Summary: Researchers have identified a previously unrecognized neural pathway that governs the brain’s shift into high-intensity fear responses. This pathway links a region of the prefrontal cortex to the amygdala and appears to play a central role in how animals escalate defensive behaviors—insights that may inform new approaches to treating conditions such as PTSD and anxiety disorders.
The discovery clarifies how cortical regions involved in planning and expectation can exert “top-down” control over ancient subcortical circuits that generate rapid survival behaviors. By mapping and manipulating this pathway in mice, scientists revealed specific cellular connections that scale fear reactions and promote transitions from immobility to active flight.
Key Facts:
- Investigators identified a novel projection from the dorsal peduncular (DP) region of the prefrontal cortex to the central amygdala (CeA) that regulates transitions to high-intensity fear behaviors.
- When this cortico-amygdala pathway is dysregulated, it may contribute to maladaptive defensive reactions seen in psychiatric conditions such as post-traumatic stress disorder (PTSD), panic disorder and anxiety.
- The study combined in vivo calcium imaging with chemogenetic and optogenetic manipulations and electrophysiology in mice to reveal the pathway’s anatomy, activity patterns and causal role in avoidance and flight behaviors.
Source: Northwestern University
New findings show a cortical circuit that controls the switch to intense fear behaviors.
The amygdala is a central hub for generating defensive responses to threats, orchestrating behaviors such as freezing, immobility and escape. However, how cortical inputs drive the amygdala to escalate defensive actions from passive to active responses has been incompletely understood. A recent study published in Nature describes a non-canonical pathway from the dorsal peduncular prefrontal cortex to the central amygdala that directly influences these high-intensity fear states.
Jones Parker, Ph.D., assistant professor of Neuroscience, Pharmacology and Psychiatry and Behavioral Sciences, was a co-author on the study. The research team used mouse models developed by the laboratory of Jonathan Fadok, Ph.D., Burk-Kleinpeter Inc. Professor in Science and Engineering at Tulane University, to map the circuits that drive escalation of defensive behavior.
Using in vivo calcium imaging, the researchers observed that a subset of DP neurons projecting to the CeA become active specifically during high-intensity threats and in a context-dependent manner. Those DP-to-CeA projection neurons are glutamatergic (excitatory) and preferentially target the medial portion of the central amygdala, a key output nucleus that relays threat information to downstream midbrain centers controlling flight.
To test causality, the team applied chemogenetic and optogenetic tools to selectively activate or inhibit the DP-to-CeA projection. Manipulating this pathway was sufficient to promote avoidance and flight behaviors, and necessary for their full expression in the behavioral paradigm used. Electrophysiological recordings further showed that DP inputs synapse onto CeA neurons that in turn project to midbrain flight centers, outlining a functional route from cortex to action.
“We have the cortex projecting to this ancient brain structure involved in fear processing; it taps into the amygdala and directly scales the level of fear that the animals are experiencing,” Parker said. Characterizing these cortical inputs at the molecular and cellular level, he added, may reveal new therapeutic targets for psychiatric disorders characterized by maladaptive fear.
Fadok emphasized the translational potential of understanding top-down cortical control over fear circuits. “By understanding what we call top-down control—cortical regulation of these ancient structures that manage fear—I think we can make major inroads to developing better treatments,” he said. His laboratory is now conducting a detailed physiological analysis of the dorsal peduncular region to define its neuronal populations and functional properties.
About this neuroscience research news
Author: Marla Paul
Source: Northwestern University
Contact: Marla Paul – Northwestern University
Image: The image is credited to Neuroscience News
Original Research: Closed access. “Top-down control of flight by a non-canonical cortico-amygdala pathway” by Chandrashekhar D. Borkar et al., published in Nature.
Abstract
Top-down control of flight by a non-canonical cortico-amygdala pathway
Appropriate selection of defensive behavior is essential for survival, and dysregulated defensive reactions are linked to psychiatric disorders such as post-traumatic stress disorder and panic disorder. Threat-evoked behaviors—including freezing and flight—are executed by neuronal circuits within the central amygdala (CeA), but the excitatory sources that drive CeA activity during high-intensity defensive responses were previously unclear.
This study combined neuroanatomical mapping, in vivo calcium imaging, functional manipulations and electrophysiology to identify and characterize a novel projection from the dorsal peduncular (DP) region of the prefrontal cortex to the CeA. DP-to-CeA neurons are glutamatergic and preferentially innervate the medial CeA, the principal amygdalar output nucleus mediating conditioned threat responses.
Using a behavioral task that elicits both conditioned freezing and flight, the authors showed that DP neurons projecting to the CeA are activated by high-intensity threats in a context-dependent fashion. Functional perturbations established that the DP-to-CeA pathway is both necessary and sufficient for avoidance and flight. Moreover, DP inputs synapse onto CeA neurons that project to midbrain flight centers, delineating a non-canonical top-down route that regulates defensive reactions.