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Neurocircuit differences between memory traces of persistent hypoactivity and freezing following fear conditioning among the amygdala, hippocampus, and prefrontal cortex

Authors
  • Takita, Masatoshi
  • Izawa-Sugaya, Yumi
Type
Published Article
Journal
AIMS Neuroscience
Publisher
AIMS Press
Publication Date
Jan 19, 2021
Volume
8
Issue
2
Pages
195–211
Identifiers
DOI: 10.3934/Neuroscience.2021010
PMID: 33709024
PMCID: PMC7940113
Source
PubMed Central
Keywords
Disciplines
  • Research Article
License
Unknown

Abstract

We aimed to investigate the persistent trace of one traumatic event on neurocircuit controls in rats. Conditioning was reflected by reductions in rates of ‘freezing’ and ‘other-than-freezing’ motor activities, between which rats could alternate on delivery of pulsed footshocks of intensity 0.5 mA but not 1.0 mA. At the latter intensity, freezing began to suppress motor activity. The conditional responses evident during both the context and tone sessions persisted when the tests were repeated on post-conditioning days 7 and 8. Thus, difficulties with fear extinction/reduction remained. However, persistence was not evident on post-conditioning days 1 and 2. One day after the 1.0 mA pulsed footshock, ibotenate lesions and corresponding sham surgeries were performed in unilateral and bilateral hemispheres of the amygdala, hippocampus, and prefrontal cortex, as well as three different disconnections (one unilateral and another contralateral lesions out of three regions, a total of nine groups), and were tested on days 7–8. The drastic restoration of freezing following bilateral amygdala lesions was also evident in animals with three types of disconnection; however, this was not the case for hypoactivity. These results imply that a serious experience can drive different neurocircuits that all involve the amygdala, forming persistent concurrent memories of explicit (e.g., ‘freezing’) or implicit (e.g., ‘other-than-freezing’ motor activity) emotions, which may exhibit mutual interference.

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