Extended Data Fig 8: Heat diffusion in the mouse spinal cord and its consequence for motor control.

a, Simulating heat diffusion in the spinal cord tissue. Step 1: Maximum temperature calculated with the Bioheat Transfer model in response to photostimulation protocols eliciting activation of ChR2 (25% duty cycle) or Jaws (95% duty cycle). Each plot has an adjusted scale allowing to view the maximum temperatures. Step 2: Temperature measurements of the LEDs in air with an infrared camera confirming maximum temperatures predicted by the model. b, Heat diffusion measure in vivo with a temperature probe. Step 1: Experimental setup. Step 2: Relationship between incremental duty cycles (every 5%) and the increase in temperature measured after 10 s and 30 s for two wavelenghts delivered over incremental photostimulation intensity (every 50 mW/mm²). Step 3: In vivo measurements of heat decay using a temperature probe inserted in the dorsal horn after 30 s of photostimulation with the settings necessary to target ChR2 (25% duty cycle, wavelength 470 nm, 2 LEDs, left) or Jaws (95% duty cycle, wavelength 620 nm, 2 LEDs, right). The plots report the changes in temperature over time for three levels of intensity. c, Heat affecting locomotion in wildtype mice. Step 1: Timeline detailing key experiments. Step 2: Experimental setup to record leg kinematics during stepping on a treadmill while photostimulation of increasing intensity is delivered over the spinal cord of a mice with a complete SCI. A serotonergic pharmacotherapy is adminstered prior to the experiment to reactivate the lumbar spinal cord below the injury. Step 3: A series of 78 gait parameters (see Supplementary Table 1) calculated from the kinematic recordings are submitted to a PC analysis. Each recorded gait pattern, depicted by each dot, are shown in the new denoised space defined by PC1 and PC2.