The Basolateral Amygdala Is Essential for Rapid Escape: A Human and Rodent Study

Area of Science:

• Neuroscience
• Comparative Psychology
• Behavioral Biology

Background:

• Rodent studies identify the basolateral amygdala (BLA) and central amygdala (CeA) roles in defensive behaviors.
• Translating these findings to human threat responses is essential for understanding anxiety and fear.
• The BLA's specific function in selecting between active escape and passive freezing requires further elucidation.

Purpose of the Study:

• To investigate the conserved role of the basolateral amygdala (BLA) in regulating active escape versus passive freezing in humans and rats.
• To compare defensive behaviors in humans with BLA lesions to rats with chemogenetically silenced BLA.
• To elucidate the neural pathways, specifically involving the CeA, through which the BLA modulates threat responses.

Main Methods:

• Comparative study of humans with natural bilateral BLA lesions and rats with chemogenetically induced BLA silencing.
• Behavioral assays measuring startle potentiation, freezing, and escape during exposure to imminent, escapable threat (Timm).
• Human neuroimaging (fMRI) and rodent neurocircuitry analysis (chemogenetics, optogenetics) to map BLA-CeA pathways.

Main Results:

• Across species, BLA damage/silencing impaired the selection of active escape, leading to increased freezing and startle potentiation in response to T_imm.
• Human neuroimaging indicated the BLA inhibits brainstem pathways via the CeA to reduce passive defensive responses.
• T_imm conditioning strengthened BLA projections to an inhibitory CeA pathway, and activating this pathway rescued behavioral deficits in BLA-silenced rats.

Conclusions:

• The BLA, acting through the CeA, plays a conserved role in adaptively regulating escape behavior from imminent threat.
• This mechanism, involving BLA-CeA inhibition of brainstem pathways, is evolutionarily conserved in rodents and humans.
• Understanding this pathway offers insights into the neural basis of fear and anxiety disorders.