Abnormal peripheral auditory asymmetry in schizophrenia

OBJECTIVE: Auditory processing difficulties have been reported in schizophrenia. This study explores peripheral auditory function in patients with schizophrenia in whom certain early disturbances of auditory message filtering have been found and may be associated with certain abnormalities which are particularly localised in the left temporal lobe. METHODS: Otoacoustic emissions, including click evoked and spontaneous emissions and measurements of functioning of the medial olivocochlear efferent system were obtained from 12 chronic schizophrenic patients and compared with normative data recorded from 12 normal controls. RESULTS: Otoacoustic emission amplitudes and medial olivocochlear functioning were similar between the normal controls and schizophrenic patients; the schizophrenic patients did, however, differ from the normal controls in otoacoustic emission intensity and in medial olivocochlear asymmetry. A tendency to a higher number of spontaneous peaks, and a significantly higher click evoked otoacoustic emission response amplitude were found in the right ear compared with the left ear of schizophrenic patients. For the medial olivocochlear system, whereas normal controls showed greater attenuation in the right than in the left ear, schizophrenic patients lacked such an asymmetry. CONCLUSION: In the absence of any attention task, the findings show disturbed peripheral lateralisation in schizophrenia of mechanisms involved in auditory information filtering. Such a lack of right ear advantage in medial olivocochlear functioning may thus be a peripheral reflection of central lateralisation anomalies.     

SEX AND HANDEDNESS DIFFERENCES IN HEARING DURATIONS OF THE RIGHT AND LEFT EARS IN HEALTHY YOUNG ADULTS

The aim of this work was to study the sex and handedness differences in hearing durations of the right and left ears in healthy young adults. The hearing durations were assessed using a modified Rinne test. The hearing durations of both the right and left ears were longer in males than females. In right-handers, the hearing duration of the right ear was longer than that of the left ear; in left-handers, the hearing duration of the left ear was longer than that of the right ear. These results suggest a male superiority in auditory perceptual acuity; a left-ear advantage in left-handers may result in the superiority of non-right-handers in musical tasks.     

Sex and handedness differences in hearing durations of the right and left ears in healthy young adults

The aim of this work was to study the sex and handedness differences in hearing durations of the right and left ears in healthy young adults. The hearing durations were assessed using a modified Rinne test. The hearing durations of both the right and left ears were longer in males than females. In right-handers, the hearing duration of the right ear was longer than that of the left ear; in left-handers, the hearing duration of the left ear was longer than that of the right ear. These results suggest a male superiority in auditory perceptual acuity; a left-ear advantage in left-handers may result in the superiority of non-right-handers in musical tasks.     

Verbal dichotic listening in right and left-handed adults: laterality effects of directed attention

Dichotic listening performance of consonant vowel stimuli was studied in 51 adult right- and left-handers in three attention conditions: non-directed and directed to either the right or left ear. In the non-directed condition, a significant right-ear advantage was found in both handedness groups with a stronger asymmetry in right-handers. There are at least three explanations for this ear bias. The classic or structural hypothesis suggests that to the right ear projects more strongly to the language dominant left hemisphere. The callosal relay hypothesis is based on the influence of inhibitory connections via the corpus callosum. The attentional hypothesis suggests that each hemisphere primarily directs attention to contralateral space and because the left hemisphere is dominant for language in both groups, and is aroused by speech stimuli, attention is primarily directed to the right ear. Neither hypothesis can explain why greater than 95% of right-handers have left hemisphere language dominance, but only 70-80% have a right ear bias. Our results demonstrate that in the directed attention conditions both groups increased their lateral biases when directed to either the right or left. The classic or structural hypothesis cannot account for these changes, thereby providing support for the attentional hypothesis. In addition, the right-handed subjects exhibited a greater shift of bias than did the left-handed subjects, when directing their attention leftward. This finding suggests that right-handed people are better able to shift their attention than left-handed people.     

Hand preference and transcranial magnetic stimulation asymmetry of cortical motor representation

Human handedness may be associated with asymmetry in the corticospinal motor system. Previous studies measuring the threshold for eliciting motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) have provided evidence consistent with this hypothesis. However, TMS asymmetry observed in previous studies may have reflected cortical or spinal differences. We therefore undertook this investigation to test the hypothesis that handedness is associated with asymmetry in cortical motor representations. We used TMS to map contralateral cortical motor representations of the right and left abductor pollicis brevis (APB) and flexor carpi radialis (FCR) muscles in nine normal subjects (three left-handed). Using focal stimulation with a figure-of-8 shaped magnetic coil, we found no differences in MEP threshold or MEP size between the preferred and the nonpreferred hand. However, we observed that the number of scalp stimulation sites eliciting MEPs was statistically greater for APB and FCR muscles of the preferred limb. We found significant asymmetry between right-handed and left-handed subjects, such that in right-handers, the representation of the right APB was larger than that of the left APB, but in left-handers the representation of right APB was smaller than that of the left APB. These results suggest that handedness is associated with asymmetry in cortical motor representation.     

Clinical importance of asymmetry and handedness differences in common carotid artery intima-media thickness

Earlier publications have reported that common carotid artery intima-media thickness (CCA-IMT) was lower on the right side than on the left side and that left-handed patients have a lower risk of sudden death of brain infarction. This study aimed to determine whether there is an asymmetry and the handedness related difference in CCA-IMT. Ultrasonographic examinations were performed with the use of Aplio US system. In total sample, male and female left-handers, CCA-IMT was greater on left side than on right side. In men, both right and left CCA-IMTs, but in women only right IMT, were lower in the left-handers than in the right-handers. Both right and left CCA-IMTs was positively correlated with age in men and in women. Handedness was a significant factor influencing CCA-IMT with adjustment for sex and age. It was greater on left side than on right side, especially in the left-handers. CCA-IMTs were lower in the left-handers than in the right-handers. These results suggest that hemodynamic stress and intimal damage was larger in the left carotid artery, which was larger in the right-handers compared to the left-handers.     

Intermanual coordination in relation to handedness, familial sinistrality and lateral preferences

Intermanual coordination assessed by alternating finger tapping and finger-tapping asymmetry were investigated in 105 healthy right- and 105 left-handers and related to handedness, familial sinistrality and lateral preferences (in hand-clasping, arm-folding and eyedness). Compared to right-handers, left-handers with less pronounced left-hand preferences (Subgroup B) showed higher values in intermanual coordination and lower values in finger-tapping asymmetry. Moreover, familial sinistrality and eyedness interacted with handedness effects. While in right-handers intermanual coordination was significantly higher in subjects with dominant left eye, in left-handers of the Subgroup B it was somewhat higher in those with dominant right eye. Higher values in intermanual coordination and reduced asymmetry in finger tapping may be associated with a greater bihemispheric control and better performance in fast bimanual movements.     

Determination of cortical language dominance using functional transcranial Doppler sonography in left-handers.

OBJECTIVE: Verbal analytical functions are primarily related to the left hemisphere in right-handers, but there is yet no agreement about cortical language dominance in left-handers. Also, there are some contradictory reports about sex differences in cortical language lateralization. The aim of this study is to investigate cortical language dominance in left-handers and to explore gender influence on cortical language representation. METHODS: We performed functional transcranial Doppler sonography (previous validated for determination of cerebral language lateralization) during a word generation task, measuring changes in mean cerebral blood flow velocity (BFVmean) in both middle cerebral arteries (MCA) in 150 healthy subjects (75 left-handers and 75 right-handers). In left-handers we observed significant increase BFVmean in right MCA in 58 (77.3%) subjects. Bilateral increase was observed in 11 (14.7%) subjects and increase in left MCA in 6 (8%) subjects. In right-handed group 93.3% subjects showed left cortical dominance, while 6.7% showed bilateral language representation. RESULTS: Current results showed significant (P<0.0001) right hemispheric language dominance in healthy left-handed subjects. CONCLUSIONS: Our results showed significant difference in hemispheric dominance for verbal function between righthanders and lefthanders. Also there is statistically insignificant female gender tendency for bilateral hemispheric language representation in both handedness.     

Hemispheric differentiation and dream recall: subjective estimates of sleep and dreams in different handedness groups

Previous investigations pointed to a relationship between hemispheric asymmetry and dream recall. Since handedness may reflect the extent to which cerebral organization is lateralized, it was hypothesized that differences in dream recall might exist between different handedness groups. A selected sample of 78 college students (38 right-handers, 25 left-handers, 15 mixed-handers) completed a seven-day sleep and dream diary upon final awakening, at home. Results showed that significantly more dreams are recalled by females compared to males and by right-handers compared to mixed-handers and left-handers. The latter finding is tentatively interpreted as due to a more direct access to aspects of oneiric material structured in the left hemisphere by right-handers, whose language centers are located in the same hemisphere. Unexplained findings of the only other investigation concerning handedness and sleep variables (Hicks, Pellegrini & Hawkins, 1979), which showed greater variability of sleep duration in mixed-handers, were not confirmed by the present study.     

The octave illusion in relation to handedness and familial handedness background

The octave illusion is produced by a dichotic sequence of tones that alternate in frequency between 400 and 800 Hz, such that when the right ear receives 400 Hz the left ear receives 800 Hz; and vice versa. Most listeners obtain the illusion of a single high tone in one ear alternating with a single low tone in the other ear. Further, most right-handers hear the high tone on the right and low tone on the left. The present study examined localization patterns in this illusion as a function of handedness and also of familial handedness background. The effect of handedness was highly significant: the tendency to hear the high tone on the right and the low tone on the left was lower among mixed handers and left-handers than among right-handers. The effect of familial handedness background was also highly significant: the tendency to hear the high tone on the right and the low tone on the left was lower among those with a sinistral familial background than among those with a purely dextral familial background. These findings are discussed in relation to the hypothesis that perception of the illusion serves as a reflection of the direction of cerebral dominance in most individuals.     

Ipsilateral and contralateral reactions to monaural lateralized stimuli.

Twelve subjects, six right-handers and six left-handers, participated in an experiment in which they were tested on an ipsilateral and contralateral auditory-manual reaction-time task. No difference in reaction-time was found between left and right ear presentation in the ipsilateral task, whereas for nearly all subjects, right-handers as well as left-handers, a difference between the left and right ear presentation was recorded in the contralateral task. The right-handers showed a tendency to a right ear preference, the left-handers to a left ear preference. The results are discussed in terms of a combination of S-R compatibility and the cerebral organization in man.     

Cerebral lateralization of praxis in right- and left-handedness: same pattern, different strength

We aimed to investigate the effect of hand effector and handedness on the cerebral lateralization of pantomiming learned movements. Fourteen right-handed and 14 left-handed volunteers performed unimanual and bimanual tool-use pantomimes with their dominant or nondominant hand during fMRI. A left hemispheric lateralization was observed in the right- and left-handed group regardless of which hand(s) performed the task. Asymmetry was most marked in the dorsolateral prefrontal cortex (DLPFC), premotor cortex (PMC), and superior and inferior parietal lobules (SPL and IPL). Unimanual pantomimes did not reveal any significant differences in asymmetric cerebral activation patterns between left- and right-handers. Bimanual pantomimes showed increased left premotor and posterior parietal activation in left- and right-handers. Lateralization indices (LI) of the 10% most active voxels in DLPFC, PMC, SPL, and IPL were calculated for each individual in a contrast that compared all tool versus all control conditions. Left-handers showed a significantly reduced overall LI compared with right-handers. This was mainly due to diminished asymmetry in the IPL and SPL. We conclude that the recollection and pantomiming of learned gestures recruits a similar left lateralized activation pattern in right and left-handed individuals. Handedness only influences the strength (not the side) of the lateralization, with left-handers showing a reduced degree of asymmetry that is most readily observed over the posterior parietal region. Together with similar findings in language and visual processing, these results point to a lesser hemispheric specialization in left-handers that may be considered in the cost/benefit assessment to explain the disproportionate handedness polymorphism in humans.     

The effects of hand preference and gender on finger tapping performance asymmetry by the use of an infra-red light measurement device

We used an infra-red device to study the effects of gender and handwriting preference on manual asymmetry in tapping rate and intertap variability. Our sample (n=102) consisted of approximately equal number of subjects with respect to gender (52 women and 50 men) and handedness (52 right-handers and 50 left-handers). Data on overall performance indicated that men performed more quickly and regularly than women. The index used for measuring manual asymmetry was the difference between the hands as a proportion of the total. Therefore, the asymmetry index was adjusted to remove the influence of overall performance. The analyses based on asymmetry scores indicated a significant handedness effect: right-handers showed greater manual asymmetries than left-handers for both tapping rate and intertap variability. In addition, right handers exhibited a significant greater asymmetry for intertap variability than tapping rate. Taken together, these data may reflect greater hemispheric differences in right-handers, specially for intertap variability.     

Patterns of hand preference and unintentional injuries among Indian attempted hand switchers and hand non-switchers

This study examines the patterns of hand preference and unintentional injuries of attempted hand switchers and hand non-switchers. Data were collected from 3698 participants in Kharagpur, India, on measures of hand preference, hand switching, and unintentional injuries. The direction of left- or right-handedness was on the basis of hand used for the item “writing on paper” and the degree of handedness was based on the average score of remaining items in the handedness inventory. Results reveal that, among attempted hand-switchers, learned right-handers were not right-sided in hand continuum as the natural right-handers, but left-handers were left-sided as natural left-handers. With increasing age the learned right-handers become less right-sided and natural right-handers become more right-sided. Females (males) are found to be more right-handed than males (females) among learned right-handers (natural right-handers). On the direction of handedness, the learned right-handers have more than twice the risk of unintentional injuries than the natural right- and left-handers. On degree of handedness, the use of inconsistent left and both hands among natural left-handers, the use of inconsistent right and both hands among natural right-handers, and the use of weak right hand among learned right-handers increase their vulnerability to unintentional injuries. Any deviation from the genetic make-up in hand use elevates the risk of unintentional injuries, suggesting that one should not change the biological hand.     

The H-reflex recovery curve from the wrist flexors: lateralization of motoneuronal excitability in relation to handedness in normal subjects

Spinal motor asymmetry was studied in relation to handedness. Hand preference was assessed by Oldfield's Questionnaire and Geschwind scores. hand skill was evaluated by a peg moving task. The motoneuronal excitability was assessed by the size and recovery curve of the H-reflex elicited by stimulation of the right and left median nerves. H-reflex was recorded by cup electrodes placed over the wrist flexors. The mean reflex latencies from the right and left sides were 23.4 and 23.2 ms, respectively. The mean amplitude of the maximum H reflex was significantly higher on the right side than the left side in right-handers without familial sinistrality (FS). There were no significant side differences in the amplitudes of H-reflexes of the right-handers with FS. A genetic factor was suggested to involve this left shift of spinal motor lateralization in right-handers with FS. The recovery curve studies showed that the motoneuronal excitability was higher on the right than the left in right-handers without FS. There was no excitability difference between the right and left sides of the right-handers with FS. In left-handers, the motoneuronal excitability was significantly higher on the left than the right side. Voluntary flexions of the wrist increased the H-reflex especially on the right side of the right-handers. There was no relationship between this corticospinal facilitation and baseline EMG activity. The H-reflex amplitude was found to be inversely correlated with hand skill in right-handers. It was concluded that motoneuronal excitability is associated with handedness and also depends on FS. It was suggested that small reflexes are especially suitable in fine motor control of rapid aimed-movements, as the well-established relation between the size of motor units and fine motor control.     

Morphological asymmetry in thyroid lobes, and sex and handedness differences in healthy young subjects

The aim of the present study was to investigate sex and handedness differences in the sizes of the right and left thyroid lobes. Subjects were 72 healthy university students (36 female and 36 male), 18 to 23 years of age. Hand preference was assessed using the Edinburgh Handedness Inventory. The volumes of the right and left thyroid lobes were measured by ultrasonography. The right lobe was larger than the left. The right and left lobes were larger in men than in women. There were no handedness difference in the total thyroid volume and the volume of right lobe. But, the left lobe was larger in right-handed subjects than in the left handed ones. The difference (right minus left) was statistically larger in left-handers than in right-handers. The sex-related differences may be attributed to the sex differences in body weight. It can be stated that handedness is associated with the asymmetry of thyroid lobes.     

Direction of hand preference: the connection with speech and the influence of familial handedness

Taking familial handedness into account, right- and left-handers with differing degrees of hand preference were monaurally presented with verbal stimuli (CVs) to which they responded using their right and left hands at separate times. This reaction time design was used to ascertain the relative cognitive functioning capacity of each hemisphere for verbal processing. However, the results disclosed more about the determination of direction of hand preference than about cognitive processing, per se. It was found that in both strong right-handers and strong left-handers with an incongruent hand preference (i.e., own handedness incongruent with family history of handedness) direction of hand preference is the result of suppression of the nonpreferred hand in the left hemisphere. Strong right- and strong left-handers with a congruent hand preference (i.e., hand preference congruent with family history of handedness) appear to have a more direct hand preference-left hemisphere mechanism. The findings of the present study are used to form part of a new theory of hand preference determination.     

Interaction between handedness and the attentional bias during tests of dichotic listening performance

Abstract

Perceptual advantages are typically interpreted as direct expressions of underlying hemispheric functional asymmetries. However, many other confounding factors including the asymmetric distribution of attention may also contribute to either the magnitude or direction of any of these advantages. In a series of experiments, Mondor and Bryden (1991, 1992a, 1992b) found that right-handed subjects bias their attention toward the right ear when faced with a difficult dichotic listening task. The present study was undertaken to determine whether the direction of the attentional bias is associated with handedness. The focus of auditory spatial attention was manipulated in a dichotic listening paradigm by presenting a pretrial tone cue to the ear from which the subject was required to report. The time period between the onset of the cue and the onset of the dichotic trial (Stimulus Onset Asynchrony - SOA) was varied in order to control the time available to orient attention to the cued ear. Whereas performance for the right ear improved substantially with SOA, that for the left ear improved only marginally. In addition, because of this differential effect of the cue on right ear and left ear performance, the magnitude of the right ear advantage was inflated at 450 ms SOA from that apparent at 150 ms and 750 ms SOA. These findings are interpreted as evidence that, in contrast to right-handers, left-handers bias their attention toward the left ear. This relation between handedness and the direction of the attentional bias is shown to have important implications for the interpretation of perceptual asymmetries.     

Does left-handedness affect the pattern of cerebral blood flow during cognitive activity?

In most people the left hemisphere of the brain is dominant for language functions. Because of an increased incidence of atypical language lateralisation in the right hemisphere of left-handed neurological patients, more systematic studies on handedness and cerebral asymmetry of language have been undertaken. The present study is aimed at clarification of the relationship between handedness and language dominance in healthy subjects. Lateralisation was measured directly using functional transcranial Doppler sonography in left-handed subjects. Twenty-six individuals participated in the study. Three kinds of tasks were used, differing in the material involved and in appropriate strategies to be employed by the subjects. Two important parameters of the MCA blood flow were analysed: mean relative increase in the blood flow velocity (MDV) and specific patterns of cognitive task performance (i.e. performance profiles). Our results indicate that the incidence of the right hemisphere dominance for language depends on the degree of handedness, since only in the group of consistent left-handers language was right lateralised. In other left-handers both cerebral hemispheres were functionally equivalent. The measurement of MCA blood flow velocity changes using transcranial Doppler ultrasonography seems to be a simple and non-invasive method of assessing the functioning of the two hemispheres of human brain.     

Eye-dominance, writing hand, and throwing hand

Handedness and eye-dominance are undoubtedly associated statistically, although a previous meta-analysis has found that the precise relationship is difficult to explain, with about 35% of right-handers and 57% of left-handers being left eye dominant. Of particular difficulty to genetic or other models is that the proportions are distributed asymmetrically around 50%. The present study asked whether this complicated pattern of association occurred because, following Peters, it is necessary to divide right-and left-handers into consistent handers (who write and throw with the same hand) and inconsistent handers (who write and throw with opposite hands). In an analysis of 10,635 subjects from questionnaire studies, 28.8% of left-handers and 1.6% of right-handers by writing were inconsistent for throwing. Our results also showed that writing hand and throwing hand both relate independently to eyedness, that throwing hand is somewhat more strongly associated with eyedness, and that the awkward asymmetry around 50% is now removed, 24.2% of consistent right-handers being left eye dominant compared with 72.3% of consistent left-handers, and 55.4% of inconsistent right-handers compared with 47.0% of inconsistent left-handers. We conclude that eyedness is phenotypically secondary to writing and throwing handedness. In our discussion we note that eyedness runs in families, we present new data suggesting that writing hand and throwing hand are co-inherited, and we argue that further data are now required to model properly the associations of writing hand, throwing hand, and eyedness, as well as probably also footedness and language dominance.