Rattractor - Instant guidance of a rat into a virtual cage using a deep brain stimulation

Abstract

Objectives: To influence animal behaviors by applying electrical stimuli in the central nervous system, we developed "Rattractor" (rat attractor), a system for electrical stimuli application in the rat brain, when the subject stays in a specified region or a virtual cage. Our results showed that our closed-loop system facilitated a self-organized control of rat locomotion to stay in the virtual cage. Approach: Nine rats had two wire electrodes implanted in the deep brain. The electrodes targeted the medial forebrain bundle (MFB), a part of the reward system in the deep brain. Following a recovery period, rats were placed on a plain field where they could move freely but wired to a stimulation circuit. An image sensor installed over the field detected the subject position which accordingly triggered the stimulator, so that rat stayed within the virtual cage. We conducted a behavioral experiment to evaluate a sojourn ratio that the rat resided in the region. Thereafter, histological analysis of the rat's brains was performed to confirm the position of the stimulated sites in the brain. Results: Seven rats survived the surgery and the recovering period without technical failures such as connector break. Then, we observed that three of them tended to stay in the virtual cage during stimulation, an effect maintained for two weeks. Histological analysis showed that the electrode tips were correctly placed in the MFB region of these rats. The other four subjects showed no apparent preference to the virtual cage. In these rats, we did not find the electrode tips in the MFB or could not determine its position. Significance: Almost half of the rats showed a tendency to stay inside the virtual cage when position-related reward stimuli were triggered in the MFB region in real time, as shown by optical observation thorough the image sensor. The experimenter only needed setting the region of the virtual cage, not requiring sequential commands for the rat. Notably, our system neither required previous training nor sequential intervention to affect the behavioral preferences of the subjects. This process is similar to the situation wherein sheep chased by a shepherd dog in the desired direcion indicated by the dog.