Hargreaves Test (Plantar Test).

The Hargreaves test was performed to evaluate the rats’ response to acute thermal stimulation. A mobile radiant heat-emitting device with an aperture of 10 mm (37370 plantar test, Ugo Basile) was used to produce acute thermal stimulation of the plantar surface of the hind paw. The rats were placed in a plexiglass chamber over a Hargreaves glass table and allowed to habituate. An average of at least 5 trials were performed to measure the latency to paw withdrawal for each testing condition. This latency was automatically recorded, and an average latency across the trials was computed. Paw withdrawals resulting from locomotion or weight shifting were not counted and the trials were repeated in such cases. Measurements were repeated at approximately 5-min intervals. An IR intensity of 70 was used to provide noxious stimulation, and IR intensity of 10 was used as control for non-noxious thermal stimulation that was not noxious. IR stimuli were terminated by paw withdrawals or held continuously for 5 s.

For online BMI experiments, the SSM was first trained with 1-5 trials (“calibration trials”) of noxious stimulus at the beginning of the experiment. Following training, an average of at least 5 trials were performed with activation of the BMI to test the efficacy of the BMI in inhibiting peripheral pain response. Measurements were repeated at 3-5 min intervals.