Volume 401, July 2026, 115734Author links open overlay panel, , , , , , Highlights•

The influence of concussion to active avoidance of perceived threats is unclear.

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Rats were trained on an active avoidance task then subjected to a closed head injury model of concussion.

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Closed head injury induced persistent avoidance by disrupting extinction.

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Cellular activity increased in the rostral insular cortex and ventral striatum, and decreased in the basomedial amygdala and CA1 of the ventral hippocampus.

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Understanding mechanisms of concussion-induced avoidance can help rehabilitation.

Abstract

Concussive brain injury is a risk factor for anxiety disorders. Pre-clinical models demonstrate that concussion increases passive fear responses, such as conditioned freezing, yet provide limited insight to active responses like avoidance of perceived threats. This is important because persistent avoidance is characteristic of anxiety disorders. Moreover, brain injury can induce an imbalance of the gut microbiome, which can alter emotions. Adult male rats were trained on a platform-mediated avoidance task where they learned to step onto a platform to avoid a foot shock following a conditioned auditory tone. A sucrose reward was provided via a lever press that is opposite to the platform. Next, closed head injury was delivered to produce a mild concussion. After recovery, separate cohorts of rats were tested to dissociate between changes in avoidance expression and extinction-related processes. Cellular activity was assessed using c-Fos immunohistochemistry in brain regions implicated in avoidance: amygdala, medial prefrontal cortex, insular cortex, ventral striatum, and ventral hippocampus. Fecal pellets were collected to extract genetic material to identify potential changes in populations of bacteria in the gut microbiome. Closed head injury induced persistent avoidance by impairing extinction. Injured rats showed decreased activity in the basomedial amygdala and the CA1 subregion of the ventral hippocampus, increased activity in the rostral insular cortex and ventral striatum, and no change in the medial prefrontal cortex. Closed head injury did not induce changes in gut microbiota. Understanding mechanisms of concussion-induced avoidance is crucial for developing rehabilitation strategies for mental health disorders impacted by brain injury.

Graphical abstractClosed head injury, as a model of mild concussion, induces excess avoidance as observed by more time spent on a platform that is placed opposite to a lever that provides sucrose reward. Excess avoidance corresponds to a disruption of cellular activity in brain regions implicated in avoidance, but does not affect gut microbiota extracted from fecal pellets.Download: Download high-res image (72KB)Download: Download full-size image

Closed head injury, as a model of mild concussion, induces excess avoidance as observed by more time spent on a platform that is placed opposite to a lever that provides sucrose reward. Excess avoidance corresponds to a disruption of cellular activity in brain regions implicated in avoidance, but does not affect gut microbiota extracted from fecal pellets.

Keywords

Traumatic brain injury

Post-traumatic stress disorder

Gut-brain axis

Gut dysbiosis

Conditioning

Context fear

Rodent

Data availabilityThe datasets are available in public online repositories. The 16S rRNA sequencing data can be accessed from the European Nucleotide Archive (ENA) under the study accession number PRJEB108858 (ERP189693). The data are available at the following link: https://www.ebi.ac.uk/ena/browser/view/ERP189693. Specific raw behavioral data can be distributed upon request via Google Drive.

© 2026 The Authors. Published by Elsevier Inc.