Multipulse transcranial electrical stimulation (TES): normative data for motor evoked potentials in healthy horses

Abstract Background There are indications that transcranial electrical stimulation (TES) assesses the motor function of the spinal cord in horses in a more sensitive and reproducible fashion than transcranial magnetic stimulation (TMS). However, no normative data of TES evoked motor potentials (MEP) is available. Results In this prospective study normative data of TES induced MEP wave characteristics (motor latency times (MLT); amplitude and waveform) was obtained from the extensor carpi radialis (ECR) and tibial cranialis (TC) muscles in a group of healthy horses to create a reference frame for functional diagnostic purposes. For the 12 horses involved in the study 95% confidence intervals for MLTs were 16.1–22.6 ms and 31.9–41.1 ms for ECR and TC muscles respectively. Intra-individual coefficients of variation (CV) and mean of MLTs were: ECR: 2.2–8,2% and 4.5% and TC: 1.4–6.3% and 3.5% respectively. Inter-individual CVs for MLTs were higher, though below 10% on all occasions. The mean ± sd of MEP amplitudes was respectively 3.61 ± 2.55 mV (ECR muscle left) and 4.53 ± 3.1 mV (right) and 2.66 ± 2.22 mV (TC muscle left) and 2.55 ± 1.85 mV (right). MLTs showed no significant left versus right differences. All MLTs showed significant (p