Effect of telencephalic ablation on appetitive instrumental learning in the goldfish (Carassius auratus)

ciative learning in a variety of training situations. In the goldfish (Carassius auratus), for example, bilateral ablations disrupt the acquisition of appetitive visual conditional discriminations (Onishi, 1997), complex spatial learning (Salas et al., 1996), the acquisition of avoidance behavior (Heinsworth et al., 1967), and the retention of preoperatively trained avoidance behavior (Overmier and Papini, 1986). Interestingly, bilateral lesions of the telencephalon do not lead to measurable disruption of learning in relatively simpler situations, such as brightness discriminations (Onishi, 1997), escape conditioning (Heinsworth et al., 1967), and aversive Pavlovian conditioning (Overmier and Curnow, 1969). Research on learning in animals suggests that often variables that have little or no effects on the acquisition of new behaviors in simple situations, lead to significant effects when animals are shifted to extinction. This is particularly noticeable when practice is administered at a rate of a single trial per day. For example, lesions of the hippocampus in rats (Jarrad et al., 1964) or of the medial pallium (the amphibian homologue) in toads (Muzio et al., 1993; Papini et al., 1995) have no consequences for the acquisition of simple running responses reinforced in all trials (i.e., continuous reinforcement, CR). However, lesioned animals from both species show abnormally high levels of persistence during the extinction of instrumental behavior. Interestingly, the same lesion has opposing effects on extinction when the instrumental behavior was acquired under partial reinforcement (PR). In rats, the hippocampal lesion decreases resistance to extinction (Jarrad et al., 1964; Jarrad and Isaacson, 1965; Winocur and Mills, 1969), whereas in toads, lesions of the medial pallium increase resistance to extinction (Muzio et al., 1993). An interesting corollary of this pattern of results is that it suggests that PR training engages different brain processes in rats and toads. Hence, the lesion manipulation has opposing effects on extinction after CR vs. PR training in rats (increased persistence after CR, but decreased persistence after PR), whereas an equivalent lesion manipulation has the same effect on extinction in toads (persistence increased after both CR and PR). Such differences in the effects of physiological manipulations are consistent with the hypothesis, suggested by purely behavioral experiments, that CR and PR training engage different learning processes in mammals, but the same underlying learning process in other vertebrates (Papini et al., 1995; Papini, 1997). One candidate mediational process in mammalian learning is provided by the hypothesis that partial Effect of telencephalic ablation on appetitive instrumental learning in the goldfish (Carassius auratus)