Frontal cortex grafts have opposite effects at different postoperative recovery times

We studied the effect of different postoperative times on the behavioral recovery following brain implants. Adult male rats received cortical tissue grafts 2 weeks after aspiration of the medial frontal cortex. Either 2 (Immediate Group) or 28 (Delay Group) days after grafting, the performance of these rats on a behavioral battery, comprising the Morris water maze task, forepaw use, and grooming, was compared to that of rats with similar lesions and postoperative recovery times but no grafts. Rats tested immediately after receiving implants performed better on the spatial navigation task than rats with similar lesions but no grafts. This improvement, however, was less than that shown by rats with lesions but no grafts permitted to recover for 28 days before testing. In contrast, in the Delay Group, rats with grafts were more greatly impaired than were their operated controls. Neither lesions nor grafts affected grooming although the Immediate Group with grafts were significantly more impaired in using their forepaws during feeding than were any of the other groups. These results lead us to conclude that differing postoperative recovery times and task requirements may account for some of the inconsistent results of the influence of brain grafts on behavioral recovery reported in the literature. We also conclude that cortical tissue implants can have two effects with different time courses and opposite net behavioral effects.     

Age-related changes in working and reference memory performance and locomotor activity in the Wistar rat

Wistar rats of three age groups were tested in an automated tunnel-maze system of variable geometry to investigate whether changes in spontaneous locomotor activity and in learning and memory develop differentially or in a correlated fashion as a function of age. Senescent (30 months) as well as mature-adult (17 months) rats showed an age-correlated decline of locomotor activity as compared to the mature-young (5 months) group. Both working-memory (measured as within-trial arm discrimination performance) and reference-memory (measured as avoidance of "blind alley" visits) were severely affected in the senescent group, whereas the middle-aged animals suffered only from a working-memory deficit. The findings provide evidence that locomotor deficits do not necessarily interfere in the assessment of age-related changes in cognitive performance. Furthermore the results support the hypothesis that working and reference memory have different underlying physiological correlates and that these neuronal systems are differentially affected by the aging process.     

Pure agraphia and Gerstmann's syndrome as a visuospatial-language dissociation: an experimental case study

A right-handed man suffered a left parieto-occipital cerebral infarction, causing agraphia with Gerstmann's syndrome but without major aphasia, alexia, or apraxia. Oral spelling was superior to written spelling. Experiments were performed involving (1) analysis of errors in writing, (2) tasks of visual imagery, and (3) identifying letters drawn without leaving a visual trace. The results suggest that the agraphia and Gerstmann's syndrome are due to a dissociation of language skills and visuospatial skills caused by a dominant parieto-occipital lesion.     

Oysters, rabbits and people: A critique of “race differences in behaviour” by J.P. Rushton

Rushton's article is criticized for its logic, the credibility of some of its sources, selectivity from the literature and from data within studies, failing to consider diversity in subgroups within races that may exceed differences between races, lack of analysis of racial differences in socioeconomic status and how this might influence group differences, and failure to apply statistical tests to minute differences between means. A wide range of phenomena assumed to be heritable are linked with the idea that they serve a reproductive end. However, there is no evidence that fertility itself is heritable. Large scale studies have shown no racial differences in diagnoses or on the MMPI that fit Rushton's theory. Rushton's analysis of international data on the EPQ is selective, ignoring the variance within racial groups and the scale of greatest relevance for his theory: P. An analysis of the data on this scale reveals no results in conformance with his theory. Data on sexual behavior is based on small and unrepresentative samples of blacks. Sizes of heads and genitals are compared with no obvious connection to the primary issue of biological fertility strategies. Everything is assumed to be on a primarily genetic basis although sexual mores have shown remarkable changes in a single generation.     

Memory and awareness in a patient with multiple personality disorder

We studied an individual with multiple personality disorder in whom each of several personalities claimed to have no direct awareness of the others and to be unable to consciously remember the experiences of other personalities. A broad selection of implicit and explicit memory tests was used to determine the extent to which one personality had access to knowledge acquired by another and the circumstances in which that knowledge would be expressed. The implicit assessment of memory was a necessary but not sufficient condition for demonstrating interpersonality access. The degree of compartmentalization of knowledge in this patient depended largely on whether the interpretation of presented information was likely to differ across personalities.     

Studies of psychosocial influences on coronary artery atherogenesis in cynomolgus monkeys

The cynomolgus macaque provides a suitable primate model for studying how psychosocial factors contribute to coronary artery atherogenesis. Important interactions with diet, sex, and behaviorally elicited cardiovascular reactivity are described.     

Concurrent-schedule performance: Effects of relative and overall reinforcer rate

Six pigeons were trained to respond on two keys, each of which provided reinforcers on an arithmetic variable-interval schedule. These concurrent schedules ran nonindependently with a 2-s changeover delay. Six sets of conditions were conducted. Within each set of conditions the ratio of reinforcers available on the two alternatives was varied, but the arranged overall reinforcer rate remained constant. Each set of conditions used a different overall reinforcer rate, ranging from 0.22 reinforcers per minute to 10 reinforcers per minute. The generalized matching law fit the data from each set of conditions, but sensitivity to reinforcer frequency (a) decreased as the overall reinforcer rate decreased for both time allocation and response allocation based analyses of the data. Overall response rates did not vary with changes in relative reinforcer rate, but decreased with decreases in overall reinforcer rate. Changeover rates varied as a function of both relative and overall reinforcer rates. However, as explanations based on changeover rate seem unable to deal with the changes in generalized matching sensitivity, discrimination accounts of choice may offer a more promising interpretation.     

Referential communication abilities of learning-disabled, language-learning-disabled, and normal school-age children

Past research in referential communication has indicated normally developing children show developmental progression in ability to communicate a specific referent to a listener. In one paradigm subjects were given lists of word-pairs in which one member of each pair was designated as the referent. It was shown that communicating about referents found in word-pairs associated in some way was more difficult than communicating about referents in dissimilar word-pairs. The present study extended this methodology to learning-disabled children. Learning-disabled, language-learning-disabled, and normally achieving children were asked to communicate about 30 pictured referents on three different tasks. On Tasks 1 and 2 each subject was asked to give a clue for the referent that would distinguish it from the other picture. Stimuli for Task 1 were 30 pairs of pictures that were related in some way and the stimuli for Task 2 were 30 pairs of unrelated pictures. Task 3 required the subjects to evaluate the adequacy of the examiner's clues for Task 1 stimuli. The disabled subjects were matched to the normally achieving subjects on the basis of receptive vocabulary age. Few differences were noted among the groups' performances on these referential communication tasks. Implications include the importance of vocabulary and concept development to referential communication.