Does Neural Activity during Reward Predict Self-relatedness?

Recent imaging investigations reveal strong neural recruitment in subcortical and cortical midline structures during presentation of stimuli specifically related to self (Northoff et al. 2006, van der Meer et al. 2010, Qin and Northoff 2011). These regions include the ventromedial prefrontal cortex (VMPFC), the perigenual anterior cingulate (PACC), and subcortical regions like the ventral striatum (VS) and the ventral tegmental area (VTA). The general aim of our study is to investigate the relationship between self-relatedness and reward in a transcultural context, comparing western (Canadian) and eastern (Taiwanese) participants. The specific aims are: (i) Using fMRI, we will investigate the spatial relationship between self and reward, with regard to the VMPFC, the VS, and the VTA. We hypothesize that neural activity in these regions during reward predicts the degree of self-relatedness assigned to the very same stimulus by the subject. (ii) Using EEG, we aim to investigate the temporal relationship between reward and self-relatedness. We hypothesize that reward induces early changes at around 100-150ms that predict the degree of self-relatedness assigned to the very same stimulus. Moreover, we assume such early changes are accompanied by increased phase synchronization and power in low frequency domains like theta and delta (and possibly infraslow bands like slow cortical potentials). (iii) We will investigate resting state concentration of Glutamate (Glx) in the VMPFC/PACC, the thalamus, and other regions (like the VS though, admittedly, difficult). We hypothesize that the concentration of Glutamate in the VMPFC/PACC predicts the degree of reward-related signal changes in the VS and the VTA and their differentiation from self-relatedness. (iv) Investigating Taiwanese subjects in Taiwan and western subjects in Canada, we aim to account for transcultural differences in the neuronal mechanisms linking self and reward. We hypothesize that although the two groups exhibit some differences as regards which stimuli are experienced as rewarding or self-related, reward and self-relatedness are, nonetheless, subserved by the same neuronal mechanisms. In other words, although Taiwanese and Canadians may well find distinct content or stimuli to be highly rewarding or highly self-related, when either group judges a stimulus to be rewarding or self-related judgment is underlain by an invariant neural substrate. A critical point is that the stimulus per se, does not determine neural activity; neural activity is determined by the degree of reward or self-relatedness. In short, we expect that cultural variation obtains at the level of stimulus content, but that invariance obtains in the neural substrate, just so long as subjects render a high reward/self-related judgment. The research is to be carried out over a three year period. Because the brain’s resting states have been shown to be crucial to understanding self, research during the first year will focus on the relationship between these two. During the second year, research will focus on the relationship between self and reward. During the third, focus will be on determining whether there is a common neural substrate for self, a substrate uninfluenced by cultural context, and how, if it obtains, it is related to reward.