Peripheral and central nervous system interactions in the processing of emotional facial dynamics: Testing feedback mechanisms

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This dissertation focused on elucidating the neural and neurophysiological
mechanisms related to the perception of emotion in Others from the study of facial
expressions. Here, I studied the observer and asked what happens when we observe
the facial expressions of Others. According to theories of embodiment, when we
perceive emotions in Others, we irrepressibly engage in imitative behaviour. We
spontaneously adopt the same muscular reactions that we observe and, in some
instances, the same affective states. In the same vein, perceiving and expressing
emotions share similar brain networks, a neural signature of simulation mechanisms.
A crucial aspect of these embodied reactions is that they may guide our subjective
experience of emotion. As a consequence, preventing embodied responses or the
capacity to engage in imitative behaviour disrupts our ability to perceive emotions
in return because feedback from our own body has been disrupted.
In a series of experiments, I attempted to test Feedback from faces and Embodiment
theories by studying the interactions and contributions of the peripheral facial
nervous system and the central nervous system dedicated to the perception and the
detection of gradual facial changes of Anger and Happiness. In this dissertation, five
studies examined the role of facial expressions in emotion perception and the impact
of facial feedback on emotional processing. Studies One and Two focused on the
peripheral nervous system. Study One focused on spontaneous muscular reactions
of the face during exposure and detection of emotional facial changes, as well as
when reporting the subjective experience of the changes. In a change detection task,
participants were exposed to video morphs of neutral faces transitioning into
expressions of anger or happiness or changes in identity. Electromyography (EMG)
measurements showed that the corrugator muscle (e.g., frown muscle) activity
selectively decreased in response to happiness, showing valence-congruency.
Conversely, against our expectations, the zygomaticus muscle (e.g., smiling muscle)
activity decreased more in response to identity changes. Moreover, we found similar
activation patterns when participants were assessing the type of identity or assessing
how vividly they experienced the change. We surmise that facial reactions from the
corrugator muscle reflected emotional valuation (e.g., positive vs negative), and the
muscle zygomaticus reflected sensitivity to categorisation processes (e.g., emotional
vs non-emotional). In Study Two, we directly tested the Facial Feedback Hypothesis
by temporarily paralysing muscles associated with anger expression (e.g., corrugator
muscle) using botulinum toxin. This potent neurotoxin causes flaccid paralysis of
the muscle, blocking activity and somatosensation. According to our hypotheses,
results indicated that the paralysis corrugator muscle specifically impaired the time
required to detect anger and suggested that facial feedback causally influences
perceptual awareness from emotional stimuli. Studies three and four focused on the
central nervous system. Study three, with the use of functional magnetic resonance
imaging, explored the activation of putative motor and affective simulation areas
during the detection of gradual facial changes in emotion. Results revealed that
emotional and non-emotional change detection shared peak activations in several
brain areas, including the bilateral anterior insula, motor and premotor cortex,
somatosensory cortex, thalamus, putamen, cingulate, and IFG (BA47/45).
Surprisingly, the specific regions distinguishing between emotional and non-
emotional faces were restricted to the bilateral inferofrontal operculum (BA44,
Broca's area), the right dorsal striatum (caudate), and the left cerebellum Crus II.
These effects were more robust when perceiving happy faces. We surmise that the
detection of gradual changes in emotion recruits a cerebello-subcortico-cortical
network that reflects predictive processes and simulation of faces. Study four
examined the causal contributions of the anterior prefrontal cortex (aPFC/BA10) in
emotional change detection.
Similar to the paralysis study with botulinum toxin, Study Four constituted a neural
disruption study assessing atypical functioning. However, instead of modulating
bottom-up information, it focused on modulating aspects of top-down information
processing. In this study, with the use of transcranial magnetic stimulation, we
applied inhibitory continuous theta burst stimulation (cTB) in the aPFC before and
after an emotional change detection task. We aimed to assess the effects of inhibition
of aPFC on emotion perception, emotion metacognition, emotional mimicry and
emotional arousal by concurrently measuring the EMG responses of the face and
the galvanic skin response (GSR). Results failed to demonstrate a causal involvement
of aPFC in emotion metacognition. Instead, data was consistent with an
improvement in relative metacognitive accuracy for detecting changes in facial
identity. Crucially, results indicated that while Sham and No treatment (NoTMS)
control groups improved their detection decision times from pre-test to post-test,
the cTB group did not. Inhibition of aPFC affected detection responses of happiness
and disrupted spontaneous zygomaticus muscle EMG responses to happy faces (i.e.,
congruency). We surmise that aPFC inhibition affected perceptual awareness of
emotional facial changes and exerted a downstream causal and regulatory effect on
emotion by disrupting congruent embodied responses.
Finally, in Study Five, instead of testing the effects of disruption of emotional
expression, we capitalised on the possible contributions of active imitation of
emotion from faces. We tested the hypothesis that either imitating or affectively
matching the facial emotions as expressed by others could facilitate the perception
of emotion. Three different groups took part in the experiment in which participants
were first exposed to static facial expressions. During exposure, and on a trial-by-
trial basis, participants had to either adopt the same facial expression (Motor group),
try to feel the same perceived emotion without moving the facial muscles (Feel
group), or simply passively observe the faces (Watch group). After the exposure task,
participants were invited to perform a gradual change detection task without
concurrent imitation instruction. The study aimed to gauge the differential effects of
voluntary facial feedback and voluntary affect simulation on emotional perception.
Results demonstrated that active facial imitation affected emotion identification
immediately during the imitation task. Conversely, the effects of affective matching
were only observed subsequently during the detection task.
Moreover, Motor matching facilitated the processing of anger but affected the
processing of Happiness. Affective Matching, however, affected the processing of
Anger alone. We surmise that both interventions were task- and time-specific. We
argue that voluntary facial imitation and affective matching differentially affect
Anger processing, possibly because of emotion (down) regulation promoted by
Facial Feedback and Simulation.
Overall, this dissertation contributed to our understanding of how the perception of
emotions in Others occurs through enaction and simulation of the emotions of
Others by ourselves. The findings highlight how emotional perception from faces is
influenced by both the peripheral and central nervous systems, each fine-tuned for
the processing of Positive (Happy) and Negative (Angry) facial expressions. The
findings support the tenets of embodied cognition at different levels and the role of
facial feedback in emotional processing, shedding light on the complex mechanisms
underlying emotion perception. The results of this dissertation open new avenues to
understand better the clinical management of emotional disorders and disorders of
emotional expression.
Original languageEnglish
Awarding Institution
  • Vrije Universiteit Brussel
  • Vandekerckhove, Marie, Supervisor
  • Cleeremans, Axel, Supervisor
Award date8 Nov 2023
Publication statusPublished - 2023


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