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PubMed2005

Hemispheric asymmetry, modular variability and age-related changes in the human entorhinal cortex.

The verrucae areae entorhinalis (VAE) are a characteristic feature of the human brain that occupy the anterior and posterolateral parts of the parahippocampal gyri and correspond to the islands of layer II neurons. We analyzed VAE in 60 neurologically normal subjects ranging from 23 to 85 years of age using a casting method. In 10 of these subjects the total number of neurons in the entorhinal islands was estimated stereologically using the optical fractionator. The number and surface area of VAE were higher in the left hemisphere compared with the right, and this leftward asymmetry was highly significant. Regression analysis showed a negative correlation between average VAE area and age in both hemispheres, representing a rate loss of about 800 microm2 per year. The estimated number of neurons obtained with the optical fractionator showed no significant difference between the left and the right hemisphere (468,000+/-144,000 vs. 405,000+/-117,000). There was a highly significant negative correlation between neuron numbers and age in both sides. In addition, clusters of small, undifferentiated layer II neurons ('heterotopias') were frequently observed in the rostral part of the entorhinal cortex in young and elderly adults. Layer II entorhinal neurons are among the first to show neurofibrillary changes during normal aging. The present data confirm the occurrence of age-related neuron loss in the entorhinal cortex. Considering the consistent projections from ipsilateral auditory association areas that, together with Broca's motor-speech area (Brodmann areas 44 and 45), show leftward asymmetry from early infancy (such as Brodmann area 22, planum temporale, and area 52 in the long insular gyrus), we speculate that functional lateralization of the human entorhinal cortex may be associated with specialization for memory processing related to language. Due to the dependence of hippocampal formation on entorhinal projections, this finding is also consistent with the greater capacity of the left hippocampus for verbal episodic memory.

Adult↗
PubMed2005

Interictal language functions in temporal lobe epilepsy.

OBJECTIVE: To evaluate interictal language functions in patients with medically intractable left and right sided mesial temporal lobe epilepsy (TLE). METHODS: Spontaneous speech, language comprehension, confrontation naming, repetition, reading, writing, and word fluency were examined in 12 patients with left sided TLE and 11 patients with right sided TLE. RESULTS: Four patients out of 23 displayed language deficits in more than one language domain. Three further patients exhibited isolated language deficits. Linguistic deficits were observed in both left TLE and right TLE. In quantitative analyses left and right TLE only differed in spontaneous speech (p = 0.02); no difference was found in other language functions, laterality quotient of Wada test, or overall IQ. Qualitative error analysis of object naming, however, showed typical errors associated only with left TLE. Patients with linguistic deficits were older at testing compared to patients without linguistic deficits (p = 0.003), whereas other factors including side of TLE, handedness, educational level, age at epilepsy onset, and duration of epilepsy did not differ between groups. CONCLUSIONS: Possible explanations for these findings include neuronal cell loss and deafferentiation in cortical areas, and disruption of the basal temporal language area pathways. Our study suggests that some patients with chronic mesial TLE exhibit linguistic deficits when specifically tested, and underlines the need to routinely investigate linguistic functions in TLE.

Adult↗
PubMed1995

Diverging asymmetries of temporo-parietal cortical areas: a reappraisal of Geschwind/Galaburda theory.

The general theory on the biological foundations of cerebral dominance formulated in 1985 by Geschwind and Galaburda entirely relies on a postulated causal relationship between anatomical asymmetry of the planum temporale and functional lateralization of the human brain, but does not take into account asymmetry of another cortical region, the parietal operculum. In 40 normal volunteers whose handedness was specified by the Edinburgh Handedness Inventory, we assessed asymmetries of these two regions on MRI sagittal scans. For both measurements, a significantly larger leftward asymmetry was found in the 24 consistent right-handers compared to the 16 non-right-handers. Moreover, the combination, for each subject, of the two indices of asymmetry, yielded four different subtypes between which handedness distribution significantly differed. We conclude that planum temporale and parietal operculum asymmetries may be divergent and that their convergence is strongly associated with right-handedness. Functional and developmental implications of these findings are discussed by reference to the Geschwind/Galaburda theory.

Adolescent↗
PubMed2003

Abnormal processing of speech during oddball target detection in schizophrenia.

Healthy subjects show increased activation in left temporal lobe regions in response to speech sounds compared to complex nonspeech sounds. Abnormal lateralization of speech-processing regions in the temporal lobes has been posited to be a cardinal feature of schizophrenia. Event-related fMRI was used to test the hypothesis that schizophrenic patients would show an abnormal pattern of hemispheric lateralization when detecting speech compared with complex nonspeech sounds in an auditory oddball target-detection task. We predicted that differential activation for speech in the vicinity of the superior temporal sulcus would be greater in schizophrenic patients than in healthy subjects in the right hemisphere, but less in patients than in healthy subjects in the left hemisphere. Fourteen patients with schizophrenia (selected from an outpatient population, 2 females, 12 males, mean age 35.1 years) and 29 healthy subjects (8 females, 21 males, mean age 29.3 years) were scanned while they performed an auditory oddball task in which the oddball stimuli were either speech sounds or complex nonspeech sounds. Compared to controls, individuals with schizophrenia showed greater differential activation between speech and nonspeech in right temporal cortex, left superior frontal cortex, and the left temporal-parietal junction. The magnitude of the difference in the left temporal parietal junction was significantly correlated with severity of disorganized thinking. This study supports the hypothesis that aberrant functional lateralization of speech processing is an underlying feature of schizophrenia and suggests the magnitude of the disturbance in speech-processing circuits may be associated with severity of disorganized thinking.

Adult↗
PubMed2003

The homing pigeon hippocampus and space: in search of adaptive specialization.

The hippocampus (HF) of birds and mammals is essential for the map-like representation of environmental landmarks used for navigation. However, species with contrasting spatial behaviors and evolutionary histories are likely to display differences, or 'adaptive specializations', in HF organization reflective of those contrasts. In the search for HF specialization in homing pigeons, we are investigating the spatial response properties of isolated HF neurons and possible right-left HF differences in the representation of space. The most notable result from the recording work is that we have yet to find neurons in the homing pigeon HF that display spatial response properties similar to HF 'place cells' of rats. Of interest is the suggestion of neurons that show higher levels of activity when pigeons are near goal locations and neurons that show higher levels of activity when pigeons are in a holding area prior to be being placed in an experimental environment. In contrast to the rat, the homing pigeon HF appears to be functionally lateralized. Results from a current lesion study demonstrate that only the left HF is sensitive to landmarks that are located within the boundaries of an experimental environment, whereas the right HF is indifferent to such landmarks but sensitive to global environmental features (e.g., geometry) of the experimental space. The preliminary electrophysiological and lateralization results offer interesting departure points for better understanding possible HF specialization in homing pigeons. However, the pigeon and rat HF reside in different forebrain environments characterized by a wulst and neocortex, respectively. Differences in the forebrain organization of pigeons and rats, and birds and mammals in general, must be considered in making sense of possible species differences in how HF participates in the representation of space.

Animals↗
PubMed1996

Production and perception of word tones (pitch accents) in patients with left and right hemisphere damage.

The present paper addresses the question of the functional lateralization of tones in tone languages. Tonal perception and production of right-hemisphere-damaged (RHD) and left-hemisphere-damaged (LHD) speakers of East Norwegian were investigated. East Norwegian is a tone language with an opposition between two tones (pitch accents). The ability to distinguish auditorily between the two accents was normal in the RHD group but reduced in the LHD group. Tonal production was near normal in the RHD group, whereas the LHD group tended to have a production deficit.

Adult↗
PubMed2001

Are human taste thresholds similar on the right and left sides of the tongue?

The human tongue is a relatively symmetrical anatomical structure and is generally assumed functionally equivalent on both sides. Experimental evaluation of this assumption is complicated by the fact that psychophysical measurements tend to vary considerably across testing sessions. To address functional laterality, we determined the detection thresholds of six right-handed and six left-handed subjects for Na saccharin, NaCl, citric acid and quinine HCl. Five pairs of interwoven, left and right unilateral thresholds were obtained for each taste stimulus in 12 subjects (n = 480 separate thresholds). In most cases mean sensitivity based on multiple measurements was found to be laterally symmetrical, however, we observed a few cases of lateral asymmetry of both general and compound-specific sensitivity. Threshold values were found to vary considerably across sessions, consistent with the test-retest variability previously reported for whole mouth thresholds. We conclude that taste threshold sensitivity is equivalent on the left and right anterior tongue for most individuals. Given the occasional exceptions to this rule, however, it is advisable to employ a counterbalanced design for any experimental or clinical testing protocol in which treatments are applied asymmetrically to the tongue.

Citric Acid↗
PubMed1995

A note on viewing functional change in later life as migration.

Empirical research on functional decline in later life is expanding our understanding of this aspect of aging. To increase the value of future research it will be necessary to develop more adequate theories of functional transitions. Toward this goal, a conceptual model that views change as mobility between states is proposed. Exploring the analogy between geographic migration and functional change suggests several migration concepts that might be borrowed by aging researchers. These concepts are useful for organizing existing findings, generating new research questions, and identifying the types of data that need to be collected.

Activities of Daily Living↗
PubMed2005

Photic inhibition of TrkB/Ras activity in the pigeon's tectum during development: impact on brain asymmetry formation.

Asymmetric photic stimulation during embryonic or post-hatch development induces a functional lateralization of the pigeon's visual system, which is accompanied by left-right differences in tectal cell sizes. The intracellular membrane-anchored GTPase Ras can be activated by a number of upstream mechanisms including binding of brain-derived neurotrophic factor to its specific TrkB receptor. Ras activity plays an important morphogenetic role in neurons and therefore might also be involved in the asymmetric differentiation of tectal cells. To investigate the role of Ras, we determined the relative levels of activated Ras and of signalling active phospho-TrkB in tecta of light- and dark-incubated pigeons and combined this with an immunohistochemical detection of Ras-GTP and TrkB receptors. While Ras activation levels did not differ between light- and dark-incubated pigeons during embryonic development, directly after hatching Ras activity was significantly decreased in the stronger stimulated left tectum of light-incubated animals. This was accompanied by lower levels of TrkB phosphorylation. Immunohistochemical staining revealed Ras-GTP-positive cell bodies within the efferent cell layer. These cells were TrkB-positive and developed enlarged soma sizes within the right tectum during the first week after hatching. This association suggests asymmetric Ras activation to be involved in the asymmetric differentiation of the efferent cells as a result of asymmetric TrkB signalling. Because asymmetric light exposure occurs only during embryonic development, the observed transient asymmetric inhibition of TrkB/Ras activity after hatching may reflect differential embryonic maturation of tectal inhibitory circuits leading to a functional superiority of the right eye in the adult organism.

Animals↗
PubMed1990

A new approach to cerebral asymmetry: RT differences in simultaneous bimanual finger movement during verbal and nonverbal tasks.

This study was aimed at testing a new approach for examination of functional laterality based on hemispheric specialization. The subjects had to perform verbal (words/nonwords) and nonverbal (similar/different patterns) discrimination. The separation of the two hemispheres during information processing was realized by requiring a simultaneous response of both index fingers. The obtained over-all reaction times (RT) were faster for verbal than for pattern tasks. Considering the RTs for solely the particular, faster response of one or the other index finger, the right index finger turned out to be faster on verbal tasks whereas the left one dominated on pattern tasks. According to the hypothesis that the faster hand indicates the more active (contralateral) hemisphere, it can be assumed that words are responded to more quickly when processed in the left hemisphere. On the other hand, patterns are responded to more quickly when the right hemisphere is active. These results suggest that each hemisphere may be capable of processing verbal and nonverbal material; the speed of information processing, however, is faster in the more adept one.

Adult↗
PubMed2006

Heritability and linkage analysis of hand, foot, and eye preference in Mexican Americans.

Functional lateralities are of interest due to their relationship with cerebral lateralisation and language development. However, genes influencing sidedness remain elusive. We measured direction and consistency of hand, foot, and eye preference in 584 Mexican-Americans from families participating in the San Antonio Family Diabetes/Gallbladder Study. Using maximum-likelihood-based variance components methods, we estimated weak (.11 <or= h2<or=.17) but significant heritability for foot preference, eye preference, several hand preferences (writing, drawing, throwing, using scissors, using spoon, striking match), and a composite hand preference trait. Self-reported handedness was significantly heritable (h2=.57), whereas hand preference for opening a box or using a toothbrush or knife was not. Many trait pairs had significant genetic correlations, and all had significant environmental correlations. Using genome-wide multipoint linkage screens using 382 highly informative autosomal STR markers, we identified suggestive linkage signals for drawing (LOD 2.10) and writing (LOD 2.00) hand preference on chromosome 12q21-23, in the region flanked by markers D12S1300 and PAH. A suggestive signal (LOD 2.46) for eye preference occurred on chromosome 22pter, near marker D22S420. No obvious candidate genes occur in these regions. Our results indicate that genes are an important component of side preferences, and suggest chromosomal regions for further investigation.

Choice Behavior↗
PubMed2003

The specialized structure of human language cortex: pyramidal cell size asymmetries within auditory and language-associated regions of the temporal lobes.

Functional lateralization of language within the cerebral cortex has long driven the search for structural asymmetries that might underlie language asymmetries. Most examinations of structural asymmetry have focused upon the gross size and shape of cortical regions in and around language areas. In the last 20 years several labs have begun to document microanatomical asymmetries in the structure of language-associated cortical regions. Such microanatomic results provide useful constraints and clues to our understanding of the biological bases of language specialization in the cortex. In a previous study we documented asymmetries in the size of a specific class of pyramidal cells in the superficial cortical layers. The present work uses a nonspecific stain for cell bodies to demonstrate the presence of an asymmetry in layer III pyramidal cell sizes within auditory, secondary auditory and language-associated regions of the temporal lobes. Specifically, the left hemisphere contains a greater number of the largest pyramidal cells, those that are thought to be the origin of long-range cortico-cortical connections. These results are discussed in the context of cortical columns and how such an asymmetry might alter cortical processing. These findings, in conjunction with other asymmetries in cortical organization that have been documented within several labs, clearly demonstrate that the columnar and connective structure of auditory and language cortex in the left hemisphere is distinct from homotopic regions in the contralateral hemisphere.

Aged↗
PubMed2005

Ex vivo analysis of T-cell function.

Our ability to analyze T-cell function in vitro has progressed in recent years to include analysis of early signaling events, such as specific protein phosphorylation, intermediate functions, such as degranulation and cytokine production, and later functions, such as proliferation. Many assays are now available to monitor these events, and comparative studies of some of these assays have been published. Major recent developments in this area include the ability to measure T-cell degranulation via cell surface exposure of CD107 and the use of polychromatic flow cytometry to examine multiple phenotypes and functions of responding T cells.

Animals↗
PubMed2001

Lateralization of olfactory cognitive functions: effects of rhinal side of stimulation.

This study investigated differences in olfactory cognitive functions, in 40 healthy young right-handed participants, with respect to side of rhinal stimulation. The targeted functions were: perceived familiarity, episodic recognition memory, free identification and repetition priming in identification. The results showed that odors presented to the right nostril were rated as more familiar than odors presented to the left nostril and also showed significant effects of repetition priming in identification. However, no differences were found between nostrils in episodic recognition memory or free identification. These latter results indicate a rather extensive inter-hemispheric interaction in higher-order cognitive functions.

Adult↗