Multiple systems for emotion-based action selection in the amygdala
Htr2a-Expressing Cells in the Central Amygdala Control the Hierarchy between Innate and Learned Fear
Tomoko Isosaka, Tomohiko Matsuo, Takashi Yamaguchi, Kazuo Funabiki, Shigetada Nakanishi, Reiko Kobayakawa, Ko KobayakawaCell. 2015 Nov 19;163(5):1153-1164. doi: 10.1016/j.cell.2015.10.047.
Highlights
- A hierarchical relationship exists between innate- and learned-fear responses
- Innate but not learned-fear stimuli suppress the activity of CeA Htr2a+ cells
- CeA Htr2a+ cell inhibition up/downregulates innate/learned freezing, respectively
- CeA Htr2a+ cells act as a hierarchy generator prioritizing innate over learned fear
A competitive inhibitory circuit for selection of active and passive fear responses
Jonathan P. Fadok, Sabine Krabbe, Milica Markovic, Julien Courtin, Chun Xu, Lema Massi, Paolo Botta, Kristine Bylund, Christian Müller, Aleksandar Kovacevic, Philip Tovote & Andreas LüthiNature. 2017 Feb 2;542(7639):96-100. doi: 10.1038/nature21047.
Abstract
When faced with threat, the survival of an organism is contingent upon the selection of appropriate active or passive behavioural responses. Freezing is an evolutionarily conserved passive fear response that has been used extensively to study the neuronal mechanisms of fear and fear conditioning in rodents. However, rodents also exhibit active responses such as flight under natural conditions. The central amygdala (CEA) is a forebrain structure vital for the acquisition and expression of conditioned fear responses, and the role of specific neuronal sub-populations of the CEA in freezing behaviour is well-established. Whether the CEA is also involved in flight behaviour, and how neuronal circuits for active and passive fear behaviour interact within the CEA, are not yet understood. Here, using in vivo optogenetics and extracellular recordings of identified cell types in a behavioural model in which mice switch between conditioned freezing and flight, we show that active and passive fear responses are mediated by distinct and mutually inhibitory CEA neurons. Cells expressing corticotropin-releasing factor (CRF+) mediate conditioned flight, and activation of somatostatin-positive (SOM+) neurons initiates passive freezing behaviour. Moreover, we find that the balance between conditioned flight and freezing behaviour is regulated by means of local inhibitory connections between CRF+ and SOM+ neurons, indicating that the selection of appropriate behavioural responses to threat is based on competitive interactions between two defined populations of inhibitory neurons, a circuit motif allowing for rapid and flexible action selection.PDF
