Fig. 2

Surgery for tetrode implantation and case fixation. a To implant the tetrodes into the brain, each anesthetized fish was fixed to an acrylic fixture on a custom-made mounting table (arrow). The anesthetic solution was circulated using a peristaltic pump. The fish back was covered with a wet towel (pink) to prevent the body from drying, and water was poured onto it with a small pump during the experiments. A bag of ice was added to the water tank every 30 min during the experiments to prevent sudden water temperature increases. b Oval hole drilled into the exposed fish skull (white arrow). A scalpel was used to excise a rectangle of epidermis in the direction of the caudal fin, starting from an imaginary guideline between each fish’s eyes. To expose the olfactory bulb, the telencephalon, optic tectum, fat, and tissue fluid were carefully removed. Anchors were screwed into holes equally spaced along the edge of the oval hole and covered with dental acrylic resin. c A ground wire and tetrode array were implanted into the medial optic tectum and target recording locations of the telencephalon using micromanipulators. The space above the brain was then filled with Vaseline, while the space between the head and electrode interface board (EIB) was filled with small, 3D-printed pieces and then covered with a dental acrylic resin. The neurologger case was attached to the EIB and covered with dental acrylic resin