Effect of Exercise on the ACC-OFC Network and Implications for Cost-Benefit Decision Making

Abstract

Increasing evidence demonstrates that physical exercise (PE) improves cognitive functioning. Improvements are particularly noted in executive functioning – a subset of cognition including functions such as cost-benefit analysis, decision-making, and problem solving. For example, following a PE regime, rats show increased tendency to select and persist with high-effort behaviour, demonstrating changes in cost-benefit decision-making. Consistent with this link between PE and improved cognition, PE is correlated with general improvements in brain health. However, the observed brain changes following PE are predominantly global, for example increased vascularisation, neurogenesis, and neurotrophin release. It is unlikely that global changes in neurophysiology produce specific improvements in executive functioning. Rather, selective improvements in executive functioning suggest that PE might be producing specific functional changes in the prefrontal cortex (PFC), an area of the brain associated with executive functioning. The anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) are two regions of the PFC that show conjoint activation during a variety of tasks, including tasks requiring cost-benefit analysis. Changes in activation/cytoarchitecture are also noted in these areas in relation to physical effort. Therefore it was hypothesised that routine exercise alters neural activity in the ACC-OFC network in a way that changes cost-benefit decision-making to promote subsequent high-effort task behaviour. To test this hypothesis, in vivo OFC and ACC activity was recorded from laboratory rats during the course of an eight-week exercise intervention. Neural and behavioural data were collected weekly during a baseline task and five decision-making tasks. Overall, there were minimal differences in behavioural measures between exercised rats and controls, therefore the hypothesis that routine exercise would promote high-effort task behaviour was not supported. Despite the absence of between group differences in cost-benefit decision-making, there were some between group differences in ACC-OFC electrophysiological measures. Exercised rats demonstrated different levels of ACC-OFC coherence, in different time patterns across the eight-week intervention, as compared to controls. One interpretation of our findings is that exercise intervention in rats may prime animals to initially exert a higher level of willed attention towards a task, be that an open field task or decision-making task. Confounds of the current experiment and avenues for future investigation are discussed.