Four weeks of exercise improves executive function and influences intracortical inhibitory circuits: a preliminary and ongoing study

Introduction. There is evidence supporting improved cognitive performance following regular aerobic exercise (delivered usually over a period of 9-12 months), but it is not clear if shorter interventions (of approximately one month) would influence cognitive performance in sedentary adults. In addition, it has been proposed that the exercise-mediated cognitive improvements can be at least partly attributed to neuroplastic changes that occur at the cortical level. Transcranial magnetic stimulation (TMS) can be used to assess corticomotor excitability and the excitability of cortico-cortical connections in a non-invasive manner in humans. Objectives. To assess if a 4-week regular aerobic exercise protocol would be associated with pre-post significant changes in cognitive performance measures and measures of brain electrophysiology using TMS. Methods. Eighteen sedentary (less than one hour of physical exercise in the last month), healthy adults (12 females, mean age=30 years) have enrolled in the study. Participants engaged in an aerobic exercise intervention (30 min daily sessions, 4x/week for 4 weeks [i.e., 16 total] delivered at 55-64% age-predicted maximal heart rate). Prior to and following the exercise protocol, participants performed a battery of test containing measures of: memory (Rey Auditory Verbal Fluency Test [RAVLT]); sustained attention (Conners’ Continuous Performance Test [CPT-2]) and executive control (Stroop Color Word Test); corticomotor excitability (amplitude of motor evoked potentials) and excitability of cortico-cortical connections (short-interval intracortical inhibition [SICI], intracortical facilitation [ICF] and long-interval intracortical inhibition [LICI]), measured with TMS. Paired t-tests were used to compare outcome measures prior to and following exercise. All subjects gave their written informed consent as approved by a local ethics committee (Beth Israel Deaconess Medical Center, protocol 2014P-000125). Results. Complete data for all outcome measures was obtained from 9 participants thus far. There was a significant pre-post improvement in the time to complete the Stroop color-word test (2.53±1.03 sec, p=0.03). In addition, there were trends toward significant increases in SICI (-193.7±92.5 mV, p=0.06), and LICI (-83.1±37.9mV, p=0.059). There were no significant pre-post changes in RAVLT, CPT-2, corticomotor excitability and ICF. Conclusion. Four weeks of moderate intensity aerobic exercise is associated with an improvement in executive control. Contrary to our hypothesis, there was a trend for increased cortico-cortical inhibition, which may suggest increased activity in GABAergic circuits involved in attentional control.