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, 94 (8), 4119-24

Emotion, Olfaction, and the Human Amygdala: Amygdala Activation During Aversive Olfactory Stimulation

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Emotion, Olfaction, and the Human Amygdala: Amygdala Activation During Aversive Olfactory Stimulation

D H Zald et al. Proc Natl Acad Sci U S A.

Abstract

Electrophysiologic and lesion studies of animals increasingly implicate the amygdala in aspects of emotional processing. Yet, the functions of the human amygdala remain poorly understood. To examine the contributions of the amygdala and other limbic and paralimbic regions to emotional processing, we exposed healthy subjects to aversive olfactory stimuli while measuring regional cerebral blood flow (rCBF) with positron emission tomography. Exposure to a highly aversive odorant produced strong rCBF increases in both amygdalae and in the left orbitofrontal cortex. Exposure to less aversive odorants produced rCBF increases in the orbitofrontal cortex but not in the amygdala. Change of rCBF within the left amygdala and the left OFC was highly intercorrelated, indicating a strong functional interaction between these brain regions. Furthermore, the activity within the left amygdala was associated significantly with subjective ratings of perceived aversiveness. These findings provide evidence that the human amygdala participates in the hedonic or emotional processing of olfactory stimuli.

Figures

Figure 1
Figure 1
Cerebral activation during aversive olfaction. Changes in rCBF are rendered in color with white indicating the greatest magnitude (Z score > 5) of activation. The relative positions of coronal sections (A, B, and C) through the frontal (a and b) and temporal (c) lobes are shown schematically in the upper left. Maximal areas of rCBF change are displayed superimposed on a standard T-1-weighted magnetic resonance image. The rCBF maxima map to the amygdala bilaterally and the left posterior lateral OFC. The right side of this figure shows the left side of the brain. VCA, vertical line through anterior commissure; CACP, intercommissural line.
Figure 2
Figure 2
Mean rCBF in the left and right amygdala during odorant (sulfides and UPSIT) and control (no odorant) conditions. Normalized rCBF was estimated as normalized regional tissue activity (counts). Both amygdalae showed significantly increased rCBF for the highly aversive sulfides but did not change significantly for the milder UPSIT odorants.
Figure 3
Figure 3
Post hoc correlational analyses of rCBF change and subjective scores (low scores indicate high aversion). Correlations are shown between subjective ratings of aversiveness and left amygdalar rCBF (A) and left OFC rCBF (B) changes and between left amygdalar and left OFC rCBF changes (C). There were no significant correlations between rCBF in these regions of interest and subjective ratings of odor intensity.

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