A new study shows for the first time that low and high exercise intensities differentially influence brain function. Using resting state functional magnetic resonance imaging (Rs-fMRI), a noninvasive technique that allows for studies on brain connectivity, researchers discovered that low-intensity exercise triggers brain networks involved in cognition control and attention processing, while high-intensity exercise primarily activates networks involved in affective/emotion processing. The results appear in a special issue of Brain Plasticity devoted to Exercise and Cognition.
“We believe that functional neuroimaging will have a major impact for unraveling body-brain interactions,” said lead investigators Angelika Schmitt, MSc, and Henning Boecker, MD, Functional Neuroimaging Group, Department of Radiology, University Hospital Bonn, Bonn, Germany.
“These novel methods allow us to ‘look’ directly into the brains of a group of athletes, and, maybe even more importantly, understand the dynamic changes in brain structure and function associated with the transition from a sedentary to a healthy lifestyle.
Twenty-five male athletes underwent individual assessments using an incremental treadmill test. On separate days they performed low- and high-intensity exercise bouts for 30 minutes. Before and after exercising, Rs-fMRI was used to examine functional connectivity of different brain regions that are linked to specific behavioral processes.
Participants also completed a questionnaire to measure positive and negative mood before and after the exercise.
After low-intensity exercise, Rs-MRI showed that networks in the brain associated with cognitive control/attention were stimulated, while after high-intensity exercise, networks associated with emotions were more active, and those related to fatigue/motor function, decreased. Image is credited to Department of Radiology, University Hospital Bonn, Bonn, Germany.
The behavioral data showed a significant increase in positive mood after both exercise intensities and no significant change in negative mood. The results of the Rs-fMRI tests showed that low-intensity exercise led to increased functional connectivity in networks associated with cognitive processing and attention.
High-intensity exercise, on the other hand, led to increased functional connectivity in networks related to affective, emotional processes. High-intensity exercise also led to a decreased functional connectivity in networks associated with motor function.
The investigators note that this is the first study to report distinct effects of exercise intensity on specific functional networks within the brain at rest. Future research in this area will help provide neurobiological evidence about what type of exercise intensity is best suited for certain neurological or behavioral modulations and may pave the way for supportive clinical applications in patients or for enhancing brain functional plasticity.
Acute physical exercise bouts are known to enhance affective, cognitive and attentional processes in a range of minutes to hours after exercise bouts. One possible mechanism by which such transient improvements appear to be mediated is an alteration of coherent neuronal activity that persists after exercise.
Such coherent neuronal activity is termed “resting state functional connectivity” (rs-FC) and brain regions that are functionally connected via distinct temporo-spatial properties are referred to as “functional networks”.
Resting state functional magnetic resonance imaging (rs-fMRI) is a potential tool to measure such transient coherent neuronal activity alterations that persist after acute exercise bouts.
Most of the previous rs-fMRI literature was, however, not focused on investigating the transient effects of acute exercise bouts, but rather on long-term effects of repeated exercise training over several months [1–4]: Stronger rs-FC was reported between the right parahippocampal gyrus and motor, sensory, and mood regulating areas after 16 weeks of training .
On the other hand, 12 weeks of exercise induced increased FC between the default mode network (DMN) and primary motor areas , eventually indicating improved motor performance.
Conversely, another study found no significant changes in intrinsic brain activity after a six months of aerobic exercise .
Less is known about the transient effects of acute exercise bouts on rs-FC: A recently published study using rs-fMRI in both older and younger healthy volunteers reported a modulation of rs-FC after a moderate exercise session on a bicycle ergometer compared to a passive control condition .
The authors found a significant increase in rs-FC in the affective-reward network (ARN), the hippocampal and the right executive control network (ECN) after exercising at 65% of their HRmax (maximum heart rate). Another study investigating the effects of a single moderate aerobic exercise session in young healthy subjects found transient changes in FC in the auditory resting state network (RSN), the sensorimotor network (SMN) and the thalamic-caudate RSN .
Taken together, these initial findings in the acute setting suggest that single exercise bouts induce transient changes in intrinsic brain activity that can be captured by rs-fMRI. Although, these studies generally report enhanced FC of intrinsic brain networks, it still remains unknown how these effects are influenced by the intensity of the exercise bout.
It is relevant to point out, based on meta-analytical data (independent of the imaging context) that the effect on cognitive performance after exercise is influenced by the intensity of the exercise and notably also by the time between the end of the exercise bout and the start of the cognitive testing .
When cognitive performance is acquired with a delay of more than 1 min, more intense exercise (very hard) appears to be more beneficial than lighter intensity exercise , whereas, when cognitive testing is performed immediately after the exercise bout, lighter intensity exercise (very light, light, moderate) appears to be more beneficial than high intensity exercise .
Chang and colleagues found that distinct types of brain executive control functions tested with the ‘Tower of London’ task are differentially improved by different intensities of acute exercise [8, 9].
Studies using MRI to investigate the neuronal underpinnings of transient effects of acute exercise bouts are rare. To the best of our knowledge, there have been only two studies comparing cerebral blood flow (CBF) after different intensities of acute exercise [10, 11], showing exercise intensity dependent changes in CBF.
One of these studies found decreases in CBF after moderate exercise intensity in the anterior cingulate, bilateral thalamus, and bilateral insula, but not after low exercise intensity . The other study found intensity dependent changes in CBF in the right somatosensory cortex in individuals with cerebrovascular disease.
The CBF in the sensorimotor cortices was reduced following low-intensity exercise and increased following moderate-intensity exercise .
A recently published study by our own group comparing the effect of low and high intensity exercise bouts on emotional face processing could show distinct changes in the brain during fearful face processing : Low-intensity exercise resulted in reduced brain activations in PCC / precuneus and high intensity exercise was associated with reduced fear-related activity in ventral basal ganglia structures. Taken together, the mentioned behavioral and imaging studies indicate distinct changes in cognitive, affective and brain function, dependent on exercise intensity.
In order to determine how the intensity of acute exercise transiently affects the intrinsic neuronal activity at rest, we designed this study to assess rs-FC changes after defined ‘low’ and ‘high’ exercise intensities (adapted to the individual fitness level of each participant).
These two forms of exercise intensity (‘low’ and ‘high’) were chosen in this study in order to fill the open gap (i.e. effects of different exercise intensities on rs-fMRI) in the literature. We predicted that ‘high’-intensity (20% above lactate threshold) exercise would alter the FC at rest differently than ‘low’-intensity (35% below lactate threshold) exercise.
This could be helpful in understanding the relation between exercise intensity and to identify interventions that specifically enhance the FC in different cognitive and affective networks.