Asymmetry in the skulls of fossil man: evidence of lateralized brain function?
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Animals↗
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Results for “Functional Laterality”
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Determination of cognitive hemispheric lateralization by "functional" transcranial Doppler cross-validated by functional MRI.
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Brain↗
The neurobiological basis of lateralized cerebral function. A review.
The first part of this review considers the empirical findings regarding the anatomical asymmetries that may be related to the left hemisphere's dominance for language. The review reveals that there are interhemispheric differences in the anatomy of the posterior sylvian region and of portions of the inferior frontal gyrus. In the second section, difficulties in attributing functional significance to these morphological asymmetries are discussed. The third section considers anatomical, behavioural and neurochemical asymmetries in animals and their relation to problems of human cerebral asymmetry.
Animals↗
Computer simulation of an ideal lateral inhibition function.
A model for lateral inhibition is presented in the context of the auditory channel. The mechanical analyzing system of the inner ear cannot alone account for the frequency resolution of hearing. Some additional mechanism, possibly lateral inhibition located in the auditory neural network, is needed to achieve the frequency selectivity observed in electrophysiological and psychoacoustical experiments. In a computer simulation study, the shape of an ideal lateral inhibition function was obtained. Such a function is applicable to all sensory modalities. In hearing, this function permits the sharpest possible frequency resolution as it can completely remove the frequency desharpening effect of the mechanical properties of the basilar membrane. In vision, it can compensate for abberations caused by the imperfections of the optical system of the eye.
Animals↗
[Functional cerebral lateralization: neurobiology and clinical aspects in childhood].
Anatomical and functional evidences of cerebral hemispheric asymmetries are reviewed in reference to fetal life, infancy and childhood. In general, left hemisphere deals with linguistic-sequenced-analytic-logic-deductive cognitive processing, whereas the right hemisphere is involved in spatial-simultaneous-inductive-intuitive tasks; attention and interactional functions predominate on the right hemisphere, too. The clinical and technological means to diagnose the functional lateralization in individual patients are discussed. A critical review is made of abnormal lateralizations and interhemispheric supplencies in various neuropsychiatric conditions of childhood: learning disabilities, epilepsy, attention deficit disorder, mental deficiency with chromosomopathies and infantile autism.
Attention↗
Effect of lithium carbonate on lateralized cognitive functions.
The effect of lithium carbonate on lateralized cognitive functions was studied by asking a patient suffering from a manic-depressive disorder to repeatedly recognize a given series of digits delivered dichotically while varying the dosage of lithium carbonate intake. The data showed that, whereas digit recognition from the right ear (left hemisphere) was about the same across tests, recognition from the left ear (right hemisphere) varied systematically with dosage variations. Specifically, it was found that an increase in dosage of lithium carbonate was associated with a decrease in recognition from the left ear. These data might indicate unilateral hemispheric effects of lithium carbonate on the dysfunctional right hemisphere of patients suffering from bipolar affective disorders. Clinical implications of the findings of the present case study are also discussed.
Adult↗
Detection of cerebral lateralization of function using EEG alpha-contingent visual stimulation.
Lateralized functional specialization of cortical processing of linguistic and spatial information and anatomical lateralization of processing of hemiretinal stimuli were investigated with a randomized factorial design in 14 right-handed male undergraduates using EEG alpha-contingent visual stimulation. Words or geometric designs of equal luminosity and size were presented by computer to randomly selected visual half-fields contingent on the occurrence of alpha at one of 4 placements (left and right occipital and left and right temporal). The replicative reliability of alpha block and, by implication, the control of each stimulus type over different cortical sites, was assessed with the alpha control ratio (mean alpha duration/standard deviation of alpha durations). The alpha control ratio was significantly greater for alpha-contingent vs. random (non-contingent) stimulation. Within alpha-contingent data alone, cerebral lateralization was significantly demonstrated in the 2-way interactions of EEG hemisphere X visual field of stimulation, and of EEG hemisphere X type of stimulus (verbal or spatial). The alpha control ratio was higher for contralateral visual half-field stimulation compared to ipsilateral stimulation. Control was also significantly higher for cognitively appropriate stimulus-hemisphere combinations (verbal stimuli and left cerebral hemisphere, or spatial stimuli and right hemisphere) vs. inappropriate combinations (verbal, right hemisphere, or spatial, left hemisphere). These electrophysiological data corroborate in normal subjects the previous conceptions of hemispheric specialization ascertained with brain-damaged patients.
Adolescent↗
Ionising radiation in infancy and adult cognitive function: radiation may not solely explain later cognitive function.
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Adult↗
Electrophysiological evidence that ethanol alters function of medial septal area without affecting lateral septal function.
Evidence is provided in this manuscript that ethanol acts directly on neurons in the medial septal area (MSA). Initially, the electrophysiological characteristics of MSA neurons in freely moving rats were characterized and found similar to that observed in rats anesthetized with urethane, but not chloral hydrate. Therefore, urethane was used to evaluate the effects of ethanol in anesthetized rats. The conclusion that ethanol influences neural function in the MSA is based on electrophysiological data that ethanol (0.75-3.0 g/kg i.p.) suppresses neural firing of medial septal cells in urethane-anesthetized as well as in unanesthetized rats in a dose-related fashion. Concurrent with the suppression of firing rate, the rhythmic bursting pattern of activity of MSA neurons is disrupted by ethanol. The changes observed in the MSA could not be attributed to an indirect action of ethanol on afferents from the lateral septum to the MSA, because ethanol did not alter neural activity of cells in the lateral septum. These data indicate that ethanol does not have a common action on all neurons. Neural activity in the MSA recovered from the acute action of ethanol at a time when blood ethanol levels were near maximal, indicating an acute tolerance to this effect of ethanol. The time course of change in neural activity in the MSA was highly correlated with the time course of a measure of behavioral sedation, but not the hypothermia produced by ethanol. Thus, the work in this manuscript supports the view that ethanol has selective actions on MSA neurons in the rat septal area and that these actions may influence the behavioral sedation induced by ethanol.
Anesthesia↗
Hand preference, extent of laterality, and functional hand use in Rett syndrome.
Residual hand use in functional tasks, extent of laterality, and right or left preference were studied in 145 2- to 24-year-old, postregression Australian subjects with Rett syndrome via parent questionnaire. Hand use was markedly restricted, more for complex than simple and for external (touching food and objects) than internal tasks (scratching, rubbing eyes), suggesting a deficit in cerebral control of external, goal-oriented hand use, which is perhaps genetically determined because there is significantly greater restriction of external tasks in subjects with demonstrated MECP2 mutations. Overall, 33.6% of patients were reported with a left-hand preference, 40.7% with a right-hand preference, and 25.7% with an equal hand preference. Extent of laterality was greater for external than internal and for complex than simple external tasks. Older subjects showed less functional hand use and possibly more overall laterality. However, their hand preference was similar to younger subjects. The anomalous pattern of hand preference in Rett syndrome may be linked to the primary apraxic deficit in this disorder rather than to late manifestation of laterality.
Adolescent↗
Cerebral lateralization of function and bilingual decision processes: is thinking lateralized?
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Brain↗
Modification of the functional reach test: analysis of lateral and anterior functional reach in community-dwelling older people.
The purpose of this study was to evaluate the validity and reproducibility of the modified lateral functional reach (FR), and to examine the associations between a variety of functional variables and the FR in community-dwelling older people (>65 years of age). A total of 383 aged Japanese participated in this study at the rural district Kahoku, Kochi, Japan, in 2002. The average age of the subjects was 78.6 years. The activity of daily living (ADL) and mental status were measured as outcomes. FR (anterior and lateral) and timed up and go (TUG) were measured as predictors. The test-retest reliability of lateral FR between the first and second measurement was very consistent. Subjects with greater lateral FR had higher basic and instrumental ADL (IADL) scores than did those with shorter lateral FR. However, there was no significant relationship between anterior FR and ADLs. The lateral FR of participants with depression was shorter than in those without depression, while the anterior FR did not correlate with the participants' scores on the geriatric depression scale (GDS). Lateral FR should be considered as a new, alternative means of assessing geriatric social activity and mental status in the elderly.
Activities of Daily Living↗
Lateralized neuropsychological functioning in depressive patients before and after drug therapy.
Several decades of research have led to different hypotheses about cognitive functioning in depression; one of the hypotheses states that there is altered functioning of the hemispheres during a depressive episode. Lateralization studies have found diminished neuropsychological functioning in depressive patients; especially right-hemisphere functions seem impaired. In our study we used conventional neuropsychological tests to study shifts in hemispheric functioning. Neuropsychological testing before and after therapy in 52 (for the most part therapy-resistant) depressives showed no substantial effects in lateralized functioning. None of the measures enabled prediction of response to treatment; however 17 different interaction variables were identified, five of which make an unique contribution.
Adult↗
Origins and functions of laterality: interactions of motoric systems.
To evaluate lateral motoric bias in response systems at different levels of the neuraxis and assess the extent of interaction between these levels in the small-eared bushbaby (Otolemur garnettii), 27 animals were tested for lateral bias in hand use and whole-body turn bias in two postural conditions. Subjects retrieved mealworms quadrupedally by reaching downwards into glass jars and bipedally by reaching upwards to baited straws. Eye bias was assessed separately. Behaviours were scored from videotape. Two subgroups were identified: SHIFTERS changed hand preference with posture and had correlations of hand/eye bias in quadrupedal posture and of hand/turn bias, with more bimanual reaching, in bipedal posture; NONSHIFTERS were consistent in hand preference and more strongly lateralised in reach and turn than SHIFTERS. Subgroups did not differ in reach efficiency. Results are interpreted to support the value of the analysis of motoric levels and their interactions in the study of the evolution of laterality. Assuming natural selection for coordinated and targeted behaviours to be the source of lateralisation, several proposals in support of a motoric theory of laterality origins and functions are advanced.
Journal Article↗
The influence of brain lateralization of function on a manual skill.
The present study considers the predictions of the brain lateralization of function hypothesis for the concurrent-task situation where the subject is required, to perform simultaneously a manual and a cognitive task. The manual task required the subject to successively press two keys with either the right or left hand, this being done concurrently with one of twelve different cognitive tasks. The cognitive tasks varied in terms of their verbal (left hemisphere) and non-verbal (right hemisphere) attributes. The results indicate that, for the concurrent verbal task conditions, only right-hand performance was disrupted while left-hand performance remained unchanged. For the non-verbal conditions both left and right hand performance was disrupted. These findings were interpreted in terms of brain lateralization of cognitive functions and possible hemispheric processes controlling manual performance.
Adult↗
Hemispheric asymmetries in language-related pathways: a combined functional MRI and tractography study.
Functional lateralization is a feature of human brain function, most apparent in the typical left-hemisphere specialization for language. A number of anatomical and imaging studies have examined whether structural asymmetries underlie this functional lateralization. We combined functional MRI (fMRI) and diffusion-weighted imaging (DWI) with tractography to study 10 healthy right-handed subjects. Three language fMRI paradigms were used to define language-related regions in inferior frontal and superior temporal regions. A probabilistic tractography technique was then employed to delineate the connections of these functionally defined regions. We demonstrated consistent connections between Broca's and Wernicke's areas along the superior longitudinal fasciculus bilaterally but more extensive fronto-temporal connectivity on the left than the right. Both tract volumes and mean fractional anisotropy (FA) were significantly greater on the left than the right. We also demonstrated a correlation between measures of structure and function, with subjects with more lateralized fMRI activation having a more highly lateralized mean FA of their connections. These structural asymmetries are in keeping with the lateralization of language function and indicate the major structural connections underlying this function.
Adult↗
Ocular correction effects on EMG activity of stomatognathic muscles in children with functional mandibular lateral- deviation: a case control study.
AIM: This study was conducted in order to determine the ocular correction effects on electromyography activity of anterior temporal, masseter, sternocleidomastoid and anterior digastric muscles in children with functional mandibular lateral-deviation. METHODS: This study was performed on 32 subjects, aged between 8 and 12 years with functional lateral deviation of mandible and oculo-extrinsic muscular tone disorders. After complete ophthalmologic evaluation and ocular correction prescription, the children were randomly divided into two groups: study and control. In the study group (16 subjects) EMG activity at rest was recorded in the following conditions: with eyes closed; with eyes open; with ocular correction modified through electromyographic control. In the control group (16 subjects) EMG activity at rest was recorded in the following conditions: with eyes closed; with eyes open; with conventional ocular correction. Data were acquired in 15-seconds trial using a SEMG K7, while the subjects maintained rest dental position. RESULTS/STATISTICS: Both groups presented a significative correlation between value of lateral-deviation and the degree of ocular-extrinsic muscular tone disorders (r=0.69). In addition, a significant statistical increase of EMG activity at rest with eyes open in both groups was observed in the anterior temporal left and right. A significant decrease of EMG activity with open eyes was observed only with ocular correction upon electromyographic control (study group). The findings, expressed as Symmetry Index, showed a significant increase of muscles imbalance right/left with conventional methods of ocular correction (p < 0.0001). CONCLUSION: The significant worsening in EMG activity, mainly observed with conventional corrective lenses, could have an important consequence in clinical diagnostic and therapeutic behaviour because anterior temporal muscles are important in postural position of the mandible. Instead EMG corrective lenses could improve tonus and balance of stomatognathic muscles and, therefore, support the functionality of orthodontic treatment. Moreover, the data suggest an interesting new tool in order to reach an interdisciplinary approach to complex growth disorders represented by functional lateral deviation of mandible and ocular-extrinsic muscular tone disorders.
Child↗
Seasonal variation in human functional cerebral lateralization and free testosterone concentrations.
Men have previously been reported to exhibit seasonal fluctuations on specific types of cognitive performance. It has been speculated that this performance variability is a result of changes in cerebral asymmetry due to lowered testosterone concentrations in the spring relative to the fall. In the present study, functional cerebral lateralization was measured in a group of men and women in the spring and fall. Free testosterone concentrations were assessed for participants to determine what associations might exist between seasonal variability in lateralization and seasonal fluctuations in testosterone exposure. Men and women tested in the spring exhibited exaggerated patterns of asymmetry compared to participants tested in the fall. Lower testosterone concentrations were observed in the spring compared to the fall in women, but not men. No direct associations between testosterone and lateralization were detected for either sex at either season. These results illustrate that seasonal fluctuations in testosterone exposure do not directly influence seasonal changes in functional lateralization patterns.
Adolescent↗