Infralimbic Parvalbumin Neurons Facilitate Active Threat Avoidance by Suppressing Freezing Behavior

Core Concepts

Infralimbic parvalbumin (PV) neurons play a causal role in suppressing freezing behavior to enable flexible avoidance responses in threatening environments.

Abstract

The content explores the role of infralimbic (IL) parvalbumin (PV) neurons in active threat avoidance behavior in mice. Key findings:

IL PV neuron activity increases specifically during movement to avoid a predicted shock, but not during movement to obtain a reward or general locomotion in neutral contexts.

The rise in IL PV activity during avoidance movement emerges immediately after the first experience of a shock, before the animal has learned the avoidance behavior. This suggests the PV signal is associated with the suppression of freezing, rather than the learning of avoidance.

Optogenetic inhibition of IL PV neurons prolongs freezing and delays the onset of avoidance behavior, without affecting movement in reward or neutral contexts. This demonstrates a causal role for IL PV neurons in enabling avoidance by suppressing freezing.

The findings suggest IL PV neurons play a key role in promoting flexible, goal-directed responses to threat by suppressing reactive defensive behaviors like freezing, rather than simply inhibiting overall neural activity in the region.

Stats

"The infralimbic cortex (IL) is essential for flexible behavioral responses to threatening environmental events."
"Reactive behaviors such as freezing or flight are adaptive in some contexts, but in others a strategic avoidance behavior may be more advantageous."
"Optogenetic suppression of PV neurons increases the duration of freezing and delays the onset of avoidance behavior, but does not affect movement toward rewards or general locomotion."

Quotes

"PV neural activity primarily reflects the avoidance movement and not tone offset."
"Inhibiting IL PV neural activity delays the avoidance movement but does not delay the movement for water reward in the approach task or the speed of voluntary locomotion in the open field test."

Key Insights Distilled From

Infralimbic parvalbumin neural activity facilitates cued threat avoidance

by Ho,Y.-Y., Ya... at www.biorxiv.org 08-18-2023

https://www.biorxiv.org/content/10.1101/2023.08.18.553864v2

Deeper Inquiries

How do other inhibitory neuron subtypes in the infralimbic cortex, such as somatostatin-expressing and vasoactive intestinal peptide-expressing neurons, contribute to the regulation of freezing and avoidance behaviors?

Other inhibitory neuron subtypes in the infralimbic cortex, such as somatostatin-expressing (SOM) and vasoactive intestinal peptide-expressing (VIP) neurons, likely play crucial roles in the regulation of freezing and avoidance behaviors. SOM neurons are known to be involved in gamma-band synchronization, which is essential for coordinating neural activity and information processing. In the context of freezing and avoidance behaviors, SOM neurons may modulate the activity of local pyramidal neurons and contribute to the suppression of freezing responses. On the other hand, VIP neurons are known to regulate the activity of both PV and SOM neurons, suggesting a complex interplay between different inhibitory neuron subtypes in the infralimbic cortex. VIP neurons may play a role in fine-tuning the balance between freezing and avoidance behaviors by modulating the activity of PV and SOM neurons.

How do the findings from this study on the role of infralimbic parvalbumin neurons in active threat avoidance relate to the broader functions of the prefrontal cortex in flexible, context-appropriate behavioral control?

The findings from this study shed light on the specific role of infralimbic parvalbumin (PV) neurons in active threat avoidance, particularly in the suppression of freezing responses and the initiation of avoidance movements. These findings contribute to our understanding of the broader functions of the prefrontal cortex in flexible, context-appropriate behavioral control. The prefrontal cortex, especially the ventromedial part like the infralimbic cortex, is crucial for supporting strategic behavior in response to environmental threats. By elucidating the role of PV neurons in facilitating avoidance behavior, this study highlights the prefrontal cortex's involvement in modulating responses to threatening stimuli and promoting adaptive behaviors. The findings underscore the importance of inhibitory neuron subtypes, such as PV neurons, in shaping neural activity and facilitating flexible behavioral responses in challenging situations.

What are the specific circuit mechanisms by which infralimbic parvalbumin neurons shape the activity of local pyramidal neurons to facilitate the suppression of freezing and the initiation of avoidance movements?

Infralimbic parvalbumin (PV) neurons likely shape the activity of local pyramidal neurons through intricate circuit mechanisms to facilitate the suppression of freezing and the initiation of avoidance movements. PV neurons are known to synapse onto and inhibit local pyramidal neurons, suggesting a role in modulating the excitability of these neurons. The activation of IL PV neurons may lead to the disinhibition of pyramidal neurons, allowing for the initiation of avoidance movements by reducing freezing responses. Additionally, PV neurons have been implicated in gamma-band synchronization, which is crucial for coordinating neural activity and facilitating the synchronization of pyramidal neuron firing. By modulating the firing patterns of local pyramidal neurons, IL PV neurons may contribute to the coordination of neural activity necessary for the execution of avoidance behaviors. Overall, the specific circuit mechanisms by which IL PV neurons shape the activity of local pyramidal neurons likely involve a delicate balance of inhibition and excitation to promote adaptive responses to threatening stimuli.