Cortical Excitability Changes on the Sensorimotor Cortex Induced by Caffeine Consumption: A TMS Study

Caffeine is a widely used psychostimulant drug and acts as a competitive antagonist at adenosine receptors. Its effect is on neurons and glial cells of all brain areas. Chronic consumption of caffeine leads to tolerance which might be associated with an increased number of binding sites in the brain. In deep brain stimulation (DBS), the production of adenosine following the release of adenosine triphosphate (ATP) explains the reduction of in tremor. Binding of adenosine to adenosine A1 receptor suppresses excitatory transmission in the thalamus and thus reduces both tremor-and DBS-induced side effects. Also, the effect of adenosine was attenuated following the administration of the 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX) adenosine A1 receptor antagonist. Therefore, the presence of a receptor antagonist such as caffeine was suggested to reduce the effectiveness of deep brain stimulation (DBS) in treating tremor and other movement disorders. In light with this finding, we anticipate that the antagonistic effect of caffeine is a culprit to the reduction of effectiveness of any stimulation protocol in non-invasive stimulation (NIBS). In particular the excitatory effects of a NIBS protocol can tentatively be blocked in the presence of caffeine. In this study, the effects of caffeine consumption on cortical excitability at the sensorimotor cortex shall be examined on focal and non-focal plasticity. Focal plasticity will be induced by paired associated stimulation (PAS) and global cortical plasticity from transcranial alternating current (tACS) stimulation. In case of tACS stimulation, 1) an excitatory protocol (tACS, 140 Hz, 1 mA) and 2) an inhibitory protocol (tACS, 140 Hz, 0.4 mA) with the active electrode over M1 and the return electrode over the orbitofrontal cortex will be used. Changes in cortical excitability are assessed using transcranial magnetic stimulation (TMS) recordings. Research goals are to examine the effects of caffeine consumption on sensorimotor