Emotion, olfaction, and the human amygdala: Amygdala activation during aversive olfactory stimulation

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 f low (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.

Attenuation of cue-induced cigarette craving and anterior cingulate cortex activation in bupropion-treated smokers: a preliminary study

“…The link between drug craving and OFC activity is the most common association found in this type of functional imaging work, and has led to the hypothesis that the OFC mediates drive and compulsive behavior associated with drug dependence (Volkow and Fowler, 2000). This region is also thought to mediate decision making that leads to reward (London et al, 2000;O'Doherty et al, 2001a;Ernst et al, 2002) and to act as a secondary processing center for gustatory (Zald et al, 1998;O'Doherty et al, 2001b) and olfactory (Zatorre et al, 1992;Levy et al, 1997;Zald and Pardo, 1997) stimuli. These putative functions of the OFC may help explain the consistent positive association between metabolism in this region and craving.…”

Left hippocampal volume loss in Alzheimer's disease is reflected in performance on odor identification: A structural MRI study

“…Nevertheless, highly significant correlations were observed in the present study between odor threshold and volume of the amygdala in normal elderly persons (see Table 3). Only rarely in neuroimaging studies of olfaction has activation been detected in mesial temporal areas of amygdala (Cerf-Ducastel & Murphy, 2001;Small et al, 1997;Sobel et al, 2000;Zald & Pardo, 1997, entorhinal cortex (Cerf-Ducastel & Murphy, 2001;Levy et al, 1997;Zald & Pardo, 2000), parahippocampal gyrus, or hippocampus (Cerf-Ducastel & Murphy, 2001;Levy et al, 1997;Small et al, 1997;Zald & Pardo, 2000); although electrophysiological and anatomical studies indicate that the anterior cortical nucleus of the amygdala, the periamygdaloid area and the lateral entorhinal cortex receive direct projections from the olfactory bulb through the lateral olfactory track (Biella & De Curtis, 2000;Carmichael et al, 1994;Price, 1985;1987). The entorhinal area also receives olfactory projections from the amygdaloid area and the piriform cortex.…”

Taste, olfactory and food texture reward processing in the brain and obesity

“…In humans, in addition to activation of the pyriform (olfactory) cortex, [56][57][58] there is strong and consistent activation of the OFC by olfactory stimuli, 49,59 and this region seems to represent the pleasantness of odour, as shown by a sensory-specific satiety experiment with banana vs vanilla odour. 60 Further, pleasant odours tend to activate the medial, and unpleasant odours the more lateral, OFC, 61 adding to the evidence that it is a principle that there is a hedonic map in the OFC, and also in the ACC, which receives inputs from the OFC.…”