Summary: Researchers have discovered a brain pathway that controls the freezing response linked to fear and anxiety. This finding points to a potential new drug target for anxiety-related disorders.
Source: University of Bristol
Neuroscientists have identified a specific cerebellar pathway that helps trigger fear and anxiety behaviors, including the characteristic “freezing” response.
A team at the University of Bristol reports that a circuit connecting the cerebellum to the periaqueductal gray (PAG) is critical for how fear memories are encoded and how freezing behavior is timed and terminated. Their work, published in eLife, suggests this cerebellar–PAG connection could become a novel target for treating anxiety disorders, which affect hundreds of millions worldwide.
Current medications for anxiety do not work for everyone and can produce unwanted side effects. A better understanding of the brain networks that shape fear and anxiety responses may help researchers develop more precise and effective treatments with fewer adverse effects.
The researchers focused on the cerebellum because it connects to multiple brain regions involved in survival circuits. The PAG sits at the center of those networks and coordinates threat responses such as freezing. To probe how these regions interact, the team recorded neuronal activity in the PAG of laboratory animals while using a classical conditioning paradigm: an auditory tone (conditioned stimulus) was repeatedly paired with a mild foot shock (unconditioned stimulus), producing a learned fear response measured by freezing.
During conditioning and later retrieval tests, a subset of PAG neurons increased their responsiveness to the conditioned tone, consistent with encoding a fear memory. The researchers then manipulated cerebellar output during conditioning and observed clear effects on PAG neuronal timing and behavior. Disrupting cerebellar signals made the timing of PAG neurons less precise and increased the duration of freezing, demonstrating that cerebellar input shapes both neural encoding of the conditioned cue and the expression of defensive behavior.
Further experiments targeted a direct projection from the medial cerebellar nucleus (MCN) to the ventral PAG (vPAG). Reversible inactivation of the MCN during the consolidation phase altered PAG responses during later retrieval: offset responses to the conditioned tone became temporally imprecise while onset responses were preserved, and freezing episodes lasted longer. Chemogenetic modulation of the MCN–vPAG pathway during fear acquisition reduced the emission of fear-related ultrasonic vocalizations and led to a slower extinction of freezing during subsequent retrieval. Together, these results indicate that cerebellar input affects fear memory formation and the dynamics of defensive behavior across multiple timescales.
Lead authors Dr. Charlotte Lawrenson and Dr. Elena Paci note: “Until now, little was understood about how the cerebellum modulates neuronal activity in other brain regions, especially those related to fear and anxiety. Importantly, our results show that the cerebellum is part of the brain’s survival network that regulates fear memory processes at multiple timescales and in multiple ways; raising the possibility that dysfunctional interactions in the brain’s cerebellar-survival network may underlie fear-related disorders and comorbidities.”
These findings expand current models of the fear and anxiety network by adding the cerebellum as a key modulator of PAG activity and fear memory encoding. By demonstrating that cerebellar signals shape both the precision of neuronal responses in the PAG and the behavioral expression of fear, the study highlights a new circuit-level target that could inform future therapeutic strategies for anxiety disorders, including post-traumatic stress disorder (PTSD).
About this anxiety and fear research news
Author: Press Office, University of Bristol
Source: University of Bristol
Contact: Press Office – University of Bristol
Image: The image is in the public domain
Original Research: Open access. “Cerebellar modulation of fear behavior and memory encoding in the PAG” by C.L. Lawrenson et al., published in eLife.
Abstract
Cerebellar modulation of fear behavior and memory encoding in the PAG
The study reinforces the pivotal role of the periaqueductal gray (PAG) in fear learning by identifying vPAG neurons in rats that encode fear memory through selective responses to the onset and offset of a conditioned auditory stimulus. Some neurons respond only at onset or only at offset, and these signals show different sensitivities to extinction, indicating distinct functional roles. Reversible inactivation of the medial cerebellar nucleus during consolidation disrupted the temporal precision of vPAG offset responses and increased freezing duration during later retrieval, while onset responses remained intact. Chemogenetic manipulation of the MCN–vPAG projection during acquisition reduced fear-related ultrasonic vocalizations and slowed extinction of freezing on subsequent retrieval. These results demonstrate that the cerebellum is an integral component of survival circuits that regulate fear memory and defensive behavior across multiple timescales, suggesting that maladaptive interactions within this cerebellar–survival network may contribute to fear-related disorders and comorbid conditions.