Abstract
Declarative memory is an explicit, long-term memory system, used in generalization and categorization processes and to make inferences and to predict probable outcomes in novel situations. Animals have been proven to possess a similar declarative-like memory system. Here, we investigated declarative-like memory representations in young chicks, assessing the roles of the two hemispheres in memory recollection. Chicks were exposed for three consecutive days to two different arenas (blue/yellow), where they were presented with two panels, each depicting a different stimulus (cross/square). Only one of the two stimuli was rewarded, i.e., it hid a food reward. The position (left/right) of the rewarded stimulus remained constant within the same arena, but it differed between the two arenas (e.g., reward always on the left in the blue context and on the right in the yellow one). At test, both panels depicted the rewarded stimulus, thus chicks had to remember food position depending on the previously experienced contextual rule. Both binocular and right-eye monocularly-tested chicks correctly located the reward, whereas left-eye monocularly-tested chicks performed at the chance level. We showed that declarative-like memory of integrated information is available at early stages of development, and it is associated with a left hemisphere dominance.
Highlights
One of the most intriguing, and at the same time debated, topics in animal cognition is how animals represent their surroundings and how these representations are created and stored in the brain [1,2,3]
The presence of a similar declarativelike memory system in animals has been well attested in several models: e.g., in the chimpanzee [8], the rhesus monkey [9], the rat [10,11], the jay [12,13] and the domestic chicken [14,15]
The model that resulted with the lowest Akaike information criterion (AIC) value (4825.8), and the one that was employed in the subsequent analysis was the one containing the predictors: stimulus value, condition, position, color and their interactions
Summary
One of the most intriguing, and at the same time debated, topics in animal cognition is how animals represent their surroundings and how these representations are created and stored in the brain [1,2,3]. Little is known about how soon this mechanism is available during the individuals’ development, and how information is represented and eventually stored in the memory system [16,17,18]. In their 2001 study, Cozzutti and Vallortigara demonstrated the presence of declarative-like memory in 5-day old domestic chicks, as evidence of the precocious development of this system. The authors found an effect of lateralization: binocular-tested chicks and right eye monocularly-tested chicks succeeded in the task, inspecting the location where the non-devaluated food had been experienced during the exposition phase. Domestic chicks have a virtually complete optic chiasm decussation, with each eye projecting exclusively to the contralateral hemisphere [19,20]
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