Summary: Scientists have identified a neural circuit within the subthalamic nucleus (STN) that, when activated, produces a pronounced sense of discomfort and aversion. This discovery clarifies how specific subthalamic pathways connect to the brain’s emotional systems and has important implications for understanding depression-like symptoms and the side effects associated with deep brain stimulation (DBS) treatments for Parkinson’s disease and other movement disorders.
Using precise optogenetic methods in mice, researchers mapped and activated distinct populations of neurons in and around the STN. The experiments revealed not only immediate avoidance behavior during stimulation but also long-lasting conditioned aversion: animals later avoided places previously associated with STN activation even when stimulation was absent. The work suggests a direct link between STN activity and affective states such as aversion, which can inform safer, more effective neuromodulation therapies.
Key facts
- The subthalamic nucleus, long known for its role in motor control, can directly drive aversive states and avoidance learning when specific neuronal populations are activated.
- Optogenetic stimulation in mice produced persistent avoidance behavior and conditioned place aversion, indicating the STN’s capacity to influence emotional memory.
- This mechanistic insight may explain why some patients receiving STN-targeted DBS for Parkinson’s disease experience mood changes or depression, and it points toward more targeted DBS approaches to minimize affective side effects.
Source: Uppsala University
Newly identified aversion circuit in the subthalamic nucleus
Researchers at Uppsala University, in collaboration with Bordeaux University, report the identification of a specific circuit within the subthalamic nucleus that produces aversive sensations when activated. The findings, published in Cell Reports, expand our understanding of how motor and emotional systems interact and provide a biological framework for affective symptoms observed after neurosurgical interventions.
“Our experiments demonstrate that a distinct region of the brain can trigger aversion and avoidance behavior when selectively stimulated,” says Åsa Mackenzie, Professor at the Department of Organismal Biology at Uppsala University and the lead author. “By precisely activating subthalamic neurons with optogenetics, we observed robust avoidance behaviors and durable learning that associated an environment with discomfort.”
Earlier work from the team showed that mice actively avoid stimulation of the subthalamus. In the present study, the researchers went further: they demonstrated that the aversive response is not only immediate but also encoded into memory, leading to conditioned avoidance of places linked to the stimulation even when the stimulation is no longer applied.
Aversion is the behavioral counterpart to reward and plays a protective role by prompting avoidance of harmful or unpleasant stimuli. In humans, excessive or prolonged activation of aversion-related circuits can contribute to mood disorders, including depression. By pinpointing STN neurons that project to emotional processing regions, the study establishes a direct anatomical and functional connection between the subthalamus and brain centers involved in negative affect.
“Recognizing that the subthalamus can generate aversive learning has two major implications,” Mackenzie explains. “First, it deepens our knowledge of how specific brain circuits shape emotional behavior and how dysregulated activity can lead to psychiatric symptoms such as depression or apathy. Second, it provides a plausible neurobiological explanation for mood-related side effects observed in some patients receiving DBS.”
DBS targeting the STN reliably improves motor symptoms in advanced Parkinson’s disease by modulating excessive subthalamic activity. The treatment is often highly effective for tremor and motor function, but a subset of patients develops affective side effects, including low mood and depression. The study suggests two possible mechanisms: DBS may inadvertently stimulate adjacent regions linked to aversion, or DBS-driven changes within the STN itself may engage circuits that produce negative affect.
“These results are foundational and aimed at improving clinical precision,” Mackenzie adds. “A clearer circuit-level map of STN outputs to emotional centers will help refine neuromodulation strategies so that therapeutic benefit for motor symptoms can be preserved without inducing severe mood side effects.”
The study received funding from several organizations, including the Bertil Hållsten Research Foundation, the Swedish Brain Foundation, the Parkinson’s Foundation, the Michael J. Fox Foundation (ASAP initiative), the Åhlén Foundation, the Wenner-Gren Foundations, and the Swedish Research Council.
Methods summary
The research team used optogenetics to selectively activate defined STN neurons in genetically modified mice. By employing promoter-based markers identified in prior studies, they distinguished STN neuronal populations (for example, Pitx2-expressing cells) from neighboring para-STN populations (for example, Tac1-expressing cells). This cellular specificity allowed the team to measure behavioral outcomes, electrophysiological responses in target regions such as the ventral pallidum, and conditioned learning following stimulation. Targeted photostimulation of STN terminals in the ventral pallidum reproduced the aversive behavioral effects, supporting a direct STN-to-ventral pallidum pathway for aversive learning.
About this neuroscience research news
Author: Elin Bäckström ([email protected])
Source: Uppsala University
Contact: Elin Bäckström – Uppsala University
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Reciprocal transmission of activating and inhibitory signals and cell fate in regenerating T cells” by Åsa Mackenzie et al., Cell Reports. DOI: 10.1016/j.celrep.2023.113328
Abstract
Reciprocal transmission of activating and inhibitory signals and cell fate in regenerating T cells
Highlights
- Pitx2, Vglut2, and parvalbumin expression in the STN, and Tac1 expression in para-STN, are highly conserved from mouse to primate.
- Optogenetic activation of STN neurons or STN terminals in the ventral pallidum produces aversive learning and conditioned avoidance.
- Photostimulation of adjacent para-STN cell populations produces qualitatively different behavioral responses, underscoring functional segregation.
- Anatomical and functional dissection of STN versus para-STN provides a framework for understanding how the subthalamus contributes to emotional affect.
Summary
The subthalamic nucleus (STN) is essential for behavioral and motor control, and its dysfunction is linked to neurological and neuropsychiatric conditions, notably Parkinson’s disease. While STN-targeted deep brain stimulation effectively relieves parkinsonian motor symptoms, affective side effects such as low mood and depression have been reported. The STN sits adjacent to the para-STN, a region involved in appetitive and aversive behavior. Using optogenetics and genetic markers to differentiate STN and para-STN neurons, the study demonstrates that acute stimulation of either region can provoke aversion, but only STN stimulation generates conditioned avoidance and disrupts ongoing reward-seeking (for example, sugar self-administration). Electrophysiological recordings reveal post-synaptic responses in pallidal neurons, and selective activation of STN terminals in the ventral pallidum reproduces STN-induced aversion. Defining the STN as a source of aversive learning provides important neurobiological context for how subthalamic activity can influence emotional affect and offer guidance for refining therapeutic neuromodulation approaches.