Altered neural representation of olfactory food reward in the nucleus accumbens after acute stress.

Acute stress affects reward processing. The nucleus accumbens (NAcc) plays a vital role in process of primary reward such as food. The present study used MRI technology and the representational similarity analysis (RSA) to investigate how acute stress influences the representation of food odor stimuli in the NAcc. Forty-eight participants were recruited. Compared to the control group, the stress group rated the high-calorie food odor as significantly more pleasure (p = 0.005). In the NAcc, the fMRI results showed that acute stress significantly reduced the dissimilarity of food and non-food odors in perceptual stage (p = 0.027) and there was a marginal reduction the dissimilarity of high and low-calorie foods in the anticipatory stage (p = 0.095). Significant negative correlations were observed between the level of NAcc representational differentiation for high-calorie vs low-calorie food odors during perception and the pleasantness rating difference between high-calorie vs low-calorie food odors (r = -0.40, p = 0.005). These findings suggest that acute stress may impair participants' ability to distinguish food odor rewards, resulting in individuals tend to seek more comfort in food odor rewards during stressful situations to maintain positive emotion.