Ultralight infrared-controlled wireless neuromodulation systems for freely behaving mice.

Neuromodulation techniques including transcranial direct current stimulation (tDCS) and deep brain stimulation (DBS) have been widely investigated for their therapeutic potential in a range of neurological and psychiatric disorders. Basic studies using freely behaving animal models are critical for elucidating the underlying mechanisms of these neuromodulation techniques. However, conventional neuromodulation systems typically rely on wired connections or wireless systems incorporating communication and control modules, which increase device weight and volume, restrict natural behavior, and may introduce confounding factors in behavioral experiments. Here, we present an ultra-lightweight wireless neuromodulation system that can be externally controlled using infrared (IR) light, eliminating the need for complex wireless communication modules. The system incorporates wavelength-selective phototransistors (810 and 950 nm) to enable independent control of tDCS and DBS. The complete tDCS device weighs less than 1.5 g, while the DBS device weighs less than 0.5 g. Characterization of the IR LED array demonstrated uniform light distribution and high thermal stability, with no detectable temperature changes in the experimental environment during prolonged illumination. Open-field behavioral testing confirmed that neither device attachment nor IR illumination affected spontaneous locomotor activity in mice. In stimulation experiments targeting the secondary motor cortex (M2), both tDCS and DBS induced robust circling behavior in freely behaving mice, demonstrating effective modulation of motor-related neural circuits. These results indicate that the proposed systems enable reliable and selective neuromodulation without constraining natural behavior, providing a versatile platform for future behavioral and mechanistic studies of neuromodulation.