Twofold path integration during hoarding in the golden hamster?

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Abstract
Golden hamsters which hoard food in darkness return from food source to their nest by relying on internal signals generated during the preceding outward journey to the food location. The question arises whether the animals are also capable of reorientating to the last food finding site on the basis of path integration. This possibility would allow the animals to exploit a profitable food source without acquiring and storing long term information about the itinerary between the nest and the last food finding site through a learning process. In each experimental trial, the subject was led at first from its centrally located nest to a (new) food source near the periphery of the experimental arena. Thereafter, the hamster returned by itself to the nest and then performed a second, unguided hoarding excursion during which it could find the food at the same location. The experiments took place in different conditions, with or without an asymmetrical nest exit or the availability of optical cues. Even when tested under infra-red light and with a completely symmetrical nest exit, the hamsters' second outward journey yielded a significant second order vector which pointed towards the last finding site. This reorientation to the food source was not systematically enhanced by optical references or an asymmetrical nest exit, which may have allowed the subjects to use a fixed vector for their repeated back and forth itineraries between the nest and the food location. It was therefore concluded that the animals relied on a twofold integration process: the subjects integrate each particular outward journey to the food location to return to the nest; likewise, they derive vector information from the immediately preceding homing itinerary to reorientate to the last finding site. In general, however, the return to the last visited food patch occurred with much less precision than the homing itinerary to the nest. This result may be explained by motivational factors as well as by differences in the capacity for using and computing different categories of spatial information during the outward and return trips.