Hippocampal specialization of food-storing birds.

Abstract

In a study of 52 individuals belonging to 35 species or subspecies of passerine birds it was shown that the volume of the hippocampal complex relative to brain and body size is significantly larger in species that store food than in species that do not. Retrieval of stored food relies on an accurate and long-lasting spatial memory, and hippocampal damage disrupts memory for storage sites. The results suggest, therefore, that food-storing species of passerines have an enlarged hippocampal complex as a specialization associated with the use of a specialized memory capacity. Other lifehistory variables were examined and found not to be correlated with hippocampal volume.Some species of birds store large numbers offood items, each in a separate place, and use an accurate, long-lasting spatial memory to retrieve their stores (1-5). We show here that the hippocampal complex (dorsomedial forebrain) (6) of foodstoring passerines is larger relative to body and brain size than that of nonstorers. Thus, across a range of species, a relationship has been found between the structure of a specific brain area outside sensory and motor areas and a specific behavior. METHODSWe measured the volume of the hippocampal complex and striatum of52 individuals belonging to 35 species or subspecies distributed among 9 passerine families [taxonomy in this paper follows that of Sibley et al. (7) based on DNADNA hybridization]. We defined the hippocampal complex as including the closely interconnected hippocampal and parahippocampal areas (6). The evidence from both embryological and connectivity studies (8-10) suggests that these two structures as a whole are homologous to the mammalian hippocampal complex, although the homology ofthe different subdivisions is not known. The behavioral consequences of damage to the avian hippocampal complex show that it is broadly functionally equivalent to the mammalian hippocampus in playing an important role in certain memory tasks, including those involving spatial memory (11)(12)(13)(14)(15)(16)(17)(18). The avian hippocampal complex is a paired structure located adjacent to the midline of the dorsal telencephalon (19). It extends from the caudal limit of the striatum along approximately two-thirds of the caudal-rostral extent of the striatum. In coronal section it is bounded medially by the midline and ventrally by the lateral horns of the ventricle and by the septum (Fig. 1). The region defined as the hippocampus by Karten and Hodos (19) is a V-shaped structure of densely packed cells lying ventrally and medially (Fig. 1). In the parahippocampal area large and small neurons are sparsely and nonuniformly distributed. The lateral boundary of the parahippocampal area is characterized by a change in the size distribution of neurons. Medial to the boundary the distribution is bimodal with peaks at cell areas of about 20 pIm2 and 130-150 pum2, while lateral to the boundary the distribution is unimodal with a peak at about 20-30 ILm2 (Fig. 2): the boundary is often clearer in food-storers than i...

Aspects of the Search for Neural Mechanisms of Memory

“…This is seen in recent research on differential experience conducted with different species of the crow family. Species that cache food in a variety of locations for future use are found to have significantly larger hippocampal formations than related species that do not cache food (Krebs et al 1989. But the difference in hippocampal size is not found in young birds still in the nest; it appears only after food storing has started, a few weeks after the birds have left the nest (Healy & Krebs 1993).…”

Mice selectively bred for high voluntary wheel running have larger midbrains: support for the mosaic model of brain evolution

“…The hippocampus is important in spatial orientation, and examples exist of enlargement of the hippocampus in both birds (Krebs et al, 1989;Krebs, 1990;Jacobs and Liman, 1991) and mammals (Sherry et al, 1992;Jacobs and Spencer, 1994;Lavenex et al, 2000) involved in seasonal caching behavior, as well as sex differences in space use (related to breeding system) in some small mammals (Jacobs and Spencer, 1994;Sherry et al, 1996;Lavenex et al, 2000). Moreover, among species of primates, enlargement of the neocortex has been correlated with the likelihood of using deception as a strategy for social advancement (Byrne and Corp, 2004).…”

“…Increases in relative brain size (relative to body mass) in mammals have been correlated with enhanced sensory abilities (Jerison, 1973;Catania, 2005), spatial memory (Krebs et al, 1989;Krebs, 1990;Jacobs and Liman, 1991;Jacobs and Spencer, 1994) and aspects of cognition (Jerison, 1973;Byrne and Corp, 2004;Peper et al, 2009;Mehlhorn et al, 2010). The 'principle of proper mass', first articulated by Jerison (Jerison, 1973), states that the size of a given neural structure reflects the complexity of the function that it subserves.…”

Hippocampal Tissue Transplants Reverse Lesion-Induced Spatial Memory Deficits in Zebra Finches (Taeniopygia guttata)

“…Volume measurements. A video camera connected to a Leica light microscope was used to capture the image of the brain sections into an Image 1.42 program in a Macintosh computer to measure the areas of the lesions within the Hf, the areas of the transplants, and the areas of the hippocampus for calculation of the estimated total lesion volume, total transplant volumes, and total Hf volume (according to the method in Krebs et al, 1989;Clayton and Krebs, 1994). The latter will be an approximate estimate because of the distortion of the Hf after lesioning and transplantation.…”