A larger hippocampus is associated with longer-lasting spatial memory

Abstract

Volumetric studies in a range of animals (London taxi-drivers, polygynous male voles, nest-parasitic female cowbirds, and a number of food-storing birds) have shown that the size of the hippocampus, a brain region essential to learning and memory, is correlated with tasks involving an extra demand for spatial learning and memory. In this paper, we report the quantitative advantage that food storers gain from such an enlargement. Coal tits (Parus ater) a food-storing species, performed better than great tits (Parus major), a nonstoring species, on a task that assessed memory persistence but not on a task that assessed memory resolution or on one that tested memory capacity. These results show that the advantage to the food-storing species associated with an enlarged hippocampus is one of memory persistence. There are at least three constituent aspects to spatial learning and memory: memory capacity (the number of locations remembered), memory persistence (the duration over which a location is remembered), and spatial resolution (the least distance at which remembered locations can be discriminated). Although volumetric studies have shown that several behavioral adaptations are associated with an enlarged hippocampus (1-6), no volumetric study, nor any of a number of experiments examining spatial memory performance (7-16), has yet been able to determine whether the observed enlargement of the hippocampus in food-storing and other species is associated with one, two, or all three of these aspects of memory. If food-storers have a greater memory capacity than the nonstorers, we predict that performance would be similar when there is only one item to remember, but would diverge with increasing number of items, with the nonstorers having a poorer performance when required to remember more items (see Fig. 1A). If the species differed only in the spatial resolution of memory, they should achieve similar performance levels when items are far apart, but the food storers should perform better when the items are close together (Fig. 1B). If the food storers only have a longer-lasting memory, then the species difference in performance should be similar regardless of number of items or their proximity ( Fig. 1C; see ref. 17 for a similar argument).In this experiment, wild-caught food storers [coal tits (Parus ater), a species with an enlarged hippocampus] and a related nonstoring species [great tits (Parus major)] were tested on all of these three aspects of spatial memory within the same experiment. All birds were presented with one to four white squares on a computer-controlled touch screen. Squares disappeared after a peck was directed at them. Once all squares had been pecked and after a retention interval, the birds were presented with a square in one of these earlier locations and a second square in a new location. They were rewarded for pecking the square in the new location (the ''target''), following a spatial nonmatching rule. Memory capacity was tested by varying the number of sample images to be remembered from on...

Using ecology to guide the study of cognitive and neural mechanisms of different aspects of spatial memory in food-hoarding animals

“…The only attempts at comparing memory capacity between species of hoarding and non-hoarding birds have focused on working memory, which is believed to be a different system from long-term memory, at least in mammals (Rolls 2000;Squire 2004). In an operant touch-screen study in which they varied working memory duration (1 -30 s), capacity (one to four items) and accuracy (distance on the screen), Biegler et al (2001) found no evidence for a larger working memory capacity in coal tits compared with great tits.…”

“…The fact that hoarding coal tits (Periparus ater) have a longer lasting working memory than non-hoarding great tits (Parus major) (Biegler et al 2001) does not speak directly to the duration of cache memories, although longer lasting working memory could translate into better memory consolidation and therefore potentially longer lasting long-term memories. compared coal tits and marsh tits (both hoarders) with blue tits (Cyanistes caeruleus) and great tits (both non-hoarders) on an avian analogue of the 8-arm radial arm maze at different retention intervals.…”

“…The other assumption that has been made is that the adaptation would be evident in all tests of spatial memory, regardless of the demands or details of the task (Kamil 1988). However, spatial memory is a multi-dimensional trait (McGregor & Healy 1999;Biegler et al 2001). Having 'good' spatial memory can mean many different things.…”

“…Having 'good' spatial memory can mean many different things. It could mean having a very high spatial resolution memory for locations (McGregor & Healy 1999), it could mean having a longer lasting memory (Biegler et al 2001), or it could mean having a larger memory capacity. It is possible that some food-hoarding animals have an adaptive specialization in only one of these aspects of spatial memory, which might not be tested in all (if any) of the laboratory tasks employed.…”

What hummingbirds can tell us about cognition in the wild

“…A decade and a half later, however, it is not clear that that promise is being realised. For example, food storing, once a model for examining questions of the evolution of cognition and possibly the wildest of all the examples discussed in Balda et al (1998), is now much less of a focus (e.g., Biegler, McGregor, Krebs, & Healy, 2001;Hampton & Shettleworth, 1996;Sherry & Vaccarino, 1989; but see Feeney, Roberts, & Sherry, 2009;Freas, LaDage, Roth, & Pravosudov, 2012). Food storing did, however, lead to perhaps the greatest recent flurry of excitement and effort in comparative cognition (Clayton & Dickinson, 1999): the examination of cognitive abilities in corvids.…”