Asymmetries for hemiface size and mobility

Lateral dominance and asymmetries in hemiface size and mobility were examined in 42 right- and left-handed males and females. In photographs, right hemifaces were found to be larger than left hemifaces. In videotapes of subjects making unilateral facial movements, a significant majority were judged to have greater left-sided facial mobility. Hemiface size and mobility were independent of sex and handedness, and unrelated to each other.     

AChE-rich magnopyramidal neurons have a left-right size asymmetry in Broca's area

Acetylcholinesterase-rich neurons (AChERN) are a particular group of pyramidal neurons, displaying a specific laminar and ontogenetic pattern in the cerebral cortex of human and nonhuman primates. Using histochemistry and morphometrical methods, we have found a layer 3 magnopyramidal AChERN left-right size asymmetry restricted to Brodmann's area 45, a component of Broca's language area. This structural feature could be related to functional lateralization associated to syntactic processing and phonological working memory, and is consistent with a non-cholinergic role of AChE possibly linked to neuroplastic processes in the human neocortex.     

An investigation of hemispheric asymmetry in size and semantic discriminations and related visual ERPs

The present study examined possible hemispheric differences in discriminations of different sizes of geometric shapes (rectangles) and different meanings of words, and determined whether left and right hemisphere derived visual event related potentials (ERPs) were related to performance. Eighteen right-handed subjects (10 male and 8 female) participated in two separate sessions conducted on different days. The visual ERPs were recorded from over left parietal (P3) and right parietal (P4) scalp locations. Subjects were required to make discriminations of three words (PARE, PAIR, PEAR) and three sizes of rectangles (small, medium, large). Each word and rectangle was singly presented for 40 msec at 1 degree 24 minutes of arc to the left and right of central fixation (LVF and RVF respectively). The major findings were as follows: 1) there were no performance and ERP differences between hemispheres in the verbal task; 2) the left hemisphere excelled in the spatial task; however, ERPs derived from the two hemispheres were similar; 3) subjects experienced greater difficulty in their discriminations of geometric size, as compared to words, regardless of field of presentation. Discrimination of size seemed to have influenced P3 (P300) latency, i.e., it was longer (both hemispheres) when subjects made size discriminations as compared to words. It was proposed that the more difficult discriminations involved in size discrimination required a greater time for stimulus evaluation and that this was reflected in the delayed P3 response.     

Development of bilateral asymmetry in sensory innervation to lobster claws

Sensory innervation to the paired claws of the lobster. Homarus americanus, was examined during their differentiation from a bilaterally symmetric state to an asymmetric state of a slender cutter and a stout crusher claw. This was done by estimating the total number and size distribution of axons in the second nerve root which provides most (approximately 90%) of the innervation to the claws and has few, bilaterally distributed motor axons. The paired claws which are undifferentiated and resemble each other in the 1st larval stage correspondingly have nerve roots that are bilaterally symmetric. In early juvenile (4th and 5th) stages when claw type is determined, as well as in subsequent (6th, 7th, 8th, 16th) juvenile stages when the claws gradually differentiate into cutter and crusher types, the paired homologous roots are also similar. It is only in adults that asymmetry in sensory innervation is seen with more axons in the crusher root than in its cutter counterpart. The difference in number of axons between the dimorphic claws is related to differences in surface area between the claws. Thus, bilateral asymmetry in sensory innervation is acquired by the continual but differential addition of axons to the paired claws.     

Reduced size and abnormal asymmetry of parietal cortex in women with borderline personality disorder.

BACKGROUND: Evidence is accumulating that suggests borderline personality disorder (BPD) and posttraumatic stress disorder (PTSD) are related to small hippocampal size. Psychotic symptoms are frequent in both disorders. Psychotic spectrum disorders are known to be related to abnormalities of temporoparietal cortices. METHODS: Using structural magnetic resonance imaging (3D-MRI), parietal cortex and hippocampal volumes were assessed in 30 young women with BPD who had been exposed to severe childhood sexual and physical abuse and in 25 healthy control subjects. RESULTS: Compared with control subjects, BPD subjects had significantly smaller right parietal cortex (-11%) and hippocampal (-17%) volumes. The parietal cortex of borderline subjects showed a significantly stronger leftward asymmetry when compared with control subjects. Stronger psychotic symptoms and schizoid personality traits in borderline subjects were significantly related to reduced leftward asymmetry. Stronger trauma-related clinical symptoms and neuropsychologic deficits were significantly related to smaller hippocampal size. CONCLUSIONS: Our results are consistent with previous findings of small hippocampal size in BPD and PTSD. Reduced right parietal cortex size in individuals with BPD may reflect a neurodevelopmental deficit of the right hemisphere.     

Magnetic resonance imaging - a method of studying the size and asymmetry of the planum temporale

The planum temporale is a triangular region on the upper surface of the temporal lobe. This area of the brain is important for language processing and shows a left-right asymmetry of size in most brains. Particular interest has been focused on the size and asymmetry of the planum temporale in brains of individuals with developmental dyslexia. Magnetic resonance imaging (MRI) is a method that produces excellent morphological details of organic structures. We have developed an MRI method of studying the size and asymmetry of the planum temporale in human brains. Because of considerable variation of anatomical landmarks in this cortical region of the brain, an evaluation of asymmetry is not possible in all brains. Furthermore, our experience with this method indicates that any indirect imaging technique of studying asymmetry of the planum temporale must be evaluated with caution. With this in mind, however, MRI may give valuable anatomical information about the planum temporale in individuals with anomalous language function.     

Development of left-right asymmetry in the habenular nuclei of Rana temporaria

An investigation of the habenular nuclei in tadpoles, young frogs, and fully matured Rana temporaria, revealed several consistent left-right asymmetries. In tadpoles and young frogs, the left nucleus is partially divided by a vertical septum; lacks cells adjoining the third ventricle along part of its length; and contains fewer free cell bodies in its lumen than the nucleus on the right. In addition, the beginnings of a second nucleus on the left can be seen, lateral to the much larger main left nucleus. The fully grown adult has two distinct left habenular nuclei and only one on the right.     

The cheek of a cheater: Effects of posing the left and right hemiface on the perception of trustworthiness

Our cognitive mechanisms are designed to detect cheaters in social exchanges. However, cheater detection can be thwarted by a posed smile, which cheaters display with greater emotional intensity than cooperators. The present study investigated the role of hemifacial asymmetries in the perception of trustworthiness using face photographs with left and right cheek poses. Participants (N?=?170) observed face photographs of cheaters and cooperators in an economic game. In the photographs, models expressed happiness or anger and turned slightly to the left or right to show their left or right cheeks to the camera. When the models expressed anger on their faces, cheaters showing the right cheek were rated as less trustworthy than cooperators (irrespective of cheeks shown) and cheaters showing the left cheek. When the models expressed happiness, trustworthiness ratings increased and did not differ between cheaters and cooperators, and no substantial asymmetries were observed. These patterns were replicated even when the face photographs were mirror-reversed. These results suggest that a cheater’s fake smile conceals an uncooperative attitude that is displayed in the right hemiface, ultimately disguising cheater detection.     

The role of structural facial asymmetry in asymmetry of peak facial expressions

Asymmetric facial expression is generally attributed to asymmetry in movement, but structural asymmetry in the face may also affect asymmetry of expression. Asymmetry in posed expressions was measured using image-based approaches in digitised sequences of facial expression in 55 individuals, N=16 men, N=39 women. Structural asymmetry (at neutral expression) was higher in men than women and accounted for .54, .62, and .66 of the variance in asymmetry at peak expression for joy, anger, and disgust expressions, respectively. Movement asymmetry (measured by change in pixel values over time) was found, but was unrelated to peak asymmetry in joy or anger expressions over the whole face and in facial subregions relevant to the expression. Movement asymmetry was negatively related to peak asymmetry in disgust expressions. Sidedness of movement asymmetry (defined as the ratio of summed movement on the left to movement on the right) was consistent across emotions within individuals. Sidedness was found only for joy expressions, which had significantly more movement on the left. The significant role of structural asymmetry in asymmetry of emotion expression and the exploration of facial expression asymmetry have important implications for evolutionary interpretations of facial signalling and facial expressions in general.     

The role of structural facial asymmetry in asymmetry of peak facial expressions

Asymmetric facial expression is generally attributed to asymmetry in movement, but structural asymmetry in the face may also affect asymmetry of expression. Asymmetry in posed expressions was measured using image-based approaches in digitised sequences of facial expression in 55 individuals, N=16 men, N=39 women. Structural asymmetry (at neutral expression) was higher in men than women and accounted for .54, .62, and .66 of the variance in asymmetry at peak expression for joy, anger, and disgust expressions, respectively. Movement asymmetry (measured by change in pixel values over time) was found, but was unrelated to peak asymmetry in joy or anger expressions over the whole face and in facial subregions relevant to the expression. Movement asymmetry was negatively related to peak asymmetry in disgust expressions. Sidedness of movement asymmetry (defined as the ratio of summed movement on the left to movement on the right) was consistent across emotions within individuals. Sidedness was found only for joy expressions, which had significantly more movement on the left. The significant role of structural asymmetry in asymmetry of emotion expression and the exploration of facial expression asymmetry have important implications for evolutionary interpretations of facial signalling and facial expressions in general.     

Human cerebral asymmetry

On gross examination the two cerebral hemispheres in man appear to be symmetrical. Under more detailed examination, using the various interdisciplinary tools available to the neuroscientist, left-right asymmetries are very apparent. In this article, the functional differences between the two hemispheres are discussed with particular reference to the processing of visual or auditory information coming into the brain, and to the control of language and speech going out.     

Cerebellar asymmetry,cortical asymmetry and handedness: Two independent networks

ABSTRACT

In 46 right-handers and 46 left-handers, we used functional magnetic resonance imaging to record activity in the frontal lobes while they generated words, the temporal lobe while they made synonym judgments, and the parietal lobe while they watched videos of manual actions. In each case we also recorded activity in the cerebellum. Laterality indices showed a significant left-hemispheric bias in each cortical lobe and a right-hemispheric bias in the cerebellum for the 2 language tasks, but not during action observation. Cerebellar asymmetry also correlated negatively with frontal and temporal asymmetry, reflecting contralateral connections, but not with parietal asymmetry. A factor analysis of the inter-correlations among laterality indices revealed 2 factors, implying independent lateralized networks, with cerebellar asymmetry strongly linked to a language network in frontal and temporal cortices, and handedness strongly linked to an action-observation network in the parietal lobe.     

Dermatoglyphic asymmetry is related to perceptual asymmetry and to interhemispheric transmission

The numbers of ridges on the fingertips is asymmetrical between hands and is also sexually dimorphic. Most people have more ridges on the right hand (rightward dermatoglyphic asymmetry; R >) and men typically have more ridges than women. The direction of dermatoglyphic asymmetry has been shown to be related to patterns of cognitive abilities in men and women and to perceptual asymmetry in homosexual men. W e assessed presumptively heterosexual, right-handed men and women who had either R > (n = 35) or L > (n = 30) ridge count, on: (1) dichotic listening to words; (2) two tachistoscopic tasks sampling visual field asymmetries (dot location and letter identification); and (3) a tachistoscopic task designed to examine interhemispheric transmission. L > subjects had a smaller right-ear advantage than R > subjects, but this was accounted for by an increased incidence of an atypical left-ear advantage in the L > group. Visual field asymmetries were also smaller in the L > group but the asymmetry measures did not reach significance, with the exception of an increased incidence of an atypical field advantage (left) for letter recognition only. On the interhemispheric transfer task, L > subjects performed relatively faster on tasks requiring interhemispheric comparisons than did R > subjects. These findings confirm an association between the direction of dermatoglyphic asymmetry and aspects of brain organisation.     

Hemispheric asymmetry and aging: right hemisphere decline or asymmetry reduction

We review evidence for two models of hemispheric asymmetry and aging: the right hemi-aging model, which proposes that the right hemisphere shows greater age-related decline than the left hemisphere, and the hemispheric asymmetry reduction in old adults (HAROLD) model, which proposes that frontal activity during cognitive performance tends to be less lateralized in older than in younger adults. The right hemi-aging model is supported by behavioral studies in the domains of cognitive, affective, and sensorimotor processing, but the evidence has been mixed. In contrast, available evidence is generally consistent with the HAROLD model, which is supported primarily by functional neuroimaging evidence in the domains of episodic memory encoding and retrieval, semantic memory retrieval, working memory, perception, and inhibitory control. Age-related asymmetry reductions may reflect functional compensation or dedifferentiation, and the evidence, although scarce, tends to support the compensation hypothesis. The right hemi-aging and the HAROLD models are not incompatible. For example, the latter may apply to prefrontal regions and the former to other brain regions.     

Probability sampling of manual asymmetry

Random sampled survey data on handedness are presented. One thousand-two-hundred-ninety-nine urban adult subjects, screened for history of significant brain damage were asked specific questions about their hand use preferences, and about use of the other hand, including any such preference earlier in their life. On the basis of these reports, the subjects were classified as consistently dextral, consistently sinistral or as having ambilateral tendencies. Case weighting and census data are employed to generate parameter estimates of the sex, race, and total population distributions of handedness, using as universe the U.S. 1970 adult population.     

Hemispheric asymmetry in amusia

The search of hemispheric dominance for music has been for long the main aim of the study of amusias. Musical abilities were first localized in the left hemisphere, then in the right one. In the light of the available data, these two diverging conceptions do not appear paradoxical anymore. Indeed, brain injury on either side can provoke musical deficits. However, the nature of the deficit seems to depend on the particular hemisphere damaged. Right-sided lesions appear to disturb the melodic aspects of musical sequences while left-sided lesions seem to deteriorate the rhythmic aspects. Although the clinical literature involves insightful suggestions on how the musical abilities are organized, especially with respect to linguistic functions, these indications are not sufficient to provide a clear picture of the nature of the functional differences for music between hemispheres. Research is not systematic. Commentaries and suggestions are proposed to guide future investigations.     

Development of neural basis for chinese orthographic neighborhood size effect

The brain activity of orthographic neighborhood size (N size) effect in Chinese character naming has been studied in adults, meanwhile behavioral studies have revealed a developmental trend of Chinese N‐size effect in developing readers. However, it is unclear whether and how the neural mechanism of N‐size effect changes in Chinese children along with development. Here we address this issue using functional magnetic resonance imaging. Forty‐four students from the 3^rd, 5^th, and 7^th grades were scanned during silent naming of Chinese characters. After scanning, all participants took part in an overt naming test outside the scanner, and results of the naming task showed that the 3^rd graders named characters from large neighborhoods faster than those from small neighborhoods, revealing a facilitatory N‐size effect; the 5^th graders showed null N‐size effect while the 7^th graders showed an inhibitory N‐size effect. Neuroimaging results revealed that only the 3^rd graders exhibited a significant N‐size effect in the left middle occipital activity, with greater activation for large N‐size characters. Results of 5^th and 7^th graders showed significant N‐size effects in the left middle frontal gyrus, in which 5^th graders induced greater activation in large N‐size condition than in small N‐size condition, while 7^th graders exhibited an opposite effect which was similar to the adult pattern reported in a previous study. The current findings suggested the transition from broadly tuned to finely tuned orthographic representation with reading development, and the inhibition from neighbors' phonology for higher graders. Hum Brain Mapp 37:632–647, 2016. © 2015 Wiley Periodicals, Inc.