Orbitofrontal Cortex Sulcogyral Anatomy and Value Signals: An Interaction of Structure and Function
The orbitofrontal cortex (OFC) has an important function in codifying individual social and motivational behaviors. Atypical organization of the OFC architecture has been linked to psychiatric disorders including schizophrenia and Autism Spectrum Disorder (ASD) (Watanabe et al, 2014). Little is known about the influence of atypical cortical organization on functional organization of the OFC. Here we characterized two types of motivational brain responses, food and social, as well as their underlying sulcogyral anatomy.
This study localizes face-selective and food-selective value signals in OFC for each individual by contrasting faces or food with all other objects. We also characterize subject’s OFC sulcogyral pattern type bilaterally, in order to determine if a pattern exists between variation in OFC sulci and OFC peak signal location for faces and food. We predict that value signals for faces are located in medial OFC and value signals for food are located in lateral OFC. We anticipate individuals with more consistent sulcogyral anatomy will have greater spatial consistency in the location of their face- and food-selective value signals.
In this experiment, 28 healthy adults (mean age: 21; 14 females) were scanned using a 3T Siemens MRI and completed the Broader Autism Phenotype Questionnaire (BAP-Q). Value signals were determined for each individual by contrasting faces or food with all other objects using a variant of a standard fMRI face localizer task that included faces, food, scenes, and objects. OFC structure was determined by classifying each hemisphere as Type I, II, or III, based on the continuity of the medial and lateral orbital sulcus.
Consistent with our hypothesis, we found that medial value signals were more often associated with faces (27/28 subjects), while only 14 subjects had medial food value signals. While lateral value signals were consistently present for both faces and food (27/28 for food; 26/28 for faces, these were found in distinct sulcogyral locations within lateral OFC. Frequency of OFC sulcogyral patterns was consistent with previously published work, with Type I the most prevalent, followed by Type II and Type III. We found that subjects with a Type II pattern (known to increase risk for schizophrenia; Lavoie et al. 2014) were more likely to have atypical value signal locations. We also found that individuals with a Type II pattern present in at least one hemisphere scored significantly higher on the Aloof subscale of the BAP-Q (p<0.05). Ongoing analysis and additional data collection to increase sample size will validate these findings and combine the functional and structural characterizations to test for an anatomo-functional relationship.
Future studies will attempt to identify the developmental trajectory and stability of object-selective patches in OFC. Understanding predictable developmental patterns of sulcogyral anatomy in typically developing healthy controls will allow us to better characterize and assess deviations that may occur in an ASD population. Observable structural and functional differences in sulcogyral pattern and value signal location may assist as predictive biomarkers of cross-diagnostic social or motivational behavior.