Object Selectivity or Motivational Relevance: Fusiform Activation to Faces and Food

Background: While activation of the fusiform gyrus is most commonly linked to face processing, this region is also activated when viewing pictures of food and increases its responsivity following a period of fasting. Because objects must compete for our visual attention, an intriguing hypothesis is one in which parts of the ventral visual stream respond to salient objects, determined by individual preferences or item value.  To our knowledge, no study has been conducted viewing activation to the ventral visual stream to both faces and food. Here, we examine whether altered motivation in one domain, such as food, will have an impact on another domain, such as faces.

Objectives: To characterize category-selectivity and brain-behavioral correlates in the ventral visual stream in response to various categories of objects in a cohort of 48 healthy college age adults using fMRI (24 female; mean age=22.33).  

Methods: In an fMRI study acquiring BOLD images, we used a block design in which 4 categories of objects were presented, including faces, scenes, clocks, and highly palatable food.  Prior to the imaging session, participants also completed the Broader Autism Phenotype Questionnaire (BAP-Q). Body mass index (BMI) was calculated based on self-reported measurements of height and weight and used as a measure of food motivation. We implemented a region of interest (ROI) analysis using parcellation maps generated by a watershed algorithm with an independent data set (Julian et al., 2012). We calculated face-selectivity in bilateral FFA by contrasting face and food blocks and correlated this with phenotyping metrics.

Results: We find a positive correlation between BMI and the BAP-Q Aloof subscore (r(46)=0.494, p<0.001), indicating that as body mass increases, social motivation decreases. We also show a significant impact of food motivation on face-selectivity in the right fusiform (r(46)=-0.288, p<0.024). That is, with increasing BMI, the right fusiform shows less of a differential response to faces relative to food. To further explore this effect, we ran analyses separately for each gender. When genders were split, we find the BMI:BAP-Q Aloof relationship was only present in females (r(22)=0.648, p<0.001) and the relationship between food motivation and face-selectivity in the right fusiform was only present in males (r(22)=-0.550; p=0.003). 

Conclusions: These findings suggest that the fusiform may not be specific to only perceptual aspects of face processing, but may also respond to other items of motivational relevance. One possibility is that the fusiform is part of a relevance detection system that typically serves the role of face processing, but can be hijacked in cases of chronically altered motivation (i.e. towards food as chronic food motivation increases).  Our findings also indicate some degree of differentiation between how atypical motivational and social relevance systems interact with gender, a finding that warrants future exploration in autism and other developmental disabilities.

References: Julian, J. B., Fedorenko, E., Webster, J., & Kanwisher, N. (2012). An algorithmic method for functionally defining regions of interest in the ventral visual pathway. Neuroimage, 60(4), 2357-2364.