Mayo Clinic researchers have found a previously unidentified "movement map" in the insula, a deep brain region. This discovery may help surgeons reduce side effects from epilepsy surgeries and could influence future treatments for speech and movement disorders.
The study, published on February 18 in the Proceedings of the National Academy of Sciences, reveals that specific areas within the insula are associated with movements of the hands, feet, and tongue. Until now, detailed maps outlining these functions in this part of the brain were lacking.
The insula is located several centimeters beneath the surface of the brain, making it hard to study using standard methods. Surgeons treating epilepsy sometimes operate near or in this region; up to 30% of patients can experience temporary issues with speech, swallowing, or hand movement after such procedures.
"For a long time, people thought this region was generally active during many tasks - more of an integrator than a structured map," says Dr. Kerezoudis. "We wanted to know whether it follows the same organized layout we see in the main motor cortex, or if it responds the same way no matter what you move."
To investigate this question, researchers at Mayo's Cybernetics and Motor Physiology Lab studied 18 patients with drug-resistant epilepsy who had electrodes placed deep in their brains as part of clinical care. Patients performed simple movements while electrical activity was recorded from both their insula and primary motor cortex.
The data showed that hand movements activated one area within the insula, tongue movements another area, and foot movements yet another—though less prominently for feet.
"We found distinct body-part representation in this deep structure," says Dr. Kerezoudis. "It is not random. There is order."
Timing analysis indicated that activity appeared first in the primary motor cortex before spreading to the insula and then leading to movement.
"This shows that the insula is not simply reacting after we move," says Kai Miller, M.D., Ph.D., a Mayo Clinic neurosurgeon and senior author of the study. "This discovery expands our understanding of how movement is supported by a distributed brain network whose parts are more tightly integrated than we previously thought. By mapping it carefully, we can make brain surgery and neuromodulation safer, more precise, and beneficial for more people."
In some patients, brief electrical stimulation confirmed communication between matching regions: stimulating hand-related areas in one part triggered responses in corresponding areas elsewhere.
"The connections respect the body map - hand connects to hand, tongue to tongue," says Dr. Kerezoudis. "That strengthens the case that this is an organized network."
These findings may help neurologists interpret seizure symptoms better—such as hand contractions or facial movements—and guide electrode placement during evaluations for epilepsy surgery. Surgeons might also use personalized maps to plan operations more precisely.
Beyond epilepsy care, understanding this network could benefit therapies for stroke survivors with speech or movement difficulties by highlighting potential new targets for interventions like targeted brain stimulation.
The research supports Mayo Clinic’s Bioelectronic Neuromodulation Innovation to Cure (BIONIC) initiative by applying advanced recording technology toward improving patient outcomes through scientific discoveries translated into practice-based strategies. It also aligns with Pre-cure’s goal of anticipating complications before they arise by identifying critical movement areas prior to surgery rather than responding after deficits occur.
