Beyond the classic extinction network: a wider, comparative view

Abstract

Extinction learning modifies the dynamics of brain circuits such that a previously learned conditioned response is no longer generated. The majority of extinction studies use fear conditioning in rodents and identified the prefrontal cortex, the hippocampus, and the amygdala as core regions of the extinction circuit. We sought to find answers to two questions: First, do we find a similar functional brain circuit in birds, which underwent a 300-million-year separate evolution from mammals? Second, do we have to incorporate the cerebellum as a key component of the central extinction circuit? We indeed show that the avian extinction pathways are not identical but highly similar to those of mammals. In addition, we reveal that the human cerebellum processes prediction errors, a key element driving extinction of learned fear responses, and contributes to context-related effects of extinction.

Molecular biology of serotonergic systems in avian brains

“…Regarding the nidopallium, previous studies have functionally associated it with the mammalian PFC, so few attempts have been made to associate the nidopallium with the mammalian amygdala ( Karten, 1997 , 2013 ; Güntürkün, 2005 ; Butler et al, 2011 ; Dugas-Ford et al, 2012 ; Herold et al, 2018 ). Although no previous studies using the Pavlovian fear conditioning paradigm have been conducted to examine the functions involved in the arcopallium and nidopallium, several studies using the pigeon appetite conditioning paradigm have been conducted to implicate parts of the arcopallium and nidopallium in extinction learning ( Lissek and Güntürkün, 2005 ; Lengersdorf et al, 2014 , 2015 ; Starosta et al, 2017 ; Gao et al, 2018 , 2019a , b ; Güntürkün et al, 2020 ). In avian, the medial and central amygdaloid structures and output projections from amygdala have been unveiled ( Abellán and Medina, 2009 ; Vicario et al, 2014 ; Hanics et al, 2017 ).…”