Nutritional deficits during early development affect hippocampal structure and spatial memory later in life.

Development rates vary among individuals, often as a result of direct competition for food. Survival of young might depend on their learning abilities, but it remains unclear whether learning abilities are affected by nutrition during development. The authors demonstrated that compared with controls, 1-year-old Western scrub jays (Aphelocoma californica) that experienced nutritional deficits during early posthatching development had smaller hippocampi with fewer neurons and performed worse in a cache recovery task and in a spatial version of an associative learning task. In contrast, performance of nutritionally deprived birds was similar to that of controls in 2 color versions of an associative learning task. These findings suggest that nutritional deficits during early development have long-term consequences for hippocampal structure and spatial memory, which, in turn, are likely to have a strong impact on animals' future fitness (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Life and Death of Immature Neurons in the Juvenile and Adult Primate Amygdala

In recent years, a large population of immature neurons has been documented in the paralaminar nucleus of the primate amygdala. A substantial fraction of these immature neurons differentiate into mature neurons during postnatal development or following selective lesion of the hippocampus. Notwithstanding a growing number of studies on the origin and fate of these immature neurons, fundamental questions about the life and death of these neurons remain. Here, we briefly summarize what is currently known about the immature neurons present in the primate ventral amygdala during development and in adulthood, as well as following selective hippocampal lesions. We provide evidence confirming that the distribution of immature neurons extends to the anterior portions of the entorhinal cortex and layer II of the perirhinal cortex. We also provide novel arguments derived from stereological estimates of the number of mature and immature neurons, which support the view that the migration of immature neurons from the lateral ventricle accompanies neuronal maturation in the primate amygdala at all ages. Finally, we propose and discuss the hypothesis that increased migration and maturation of neurons in the amygdala following hippocampal dysfunction may be linked to behavioral alterations associated with certain neurodevelopmental disorders.     

Spatial versus nonspatial relational learning in free-ranging fox squirrels (Sciurus niger).

This experiment was designed to assess spatial and nonspatial relational learning in free-ranging squirrels. The authors tested the possible use of proximal landmarks as conditional information to predict the locations of nuts, hidden in small dishes distributed on a plastic board. Squirrels were trained to associate the presence of 1 object, at the center of the board, with 1 set of baited dishes, whereas the presence of a 2nd object, placed alternatively at the same location, was associated with another set of dishes. They did not acquire the nonspatial relational task on the basis of proximal landmarks. They developed a win-stay spatial strategy relying on directional information derived from distant visuospatial cues and neglected proximal spatial information when it conflicted. They relied on their memory of the food locations in the previous trial to predict the nuts' locations, even though the objects were the only predictors of these locations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The expression of social dominance following neonatal lesions of the amygdala or hippocampus in rhesus monkeys (Macaca mulatta).

As part of ongoing studies on the neurobiology of socioemotional behavior in the nonhuman primate, the authors examined the social dominance hierarchy of juvenile macaque monkeys (Macaca mulatta) that received bilateral ibotenic acid lesions of the amygdala or the hippocampus or a sham surgical procedure at 2 weeks of age. The subjects were reared by their mothers with daily access to large social groups. Behavioral observations were conducted while monkeys were given access to a limited preferred food. This testing situation reliably elicited numerous species-typical dominance behaviors. All subjects were motivated to retrieve the food when tested individually. However, when a group of 6 monkeys was given access to only 1 container of the preferred food, the amygdala-lesioned monkeys had less frequent initial access to the food, had longer latencies to obtain the food, and demonstrated fewer species-typical aggressive behaviors. They were thus lower ranking on all indices of social dominance. The authors discuss these findings in relation to the role of the amygdala in the establishment of social rank and the regulation of aggression and fear. (PsycINFO Database Record (c) 2010 APA, all rights reserved)