INVOLVEMENT OF SUBCORTICAL AND CORTICAL AFFERENTS TO THE LATERAL NUCLEUS OF THE AMYGDALA IN FEAR CONDITIONING MEASURED WITH FEAR-POTENTIATED STARTLE IN RATS TRAINED CONCURRENTLY WITH AUDITORY AND VISUAL CONDITIONED-STIMULI
S. Campeau et M. Davis, INVOLVEMENT OF SUBCORTICAL AND CORTICAL AFFERENTS TO THE LATERAL NUCLEUS OF THE AMYGDALA IN FEAR CONDITIONING MEASURED WITH FEAR-POTENTIATED STARTLE IN RATS TRAINED CONCURRENTLY WITH AUDITORY AND VISUAL CONDITIONED-STIMULI, The Journal of neuroscience, 15(3), 1995, pp. 2312-2327
The goal of this work was to test the involvement, in fear conditionin
g, of afferents to the lateral nucleus of the amygdala originating fro
m the auditory thalamus, auditory cortex, and perirhinal area. The aco
ustic startle reflex was used as the behavioral index of conditioning
because it is reliably enhanced in the presence of a conditioned stimu
lus (CS) previously paired with a footshock. Auditory and visual CSs w
ere used to assess the modality specificity of lesions to the above br
ain areas. Pre- or posttraining lesions of the entire auditory thalamu
s including the ventral, dorsal, and medial divisions of the medial ge
niculate body, the posterior intralaminar nucleus, and the supragenicu
late nucleus, completely blocked fear-potentiated startle to the audit
ory CS, but had no effect on fear-potentiated startle to the visual CS
. Posttraining lesions mostly restricted to the ventral and dorsal div
isions of the medial geniculate body specifically disrupted fear-poten
tiated startle to the auditory CS. However, retraining in rats sustain
ing ventral and dorsal medial geniculate body lesions led to reliable
fear-potentiated startle to the auditory CS. Posttraining lesions most
ly restricted to the medial division of the medial geniculate body, po
sterior intralaminar, and suprageniculate nuclei did not disrupt fear-
potentiated startle. These results indicate that the auditory thalamus
is specifically involved, through either its direct or indirect amygd
aloid afferents, in fear conditioning to auditory CSs. Pre- or posttra
ining lesions mostly restricted to the primary auditory cortex did not
reliably attenuate fear-potentiated startle to the auditory or visual
CSs. Extensive posttraining lesions of the perirhinal area (including
secondary auditory cortices), but not its rostral aspect alone, block
ed fear-potentiated startle to both CSs. However, reliable potentiated
startle was observed to both CSs following similarly extensive pretra
ining lesions of the perirhinal area. Because post- but not pretrainin
g lesions of the perirhinal area blocked fear-potentiated startle nons
pecifically, at least with regard to auditory and visual CSs, the resu
lts are consistent with the involvement of the perirhinal area in gene
ral memory functions such as information storage or retrieval. Alterna
tively, the secondary auditory and/or perirhinal cortices might functi
on as multimodal sensory relays to the amygdala.