No description available.

Several lines of evidence suggest that the hippocampus is a part of the neural mechanism regulating self-stimulation behavior. Self-stimulation areas in the hypothalamus and septum have reciprocal connections with the hippocampus, in particular via the fornix system (Nauta, 1956). [...]

A standard set of experimental conditions for studying the effects of lesions to the three brain areas using the 8-arm radial maze was used: a win-shift version, a win-stay version, and a conditioned-cue preference (CCP) version. Damage to the hippocampal system impaired acquisition of the win-shift task but not the win-stay or CCP. Damage to the dorsal striatum impaired acquisition of the win-stay task but not the win-shift or CCP. Damage to the lateral amygdala impaired acquisition of the CCP but not the win-shift or win-stay task. These results are consistent with the hypothesis that the mammalian brain may be capable of acquiring different kinds of information with different, more-or-less independent neural systems. A neural system that includes the hippocampus may acquire information about the relationships among stimuli and events. A neural system that includes the dorsal striatum may mediate the formation of reinforced stimulus-response associations. A neural system that includes the amygdala may mediate the rapid acquisition of behaviors based on biologically significant events with affective properties. (Abstract shortened by UMI.)

A clear double dissociation between the effects of left and right temporal-lobe excisions was demonstrated for two identically-designed learning tasks that utilized different memoranda. Patients with left temporal-lobe lesions showed a deficit for the verbal task and normal performance for the non-verbal analogue, whereas the converse was evident for patients with right temporal-lobe lesions. Again, on two formally similar tests of short-term recall with interpolated activity, this same pattern of dissociation was observed for the retention of verbal as compared with non-verbal information. For both pairs of experiments, the severity of the material-specific learning and retention deficits was directly related to the extent of surgical encroachment upon the hippocampal zone of the affected hemisphere. These studies implicate the hippocampal region in the crucial transfer of experience from a temporary storage system (primary memory) to more permanent long-term storage (secondary memory). / fr

No description available.

Mechanical testing of living brain with control or measurement of all potential sources of variability is difficult and not often or consistently performed. The primary objective of the current work is to compare mechanical properties of the living rabbit brain across relatively high and low groupings of arterial blood partial pressure of carbon dioxide (pCO2) and mean arterial pressure (MAP), with control or measurement of all deformation, anatomical, and other physiological variables. It is hypothesized that there are significant differences in relative viscoelastic properties of the living rabbit brain under different combinations of pCO2 and blood pressure. Stress-relaxation brain indentations were performed on seven consecutive anesthetized living rabbits, with control or measurement of all possible variables.. Five indentations were performed on each animal, with 15 minute periods of rest between each indentation, with the following relative physiological parameters: Indentation 1. Low MAP and low pCO2. Indentation 2. High MAP and low pCO2. Indentation 3. Low MAP and high pCO2. Indentation 4. High MAP and high pCO2. Indentation 5. Low MAP and low pCO2. The data were fitted to a generalized Maxwell model that incorporated two viscoelastic terms and one equilibrium elastic term. The relative stress-relaxation coefficients and material properties were determined, and compared using statistical analysis. Peak stresses encountered with relative step-loading ranged from approximately 2-4 x 103 Pa, with corresponding “instantaneous” elastic moduli approximating 4-8 x 103 Pa. A short and long Time of Relaxation was determined for each viscoelastic term of the model, and ranged from 0.03 – 1.72 s and 9.92 – 32.55 s respectively. Comparison of stress-relaxation coefficients and material properties reveals statistically significant differences in the stress coefficients and their respective elastic moduli across different combinations of pCO2 and MAP, and between the last indentation group and previous indentations. There were no significant differences found in Time of Relaxation coefficients. In conclusion, mechanical properties of step-loaded living rabbit brain are relatively dependent on pCO2 and MAP, and repetitive deformations. This may be important for further understanding of the brain in different physiological states and accurate mechanical characterization of the brain. It also highlights the need to control for these parameters during the mechanical testing of brain.

The clinical literature on the intellectual effects of human brain damage reveals a constant preoccupation with the problem of the role of the frontal lobes, with a corresponding neglect of other parts of the cerebral cortex. In particular there is not a single systematic investigation of the effects of temporal-lobe damage in man, althrough there are several isolated and highly suggestive reports of individual cases. Fortunately the situation is quite different with regard to animal work, where the last few years have yielded numerous reports dealing with the effects of temporal-lobe lesions of varying extent on the learning ability of lower primates. This material is highly relevant to the present investigation, since it draws attention to types of deficit which might well be found at the human level also, but which have been neglected; for this reason the animal data will be presented in some detail, before passing to a review of the clinical literature. Since the present study deals only with cognitive functions, there will be no detailed discussion of the emotional changes often seen in temporal-lobe damage. In the monkey, a decrease in emotional reactivity regularly follows deep-temporal removals (Brown and Schafer, 1888; Kluver and Bucy, 1938; Bard, 1950; Thomson and Walker, 1951; Mishkin, 1951; Poirier, 1952); in man, electrographic abnormality in the anterior temporal region frequently gives rise to personality disturbances (Bailey and Gibbs, 1949) [...]

Kiwi (Apteryx spp.) have evolved under unique evolutionary pressures and uniquely occupy a nocturnal, ground-dwelling niche. They share few traits with other birds: they have small eyes, an elongated bill, and several features more characteristic of mammals. Early anatomical studies described a number of unique features in the kiwi brain, but their relevance to the behaviour and ecology of the species was not clearly established. This study aims to describe the structure of the primary cranial sensory systems of kiwi and comment on the evolutionary pressures that may have shaped their current form. The external morphology and relatively large size of the brain of kiwi, in particular those of the telencephalon, contrast with those of other Palaeognaths. The relative size of the cerebral hemispheres is rivalled only by a handful of parrots and songbirds. This enlargement results from a differential enlargement of the nidopallium, mesopallium and, to a lesser extent, of the basal ganglia. In other birds these regions are associated with the integration of information, cognition and learning. Kiwi brain centres processing visual information were small, although the retina structure showed an adaptation to dim light. The olfactory and trigeminal systems associated with the bill were hypertrophied. The auditory system shows specialisations associated with an overrepresentation of high frequency coding areas that originates in the cochlea and is preserved throughout the auditory brainstem. In absolute terms, the upper frequency response limit, based on hair cell morphology, is estimated to be about 5 kHz, the lower limit to be about 500 Hz, with a slightly higher frequency range predicted from the morphology of central auditory structures. The organisation of both nucleus angularis (NA) and nucleus laminaris (NL) in kiwi suggest that the central auditory system has retained the ancestral organisation except for the morphological features associated with the overrepresentation of high frequencies. Overall, the brain and sensory structures of kiwi have evolved neural adaptations that accompany the very different behavioural strategies associated with the unique niche the birds occupy. A large telencephalic size and shift away from vision towards an increased reliance on olfactory, tactile and auditory cues constitute a collection of features that make kiwi unique among birds. These findings provide a unique glimpse of the evolutionary history that has led to this unusual design, in particular, and challenge many of our current views about the evolution of brains and encephalisation, in general.

Kiwi (Apteryx spp.) have evolved under unique evolutionary pressures and uniquely occupy a nocturnal, ground-dwelling niche. They share few traits with other birds: they have small eyes, an elongated bill, and several features more characteristic of mammals. Early anatomical studies described a number of unique features in the kiwi brain, but their relevance to the behaviour and ecology of the species was not clearly established. This study aims to describe the structure of the primary cranial sensory systems of kiwi and comment on the evolutionary pressures that may have shaped their current form. The external morphology and relatively large size of the brain of kiwi, in particular those of the telencephalon, contrast with those of other Palaeognaths. The relative size of the cerebral hemispheres is rivalled only by a handful of parrots and songbirds. This enlargement results from a differential enlargement of the nidopallium, mesopallium and, to a lesser extent, of the basal ganglia. In other birds these regions are associated with the integration of information, cognition and learning. Kiwi brain centres processing visual information were small, although the retina structure showed an adaptation to dim light. The olfactory and trigeminal systems associated with the bill were hypertrophied. The auditory system shows specialisations associated with an overrepresentation of high frequency coding areas that originates in the cochlea and is preserved throughout the auditory brainstem. In absolute terms, the upper frequency response limit, based on hair cell morphology, is estimated to be about 5 kHz, the lower limit to be about 500 Hz, with a slightly higher frequency range predicted from the morphology of central auditory structures. The organisation of both nucleus angularis (NA) and nucleus laminaris (NL) in kiwi suggest that the central auditory system has retained the ancestral organisation except for the morphological features associated with the overrepresentation of high frequencies. Overall, the brain and sensory structures of kiwi have evolved neural adaptations that accompany the very different behavioural strategies associated with the unique niche the birds occupy. A large telencephalic size and shift away from vision towards an increased reliance on olfactory, tactile and auditory cues constitute a collection of features that make kiwi unique among birds. These findings provide a unique glimpse of the evolutionary history that has led to this unusual design, in particular, and challenge many of our current views about the evolution of brains and encephalisation, in general.

Kiwi (Apteryx spp.) have evolved under unique evolutionary pressures and uniquely occupy a nocturnal, ground-dwelling niche. They share few traits with other birds: they have small eyes, an elongated bill, and several features more characteristic of mammals. Early anatomical studies described a number of unique features in the kiwi brain, but their relevance to the behaviour and ecology of the species was not clearly established. This study aims to describe the structure of the primary cranial sensory systems of kiwi and comment on the evolutionary pressures that may have shaped their current form. The external morphology and relatively large size of the brain of kiwi, in particular those of the telencephalon, contrast with those of other Palaeognaths. The relative size of the cerebral hemispheres is rivalled only by a handful of parrots and songbirds. This enlargement results from a differential enlargement of the nidopallium, mesopallium and, to a lesser extent, of the basal ganglia. In other birds these regions are associated with the integration of information, cognition and learning. Kiwi brain centres processing visual information were small, although the retina structure showed an adaptation to dim light. The olfactory and trigeminal systems associated with the bill were hypertrophied. The auditory system shows specialisations associated with an overrepresentation of high frequency coding areas that originates in the cochlea and is preserved throughout the auditory brainstem. In absolute terms, the upper frequency response limit, based on hair cell morphology, is estimated to be about 5 kHz, the lower limit to be about 500 Hz, with a slightly higher frequency range predicted from the morphology of central auditory structures. The organisation of both nucleus angularis (NA) and nucleus laminaris (NL) in kiwi suggest that the central auditory system has retained the ancestral organisation except for the morphological features associated with the overrepresentation of high frequencies. Overall, the brain and sensory structures of kiwi have evolved neural adaptations that accompany the very different behavioural strategies associated with the unique niche the birds occupy. A large telencephalic size and shift away from vision towards an increased reliance on olfactory, tactile and auditory cues constitute a collection of features that make kiwi unique among birds. These findings provide a unique glimpse of the evolutionary history that has led to this unusual design, in particular, and challenge many of our current views about the evolution of brains and encephalisation, in general.