A common observation in deep brain stimulation studies is that after implant patients see improvements first, then stimulation is turned on. This common effect is attributed to micro-legions. We undertook a study to map the implant damage in rats from depth electrodes placed in the ventral hippocampus. Not only did we observe damage near the implant trajectory, but we were able to track degeneration into the contralateral hippocampus. Current discussions in the invasive brain-machine-interface literature include the objective of finding better implant materials and methods for implantation that will provide long, stable recordings that minimize short term and long term tissue damage. Proposed approaches are to either find ‘softer’ materials, or ones with much smaller size format. I’ll review some of the evidence for and competing against these approaches.