Information Cascade from Primary Auditory Cortex to the Amygdala: Corticocortical and Corticoamygdaloid Projections of Temporal Cortex in the Rat

Abstract

Corticocortical and corticoamygdaloid connections of temporal cortext and perirhinal cortex (PRh) were examined in the rat with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). Iontophoretic injections of PHA-L into area TE1 resulted in columnar axonal terminations in surrounding and contralateral regions of temporal neocortex and in the striatum, but not in the amygdala. Within temporal neocortex, labeled fibers were present locally in adjacent regions of TE1, as well as in TE2d, TE1v, TE3v, and TE2c. Injection of cortical areas TE1v, TE3v, and TE2c, which received projections from TE1, or injections of perirhinal periallocortex, which received projections from TE1v, TE2v, and TE3v, resulted in projections to the amygdala. The pattern of corticocortical and corticoamygdaloid projections differed among the divisions of auditory cortex. TE1 exhibited extensive ipsilateral and contralateral projections to temporal cortical regions and no projections to the amygdala. In contrast, areas of temporal neocortex ventral and posterior to TE1, including TE1v, TE3v, TE2c, and PRh, had more limited ipsi- and contralateral corticocortical projections but had an increased connectivity with the subcortical forebrain, especially the lateral nucleus of the amygdala (AL). There was a topographic organization to the AL afferents. The dorsal subdivision of AL received projections from TE1v, TE3v, TE2c, and PRh, while the ventrolateral division received projections from TE3v, TE2c, and PRh. The ventromedial division received projections only from PRh, which, unlike other temporal cortical areas, also projected to the basolateral and basomedial nuclei of the amygdala. These findings define the complete sequence of connections linking primary auditory cortex with the amygdala in the rat. In addition, the findings indicate that the ventral portion of TE1, designated TE1v, has connections that distinguish it from dorsal TE1, namely, dense projections to AL and a diminished number of corticocortical projections ipsilaterally and contralaterally. Finally, the results suggest a topographic organization to the cortical terminations within the amygdala.

Altered regional homogeneity in post-traumatic stress disorder: a restingstate functional magnetic resonance imaging study

“…The middle temporal gyrus can inhibit the function of the amygdala, facilitate the extinction of fear conditioning [52,53] , and is linked to episodic memory as well as language processing [54] . Lower…”

Region- and Layer-Specific Activation of the Higher Order Auditory Cortex Te2 after Remote Retrieval of Fear or Appetitive Memories

“…The fact that zif268 staining in this layer is unchanged in rats retrieving appetitive remote memories suggests that this pathway is not engaged as a result of tones with appetitive-related features. Sensory information about appetitive CSs may reach the Te2 cortex via layers II/III, which is connected to the Te1 auditory cortex (Romanski and LeDoux 1993a) and which also receives some sparse afferents from subcortical nuclei. In addition, a recent study showed that thalamic inputs to the cortex terminate also in the layer V/VI (Constantinople and Bruno 2013), two of the layers in which we found enhanced activity after memory retrieval.…”

“…The major corticofugal projections are glutaminergic (Paxinos 2004). Unlike the primary auditory cortex Te1, the Te2 sends axons to the lateral amygdala (Romanski and LeDoux 1993a;Shi and Cassell 1997), a key site for fear memory. In vitro studies have shown that descending axons from the auditory cortex to the lateral amygdala display long-term potentiation (LTP) (Bissière et al 2003;Fourcaudot et al 21 2009).…”

Long-term cortical plasticity evoked by electric stimulation and acetylcholine applied to the auditory cortex

“…A large lesion of the AC does not prevent the acquisition of conditioned behavioral responses (28,38,39). These findings indicate that the cortical BF shift is not directly involved in evoking conditioned behavioral responses.…”

“…Therefore, it has been concluded that the AC is not necessary for but can mediate simple fear conditionings (38). The neuronal circuit in adult animals for auditory signal processing is plastic (44).…”