Fig. 1.
Experimental diagram. A, Rats were prepared for chronic recording by the formation of receptacles of dental cement to accept artificial earbars. Electrodes were implanted in the ventral tegmental area for ICSS. The rat was trained to lick when the spout was automatically placed close to its mouth. Licking was signaled by a photoelectric sensor triggered by the tongue. Electric shock was delivered from the grid on a floor of a restraining cage.B–D, Time chart of reward task (B), avoidance task (C), and reward task with delay (D). In the reward associative task, one of conditioned sensory stimuli (tone, light, or configural stimuli) associated with and without rewarding stimulus (ICSS or sucrose solution) was presented for 2.0 sec before the spout was placed close to the rat’s mouth (B). In the avoidance task, the rat could avoid electric shock if the spout was licked within 2.0 sec after the conditioned auditory stimulus (C). In the reward task with delay, a conditioned auditory stimulus was presented as in the reward task, but the rat had to wait for a delay period (2.4 sec) before licking a spout. Suc, 0.3 m sucrose solution.