Cardiorespiratory fitness predicts effective connectivity between the hippocampus and default mode network nodes in young adults

Abstract

Rodent and human studies examining the relationship between aerobic exercise, brain structure, and brain function indicate that the hippocampus (HC), a brain region critical for episodic memory, demonstrates striking plasticity in response to exercise.Beyond the hippocampal memory system, human studies also indicate that aerobic exercise and cardiorespiratory fitness (CRF) are associated with individual differences in large-scale brain networks responsible for broad cognitive domains. Examining network activity in large-scale resting-state brain networks may provide a link connecting the observed relationships between aerobic exercise, hippocampal plasticity, and cognitive enhancement within broad cognitive domains. Previously, CRF has been associated with increased functional connectivity of the default mode network (DMN), specifically in older adults. However, how CRF relates to the magnitude and directionality of connectivity, or effective connectivity, between the HC and other DMN nodes remains unknown. We used resting-state fMRI and conditional Granger causality analysis (CGCA) to test the hypothesis that CRF positively predicts effective connectivity between the HC and other DMN nodes in healthy young adults.Twenty-six participants (ages 18-35 years) underwent a treadmill test to determine CRF by estimating its primary determinant, maximal oxygen uptake (VO 2max ), and a 10-min resting-state fMRI scan to examine DMN effective connectivity. We identified the DMN using group independent component analysis and examined effective connectivity between nodes using CGCA. Linear regression analyses demonstrated that CRF significantly predicts causal influence from the HC to the ventromedial prefrontal cortex, posterior cingulate cortex, and lateral temporal cortex and to the HC from the dorsomedial prefrontal cortex. The observed relationship between CRF and Corey A. Kronman and Kathryn L. Kern share the first authorship.

Poor physical fitness is associated with impaired memory, executive function, and depression in institutionalized older adults: a cross-sectional study

“…Brain connectivity and mental health have been associated with cardiorespiratory fitness. 23,24 Recently, Plá cido et al 10 found a strong association among cardiorespiratory fitness measured through the 2-minute step test, Alzheimer's disease (AD), and mild cognitive impairment (MCI). The authors showed that people at risk of functional loss were most likely to be diagnosed with mild (OR = 10.7; p = 0.001) to moderate (OR = 14.7; p = 0.002) AD, whereas individuals with low aerobic fitness were 4.5 times more likely to present with MCI (p = 0.05).…”

“…Physical fitness and cognition in elders brain regions, such as the medial prefrontal cortex and default mode network (DMN), 23 explaining the link between physical capacity and improved cognition and depression. The hippocampus and DMN are closely associated to cognition and depression, 23,26 reinforcing the perspective of physical fitness improving mental health. This is relevant because persons living in LTCFs have poor physical fitness and high physical dependence, which could be associated to poor mental health.…”

“…24,28 Many neurobiological processes related to physical fitness, such as improved cerebral blood flow, increased trophic factors, neurotransmitter synthesis, and synaptic branch enhancement, could be associated with brain integrity. 29,30 Recently, Kronman et al 23 found a relationship between cardiorespiratory fitness and improved hippocampus and prefrontal cortex connectivity. The authors showed that people with high levels of cardiorespiratory fitness had more effective connections from the hippocampus to the ventromedial prefrontal cortex, posterior cingulate cortex, lateral temporal cortex, and dorsomedial prefrontal cortex.…”

Cardiorespiratory fitness, hippocampal subfield volumes, and mnemonic discrimination task performance in aging

“…Before testing at the Boston University Fitness and Recreation Center, study staff instructed participants to refrain from aerobic exercise and/or resistance training for 24 hr prior to testing and refrain from any caffeine consumption for 3 hr prior to testing. The incremental treadmill test protocol implemented by our laboratory (Kronman et al, 2020; Nauer, Dunne, et al, 2020; Nauer, Schon, & Stern, 2020) includes three phases: 3 min of warm‐up, approximately 8–12 min of incremental exercise, and 3 min of cool‐down. Throughout the duration of the test, a study staff member monitored the participant's heart rate.…”

Daily-life Physical Activity of Young Healthy Adults Associates with Function and Structure of the Hippocampus

“…For example, Ezama et al (2021) found that during the resting-state, anterior sections of the hippocampus coactivated with brain regions typically associated with the somatomotor network, whereas middle/posterior sections of the hippocampus co-activated with brain regions typically associated with the default mode network. Thus, whereas previous studies have shown that PA affects the connectivity between the hippocampus and the default mode network (Kronman et al, 2020;Stillman et al, 2018;Raichlen et al, 2016), how PA is associated to the connectivity between the hippocampus and the somatomotor networks remains unknown.…”