The hippocampal connection to the autonomic network

There is mounting evidence to suggest that cardiovascular arousal is associated with a network of cortical regions defined primarily by the medial prefrontal cortex (MPFC), the bilateral insular cortex, and the anterior cingulate cortex. Based on recent psychological evidence structurally linking the MPFC to the hippocampus (HC), this study tested the hypothesis that the actions of the MPFC are entrained to the rhythm of the HC suggesting a functional connection between these two regions. Twelve young, healthy individuals (6 M, 6 F; 26±1 years) performed graded handgrip exercise (HG; 35% maximal contraction) while heart rate (HR) and cortical activity were recorded using functional magnetic resonance imaging with blood oxygen level-dependent contrast. Consistently across all but one participant, HR was elevated with the HG exercise and was correlated with deactivation in the MPFC and the HC. To further test our hypothesis, we examined this relationship in older aged adults (n=23; 60±1 years) who have an inconsistent HR response to exercise. In this group, 9/23 subjects showed conjoint HR, MPFC and HC responses; 2/23 had a HR and MPFC response but lacked HC activity; and 12/23 had no HR response and inconsistent patterns in the MPFC and HC. These results raise the possibility that the interaction between the MPFC and the HC modulates an autonomic response.