Effects of telencephalic ablation on short-term memory and attention in goldfish

Two hypotheses regarding the functions of the teleost telencephalon (short-term memory and nonspecific arousal hypotheses) were examined by using a Y-maze training paradigm. A delayed reinforcement method, which allowed the separation of choice process (a process in which choice responses are evoked) and reward process (a process in which choice responses are reinforced), showed that normal fish can acquire clear learned responses to choice stimuli under different stimulus conditions between the choice process and the reward process, while telencephalon-ablated fish showed greatly impaired learning performance. Neither normal nor telencephalon-ablated fish could acquire learned responses to choice stimuli under neutral stimulus conditions in the reward process with respect to choice stimuli in the choice process. These results suggest that the telencephalon facilitates extratelencephalic short-term memory function essential for memory retention of choice stimuli and evoked choice responses until reinforcement, and support the supplementary function of the telencephalon suggested previously [Ohnishi, K., Telencephalic function implicated in food-reinforced colour discrimination learning in the goldfish, Physiol. Behav., 46 (1989) 707-712 and Savage, G.E., Temporal factors in avoidance learning in normal and forebrainless goldfish (Carassius auratus), Nature, 218 (1968) 1168-1169]. In addition, it was shown that cue information in the reward process is very important for the fixation of short-term memory of choice stimuli and choice responses. Furthermore, telencephalon-ablated fish also showed clear visual aspect selection, as did normal fish, when they were reinforced to a visual compound stimulus containing heterogeneous aspects (pattern and colour). This result shows that the telencephalon-related arousal or attentional function is not critical for aspect selection in goldfish. It seems that visual aspect selection in goldfish is performed without paying telencephalon-related 'selective attention' to an aspect.