The following studies are samples from the Facial Feedback literature review by Katherine Wright and published in 2022 in the Undergraduate Research Journal of the University of Utah. To learn more about the following studies (including statistics) and additional Facial Feedback research, read the full Facial Feedback literature review.
Botulinum Toxin Injections Immobilize Frown Muscles and Alter Emotional Response
A study led by Andreas Hennenlotter (2008) noted that the Facial Feedback Hypothesis (FFH) suggests there are neural connections between facial musculature and regions of the brain involved in producing emotions, such as the amygdala (Carr et al., 2003; Wild et al., 2003; Lee et al., 2006). The amygdala is especially active during negative emotions (Hamann et al., 2002). It is the most connected structure in the forebrain and contains receptors for many hormones and neurotransmitters involved in emotion, such as dopamine, serotonin, and norepinephrine (Gazinga, 2019).
Hennenlotter’s research group investigated the face-brain connection of the Facial Feedback Hypothesis by examining neural correlations with functional magnetic resolution imaging (fMRI) during facial expression mimicking after botulinum toxin (BTX) treatment immobilized facial muscles.
Image created by the author with data from Hennenlotter et al. study (2008)
Emotional Response Compared Before and After BTX Treatment
Thirty-eight healthy study subjects planning to have cosmetic BTX between their eyebrows for frown line treatment were divided into two groups: a before BTX (Control) group and an after BTX (BTX-treatment) Group. All the subjects observed and replicated angry, neutral, and sad facial expressions, while fMRI brain images were made of their amygdala response.
The strength of the subjects’ eyebrow-lowering intensity during the test was measured with the Facial Activation Coding System (FACS) devised by researchers Paul Ekman and Wallace Friesen (1978).
The Amygdala is Activated by Lowering the Eyebrows
In both groups, researchers found the subjects’ left and right amygdalas were more activated (compared to baseline) when the subjects replicated angry and sad facial expressions. However, the subjects’ amygdalas did not activate more when the subjects observed the facial expressions.
The left amygdala showed significantly less activation in the BTX-Treated group than the Control group during the imitation of angry expressions but not during sad facial expressions. Activation of the left amygdala and the intensity of eyebrow lowering during angry facial expressions of the control group showed a significant linear correlation (see chart above), supporting the monotonicity hypothesis of the FFH.
Although BTX treatment did not alter the amygdala response during sad facial expressions, the BTX group did show significantly reduced activation of other brain regions during sad expressions, including the left lateral orbitofrontal cortex, which is known to affect how an individual feels about their emotional experience (Rolls, 2019).
Facial Expressions Impact Autonomic Nervous System
Hennelotter’s research group was also interested to see how facial expressions affect the pairing between the amygdala and the hypothalamus/brain stem. Interactions between these regions trigger the body’s autonomic nervous system—impacting heart rate, respiratory function, and digestive systems. The study’s fMRI results indicated less pairing in the BTX-treated group between the left amygdala and the dorsolateral pons in the brain stem. The amygdala sends projections to three nuclei in the pontine: periaqueductal gray (PAG), reticular formation, and the parabrachial nucleus (LeDoux, 2000). The PAG is particularly interesting, as the more recent development of 7-Tesla-powered fMRI machines helped discover that the PAG is an essential center of emotion processing (Gazinga et al. 2019).
Facial Expression Measurements Predict fMRI Measurements of Amygdala
A study on reappraising negative provocations, led by Hyjeen Lee et al. (2012), examined the human ability to regulate emotion and the brain’s networks used in the regulation. Previous researchers have identified that the amygdala detects the significance of emotional situations and responds accordingly (Phelps and LeDoux, 2005). The prefrontal cortex (PFC) in the front part of the brain is involved in reducing or maintaining emotional responses (Miller and Cohen, 2001). When people reappraise negative emotional situations, there is a give-and-take relationship between the PFC and the amygdala (Banks et al., 2007). The amygdala becomes activated by upsetting events, and the prefrontal cortex reassesses the situation to minimize the emotional reaction.
Neural Differences in Emotional Responses Evaluated
Lee’s research group noted that although human activity in these brain regions is pretty reliable, differences exist between individuals’ neural responses to negative events. Consequently, Lee’s group examined the neural processes of study participants’ emotion regulation with electromyography (EMG)—which measures emotional responses, followed by fMRI of the same subjects doing the same tasks.
Fifty-six male participants were shown emotionally arousing pictures and instructed to enhance, suppress, or maintain their emotional responses. In session one, the subjects regulated their emotions while viewing negative images, while EMG measured the magnitude of their between-eyebrow-frowning muscle movement. In session two, fMRI was used to identify the participants’ neural processes during emotion regulation as subjects viewed the same negative images.
Frown Muscle Measurements Predict Amygdala Activation
Results showed that the emotion regulation skills of participants from session one, indicated by their EMG frown-muscle measurements, predicted their fMRI amygdala activation in session two. The correlation of frown magnitude with amygdala activation supports the hypothesis that facial expressions and the brain’s emotional processes are connected.
Neural Communication from the Face to the Brain
The human face has two sets of neural communication: the facial and trigeminal nerves. The facial nerve provides efferent (brain to the face) motor neural signals for facial expressions. The trigeminal nerve provides afferent (face to the brain) communication for facial sensation. It is also possible that the trigeminal nerve’s afferent signals provide a conduit for facial feedback. It is already known that trigeminal afferent-neural pathways reach regions in the brain involved in emotional processes (Cook, et al., 2014). Researchers have noted that there are many unexpected connection points (called anastomoses) that exist between the facial and trigeminal nerves (Baumel, 1974).
Communication Between Facial and Trigeminal Nerves
Researchers Odobescu, Williams, and Gilardino (2012) sought to understand the frequency and significance of the anastomoses between the facial nerve’s temporal branch and the trigeminal’s zygomaticotemporal branch nerve. They studied 17 cadaveric faces and observed a consistent connection between one or two branches in the zygomaticotemporal region in 14 of the 17 faces. Researchers found myelinated fibers in the connections, which could be proprioceptive (body awareness) or motor fibers.
Twentieth-century psychology researchers suggested that facial proprioception might be an integral part of the Facial Feedback mechanism (Gellhorn, 1964; Izard, 1977), relying on afferent neural communication such as the trigeminal nerve for communication.
Questions or comments? We would love to hear from you.
awarded to Katherine Wright
References
Banks, S. J., Eddy, K. T., Angstadt, M., Nathan, P. J., & Phan, K. L. (2007). Amygdala-frontal connectivity during emotion regulation. Social cognitive and affective neuroscience, 2(4), 303–312. https://doi.org/10.1093/scan/nsm029
Baumel, J.J. (1974). Trigeminal-facial nerve communications: Their function in facial muscle innervation and reinnervation. Archives of Otolaryngology (1960), 99(1), 34–44. https://doi.org/10.1001/archotol.1974.00780030038007
Carr, L., Iacoboni, M., Dubeau, M-C., Mazziotta, J. C., & Lenzi, G. L. (2003). Neural mechanisms of empathy in humans: A relay from neural systems for imitation to limbic areas. Proceedings of the National Academy of Sciences – PNAS, 100(9), 5497–5502. https://doi.org/10.1073/pnas.0935845100
Cook, I. A., Espinoza, R., & Leuchter, A. F. (2014). Neuromodulation for depression: invasive and noninvasive (deep brain stimulation, transcranial magnetic stimulation, trigeminal nerve stimulation). Neurosurgery Clinics of North America, 25(1), 103–116. https://doi.org/10.1016/j.nec.2013.10.002
Ekman, P., Friesen W.V. (1978). Facial action coding system: A technique for the measurement of facial movement. Palo Alto: Consulting Psychologists Press.
Gazinga, M., Ivry, R., Mangun, G., (2019). Cognitive Neuroscience: The biology of the mind. (4th ed.) W.W. Norton.
Gellhorn, E. (1964). Motion and emotion: The role of proprioception in the physiology and pathology of the emotions. Psychological Review, 71, 457–472. http://dx.doi.org/10.1037/h0039834
Hamann, S.B., Ely, T. D., Hoffman, J. M., & Kilts, C. D. (2002). Ecstasy and Agony: Activation of the Human Amygdala in Positive and Negative Emotion. Psychological Science, 13(2), 135–141. https://doi.org/10.1111/1467-9280.00425
Hennenlotter, A., Dresel, C., Castrop, F., Ceballos-Baumann, A. O., Wohlschläger, A. M., & Haslinger, B. (2008). The link between facial feedback and neural activity within central circuitries of emotion—New insights from botulinum toxin-induced denervation of frown muscles. Cerebral Cortex, 19(3), 537–542. https://doi.org/10.1093/cercor/bhn104
Izard, C. E. (1981). Differential emotions theory and the facial feedback hypothesis of emotion activation: Comments on Tourangeau and Ellsworth’s “The role of facial response in the experience of emotion.” Journal of Personality and Social Psychology, 40(2), 350–354. https://doi.org/10.1037/0022-3514.40.2.350
Ledoux, J.E. (2000). Emotion circuits in the brain. Annual Review of Neuroscience, 23(1), 155–184. https://doi.org/10.1146/annurev.neuro.23.1.155
Lee, H., Heller, A. S., van Reekum, C. M., Nelson, B., & Davidson, R. J. (2012). Amygdala–prefrontal coupling underlies individual differences in emotion regulation. NeuroImage, 62(3), 1575–1581. https://doi.org/10.1016/j.neuroimage.2012.05.044
Lee T., Josephs, O., Dolan, R. J., & Critchley, H. D. (2006). Imitating expressions: emotion-specific neural substrates in facial mimicry. Social Cognitive and Affective Neuroscience, 1(2), 122–135. https://doi.org/10.1093/scan/nsl012
Miller, E.K., & Cohen, J. D. (2001). An integrative theory of prefrontal cortex function. Annual Review of Neuroscience, 24(1), 167–202. https://doi.org/10.1146/annurev.neuro.24.1.167
Odobescu, A., Williams, H.B, & Gilardino, M. (2012). Description of a communication between the facial and zygomaticotemporal nerves. Journal of Plastic, Reconstructive & Aesthetic Surgery, 65(9), 1188–1192. https://doi.org/10.1016/j.bjps.2012.03.033
Phelps, E.A., & LeDoux, J. E. (2005). Contributions of the Amygdala to Emotion Processing: From Animal Models to Human Behavior. Neuron (Cambridge, Mass.), 48(2), 175–187. https://doi.org/10.1016/j.neuron.2005.09.025
Rolls, E.T. (2019). The orbitofrontal cortex and emotion in health and disease, including depression. Neuropsychologia, 128, 14–43. https://doi.org/10.1016/j.neuropsychologia.2017.09.021
Wild, B., Erb, M., Eyb, M., Bartels, M., & Grodd, W. (2003). Why are smiles contagious? An fMRI study of the interaction between perception of facial affect and facial movements. Psychiatry Research. Neuroimaging, 123(1), 17–36. https://doi.org/10.1016/S0925-4927(03)00006-4