title: Habituation and extinction of fear recruit overlapping forebrain structures.
abstract: Establishing the neurocircuitry involved in inhibiting fear is important for understanding and treating anxiety disorders. To date, extinction procedures have been predominately used to examine the inhibition of learned fear, where fear is reduced to a conditioned stimulus (CS) by presenting it in the absence of the unconditioned stimulus (US). However, learned fear can also be reduced by habituation procedures where the US is presented in the absence of the CS. Here we used expression of the activity marker c-Fos in rats to compare the recruitment of several forebrain structures following fear habituation and extinction. Following fear conditioning where a tone CS was paired with a loud noise US, fear was then reduced the following day by either presentation of the CS or US alone (i.e. CS extinction or US habituation, respectively). This extinction and habituation training recruited several common structures, including infralimbic cortex, basolateral amygdala, midline thalamus and medial hypothalamus (orexin neurons). Moreover, this overlap was shared when examining the neural correlates of the expression of habituation and extinction, with common recruitment of infralimbic cortex and midline thalamus. However, there were also important differences. Specifically, acquisition of habituation was associated with greater recruitment of prelimbic cortex whereas expression of habituation was associated with greater recruitment of paraventricular thalamus. There was also less recruitment of central amygdala for habituation compared to extinction in the retention phase. These findings indicate that largely overlapping neurocircuitries underlie habituation and fear extinction and imply common mechanisms for reducing fear across different inhibitory treatments.
authors.affiliation: School of Psychology, University of New South Wales, Sydney 2052, Australia.
authors.forename: Teri M
authors.initials: TM
authors.lastname: Furlong
authors.affiliation: School of Psychology, University of New South Wales, Sydney 2052, Australia.
authors.forename: Rick
authors.initials: R
authors.lastname: Richardson
authors.affiliation: School of Psychology, University of New South Wales, Sydney 2052, Australia. Electronic address: g.mcnally@unsw.edu.au.
authors.forename: Gavan P
authors.initials: GP
authors.lastname: McNally
mesh_terms: D000161:Acoustic Stimulation; D000679:Amygdala / Q000378:metabolism; D000818:Animals; D001362:Avoidance Learning / Q000502:physiology; D003214:Conditioning, Classical / Q000502:physiology*; D005108:Extinction, Psychological / Q000502:physiology*; D005239:Fear / Q000502:physiology*; D006185:Habituation, Psychophysiologic / Q000502:physiology*; D007031:Hypothalamus / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D017397:Prefrontal Cortex / Q000378:metabolism; D016548:Prosencephalon / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013788:Thalamus / Q000378:metabolism
chemical_list: D016760:Proto-Oncogene Proteins c-fos
keywords: Amygdala; Extinction; Fear inhibition; Habituation; Infralimbic cortex; c-Fos