A simple dual-task study of laterality, sex-differences and handedness

The Neuromodulatory Effects of Sex Hormones on Functional Cerebral Asymmetries and Cognitive Control

Abstract. Nearly 20 years ago, Hausmann and Güntürkün (2000a, 2000b) published a review article in the Journal of Neuropsychology/Zeitschrift für Neuropsychologie on the influences of sex hormones on functional cerebral asymmetries (FCAs). They further presented a neuroendocrinological model (Hausmann & Güntürkün, 2000c) that could potentially explain how sex hormones modulate FCAs. Their model proposed that high levels of progesterone reduce the synaptic efficiency of cortico-cortical transmission, leading to a reduction of FCAs. However, empirical data testing their hypothesis directly were missing. Using various approaches, we have now gathered behavioral, electrophysiological, and neuroimaging data that partly support the original idea, while also pointing toward estradiol-modulating FCAs. The current review provides an update on this fascinating topic and briefly explores clinical applications.

Comparison of the Halstead-Reitan and Infrared Light Beam Finger Tappers

Computer mediated motor tests can provide highly reliable means for evaluating gross and subtle aspects of psychomotor speed and rhythmicity. A computer mediated test of finger and foot tapping, making use of infrared light beam technology, was recently developed, but little is known regarding its psychometric properties. The purpose of this study was to compare performance of healthy right-handed respondents on the new Light Beam Finger & Foot Tapping Device to a traditional finger tapping test used in the Halstead-Reitan Neuropsychological Battery. Performance on the Halstead-Reitan Finger Tapping Test and on the Light Beam Finger Tapping Test was compared in 16 men and 17 women. The light beam test showed similar psychometric properties to those of the Halstead-Reitan Finger Tapping Test, and scores were moderately correlated between the two tests. Respondents had faster scores on the light beam test; on both tests men were faster than women, and all respondents tapped faster with their dominant hand. Tapping was faster on the Light Beam Finger Tapping Test, possibly because it does not require application of pressure to a mechanical key and a smaller movement registers a tap. In addition to measures of right- and left-hand tapping speed, the light beam test assesses synchronous and alternating tapping and foot tapping. Scores between these subtests showed moderate to high correlations.

Semantic and affective verbal fluency: sex differences

Sex may have an important influence on verbal fluency. The aim of this study is to examine possible sex differences in different types of verbal fluency. Four tasks of verbal fluency were used in this study: two tasks of semantic verbal fluency (Animals, Fruits) and two tasks of affective verbal fluency (Pleasant, Unpleasant). The results were analysed for 200 adults aged 18 to 70 years. The number of correctly enumerated words, the number of phonemic clusters, the number of semantic clusters, and the number of phonemic and semantic switches were recorded. The results confirmed data about sex differences in verbal fluency performance. Statistically significant differences in verbal fluency between men and women were found only in affective tasks. Sex is not a strong predictor of semantic verbal fluency performance, but a statistically significant predictor for negative affective verbal fluency.

No specific role for the manual motor system in processing the meanings of words related to the hand

The present study explored whether semantic and motor systems are functionally interwoven via the use of a dual-task paradigm. According to embodied language accounts that propose an automatic and necessary involvement of the motor system in conceptual processing, concurrent processing of hand-related information should interfere more with hand movements than processing of unrelated body-part (i.e., foot, mouth) information. Across three experiments, 100 right-handed participants performed left- or right-hand tapping movements while repeatedly reading action words related to different body-parts, or different body-part names, in both aloud and silent conditions. Concurrent reading of single words related to specific body-parts, or the same words embedded in sentences differing in syntactic and phonological complexity (to manipulate context-relevant processing), and reading while viewing videos of the actions and body-parts described by the target words (to elicit visuomotor associations) all interfered with right-hand but not left-hand tapping rate. However, this motor interference was not affected differentially by hand-related stimuli. Thus, the results provide no support for proposals that body-part specific resources in cortical motor systems are shared between overt manual movements and meaning-related processing of words related to the hand.

Putative sex differences in verbal abilities and language cortex: a critical review

This review brings together evidence from a diverse field of methods for investigating sex differences in language processing. Differences are found in certain language-related deficits, such as stuttering, dyslexia, autism and schizophrenia. Common to these is that language problems may follow from, rather than cause the deficit. Large studies have been conducted on sex differences in verbal abilities within the normal population, and a careful reading of the results suggests that differences in language proficiency do not exist. Early differences in language acquisition show a slight advantage for girls, but this gradually disappears. A difference in language lateralization of brain structure and function in adults has also been suggested, perhaps following size differences in the corpus callosum. Neither of these claims is substantiated by evidence. In addition, overall results from studies on regional grey matter distribution using voxel-based morphometry, indicate no consistent differences between males and females in language-related cortical regions. Language function in Wada tests, aphasia, and in normal ageing also fails to show sex differentiation.

MOTOR PERFORMANCE AS A FUNCTION OF VERBAL, NONVERBAL INTERFERENCE AND HANDEDNESS

The effect of verbal and nonverbal interference on finger-tapping performance was analyzed in self-classified left (n = 15) and right-handed (n = 15) subjects. Data were analyzed with a Group (left hander, right hander) x Condition (with interference [verbal, nonverbal], without interference) x Hand (left hand, right hand) mixed factorial ANOVA with repeated measures in Condition and Hand factors. Verbal as well as nonverbal interference conditions, as compared to non-interference conditions, significantly impaired finger-tapping performance of the left relative to right handers.

Lateralization of speech production using verbal/manual dual tasks: meta-analysis of sex differences and practice effects

The present paper reviews the findings of 30 years of verbal/manual dual task studies, the method most commonly used to assess lateralization of speech production in non-clinical samples. Meta-analysis of 64 results revealed that both the type of manual task used and the nature of practice that is given influence the size of the laterality effect. A meta-analysis of 36 results examining the effect size of sex differences in estimates of lateralization of speech production indicated that males appear to show slightly larger laterality effects than females.

Sex differences in line bisection as a function of hand

If subjects are asked to indicate the midpoint of a horizontal line, they tend to bisect it left of the center, a phenomenon called 'pseudoneglect'. Assuming that this task evokes visuospatial processes, the left bias is generally considered to arise from a right-hemispheric activation. Numerous factors affect pseudoneglect. Although, only few studies have examined the influence of sex in visual line bisection, most of theses studies reported no significant main effect of sex. Possible interactions between sex and other performance factors that are linked to the motor component of this task, e.g. hand use, are rarely examined. We studied the interaction of these two variables using right-handed females and males in a line bisection task. The results clearly indicate that hand use and sex interact, with females showing the left bias to a similar extent with both hands while males show the bias predominantly with the left hand. Moreover, the position of the lines (left, middle and right) significantly affect left bias in visual line bisection and interact with hand use. It is hypothesized that the larger cross-section of the posterior corpus callosum in females enables a stronger interhemispheric connectivity of visuospatial cortical areas resulting in a strong left-sided bias in hand motor cortical areas of both hemispheres. In males, motor cortical activation would accordingly be mainly restricted to the right hemisphere.

Sympathetic mouth movements accompanying fine motor movements in chimpanzees (Pan troglodytes) with implications toward the evolution of language

Some theories concerning the evolution of language include a gestural stage prior to glottogenesis. These theories propose that connections observed between fine motor movements of the hands and mouth may be responsible for the transfer of human language from one that was primarily gestural to one that is spoken. The fine motor manipulation of objects by five captive chimpanzees was examined to determine whether sympathetic mouth movements accompanied fine and gross motor movements. Sympathetic mouth movements were observed significantly more often during fine motor manipulation for all five participants. A significant increase in the presence of sympathetic mouth movements was observed in behaviors along a continuum of precision of manipulation from precision grip to gross motor manipulation without prehension. The results are discussed in regard to current theories of language evolution and neurological processes.

Steroid fluctuations modify functional cerebral asymmetries: the hypothesis of progesterone-mediated interhemispheric decoupling

This study examines the modulation of functional cerebral asymmetries by gonadal hormones in three distinct groups. Young, normally cycling women performed a prototypical left (lexical decision) and two prototypical right-hemispheric tasks (figural comparison and face discrimination) during the low steroid menses and the high steroid midluteal phase. Saliva progesterone levels were measured with radioimmunoassay (RIA). Parallel to younger females, young men, and postmenopausal women were tested at matching time intervals. Results revealed significant interactions between cycle phase and visual half-field in the accuracy of all three tasks for the younger women; stronger lateralization patterns occurring during menses, while a more bilateral or at least less asymmetric cerebral organization predominated the midluteal phase, when highest levels of progesterone appear. Progesterone seemed to have a significant influence on lateralization in the figural comparison task, with high hormone levels enhancing the performance of the left hemisphere (for this task subdominant), thereby decreasing asymmetry. After menopause, when the levels of gonadal hormones are lower and more stable, the lateralization patterns for all three tasks were similar to those of men and normally cycling women during menses. These results make it likely that steroids and especially progesterone are able to reduce cerebral asymmetries. We hypothesize that progesterone attenuates the effect of glutamate on non-NMDA receptors. This could diminish cortico-cortical transmission which is mostly dependent on a glutamate-induced initial EPSP in pyramidal neurons which receive transcallosal input. The reduction in callosal transfer could then suppress the functional asymmetries.

Sex differences in functional cerebral asymmetries in a repeated measures design

The aim of the present study was to analyze whether task repetitions which are an inevitable part of repeated measures designs might induce performance alterations specific for gender and hemisphere. Male and female subjects conducted twice a lexical decision, a polygon recognition, and a face discrimination task as a visual half field paradigm with the two experimental sessions repeated by 2 weeks. The results show that only in female subjects can a session effect for the lexical decision and the polygon recognition task be demonstrated which is hemisphere specific. Thus, repeated measures designs seem to have a gender- and hemisphere-specific effects of their own which could confound with other variables under study.

Hemispheric dominance and gender in the perception of an illusion

Perception of geometric illusions is a visuo-spatial process. As such processes often have been found to be predominantly the domain of the right hemisphere, this hemisphere may be expected to perceive such illusions more readilly than the left hemisphere. Using the herringbone illusion in a reaction-test paradigm, we found that in right-handed males the right hemisphere was significantly more often deceived than the left, whereas no significant hemispheric difference was observed in females. This is the first demonstration of gender differences in the lateralized perception of an illusion.

The hand performance test with a modified time limit instruction enables the examination of hand performance asymmetries in adults

Asymmetry of hand performance was investigated with the paper-and-pencil test of hand dominance originally developed by Steingruber in 1971. This test, originally constructed to measure asymmetry of hand performance in children, gave appropriate scores on asymmetry of hand performance in adults if a shorter time limit than originally proposed was applied. Asymmetry of hand performance in adults as measured with the new instruction showed reliable asymmetries in performance which are similar to those obtained on different widely accepted tests measuring asymmetries of hand performance.

Hand motor performance and degree of asymmetry in monozygotic twins

To determine whether the absolute degree of asymmetry of hand motor performance (irrespective of direction of this asymmetry) may have a heritable component we examined 20 pairs of monozygotic (MZ) twins of whom 10 pairs were concordantly right-handed (MZ-RR) and 10 pairs discordant for handedness (MZ-RL). The tests comprised measurements of the maximum left and right hand tapping rate as well as a paper-and-pencil test of left and right hand motor proficiency. Intraclass correlations within MZ-RR and MZ-RL for absolute degree of hand motor asymmetry were not significant. In contrast, significant intrapair correlations emerged for overall hand motor performance, a measure unrelated to laterality. These results demonstrate that at least in MZ twins the degree of hand motor asymmetry is mainly determined by non-genetic factors, whereas overall hand motor skill is more likely to be influenced by the genome. In addition, the lack of a difference in overall hand motor performance between MZ twins and 40 singletons studied as controls would not support hypotheses explaining behavioural asymmetry in twins, or their discordance for asymmetry, by developmental dysfunction.

Right-handers and left-handers show differences and important similarities in task integration when performing manual and vocal tasks concurrently

For a sample of 73 consistent left-handers, 46 inconsistent left-handers and 65 right-handers, reciprocal interactions between unimanual or bimanual tasks and concurrent reading tasks were shown to be a complex function of task characteristics and sample composition. The suggestion that subgrouping of left-handers [Hellige and Key, Cerebral Control of Speech and Limb Movements, North Holland, Amsterdam, 1990] influences task interactions in left-handers was borne out. Both manual and vocal performance were measured. The effects of the vocal task on the manual task were variable for groups and conditions, but an important common trend emerged: all handedness groups showed the same robust effect: vocal task performance was better when the right hand performed the manual task. Finally, speaking rate increased and tapping rate decreased during concurrent single hand tapping [cf. Hiscock, Brain Cognit. 1, 119-131, 1982]; and there was an opposite effect with concurrent bimanual tapping. The results favour a task integration model rather than an interference in cerebral functions space model.

A differential effect of concurrent verbal activity on right arm movements rightwards and leftwards

Twenty right-handed male subjects had to follow a target which moved horizontally with a velocity of 40 degrees/s either rightwards or leftwards by moving their right arm. During the pursuit movement, subjects had to speak a sentence or to accomplish this procedure without speaking. It could be shown that while subjects spoke, the pursuit movement was performed more inaccurately than during the control session. Furthermore, it was shown that during concurrent speaking, pursuit movements rightwards were more inaccurate than movements to the left. This result is in line with theoretical implications according to which visually guided right-arm movements rightwards are controlled by a neural network located in the left hemisphere, whereas right-arm movements leftwards are controlled by a neural network distributed over both hemispheres.