network responsible for MR, with limited evidence whether the primary motor cortex (M1) is part of this. We expanded our previous findings with regards to the role of an implicit normal-weight-body preference in the MR mechanism. At the same time, we tested the functional relevance of M1 to MR, by using a transcranial direct current stimulation (tDCS) protocol. Seventeen normal-weight and 17 overweight participants were asked to observe normal-weight or overweight actors reaching and grasping a light or heavy cube, and then, at the end of each video-clip to indicate the correct cube weight. Before the task, all participants received 15 min of sham or cathodal tDCS over the left M1. Measures of anti-fat attitudes were also collected. During sham tDCS, all participants were better in simulating the actions performed by normal-weight compared with overweight models. Surprisingly, cathodal tDCS selectively improved the ability in the overweight group to simulate actions performed by the overweight models. This effect was not associated with scores of fat phobic attitudes or implicit anti-fat bias. Our findings are discussed in the context of relevance of M1 to MR and its social modulation by anti-fat attitudes.