A multiple choice apparatus for electrophysiological investigations of spatial working memory in rats

A multiple choice apparatus, minimizing the rat's movements and thus simplifying brain stimulation and/or recording in working memory experiments, consists of a dodecagonal enclosure (30 cm diameter, 100 cm high) with a horizontal platform assuming either an upper or a lower position, 43 or 65 cm below the top of the wall, respectively. The platform is moved between these two levels by a pneumatic system controlled by solid-state programming circuits. Each wall segment contains a choice window, 7 cm above the upper floor level, providing access to a recessed feeder. When the platform with a food-deprived rat moves into the upper position, the animal opens the hinged shutter of one window and gets the pellet. Five seconds later, a self-locking relay marks the visited window and the floor descends to the low position where it remains for a predetermined interval (e.g. 20 s), until it is raised again. The above cycle repeats as a long as different windows are chosen. When a choice is directed to an already visited window (error), the floor returns to the low position at once. During one trial, the animal is allowed 12 choices and the number of errors (i.e. choices directed to already entered windows) is recorded. In spite of the great reduction of kinaesthetic and vestibular signals and the almost complete elimination of visual extramaze cues, the working memory performance is similar to that in analogous radial maze.