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Abstract:
We have previously reported activation of anterior cingulate
cortex and bilateral insulae together with rapid habituation of
amygdala responses during aversive delay conditioning using visual
CS and auditory US. Here we tested the hypothesis that those
activations were not linked to the modality of the CS (visual) or
the specific type of classical conditioning (delay conditioning).
We used event-related functional magnetic resonance imaging (efMRI)
to characterise neural responses during trace conditioning in which
one of two tones (600Hz and 1400Hz) was conditioned by pairing with
an aversive auditory US (1 kHz, 100-110dB(A), 0.5 s). The US
followed a silent "trace" period of 1 second following a 3 s
presentation of the CS+. Evoked hemodynamic responses to the CS+
were assessed in the absence of the US by using 50% partial
reinforcement. Data analysis was performed with SPM97. Online skin
conductance responses confirmed the acquisition of conditioned
autonomic responses. The critical comparison, between the CS+
auditory evoked response and those evoked by the CS- revealed
differential activation of bilateral anterior cingulate gyri and
bilateral anterior insulae. Responses in bilateral amygdalae showed
rapid habituation. This result confirms our hypothesis that the
observed activations are independent of the CS modality.
Furthermore we have demonstrated that the amygdala shows a similar
habituation during trace conditioning as during delay
conditioning.
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