![]() ![]() Furthermore, it is probable that restricted telencephalic areas will be directly involved in this function as a part of various specialized systems of memory, as has been proposed in land vertebrates ( Schacter and Tulving, 1994). ![]() Ablation of the telencephalon therefore disrupts avoidance conditioning because it prevents engagement between two processes of learning (Pavlovian and instrumental). ( 1976) proposed, on the basis of Mowrer's theory, that the function of the fish telencephalon is to use the emotional states as conditioned reinforcers to produce instrumental responses. Interestingly, complete telencephalic ablation in fish produces devastating effects on the acquisition and maintenance of a two-way conditioned avoidance response (Overmier and Papini, 1985, 1986 Papini, 1985 Overmier and Hollis, 1990). The behavioral nature of the conditioned avoidance response in tetrapods has been explained by means of the two-process theory of Mowrer ( 1960). The medial pallium has been proposed as homologous to pallial amygdala ( Marino-Neto and Sabbatini, 1983 Nieuwenhuys and Meek, 1990 Braford, 1995 Northcutt, 1995 Butler, 2000). In actinopterygian fish, the lateral telencephalic pallium has been proposed as homologous to the hippocampus on the basis of both neuroanatomical evidence ( Nieuwenhuys and Meek, 1990 Braford, 1995 Northcutt, 1995 Butler, 2000) and the involvement of this area in place learning by means of allocentric frames of reference ( Rodríguez et al., 2002). Thus, the hippocampus is involved in spatial learning ( O'Keefe and Nadel, 1978), in relational memory ( Eichenbaum et al., 1992 Squire, 1992), and in the processing of temporal attributes of events and situations ( Kesner and DiMattia, 1987). However, these lesions produce harmful effects when the contextual or time cues are significant for the conditioning process, as in the case of avoidance learning or trace emotional conditioning procedures ( Woodruff and Kantor, 1983 Moyer et al., 1990 Phillips and LeDoux, 1992). It is known that hippocampal and septal lesions facilitate avoidance learning in mammals in some circumstances ( O'Keefe and Nadel, 1978 Sara and David-Remacle, 1981 Gray and McNaughton, 1983 Weiner et al., 1998). It is also involved in avoidance learning because lesions of amygdala nuclei abolish the acquired conditioned response ( Sánchez-Riolobos, 1986 Ambrogi-Lorenzini et al., 1991). The amygdala is involved in emotional behaviors and emotional memory ( LeDoux, 1995). In mammals, the amygdalar and hippocampal systems accomplish an important role in the acquisition and retention of conditioned avoidance response ( McIntyre and Stein, 1973 Grossman et al., 1975 Sánchez-Riolobos, 1986 Rawlins et al., 1993 Winocur, 1997). We conclude that these specialized systems of memory could have appeared early during phylogenesis and could have been conserved throughout vertebrate evolution. ![]() Moreover, these differential effects were similar to those produced by amygdalar and hippocampal lesions in mammals. These data support the presence of two different systems of memory in fish, based on discrete telencephalic areas: the MP, involved in an emotional memory system and the LP, involved in a spatial, relational, or temporal memory system. An MP lesion affected the retention of the avoidance response in both procedures in contrast, an LP lesion impaired the retention only in the trace-conditioning procedure. In the second experiment, fish were trained in trace avoidance conditioning in which temporal cues were crucial for the learning process. In the first experiment, fish were trained in nontrace avoidance conditioning. This work was aimed at studying the effects of ablation of the medial telencephalic pallia (MP) and lateral telencephalic pallia (LP) in goldfish on the retention of a conditioned avoidance response previously acquired in two experimental conditions. The medial and lateral pallia of actinopterygian fish have been proposed as homologous to the mammalian pallial amygdala and hippocampus, respectively, on the basis of neuroanatomical findings. The hippocampus and the amygdala are involved in avoidance learning in mammals. ![]()
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