Elsevier

Brain Research Bulletin

Volume 79, Issue 6, 14 August 2009, Pages 388-395
Brain Research Bulletin

Research report
Effective connectivity of a reward network in obese women

https://doi.org/10.1016/j.brainresbull.2009.05.016Get rights and content

Abstract

Exaggerated reactivity to food cues in obese women appears to be mediated in part by a hyperactive reward system that includes the nucleus accumbens, amygdala, and orbitofrontal cortex. The present study used functional magnetic resonance imaging (fMRI) to investigate whether differences between 12 obese and 12 normal-weight women in reward-related brain activation in response to food images can be explained by changes in the functional interactions between key reward network regions. A two-step path analysis/General Linear Model approach was used to test whether there were group differences in network connections between nucleus accumbens, amygdala, and orbitofrontal cortex in response to high- and low-calorie food images. There was abnormal connectivity in the obese group in response to both high- and low-calorie food cues compared to normal-weight controls. Compared to controls, the obese group had a relative deficiency in the amygdala's modulation of activation in both orbitofrontal cortex and nucleus accumbens, but excessive influence of orbitofrontal cortex's modulation of activation in nucleus accumbens. The deficient projections from the amygdala might relate to suboptimal modulation of the affective/emotional aspects of a food's reward value or an associated cue's motivational salience, whereas increased orbitofrontal cortex to nucleus accumbens connectivity might contribute to a heightened drive to eat in response to a food cue. Thus, it is possible that not only greater activation of the reward system, but also differences in the interaction of regions in this network may contribute to the relatively increased motivational value of foods in obese individuals.

Section snippets

Materials and methods

The data used for the path analysis were the same data reported in Stoeckel et al. [77]. With the exception of the section discussing the methods of path analysis, the information below is provided in greater detail in Stoeckel et al. [77].

Results

All of the estimated path coefficients were significantly different from zero for the obese group and controls for both hemispheres in both the high- and low-calorie food models, consistent with the specified connectivity model (p values < 0.001; Table 1).

Discussion

Previous research has shown that food cues, especially those associated with high-calorie foods, trigger hyperactivity in brain regions including NAc, AMYG, and OFC thought to mediate or at least code for motivational and emotional processes in obese individuals (e.g., [68], [77]). In the present study, we tested whether there were differences in network connections between NAc, AMYG, and OFC in response to high- and low-calorie food images within and between obese and normal-weight groups. It

Conclusions and summary

In summary, our neuroimaging study found aberrant reward network connectivity in obese individuals compared to controls, with reduced connectivity from AMYG to OFC and NAc and increased connectivity in OFC  NAc in these participants. These results add to previous reports in showing that there is not only exaggerated reward system activation in response to foods, but also an abnormal interaction between regions in this network in obese individuals. In particular, we think overeating in obese

Conflict of interest statement

The authors declare that they have no competing financial interests.

Acknowledgments

Supported by the NIH-NIDCD Intramural Research Program, the GCRC grant M01 RR-00032 from the National Center for Research Resources, the Procter and Gamble Co., and resources of UAB's Center for the Development of Functional Imaging (CDFI).

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