Relevance of embodied simulation for visual recognition of emotional expressions

Background: Understanding the emotions of others is fundamental for social life. However, the functional and neural mechanisms underlying the ability to perceive and understand others’ emotions are poorly understood. Embodied simulation theories suggest that, since covert emotional states (e.g., happiness) are often associated with overt motor behaviors (e.g., smiling, joyful body postures and gestures), observers can understand the unobservable emotional states of others by embodying their observable motor behavior through motor resonance (i.e., mirror neurons-like) mechanisms that tap onto the somato-motor response associated with generating the perceived expression (Adolphs 2002; Gallese et al. 2004; Goldman and Sripada 2005; Keysers and Gazzola 2009; Oberman et al. 2007; Iacoboni, 2009; Niedenthal et al. 2010; Gallese and Sinigaglia 2011). However, in humans, direct neurophysiological evidence of embodied simulation mechanisms involved in mapping an observed emotional expression onto the observer’s motor system are very scant. Moreover, although recent studies started to demonstrate that resonant activity within the motor system may indeed play a causal role in visual recognition of emotionally neutral actions (Cattaneo et al. 2011; Avenanti and Urgesi, 2011; Avenanti et al. 2013b), no studies to date have provided similar causal evidence for the recognition of others’ emotional motor behavior.

Goals: The general goal of the present project is to investigate the functional mechanisms and neural substrates underlying visual perception of others’ body emotional expressions. In particular, we will focus on resonance activity within the motor cortex in order to directly test whether such activity is critical for perceiving and understanding others’ emotional states as suggested by embodied simulation theories. To accomplish this goal, we will combine correlational and causal transcranial magnetic stimulation (TMS) approaches to investigate: 1) the time-course of embodied simulation processes within the motor cortex (and thus establish “when” in time neural signature of embodied simulation can be detected in the motor cortex); 2) the functional relevance of embodied simulation activity for visual recognition of emotional expressions.

Proposed research streams (RSs) and methodology: In all the studies healthy participants with no contraindication to TMS will be recruited (Rossi et al. 2009). Participants will be asked to observe pictures of actors expressing various emotions thought the upper limbs (basic emotions like happiness, fear, anger etc. and neutral actions with similar motor features) and actively recognize the emotion expressed by the actor. To focus on the processing of emotional body language, facial and contextual cues will be eliminated from the stimuli (as in Borgomaneri et al., 2012). During this emotion recognition task, online TMS will be administered at various locations and timing, to test the effect of visual condition on motor excitability (Research stream 1, RS 1) or the effect of TMS interference on visual recognition (RS 2).

RS 1: When does embodied simulation occur in the motor cortex?

The goal of RS1 is to identify when in time embodied simulation occurs in the observer’s motor cortex. TMS will be applied over the motor cortex during the emotion recognition task. This way we will assess changes in motor excitability contingent upon the observation of the different emotional expressions. We will test when in time motor excitability of the observers starts to match the motor activation pattern of the observed emotional expressions.

Motor excitability will be assessed through motor-evoked potentials (MEPs, i.e. electromyography responses induced by TMS). We will simultaneously record MEPs from upper limb muscles involved in the observed expressions and from muscles not involved in the expressions, as a control, using established procedures derived from the action observation literature (Fadiga et al. 2005; Avenanti et al., 2007, 2013a). Anatomical location of the TMS coil will be determined by functional methods (assessment of MEPs) and will be assisted by anatomical methods using a neuronavigation system.

Importantly, TMS will be administered at various delays after stimulus onset (50-500 ms temporal window, in steps of 25 ms) to assess the time-course of changes in motor excitability during the observation of emotional expressions.

Expected Results and implications: Based on the known time-course of motor cortex activation during the observation of neutral body movements (Nishitaniet al., 2004; Barchiesi and Cattaneo, 2013) we predict embodied simulation processes to be detected within the first 200-350 msafter stimulus onset - and possibly earlier. This research stream will establish the temporal dynamics of embodied simulation during the sight of emotional body language and will allow to showhow embodied simulation build up over time within the observer’s motor cortex. These correlational data will represent a first and necessary step for accomplishing the goal of the second research stream.

RS 2: Is neural activity reflecting embodied simulation relevant for behavior?

The goal of the RS 2 is to test the critical question of whether (and when) embodied simulation activity play an active causal role in the visual recognition of emotional expressions. To provide this causal evidence short trains of repetitive TMS (rTMS) will be applied over the motor cortex, to interfere with its functioningduring the emotion recognition task. Participants’ task performance (RT and accuracy) will be recorded during the following stimulation conditions: i) sham TMS (placebo), serving as a baseline condition; ii) active TMS of the motor cortex upper limb area i.e. the sector of the motor cortex involved in the embodied simulation of the observed upper limb expression; iii and iv) active TMS of sectors of the motor cortex that should not be involved in the simulation of the observed expression (face, leg sectors); v) active TMS of additional non-motor control region (e.g. the visual cortex).Subthreshold stimulation will be used to avoid over motor responses. Similarly to RS1, anatomical localization will be established using both functional (MEPs) and anatomical (neuronavigation) methods. Critically, the results of RS 1 will provide a guide for the selection of the latency of rTMS application, and thus choose the temporal windows in which TMS should interfere most with embodied simulation processes.

Expected Results and implications: By combining time specificity (temporal information derived from RS1 to guide interferential TMS) with anatomical specificity (anatomical localization of the specific sectors of the motor cortex that might be involved in the embodied simulation of the observed expression), this RS will allow to establish the causal role of neural activity reflecting embodied simulation in the visual recognition of emotional expressions. If embodied simulation is indeed critical for perceiving and recognizing others’ emotions, we expect that interference with upper limb cortical motor representations at the specific timing in which embodied simulation processes occur in the motor cortex (see RS1) should impair performance in the emotion recognition task.

General implications of the study and potential applications: This research program has the potential to directly test the functional relevance of embodied simulation mechanisms in the motor cortex. In addition to its theoretical implications for cognitive science, this research may pave the way to more applied research. In a clinical perspective, the exploration of the functional and neural bases of emotion perception may allow to implement specific psychophysiological-based assessment of patients with impaired emotion processing or poor social functioning (e.g. autism spectrum disorders, sociopathy, schizophrenia, stroke patients etc.). On the other hand, a better knowledge of the possible impaired mechanisms underlying these pathologies (e.g. embodied simulation mechanisms) may allow to develop clinical applications aimed at boosting these mechanisms with behavioral and brain stimulation methods.

References:

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Attività formativa dell’assegnista:

L’attività formativa sarà incentrata su:

1 - approfondimento delle conoscenze dei modelli teorici fondamentali e delle principali aree tematiche riguardanti le neuroscienze cognitive, in generale, e della percezione di azioni ed emozioni, in particolare.

2 - acquisizione della metodologia di ricerca scientifica (qualitativa e quantitativa) per la progettazione e la realizzazione di progetti di ricerca nelle neuroscienze cognitive;

3 - acquisizione delle conoscenze sulle tecniche di analisi statistiche appropriate con l’utilizzo dei più significativi pacchetti statistici;

4 - acquisizione delle competenze tecniche e teoriche per l’utilizzo della stimolazione magnetica transcranica (TMS);

5 - acquisizione di competenze di ideazione, progettazione, realizzazione di un progetto di ricerca scientifica;

6 - acquisizione delle competenze per la diffusione dei risultati della ricerca scientifica (congressi nazionali ed internazionali e pubblicazioni scientifiche nazionali e internazionali);

7 - acquisizione delle competenze per l’applicazione dei risultati della ricerca scientifica per l’ideazione e lo sviluppo di nuovi trattamenti riabilitativi.