The differential hemispheric processing of emotion: a comparative analysis in strongly-lateralized sinistrals and dextrals

The neural processing of emotion and the differential processing of affect and cognition are thus far poorly understood. Complex results across studies suggest involvement of the left hemisphere, the right hemisphere, or both. Since handedness is related to cerebral dominance, the present study undertook a comparative analysis of neural processing in strongly lateralized left- and right-handed populations. Parietal EEG and bilateral electrodermal activity were recorded while carefully selected subjects were exposed to emotional stimuli under cognitive, affective, and neutral conditions. Results showed greater lateral differentiation and differentially greater left-hemisphere activation in dextrals but greater overall activation in sinistrals. These findings are consistent with the common observation that cerebral organization is more diffuse in left-handed populations. It seems clear that the comparative study of sinistrals and dextrals can help us to better understand how emotion is processed in the brain.     

Inferring patterns of hemispheric specialization for individual subjects from laterality data: a two-task criterion

Sixty-three subjects (31 dextrals and 32 sinistrals) were given two visual half-field laterality tasks (recognition of words and faces). Subjects were classified as having typical or atypical hemispheric specialization on the basis of the relative magnitude of their asymmetry scores on the two laterality tasks. Those subjects whose word asymmetry scores were larger than their face asymmetry scores (asymmetry scores computed as RVF-LVF for both tasks) were classified into Group Typical and those subjects whose word asymmetry scores were smaller than their face asymmetry scores were classified into Group Atypical. For both dextrals and sinistrals, the proportion of subjects classified into Groups Typical and Atypical was consistent with estimates of the incidence of typical and atypical hemispheric asymmetry patterns based on sodium amytal testing. These results support the hypothesis that the relative magnitude of asymmetry scores on left and right hemisphere specialized tasks index individual differences in patterns of hemispheric specialization.     

Right hemisphere language and cognitive deficit in sinistrals?

Ninety-six student subjects were studied in a strictly balanced design contrasting sex, handedness and familial dextrality/sinistrality. WAIS scores were obtained, and two tachistoscopic tasks (RT responses) administered, involving laterally presented verbal stimuli (word/non-word decisions with high frequency, concrete, imageable and low frequency, abstract non-imageable words), and a face discrimination task designed to generate right hemisphere processing. There was a striking WAIS Performance deficit among sinistrals, particularly familial; familial dextrals proved overall fastest; directional asymmetries were weakest for the sinistrals, particularly the non-familial; non-familial dextrals were no less lateralized than familial dextrals; parental handedness was a better predictor of performance than sibling handedness; and no differential pattern of field asymmetries appeared for the two classes of word stimuli. Some theoretical implications of these findings are discussed.     

Influence of sex and handedness on hemispheric functioning

Forty normal adult volunteers comprising an equal number of right- and left-handed males and females solved simple multiplication problems presented visually to one cerebral hemisphere while various competing stimuli were simultaneously presented to the other hemisphere. The contribution of sex of subject, handedness, hemisphere of presentation and the nature of the competing stimulus in relation to task performance was examined. Each of these variables was significantly associated with correct responses and errors, with few statistically significant interactions. Females and dextrals made more correct responses than males or sinistrals. Type of error depended upon which hemisphere received the problem, with the right hemisphere yielding more errors of commission and the left more errors of omission. Simultaneously presented identical or different arithmetic problems resulted in the most errors compared to the other competing stimuli.     

Pseudoneglect and reversed pseudoneglect among left-handers and right-handers.

Two experiments were carried out to examine specific hand contribution to pseudoneglect and reversed pseudoneglect phenomena in dextrals and sinistrals when bisection tasks were conducted exclusively in the midline spatial condition. Both dextrals and sinistrals showed the same overall pattern deviation: in the tactile scanning task, both right and left hands deviated to the left of the midpoint and in the kinesthetic scanning tasks, the right hand deviated to the left and the left hand to the right of the midpoint. However, when these deviations were tested against zero (i.e. the objective midpoint) clear differences appeared related to hand, task and handedness. These results were discussed with respect to "enhancement theory".     

Contrastive patterns of intrahemispheric interference to verbal and spatial concurrent tasks in right-handed, left-handed and stuttering populations

A time-sharing paradigm was used to assess hemispheric lateralization for both language and visuo-spatial processing in right-handed, left-handed and stuttering populations. A right hand only tapping disruption, indicative of left hemisphere interference, accompanied concurrent verbal tasks only in the dextral group. Left-handers and stutterers revealed symmetrical patterns of hemispheric language interference. Significantly different absolute levels of language interference were found for the three groups, with dextrals having the least, followed by sinistrals, and being greatest for stutterers. These magnitude differences were explained in relation to a hypothesis of strength of language representation within a given hemisphere. Visuo-spatial right hemisphere interference was shown for left-handers with a concurrent object chimera task.     

Absence of aphasia in a dextral with a left hemisphere lesion: A case report

Abstract

Right-handed patients with aphasia due to a right hemisphere lesion, or sinistral aphasics with a left hemisphere lesion, are referred to as crossed aphasics (Bramwell 1899). Since left damaged sinistrals with aphasia are the rule (Brown and Hecaen 1976), it is the dextral with a right hemisphere lesion that has received most of the attention. When we reviewed the topic of crossed aphasia in dextrals some years ago in relation to a case report (Brown and Wilson 1973). only seven other cases could be found that satisfied the minimal criteria of a clearcut aphasia dextrality and a negative family history ofleft handedness, but since this paper there have been many additional observations (e.g. Assal, Perentes and Dervaz 1981, Donoso, Santander and Pavez 1984, Pillon, Desi and Lhermitte 1979, Wechsler 1976; see Joanette, Puel, Nespoulos, Rascol and Lecours [1982] and Castro-Caldas and Confraria [1984] for review).     

Evidence of a possible isolation of left hemisphere visual and motor areas in sinistrals employing an inverted handwriting posture

Levy's hypothesis of ipsilateral motor control of the lateral distal musculature in left handers employing an inverted handwriting posture was tested in a true simple reaction time paradigm. Left-handers employing a non-inverted handwriting posture (NHP) showed performances consistent with normal (contralateral) motor control organization. Inverted handwriting posture (IHP) sinistrals showed performances that were not consistent with Levy's hypothesis nor with the simple hypothesis of normal (contralateral) control. The results for IHP sinistrals were compatible with a model of stimulus-response mediation which posits contralateral motor control and an intrahemispheric “disconnection” of left hemisphere visual areas from left hemisphere manual motor areas. The hypothesis that IHP sinistrals must utilize interhemispheric pathways for motor responses to stimuli channeled to, or formulated in, the left hemisphere was discussed in relation to the hypothesis of topographic inversion consequent to transcallosal relay. The proposed model suggests that hand inversion in writing is an accommodation to the consequences of interhemispheric relay and not to ipsilateral motor control.     

A word-naming deficit in nonfamilial sinistrals? Laterality effects of vocal responses to tachistoscopically presented letter strings

Dextral, familial and nonfamilial sinistral Undergraduates, balanced by sex and all strongly dextral or sinistral, called out laterally presented words and nonwords. Vocal latencies, accuracy and field differences consistently discriminated between the three groups, dextrals performing best and nonfamilial sinistrals the worst. Subjects with a left field superiority had significantly smaller field differences and more errors than the right-superior, and a tendency to a higher birth stress index, which also characterized nonfamilial sinistrals. However sinistrals writing with an inverted hand position did not show greater field superiorities. Familial sinistrals appear closer to dextrals than nonfamilials, and either type of sinistrality, but particularly when non-familial and/or associated with reversed field asymmetries, seems detrimental to reading tachistoscopically-flashed letter strings and words in a student population.     

Crossing the midline by four to eight year old children

In Experiment 1 children (Kinder, 4-5 yr; Prep, 5-6 yr; Grade 1, 6-7 yr; Grade 2, 7-8 yr) bisected horizontal lines placed to the left, right or across the midline. The youngest groups displayed symmetrical neglect, erring to the left with the left hand and to the right with the right, the adult pattern of leftwards error not appearing until about Grade 2. However, while Prep, Grade 1 and Grade 2 sinistrals showed bigger between-hand differences than dextrals, this was not, unlike an earlier study, true of the youngest Kinder group, and symmetrical neglect did not appear to be peculiar to young sinistrals. A timed peg-moving task in Experiment II showed that performance did not slow when crossing the midline; nor did young sinistrals perform better with centrifugal abductive movement. These and other findings were incompatible with the idea of callosal immaturity in young sinistrals.     

Aesthetic preference in dextrals and sinistrals

In one study, dextrals preferred pictures with a rightward-balance and sinistrals preferred leftward-balance (LB) pictures. In a second study, sinistrals again preferred LB pictures and were different from dextrals who showed no preference. Aesthetic preferences for asymmetric pictures seem determined by the direction of cerebral asymmetry.     

Deriving estimates of contralateral footedness from prevalence rates in samples of Brazilian and non-Brazilian right- and left-handers

Although footedness is closely associated with handedness, accurate prevalence rates of contralateral footedness in right- and left-handed populations were previously unavailable to researchers studying the relationship between phenotypic and hemispheric asymmetries. We collected preference data from 2081 Brazilian children and adolescents, and relate the prevalence of crossed hand/foot preferences to values reported elsewhere in the literature. In our samples, about 4% of the dextrals and 33% of the sinistrals exhibited a contralateral kicking preference. This is in close agreement with the weighted means from our analysis of 19 papers in the literature, which yields 4.0% left-footed kicking in dextrals and 33.5% right-footed kicking in sinistrals. These values are in marked contrast to the 50% figure for right-footed kicking in sinistrals as given by MacNeilage and colleagues (1988, 1991). Among Brazilians with mixed handedness, there was a substantial increase in incongruent footedness. Male consistent right- and left-handers showed a higher prevalence of cross-footed preferences in their kicking preference than females. The sex difference in dextrals was attributed to a training effect in soccer-related activities, and to a sampling bias in sinistrals.     

Crossed aphasia in right-handed patients. I. Review of the literature

More than 70 cases of crossed dextral aphasia have been reported in the literature since the end of the XIXth century. If a genetic, environmental or even pathological factor--or lack of information about it--could be suspected to be responsible of a majority of these cases, 10 of them in which all these factors were eliminated still remain. A summary of the neurological, neuropsychological and neurolinguistic features of these 10 cases shows, among other things: 1. that nearly all of them present a (left) motor deficit associated with a quite large and deep right-hemispheric lesion; 2. that most of them also report the presence of one or the other of the neuropsychological signs usually seen in right hemisphere lesions in dextrals; 3. that if reduction and agrammatism are frequent aphasic signs, fluent jargon is also reported, more so in written than in oral expression. Some of the hypotheses put forward to explain crossed aphasia in dextrals are discussed in the light of these facts. It appears that none of these hypotheses can satisfactorily account for the occurrence of a right hemisphere aphasia in some dextrals.     

Hand and hemispace effects in tactual tasks in children

In Experiment I, 3-and 5-yr-old dextrals matched textures better by either hand when it operated in left hemispace. Girls and 3-yr olds were the more disadvantaged by non-alignment of hand and hemispace. In Experiment II, 8-yr-olds reproduced finger sequences; dextrals demonstrated a right-hand and sinistrals a right-hemispace superiority. In Experiment III, both a left-hand and a left-hemispace superiority appeared when 5-yr-old dextrals reproduced a static configuration of finger spacing. Asymmetries were generally stronger for the side of presentation than for the side of response. Our findings are consistent with the operation of two semi-independent systems, one involving hand-hemisphere connections, and the other mapping of extracorporeal space by the hemispheres.     

Deriving estimates of contralateral footedness from prevalence rates in samples of Brazilian and non-Brazilian right- and left-handers

Although footedness is closely associated with handedness, accurate prevalence rates of contralateral footedness in right- and left-handed populations were previously unavailable to researchers studying the relationship between phenotypic and hemispheric asymmetries. We collected preference data from 2081 Brazilian children and adolescents, and relate the prevalence of crossed hand/foot preferences to values reported elsewhere in the literature. In our samples, about 4% of the dextrals and 33% of the sinistrals exhibited a contralateral kicking preference. This is in close agreement with the weighted means from our analysis of 19 papers in the literature, which yields 4.0% left-footed kicking in dextrals and 33.5% right-footed kicking in sinistrals. These values are in marked contrast to the 50% figure for right-footed kicking in sinistrals as given by MacNeilage and colleagues (1988, 1991). Among Brazilians with mixed handedness, there was a substantial increase in incongruent footedness. Male consistent right- and left-handers showed a higher prevalence of cross-footed preferences in their kicking preference than females. The sex difference in dextrals was attributed to a training effect in soccer-related activities, and to a sampling bias in sinistrals.     

Interhemispheric transfer in children with early-treated phenylketonuria

Abstract

Phenylketonuria (PKU) is a genetic disorder of amino acid metabolism that is associated with brain catecholamine depletion and deficient myelination. Although neuropsychological deficits have been documented in children with early-treated PKU (ETPKU), no study to date has examined possible effects of impaired myelination in this population. In the present study, interhemispheric transfer time was assessed for 14 children with ETPKU, 22 children with attention deficit-hyperactivity disorder, and 48 normal children, using a manual reaction time paradigm previously validated with callosal agenesis patients (Milner, 1982). Children with ETPKU demonstrated slowed interhemispheric transfer from the left to the right hemisphere as compared with the two other groups. The magnitude of slowing was correlated with age and phenylalanine levels at birth. Results support the hypothesis that abnormal myelination disrupts the development of interhemispheric connections in ETPKU, and suggest that left hemisphere projections may be particularly susceptible to such disruption.     

A dichotic listening study of differences in cerebral organization in dextral and sinistral subjects

The purpose of the present study was to compare immediate recall of paired dichotic presentation of CV-syllables in a dextral and a sinistral group when considering both gender, familial sinistrality, and hand-posture during writing. Forty subjects (20 dextrals and 20 sinistrals) were given 306 presentations of the six Swedish stop-consonants paired with the vowels a, i, and u in a dichotic-listening test. The results showed significant differences between the two groups with fewer consonant-errors observed for the right ear input in the dextral group, and fewer consonant-errors in the left ear input in the sinistral group. Thus, a REA was demonstrated for the dextral group, and a LEA was demonstrated for the sinistral group. The results were most clear-cut for the consonants whereas vowels yielded insignificant differences. It is concluded that the present design allows for the separation of left- and right-hemisphere language dominance for right- and left-handed subjects.     

Increasing the power of dichotic methods: The fused rhymed words test

A dichotic test made up of monosyllabic rhymed CVC words was modified to minimize stimulus dominance and errors and then administered to 194 dextrals and 175 sinistrals in four different laboratories. The proportion of subjects with left ear advantages in both the right and left-handed groups closely approximated that expected from neurologic data. This dichotic test appears to reflect hemispheric specialization for language function more accurately than previously available tests. Further direct validation studies are needed, however, comparing direction of ear asymmetry and other indices of hemispheric specialization for language on a subject by subject basis.     

Reliability of the sodium amobarbital test for memory

Two studies were conducted on epileptic patients to examine the reliability of Milner's protocol for testing memory after the unilateral injection of sodium amobarbital into the carotid artery. The first study examined alternate-form reliability in 10 patients who underwent 18 repeat injections of the same hemisphere. Major changes in memory performance from pass to fail or vice versa occurred in 8 of 18 repeat injections. Seven of the eight changes were associated with identifiable variation in external factors (e.g., technically unsatisfactory first injections or reported deterioration in functioning over time). Of the eight injections that were technically satisfactory but were repeated to re-examine the initial memory score, seven outcomes remained stable across both injections, despite variability between test-retest conditions. In the second study, data from 70 patients given bilateral injections were analyzed, and no evidence for a practice effect was found when comparing memory scores from the first to the second injection. Whether the left or right side was injected first did not affect memory scores, nor did other variables such as sex, hand preference, or hemisphere injected. As expected, memory functions were more impaired for the injection contralateral than ipsilateral to the major temporal lobe seizure focus. We concluded that reliable results can be obtained from a sodium amobarbital memory protocol, adapted from Milner, which employs a pass/fail criterion based on chance performance.     

Age and hemispheric asymmetry in nonverbal tactual memory

The left and the right hand recognition of 120 age-differentiated volunteers (20 to 84 yr) were tested separately in a recurrent tactual recognition task using four non-meaningful wire shapes as targets among a 24-item distractor series. Signal detection measures of tactual memory were found to be progressively lower with age. Young persons of age range 20–29 and 30–39 yr showed a right hemisphere superiority which was considerably reduced in old persons (60–69, and over 70). The results suggested that loss in asymmetry can be ascribed to an age decrement in the ability of the right hemisphere to process tactual memory to which the left hemisphere has access.