Journal of Neuroscience, Vol 15, 2796-2807, Copyright © 1995 by Society for Neuroscience
Development of memory and the hippocampus: comparison of food-storing and nonstoring birds on a one-trial associative memory task
NS Clayton
Department of Zoology, Oxford University, United Kingdom.
Food-storing birds, for example, marsh tits, Parus palustris, use memory to
retrieve stored food and have a larger hippocampus relative to the rest of
the telencephalon than do species that store little or no food such as the
blue tit, P. caeruleus. The difference between food storers and nonstorers
in relative hippocampal volume occurs after the young birds have fledged
from the nest and is dependent upon some aspect of memory for retrieving
caches of stored food. To test whether or not species differences in memory
and volumetric changes in the hippocampus could be triggered by experience
of memory tasks other than retrieval of stored food, groups of hand-raised
marsh tits and blue tits were tested between days 35 and 192 posthatch on a
one-trial associative memory task in which they were rewarded in phase II
for returning to the feeder where they had eaten part of a peanut 20 min
earlier. No species differences were found when the peanut was visible in
phase I, but when the peanut was hidden in phase I, marsh tits performed
better than blue tits, irrespective of whether or not they had had previous
experience of storing and retrieving food. In dissociation trials
(transformed array of feeders), marsh tits with food-storing experience
responded preferentially to spatial cues, whereas blue tits responded
equally to both spatial position and object- specific cues. These species
differences are also found in wild-caught adults. However, marsh tits
without food-storing experience responded equally to both spatial position
and object-specific cues, which suggests that experience of storing and/or
retrieving caches is required in order for marsh tits to develop the
spatial preference seen in adult food storers. Both marsh tits with
experience of the one-trial associative memory task and those that had also
had food-storing experience had larger relative hippocampal volumes than
did controls, independent of age. Of the marsh tits trained on the
one-trial associative memory task, there was no difference between those
that had had food-storing experience and those that had not. However, in
blue tits, there was no effect of experience on relative hippocampal
volume. No volumetric differences were observed in ectostriatum, which
served as a control brain region. The results suggest that some aspect of
memory for retrieving food (whether or not stored by the bird) directly
influences growth of the hippocampal region in marsh tits, the food-
storing species, but not in blue tits, the nonstoring species.