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Anatomical asymmetries and functional laterality.

Anatomical and functional asymmetries were measured using MRI and dichotic, visual field and hand performance laterality tasks in 104 normal right- and left-handed male and female adults. Comprehensive linear and area measures showed consistently larger brains when handedness and language laterality were in the same direction. Right-handers with left cerebral dominance for dichotic listening and left-handers with right cerebral dominance had larger structures. Hand performance was the strongest functional laterality related to anatomical asymmetries. Left hemisphere dominance on this task was associated with larger right frontal and left occipital widths. Dichotic listening or visual field laterality alone was not associated with contralaterally larger temporal, parietal or occipital measurements. Left visual field dominance for reading, interacting with right-handedness, was associated with wider left parietal width. The complex associations between anatomical and functional asymmetries contribute to individual differences in cerebral organization. The demonstrated association of coincident hand performance and language laterality measures with larger anatomical structures may confer biological advantage. Morphometric analysis in vivo may have increasing importance in interpreting behaviour.

Adult

The effects of early experience on callosal development and functional lateralization in pigmented BALB/c mice.

A proportion of animals of the BALB/c inbred mouse strain have an unusually small (sometimes absent) midsagittal area of the corpus callosum (CC). In this study, we used a large sample of both males and females (total n = 198) from a pigmented congenic BALB/c line to investigate the relations among preweaning handling, area of CC, and direction and degree of lateralization as measured by Collins' paw preference task. Twenty litters were handled daily from the day after birth until day 25 (weaning) according to Denenberg's procedure and 18 litters were left undisturbed until weaning. All animals were tested for degree and direction of paw preference in a modification of Collins' apparatus at about 60 days and measures taken on CNS structures at 100 days of age. There were no handling or sex effects on degree or direction of paw preference or on the extent of CC defects, but for animals in the normal range (CC > or = 0.7 mm2), those which had been handled had significantly smaller callosa. No significant differences were detected between right and left hemisphere weights, and these measures did not appear to be related to the behavioural measures. There was no significant correlation between CC area and degree of paw preference nor was there any relationship between total agenesis and degree of handedness. This last result is particularly interesting in light of recent evidence that ILn/J mice, all acallosal, are exclusively ambilateral.

Animals

Intrahemispheric visual-motor information processing and cerebral functional lateralization.

A series of stimuli, words and faces, were presented tachistoscopically to 24 dextrals and 12 sinistrals. The stimuli were presented to one eye at a time and the subjects were instructed to respond to specific words or stimuli with a specific hand. The results indicate that (1) cerebral functional asymmetry is related to handedness; in the dextrals, the left hemisphere is more specialized in verbal recognition, while in the sinistrals, the right hemisphere is more specialized in recognizing non-verbal material. (2) An ipsilateral hand-and-eye combination is a valid method of measuring intrahemispheric information processing, provided that the tachistoscopically presented visual stimuli are capable of inciting specialized hemispheric function. The dominant relationship among the crossed and non-crossed visual pathways is discussed.

Adult

Trajectories of functional impairment in later life.

Functional impairment trajectories in late adulthood over a decade are characterized using the Longitudinal Retirement History Study (LRHS) data set. Non-linear patterns of age-related increase in impairment are documented with longitudinal data. Subsets of panelists from the initial large, nationally representative probability sample of employed males and unmarried employed females (N = 11,000) also exhibit differential non-linear trajectories of impairment by sex, income, and educational attainment. Concurrent analysis of the relationship over a decade among sex, SES, and functional impairment suggests that in health research, both sex and SES are broad proxy variables whose usefulness for understanding health outcomes and for policy analysis would be enhanced by the specification of components.

Activities of Daily Living

Physiological characterization of lateral line function in the Antarctic fish Trematomus bernacchii.

The Antarctic notothenioids are a monophyletic radiation of fishes that have evolved under conditions of low light and cold, where non-visual sensory systems, such as the mechanosensory lateral line system, would be of importance. As part of a study of the structure and function of the mechanosensory lateral line system in these fishes we systematically characterized the function of the anterior lateral line system in one of the common benthic species, Trematomus bernacchii. Frequency-response and threshold-tuning curve methods yield similar functional characterizations of single afferent fibre responses to vibrational stimulation. Curve fitting of generalized transfer function to frequency-response curves allows an objective splitting of responses into velocity and acceleration sensitive populations thought to correspond to superficial and canal neuromasts, respectively. Both response types are characterized by a low-pass frequency-response curve, with a relatively low upper frequency cut-off when compared with data from temperate species. The sensitivity of the lateral line system of T. bernacchii is comparable to that of the mottled sculpin Cottus bairdi.

Acceleration

Nature and severity of hydrocephalus and its relation to later intellectual function.

In 102 cases of infantile hydrocephalus, treated within 365 days of birth, the possibilities of predicting later intelligence were investigated, largely by means of multiple regression methods. No significant effect of aetiology, date of shunting or severity (measured in various ways) could be demonstrated. Within the spina bifida group however the 3 cases of encephalocele had considerably lower IQ's. There was no effect of lesion level in the rest of this group. Educational level of the parents had a significant, but not very marked impact on the IQ's of their children. Most outstanding was the difference between non-communicating and communicating hydrocephalus: nearly 50% of the non-communicating cases were mentally retarded, while this percentage was 22 for the communicating ones.

Adolescent

Sensitivity to laterality as a function of handedness.

This study tested the hypothesis that left-handed individuals are more aware than right-handed individuals of others' handedness. 18 left-handed and 18 right-handed college students were shown a drawing of 8 children at a party. Seven children held objects in the left hand, while one held an object in the right hand. After 2 1/2 min. the drawing was removed and subjects answered 15 questions about its contents. Included were 2 questions asking how many children were holding something in the right or left hand. Compared with right-handed subjects, left-handed subjects reported significantly more children holding something in the left hand and significantly fewer holding something in the right hand. The two groups did not differ on any other questions.

Awareness

Function of lateral reticular nucleus in central cardiovascular regulation in the cat.

The role of the lateral reticular nucleus (LRN) in central cardiovascular regulation was investigated in cats. In 15 cerebellectomized and nine intact chloralosed cats stimulation of 115 histologically verified sites in the LRN elicited increases in arterial pressure and heart rate; the latter was abolished by propranolol but not by bilateral cervical vagotomy. The pressor response was significantly greater in intact animals. Electrical activity was recorded from the right inferior cardiac nerve (ICN) during stimulation fo the LRN and of a vasomotor region in the posteromedial hypothalamus (PMH). Stimulation of sites in the LRN and in the PMH, on both sides, elicited a response in the right ICN that was consistently abolished during baroreceptor excitation. Medullary transection 3 mm rostral to the LRN did not abolish the ICN response to LRN stimulation. The conclusions are drawn that stimulation of the LRN elicits cardiovascular responses probably due to excitation of groups of neurons in this nucleus located in a descending sympathetic pathway originating in the PMH and that these responses can be inhibited by excitation of baroreceptors. In view of the known functional connections of the LRN with the somatomotor system it is suggested that this nucleus may play a major role in somatosympathetic reflexes.

Animals

Symmetrical lateralization of function in the auditory system of the cat: effects of unilateral ablation of cortex.

We have presented behavioral evidence suggesting that one function of auditory cortex is to attend to stimuli at the contralateral ear. Further, behavioral and anatomic evidence shows that the neural mechanisms for this function probably depend on a pathway that crosses at the level of the medulla, bypasses the superior olive, and ascends to the contralateral inferior colliculus. At higher centers there are several auditory pathways from thalamus to cortex, as well as descending pathways from cortex, and some of these pathways may play a role in selective listening with one ear.

Acoustic Stimulation

Radiographic evidence of impaired pulmonary function in laterally recumbent anaesthetised horses.

Studies in conscious and anaesthetised ponies demonstrated that starvation, anaesthesia and changes in body position influence the radiographic appearance of the lungs in the lateral and dorsoventral views. Radiographic appearances could not be closely correlated with blood gas values, but they suggested that the volume of the lowermost lung of the laterally recumbent animal is greatly reduced.

Anesthesia