Huntington's disease is a devastating brain disorder in which decaying nerve cells lead to progressively worsening cognitive and movement abilities. While the genetic mutation responsible for the condition is well known, the intricate details of how the disease disrupts specific brain circuits have not been clearly understood. This gap has complicated efforts to develop effective therapies, and the disease remains fatal with no known cure.
University of California San Diego neurobiologists, working with scientists in Germany, identified and tracked neurons involved in Huntington's disease progression. They then used a cutting-edge light-based genetics technique to selectively activate these neurons and improve the debilitating deficits of the condition.
"This work shows that correcting specific imbalances in brain circuits can restore function, even in a complex neurodegenerative condition, and highlights the potential of targeting defined cell types to promote recovery," said study senior author Takaki Komiyama, a professor in the UC San Diego Departments of Neurobiology (School of Biological Sciences) and Neurosciences (School of Medicine).
The study is published July 1, 2026, in Nature.
Huntington's disease is caused by an inherited mutation in the Huntingtin (HTT) gene, when DNA building blocks cytosine, adenine and guanine, or "CAG," excessively repeat, leading to motor skill and cognitive damage. But while the mutation is well known, the neural networks connected with the disease progression have been more elusive.
The new project, led by Assistant Project Scientist Sonja Blumenstock, aimed to map the neural circuits that expose the networks involved at the onset and spread of the disease's debilitating symptoms. In transgenic mice carrying the same mutation as human patients, the researchers evaluated how different types of brain cells in the motor cortex — a region known to be critical for controlling movement — are affected in Huntington's disease. Advanced imaging techniques allowed the researchers to track the activity of these cortical neurons as the disorder progressed.
Working with Irina Dudanova's lab (previously based at the Max Planck Institute for Biological Intelligence, now at the University of Würzburg) in Germany, the researchers found that the disease disrupts the balance of activity across different cell types, including cortical inhibitory neurons. "Cortical inhibitory cells have received little attention in Huntington's disease, as for a long time they were considered to be spared from neurodegeneration," said Dudanova. "Surprisingly, we detected profound changes in their activity, with some cell types being overactive and some nearly silent." In particular, a class of inhibitory neurons known as vasoactive intestinal peptide neurons, or VIP inhibitory neurons, exhibited significantly reduced activity. Previous studies in Komiyama's lab found that VIP neuron activity is essential for normal learning, as these cells enable the brain to adapt and refine brain circuits during learning.
The research teams then probed these neurons as targets for potential therapeutic treatments. Reduced VIP neuron activity, the researchers reasoned, could be impairing the brain's ability to function and learn properly. They sought to artificially activate these cells to re-engage brain states that support learning. They tested this idea using optogenetics, a targeted, light-based technique that allows precise control of brain cells, to stimulate VIP neurons. "By activating the VIP inhibitory cell type, we gradually restored more normal activity patterns, and, very importantly, we also saw an improvement in the ability of the mouse to learn a motor task," said Blumenstock.
The results confirm VIP neurons as a key point of vulnerability in Huntington's disease as well as a promising target for therapy. As to how this process works, the scientists believe the results suggest that modulating VIP neurons opens a "gate" that enables learning-related brain plasticity.
"This intervention restored more normal patterns of activity in the brain and improved movement in affected mice," said Komiyama. "Importantly, the improvements persisted for days after stimulation ended, suggesting that the treatment triggered lasting beneficial changes in brain circuits rather than only temporary effects."
While the technique the researchers used is not yet directly applicable in humans, the study provides important indications of where research could focus to normalize human brain function and facilitate brain recovery. Komiyama envisions a future scenario in which scientists could non-invasively activate the brain from outside the skull using novel approaches.
"Our study shows that despite the genetic defect, a precise intervention into the brain circuitry can lead to significant improvements in motor symptoms," said Dudanova. "If we know which cells to target, we can retune the brain's abnormal activity patterns. This giv hope for future therapies."
From a broader disease perspective, the research shows that corrections to specific brain circuit imbalances can restore function in a highly complex neurodegenerative condition, with similar potential in other disorders.
"We have come up with a way to allow the diseased brain to learn better," said Komiyama. "The approach can improve behavior in diseased mice, and our hope is that a related approach will help people with impairment in their learning abilities."
