Learning and generalization in healthy aging: implication for frontostriatal and hippocampal function.

Damage to the hippocampal and frontostriatal systems can occur across the adult life span. As these 2 systems are involved in learning processes, mild impairments of learning and generalization might be observed even in healthy aging. In this study, we examined both learning and generalization performance in 3 groups of older adults: young-older (ages 45 to 60 y), middle-older (ages 61 to 75 y), and oldest-older (ages 76 to 90 y).

Neuronal localization of cholecystokinin mRNA in the rat brain by using in situ hybridization histochemistry.

The distribution of cholecystokinin (CCK) mRNA in the rat brain was determined by means of in situ hybridization histochemistry. Our results demonstrate a widespread distribution of neurons containing CCK mRNA throughout the rat brain. Hybridization-positive neurons were distributed throughout the neocortex, olfactory bulb, claustrum, amygdala, the dentate gyrus and hippocampus proper, and several subnuclei of the thalamus and the hypothalamus.

Neonatal sensory deprivation reduces tufted cell number in mouse olfactory bulbs.

Quantitative morphometric methods were used in mice to study the effect postnatal olfactory deprivation has on tufted cell size and number. The two layers containing tufted cells, the external plexiform and glomerular layers, are considerably smaller in the deprived olfactory bulbs than in the contralateral, experienced olfactory bulbs. While most of this volumetric deficit may be due to an attenuation of synaptogenesis and dendritic elaboration, an additional factor contributing to the reduced volume of these bulbar layers is a substantial loss of tufted cells.

Effects of early anosmia on two classes of granule cells in developing mouse olfactory bulbs.

Quantitative morphometric methods were used to examine the effects of early unilateral anosmia on two classes of granule cells in developing mouse olfactory bulbs. Volumetric results show that the internal granule cell layer in the deprived olfactory bulb is significantly smaller than the same layer in the experienced olfactory bulb. The major factor contributing to this retarded development is a selective loss of one class of interneurons; dark granule cell number is substantially reduced, while light granule cell number is not.

Patterns of deoxyglucose and glucose labeling in the optic tectum of monocularly stimulated bass.

Uniformly labeled deoxyglucose and glucose were used to examine patterns of altered metabolic activity in the optic tectum of largemouth bass. Autoradiographs from fish which viewed moving vertical stripes with one eye show that the metabolites of the two sugars procedure similar patterns of activity-related labeling in the tectum: tangentially arranged bands of increased optical density through the SFGS and the SGC. In addition, aldehyde fixation was found to improve the histological quality of the sections without altering the patterns of labeling.

Tangential organization of olfactory, association, and commissural projections to olfactory cortex in a species of reptile (Trionyx spiniferus), bird (Aix sponsa), and mammal (Tupaia glis).

Small amounts of tritiated leucine were injected into the olfactory bulb or anterior olfactory cortex of softshell turtles, wood ducks, and tree shrews in order to compare quantitatively the laminar distribution of olfactory bulb, association, and commissural projections to olfactory cortex. In all three species, a similar colaminar distribution of olfactory and association projections was found: the olfactory projections are restricted to the superficial cortical layer Ia, while the association projections are distributed into the deeper cortical layers Ib, II, and III. Differences among these three species were found in the origin and distribution of commissural projections.

Olfactory bulb interconnections in soft shell turtle.

Unilateral injections of horseradish peroxidase and radioactive amino acids in the olfactory bulbs of soft shell turtles revealed unique pathways for interbulbar communication. The two olfactory bulbs exchange dendrites and axons directly through their fused external plexiform and internal plexiform laminae.

Origins of anthropoid intelligence IV. Role of prefrontal system in delayed alternation and spatial reversal learning in a conservative eutherian (Paraechinus hypomelas).

A conservative eutherian mammal (the hedgehog, Paraechinus hypomelas) was tested on delayed alternation performance and spatial reversal learning before and after ablations of the prefrontal cortex. The anatomical results show that the cortical focus of the projections of the medial dorsal nucleus, the prefrontal cortex, does not include the neocortex on the dorsal convexity of the hedgehog's frontal lobe but, instead, the perirhinal and pregenual neocortex immediately surrounding the frontal convexity. The behavioral results show that normal performance of hedgehogs on these two behavioral tests depends upon the integrity of their prefrontal cortex, but not on the integrity of their frontal convexity or olfactory bulbs.

Topographic organization of the orientation column system in the striate cortex of the tree shrew (Tupaia glis). II. Deoxyglucose mapping.

The topographic organization of the orientation column system in the tree shrew striate cortex was examined by using 2-deoxyglucose autoradiography to map the cortical sites of increased metabolic activity produced by visual stimulation with stripes of a single orientation. Awake experimental tree shrews (freely moving, restrained, or paralyzed) were given injections of deoxyglucose label and then stimulated with vertical, horizontal, or oblique stripes for 45--75 min. Autoradiographs of coronal sections through the striate cortex revealed regularly spaced radial zones of increased deoxyglucose uptake 150--350 micrometers wide, extending from the cortical surface to the white matter, separated by interzone regions of lower uptake.

Efferent projections of the main and the accessory olfactory bulb in the tree shrew (Tupaia glis).

The projections of the main and the accessory olfactory bulb in the tree shrew (Tupaia glis) have been analyzed with anterograde degeneration and autoradiographic methods for identifying axonal projections, and with the horseradish peroxidase method for identifying the distribution of neurons from which these projections originate. The cytoarchitectonic features of the paleocortical areas which receive projections from the main and the accessory olfactory bulb have also been described. The efferent projections of the accessory olfactory bulb are distributed to the bed nucleus of the accessory olfactory tract, the medial amygdaloid area, the posteromedial cortical amygdaloid area, and to the caudal portion of the bed nucleus of the stria terminalis.

Origins of anthropoid intelligence. III. Role of prefrontal system in delayed-alternation and spatial-reversal learning in a prosimian (Galago senegalensis).

A species of prosimian (bush baby, Galago senegalensis) was tested on delayed-alternation and spatial-reversal learning before and after ablation of prefrontal cortex. The results show that normal performance on the two behavioral tasks depend on different subdivisions of the MD-prefrontal system. Delayed alternation is disrupted by prefrontal lesions which cause degeneration in the lateral division of MD while spatial-reversal learning is disrupted by lesions causing degeneration of the medial division of MD.

Origins of anthropoid intelligence.

The development of the extrastriate visual system relative to the striate system was estimated indirectly by measuring the volumes of the lateral posteriorpulvinar complex and lateral geniculate nucleus in six varieties of mammals selected on the basis of their propinquity with Anthropoidea [oppossums, hedgehogs, rats, squirrels, tree shrews and bushbabies]. The same animals were tested on two related behavioral tasks [spatial and visual reversal learning] whose successful achievement requires a simple sort of abstraction. The results show that the ability to learn visual reversal, but not spatial reversal, corresponds closely to the relative degree of development of the extrastriate system.