Miniaturized Wireless tDCS With Concentric Electrodes for Targeted Cortical Stimulation in Freely Moving Mice.

Transcranial direct-current stimulation (tDCS) emerges as a promising non-invasive technique for modulating brain activity. However, conventional systems remain limited in behavioral neuroscience due to low spatial resolution and reliance on tethered setups. Here, a miniaturized, fully wireless tDCS system is presented that employs concentric electrodes (CEs) to enable focal cortical stimulation in freely moving mice. Electric field simulations confirm that the CE design more effectively restricts current spread compared to conventional electrode configurations. The CEs, fabricated using a flexible printed circuit board process, conform to the curvature of the mouse skull, ensuring stable contact and precise stimulation. The wireless system weighs 2.64 g and integrates a boost converter capable of delivering an 11 V stimulation output, along with a Bluetooth-controlled switching circuit. This compact design supports chronic implantation without restricting movement. Behavioral validation demonstrates that targeted stimulation of the left or right secondary motor cortex (M2) selectively induces direction-specific circling behavior in mice. These findings underscore the system's ability to deliver spatially confined and behaviorally effective neuromodulation. Overall, the CE-tDCS system offers a robust and high-resolution platform for investigating the causal relationships between localized brain stimulation and behavior in untethered animal models.