(A) Experimental set-up for in vivo magnetothermal stimulation of motor behavior in awake mice. A water-cooled two-turn coil around the arena generated the AMF. The AMF in the coil was powered by the same system as for the in vitro experiments. An overhead camera was used to record the mouse’s behavior in the arena. (B) Photograph of mouse in the observation arena; two-turn water-cooled coil visible as black ring. (C) Representative trajectory recorded from a mouse stimulated in the motor cortex before (black), during (red), and after (blue) field application (each 1 min long). The black circular border denotes the actual boundary of the chamber. (Also see Figure 4—figure supplement 1 for injection locations; and Videos 1 and 2). (D) (Top) Position of the mouse’s head, (x green; y orange) measured taking the center of the arena to be the origin. (Middle) Black trace shows the linear speeds of the mouse. Speed markedly increases during all AMF applications (Grey bars). After each AMF application, the mouse slows down regular exploratory motion (Bottom). Total turns made by the mouse was tracked versus time. Counter-clockwise angular changes were counted as a positive change in angles. During AMF application, the mouse turned unilaterally significantly more than between the AMF applications. (E) Comparison of linear speed of this TRPV1+ / MNP+ mouse, injected in the motor cortex, with and without AMF. The average linear speed increased 16-fold after AMF application, from 5.3 ± 2.75 mm/s, before AMF, to 83.8 ± 3.75 mm/s, during AMF (one mouse, four trials, the error bars are smaller than the symbols; p=5.9·10−6, 95% confidence intervals [0.9, 9.7] and [77.8, 89.8] mm/s). (F) Comparison of the angular speed from the same mouse as in (E). The angular speed during the AMF was 3.27 ± 0.30 rev/min versus 0.21 ± 0.19 rev/min between the AMF applications (one mouse, four trials, error bars are smaller than symbols; p=0.0003, 95% confidence intervals [−0.10, 0.53] and [2.78, 3.74] rev/min). (G) Comparison of angular velocity, or speed of circling the arena, measured for all TRPV1+ / MNP+ mice, injected in the motor cortex, with or without AMF. The speed of circling the arena in revolutions per minute increased 8-fold with AMF, from to 0.34 ± 0.08 rev/min to 2.81 ± 0.20 rev/min (6 mice, 14 trials; p=5.2·10−9; 95% confidence intervals [0.29, 0.39] and [2.69, 2.93] rev/min). (H) Latency of behavioral response onset and end after turning field on and off, respectively (n = 21). (I) Speed of rotation for control and experiment animals (independent mice): Control1: PBS instead of MNP injected (TRPV1+ / MNP-, n = 4; Video 3 ); Control2: PBS instead of virus injected (TRPV1- / MNP+, n = 4; Video 4); and Experiment (TRPV1+ / MNP+). There was no significant difference in the observed speeds with or without AMF (AMF+ and AMF-, respectively) in the control cases. With TRPV1+ / MNP+, the mice exhibited a highly significant increase in speed with AMF, 3.17 ± 0.17 rev/min, as compared to the mice without AMF application, 0.42 ± 0.07 rev/min (n = 10, p=1.1·10−5; unpaired T-test; 95% confidence intervals [0.32, 0.52] and [2.94, 3.40] rev/min). In the experiments and controls 1 and 2 and MNP were injected with A2B5 antibody (AB). Control3: MNP without antibody injected (TRPV1+ / MNP+, AB-, n = 3).