Memory for recent actions in the bottlenosed dolphin (Tursiops truncatus): Repetition of arbitrary behaviors using an abstract rule

Abstract

Little is known about how animals represent their own actions in working memory. We investigated whether bottlenosed dolphins could recall actions they had recently performed and reveal those recollections using an abstract rule. Two dolphins were trained to respond to a specific gestural command by repeating the last behavior performed. Both dolphins proved to be able to repeat a wide variety of behaviors on command and were able to generalize the repeating rule to novel behaviors and situations. One dolphin was able to repeat all 36 behaviors she was tested on, including behaviors involving multiple simultaneous actions and self-selected behaviors. These results suggest that dolphins can flexibly access memories of their recent actions and that these memories are of sufficient detail to allow for reenactments. The repeating task can potentially be used to investigate short-term action and event representations in a variety of species.Animals act under the influence of mental representations that result from a variety of internal and external factors. Understanding how animals create, activate, and manipulate such representations is a central concern for studies ofanimal learning and memory. A variety of techniques (e.g., delayed matching-to-sample tasks and maze tasks) have been developed to gain access to "unobservable" neural representational systems (for a review, see Roitblat, 1982Roitblat, , 1987. These techniques have been used extensively to investigate how animals represent external stimuli (e.g., objects, sounds, locations, and events) that they have experienced in the recent past. In contrast, few studies have investigated how animals represent recent internal events, such as the production of behaviors. Consequently, more is currently known about how animals represent environmental conditions in working memory than about how they represent their recent actions. An animal's short-term memory for its own actions can be interpreted as a type ofmetaknowledge; self-reports based on such memories can be used to measure an animal's ability to explicitly recall past behaviors (Shimp, 1982).

Episodic-like memory in pigeons

“…The present data, together with those reported by Mercado et al (1998), provide convergent evidence that processes similar to episodic memory occur in animals. Furthermore, the fact that these findings were obtained with pigeons, a species quite different from humans and dolphins, suggests that this form of memory may represent a general capacity in animals.…”

“…A similar but more sophisticated approach to episodic memory in animals has been taken recently by Mercado, Murray, Uyeyama, Pack, and Herman (1998). They used dolphins that had been extensively trained to perform a number of complex responses when given an arm-gesture command.…”

Cued repetition of self-directed behaviors in macaques (Macaca nemestrina).

“…To our knowledge, the only animals to have previously been trained to respond to a 227 repeat signal are bottlenosed dolphins (Mercado et al, 1998) …”

Cetacean brains: How aquatic are they?

“…On the other hand, the amygdala is large and welldeveloped in odontocetes and other cetaceans (Schwerdtfeger et al, 1984), reflecting the maintenance of substantial nonolfactory sources of input to this structure. The reduction of the hippocampus and related structures in odontocetes is particularly striking in light of the fact that odontocetes possess robust memory and learning skills (Mercado et al, 1998(Mercado et al, , 1999 which, in other mammals, depend highly on the hippocampus. An interesting possibility is that some learning and memory functions were transferred from the reduced hippocampal formation to the extremely well-developed cortical limbic lobe (periarchicortical field above the corpus callosum and the entorhinal cortex) in odontocetes (Oelschlager and Oelschlager, 2002;Marino et al, 2003Marino et al, , 2004b.…”