Vive les differences! Individual variation in neural mechanisms of executive control

Abstract

Investigations of individual differences have become increasingly important in the cognitive neuroscience of executive control. For instance, individual variation in lateral prefrontal cortex function (and that of associated regions) has recently been used to identify contributions of executive control processes to a number of domains, including working memory capacity, anxiety, reward/motivation, and emotion regulation. However, the origins of such individual differences remain poorly understood. Recent progress toward identifying the genetic and environmental sources of variation in neural traits, in combination with progress in identifying the causal relationships between neural and cognitive processes, will be essential for developing a mechanistic understanding of executive control.

Figure 1. A trend toward increasing use of individual differences measures in executive control cognitive neuroscience research over the past 10 years

The graph illustrates a shift from proportionally fewer individual difference studies early in the decade to a proportionally larger number of individual difference studies over the last several years. The blue line illustrates individual difference studies of the neural basis of executive control, while the red line illustrates such research not including individual difference terms (see below). The publication data were normalized by dividing the number of publications per year by the total number of publications (between 1999 and 2009) in each category. Source: Scopus. Search used: (“individual differences” OR IQ OR PERSONALITY OR “individual variability”) AND (“cognitive control” OR “executive control” OR “working memory” OR “response inhibition” OR attention) AND (fMRI OR MRI OR ERP OR EEG OR PET OR MEG OR TMS)

Figure 2. Complementary within-subject and between-subject effects may be present within a single region

In a large fMRI study of working memory (N = 94; unpublished data), A) medial posterior parietal cortex (mPPC) showed a convergence of within-subject and between-subject effects, B) including both trial-by-trial differences in response accuracy (greater activation for correct responses than in correct responses on high interference [lure] as well as low interference [non-lure, target] trials) and C) individual differences in mean response accuracy (the correlation is plotted separately for each trial type, and only for correct responses).

Figure 3. Explaining individual variation in PFC function: An example of how neural mechanisms can bridge the gap between genetic/environmental factors and individual differences

A) PFC activity covaries with the COMT val¹⁵⁸met variant (on right) [52]. One explanation for this correlation involves the differential breakdown of dopamine in PFC across val (more breakdown) and met (less breakdown) genotype variants (on left). B) PFC dopamine receptor binding (left) and PFC activity during a WM task (right) are modulated by practice performing particular WM tasks [66,67], suggesting that frequently performed day-to-day tasks (e.g., frequently dialing phone numbers from memory) may affect PFC function, which in turn may increase WM capabilities. C) Further research is necessary to establish clear gene X environment interactions between COMT variants, PFC function, and individual differences in behavior. We suggest that the met variant, which involves slower breakdown of DA, may promote an increase in DA receptor binding (and a possible increase in DA receptors) to allow for faster/stronger increases in WM capacity with practice.