When the heart inhibits the brain: cardiac phases modulate Short-interval intracortical inhibition

Background: The phasic cardiovascular activity influences the central nervous system through the systolic baroreceptor inputs, inducing widespread inhibitory effects on behaviour. Despite this, few studies assessed how the cardiac systole affects neurotransmission within our nervous system.
Hypothesis: Phasic systolic baroreceptor inputs affect the motor system through intracortical-inhibition modulation, in particular of fast-acting inhibitory postsynaptic potentials GABAA neurotransmission.
Methods: Through Transcranial magnetic stimulation (TMS) delivered during resting-state over the left primary motor cortex and across the different cardiac phases, we measured corticospinal excitability-(CSE) and distinct indices of intracortical motor inhibition: short-(SICI) and long-(LICI) interval, corresponding to GABAA and GABAB neurotransmission, respectively.
Results: We found a significant interaction between the cardiac phase and intracortical inhibition specific for SICI only. SICI was stronger at systole than at diastole.
Conclusions: These results show a tight relationship between the cardiac cycle and the inhibitory neurotransmission within M1, and in particular with GABAA–ergic mediated motor inhibition.