What is it about?
Like humans, other primates communicate socially through facial expressions, yet how the brain generates these movements remains poorly understood. The dominant view, built from case reports of patients with focal brain lesions, proposes two separate brain circuits for facial motor control: one originating in medial frontal cortex for emotional expressions, and another in lateral motor and premotor areas for voluntary movements like chewing. However, anatomical evidence suggests these medial and lateral areas are directly connected and may operate as a single network. To test these contrasting ideas, we recorded neural activity from medial and lateral motor areas, as well as the somatosensory cortex, in macaque monkeys while they produced emotional expressions and voluntary facial movements. By stimulating one brain region and recording the neural response in others, we found that medial and lateral motor areas can significantly influence each other’s neural activity. When we tracked the ongoing brain activity during facial expressions, medial and lateral areas showed coordinated communication, particularly at certain frequencies. During voluntary movements like chewing, this communication still occurred but shifted to lower frequencies. Crucially, the pattern of brain network communication differed depending on the type of facial movement. Our results challenge the traditional view that emotional and voluntary facial movements are controlled by separate cortical circuits. Instead, we found that cortical areas governing facial movement control work together as a single interconnected sensorimotor network, adjusting their coordination based on the movement being produced. Thus, facial motor control at the cortical level appears dynamic and flexible rather than routed through fixed, independent pathways.
Featured Image
Photo by Anna Keibalo on Unsplash
Why is it important?
Primates communicate socially through facial expressions, vocalizations, and speech, all of which require precise control of facial muscles. Yet compared to other movements like reaching or grasping, we know surprisingly little about how the brain controls them. Our findings help fill this gap by revealing how different brain regions coordinate to produce facial movements. Compared to reaching/grasping, facial movements have different anatomical properties, distinct forms of proprioceptive feedback, and serve a unique social purpose. By studying how the brain controls facial movements, we can begin to understand which motor control strategies the brain uses universally versus specifically for different effectors/body systems. This knowledge has clinical relevance too: facial palsy affects over 60% of stroke patients, causing significant functional and social impairments. Understanding how this network operates could inform new treatments targeting specific regions or connections to restore facial movement.
Perspectives
In the words of Geena R. Ianni: ‘So much of primate communication is nonverbal (even when we are speaking!). I think about when my young nephews ask for ice cream before dinner and I said “no” — the meaning of which, is entirely dictated by whether the word is punctuated with a smirk or a stern frown. Many patients with various types of brain injury lose these simple abilities that we take for granted. There have been such fabulous, impressive advances in the field of assistive communication devices even since I started on this project. I hope our work goes towards enabling the field, even the tiniest bit, towards more naturalistic and rich communication designs that will improve lives of patients.’ ‘As large-scale recordings become routine, distinguishing functionally relevant neural dynamics from epiphenomenal ones grows increasingly important. Using causal manipulation in non-human primates, we confirm that the region-region interaction dynamics we observed are not merely epiphenomenal but functionally relevant.’
Yuriria Vazquez
Read the Original
This page is a summary of: Neural synchrony links sensorimotor cortices in a network for facial motor control, Proceedings of the National Academy of Sciences, December 2025, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2512604122.
You can read the full text:
Contributors
The following have contributed to this page
