Equipotentiality of thalamo-amygdala and thalamo-cortico-amygdala circuits in auditory fear conditioning

Abstract

The goal of the present study was to examine the contribution of thalamo-amygdala and thalamo-cortico-amygdala projections to fear conditioning. Lesions were used to destroy either the thalamo-cortico-amygdala projection, the thalamo-amygdala projection, or both projections, and the effects of such lesions on the acquisition of conditioned fear responses (changes in arterial pressure and freezing behavior) to a tone paired with footshock were measured. In each group of animals examined, a large lesion of the acoustic thalamus, including all nuclei of the medial geniculate body and adjacent portions of the posterior thalamus, was made on one side of the brain to block auditory transmission to the forebrain at the level of the thalamus on that side. In this way, experimental lesions could be made on the contralateral side of the brain. Thus, animals with thalamo-amygdala pathway lesions received a large lesion of the acoustic thalamus on one side. Contralaterally, only the nuclei that project to the amygdala (the medial division of the medial geniculate body, the posterior intralaminar nucleus, and the suprageniculate nucleus) were selectively destroyed, leaving much of the thalamo-cortico-amygdala projection intact. For thalamo-cortico-amygdala pathway lesions, the acoustic thalamus was destroyed on one side and temporal and perirhinal cortices were ablated contralaterally. In these animals, thalamo-amygdala projections were intact on the side of the cortical lesion. Destruction of either pathway alone had no effect on auditory fear conditioning. However, combined lesions of the two sensory pathways disrupted conditioning.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathways for emotion: interactions of prefrontal and anterior temporal pathways in the amygdala of the rhesus monkey

“…The amygdala increases its activity when viewing masked fearful faces, when there is no awareness of the event (Whalen et al, 1998). Moreover, a subcortical loop connecting the amygdala with the thalamus can support fear conditioning (Romanski and LeDoux, 1992). Since the experience of emotions likely involves the cortex (Kennard, 1945), the robust bidirectional pathways linking the amygdala with orbitofrontal cortices may underlie this process.…”

Specific long-term memory traces in primary auditory cortex

“…However, bilateral destruction of A1 does not impair fear conditioning to a tone 83 and ablation of A1 does not prevent auditory stimuli from accessing the amygdala 84 . The Weinberger model hypothesizes that specific memory traces in A1 are not tied directly to immediate fear behaviours but serve a flexible function that can promote adaptive behaviour in unforeseen future situations.…”

The rat perirhinal cortex: A review of anatomy, physiology, plasticity, and function

“…Overall, this points to an associative role for the perirhinal cortex and, as in recognition memory, contextual processing most likely require interaction with the amygdala (Romanski and LeDoux, 1992b;Campeau and Davis, 1995;Sacchetti et al, 1999Sacchetti et al, , 2007, thalamus (Romanski and LeDoux, 1992a,b;Sacchetti et al, 1999;Shi and Davis, 2001), medial prefrontal cortex (Goldstein et al, 1994;Campeau et al, 1997;Sacchetti et al, 2002) or the hippocampus (Phillips and LeDoux, 1995;Sacchetti et al, 1999). However, the perirhinal cortex's role in recognition memory cannot be discounted as recognition and familiarity do seem to be part of the perirhinal cortex's role in fear conditioning; the rostral ventral perirhinal cortex shows increased c-Fos expression when the animal is exposed to previously acquired (i.e.…”