The DREAM implant: A Lightweight, Modular and Cost-Effective Implant System for Chronic Electrophysiology in Head-fixed and Freely Behaving Mice

Chronic electrophysiological recordings in rodents have significantly improved our understanding of neuronal dynamics and their behavioral relevance. However, current methods for implanting electrodes chronically present steep trade-offs between cost, ease of use, size, adaptability and long-term stability. This protocol introduces a novel chronic electrode implant system for mice called the DREAM (Dynamic, Recoverable, Economical, Adaptable and Modular), designed to overcome the trade-offs associated with currently available options. The system provides a lightweight, modular and cost-effective solution with standardized hardware elements that can be combined and implanted in straightforward steps, and explanted safely for recovery and multiple re-use of probes, significantly reducing experimental costs. The DREAM implant system integrates three hardware modules: (1) a microdrive that can carry all standard silicon probes, allowing experimenters to adjust recording depth across a travel distance of up to 7mm; (2) a 3D-printable, open-source design for a wearable Faraday cage covered in copper mesh for electrical shielding, impact protection and connector placement, and (3) a miniaturized head-fixation system for improved animal welfare and ease of use. The corresponding surgery protocol was optimized for speed (total duration: 2 hours), probe safety and animal welfare. The resulting implants had minimal impact on animals' behavioral repertoire, were easily applicable in freely moving and head-fixed contexts, and delivered clearly identifiable spike waveforms and healthy neuronal responses for several months post-implant. Infections and other surgery complications were extremely rare using this protocol. As such, the DREAM implant system is a versatile, cost-effective solution for chronic electrophysiology in mice, enhancing animal well-being and enabling more ethologically sound experiments. Its design simplifies experimental procedures and is adaptable to various research needs, increasing accessibility of chronic electrophysiology in rodents to a wide range of research labs. ### Competing Interest Statement TS, AN, and MNH are co-founders of 3Dneuro bv, which manufactures the open-source microdrives and Faraday crowns used in this protocol. FB and PT are part of the scientific advisory board of 3Dneuro. FB and PT do not receive any financial compensation for this position.