Cortical motor threshold determination in dogs

In humans, determining the cortical motor threshold (CMT) is a critical step in successfully applying a transcranial magnetic stimulation (TMS) treatment. Stimulus intensity, safety and efficacy of a TMS treatment are dependent of the correct assessment of the CMT. Given that TMS in dogs could serve as a natural animal model, an accurate and reliable technique for the measurement of the CMT should be available for dogs. Using a visual descending staircase paradigm (Rossini paradigm), the CMT repeatability was assessed and compared to the electromyographic (EMG) variant. The influence of a HF-rTMS treatment on the CMT was examined. Subsequently, the CMT was measured under sedation and general anaesthesia. Finally, the coil-cortex distance was associated with the CMT, weight, age and gender. During one year the CMT was measured three times, during which it remained constant, although a higher CMT was measured (40% higher machine output) when using EMG (P-value < .001) and under general anaesthesia (P-value = .005). On average, a 40% and 12% higher machine output were registered. An aHF-rTMS protocol does not influence the CMT. Males have on average a 5.2 mm larger coil cortex distance and an 11.81% higher CMT. The CMT was positively linearly associated (P-value < .05) with the weight and age of the animals. Only within female subjects, a positive linear association was found between the CMT and the coil-cortex distance (P-value = .02). Using the visual Rossini paradigm, the CMT can be reliably used over time and during a TMS treatment. It has to be kept in mind that when using EMG or assessing the CMT under general anaesthesia, a higher CMT is to be expected. As in humans, every parameter that influences the coil-cortex distance may also influence the CMT.