Cortical Excitability in Cyclic Vomiting Syndrome

This exploratory study will determine if there are differences in cortical excitability between patients suffering from cyclic vomiting syndrome (CVS) and healthy control subjects, as assessed by a non-invasive method of brain stimulation (Transcranial Magnetic Stimulation, TMS). Using the paired-pulse TMS paradigm, intracortical inhibition and facilitation of cortical circuitry will be assessed by stimulating the motor cortex and using the electromyographic (EMG) response of a target muscle as readout. In such studies, a conditioning stimulus modulates the amplitude of the motor-evoked potential (MEP) produced by the test stimulus. Depending on the inter-stimulus interval, effects can be attributed to different aspects of cortical processing. Brief intervals (1-5 ms) will be used to assess short-interval intracortical inhibition (SICI) and short-interval intracortical facilitation (SICF), intermediate intervals (7-20 ms) to assess intracortical facilitation (ICF) and long intervals (50-200 ms) to assess long-interval intracortical inhibition (LICI). Some clinical, demographic, and autonomic data (i.e. EKG) will be recorded and used as covariates to investigate any systematic impact on cortical excitability measures collected with the paired-pulse protocols.