Sex Differences In Laterality Research Articles

Sex differences in laterality of motor unit firing behavior of the first dorsal interosseous muscle in strength-matched healthy young males and females

PurposeThe purpose of this study was to compare laterality in motor unit firing behavior between females and males.MethodsTwenty-seven subjects (14 females) were recruited for this study. The participants performed ramp up and hold isometric index finger abduction at 10, 30, and 60% of their maximum voluntary contraction (MVC). High-density surface electromyography (HD-sEMG) signals were recorded in the first dorsal interosseous (FDI) muscle and decomposed into individual motor unit (MU) firing behavior using a convolution blind source separation method.ResultsIn total, 769 MUs were detected (females, n = 318 and males, n = 451). Females had a significantly higher discharge rate than males at each relative torque level (10%: male dominant hand, 13.4 ± 2.7 pps vs. female dominant hand, 16.3 ± 3.4 pps; 30%: male dominant hand, 16.1 ± 3.9 pps vs. female dominant hand, 20.0 ± 5.0 pps; and 60%: male dominant hand, 19.3 ± 3.8 vs. female dominant hand, 25.3 ± 4.8 pps; p < 0.0001). The recruitment threshold was also significantly higher in females than in males at 30 and 60% MVC. Furthermore, males exhibited asymmetrical discharge rates at 30 and 60% MVC and recruitment thresholds at 30 and 60% MVC, whereas no asymmetry was observed in females.ConclusionIn the FDI muscle, compared to males, females exhibited different neuromuscular strategies with higher discharge rates and recruitment thresholds and no asymmetrical MU firing behavior. Notably, the findings that sex differences in neuromuscular activity also occur in healthy individuals provide important information for understanding the pathogenesis of various diseases.

Learning and laterality in wild-caught Namaqua rock mice (Micaelamys namaquensis)

Individuals often exhibit differences in cognition and/or preferences for one side over the other. Such differences have been attributed to the mating system and lateralization of the brain hemispheres that can differ between the sexes, respectively. Despite the hypothesized significant effects on fitness, only a limited number of rodent studies addresses sex differences in laterality and most focus on laboratory rodents. Here we examined whether wild-caught Namaqua rock mice (Micaelamys namaquensis), a rodent widespread in sub-Saharan Africa, exhibit sex differences in learning and laterality in a T-maze. Food-deprived animals entered the maze significantly faster over subsequent learning trials, suggesting that the sexes learned to find the food reward at the end of the maze arms equally. Although we could not confirm a side preference at the population level, the animals were strongly lateralized at an individual level. When the sexes were considered separately, females exhibited a preference for the right maze arm while the opposite was observed in males. The lack of comparable studies of sex-specific lateralization patterns in rodents makes the generalization of our results challenging and highlights the need for more such studies in rodents at both the individual and population levels.

Sex Differences in Laterality Are Associated with Reproduction in Threespine Stickleback.

AbstractLaterality, the partitioning of information processing into specific brain hemispheres, is widespread across animal taxa. Substantial unexplained variation in this trait exists, particularly between the sexes, despite multiple identified advantages of lateralization. Here, we demonstrate a relationship among laterality (measured as directional biases), reproduction, and experience of mating and parenting. Using threespine sticklebacks (Gasterosteus aculeatus), a species with uniparental male care, we showed that individuals of the caring sex (males) were more strongly lateralized than the noncaring sex (females) during reproduction and that laterality was reduced outside the breeding season in males. Additionally, males with experience of mating and parenting were more strongly lateralized than males without this experience. Our findings suggest that fitness-related behaviors that vary between the sexes, such as reproductive behaviors including courtship, spawning, and parenting, are significant but previously unidentified sources of variation in laterality.

Response format, magnitude of laterality effects, and sex differences in laterality

The present study examined the evidence for the claim that response format might affect the magnitude of laterality effects by means of a meta-analysis. The analysis included the 396 effect sizes drawn from 266 studies retrieved by Voyer (1996) and relevant to the main effect of laterality and sex differences in laterality for verbal and non-verbal tasks in the auditory, tactile, and visual sensory modality. The response format used in specific studies was the only moderator variable of interest in the present analysis, resulting in four broad response categories (oral, written, computer, and pointing). A meta-analysis analogue to ANOVA showed no significant influence of response format on either the main effect of laterality or sex differences in laterality when all sensory modalities were combined. However, when modalities were considered separately, response format affected the main effect of laterality in the visual modality, with a clear advantage for written responses. Further pointed analyses revealed some specific differences among response formats. Results are discussed in terms of their implications for the measurement of laterality.

Laterality of basic auditory perception

Laterality (left–right ear differences) of auditory processing was assessed using basic auditory skills: (1) gap detection, (2) frequency discrimination, and (3) intensity discrimination. Stimuli included tones (500, 1000, and 4000 Hz) and wide-band noise presented monaurally to each ear of typical adult listeners. The hypothesis tested was that processing of tonal stimuli would be enhanced by left ear (LE) stimulation and noise by right ear (RE) presentations. To investigate the limits of laterality by (1) spectral width, a narrow-band noise (NBN) of 450-Hz bandwidth was evaluated using intensity discrimination, and (2) stimulus duration, 200, 500, and 1000 ms duration tones were evaluated using frequency discrimination. A left ear advantage (LEA) was demonstrated with tonal stimuli in all experiments, but an expected REA for noise stimuli was not found. The NBN stimulus demonstrated no LEA and was characterised as a noise. No change in laterality was found with changes in stimulus durations. The LEA for tonal stimuli is felt to be due to more direct connections between the left ear and the right auditory cortex, which has been shown to be primary for spectral analysis and tonal processing. The lack of a REA for noise stimuli is unexplained. Sex differences in laterality for noise stimuli were noted but were not statistically significant. This study did establish a subtle but clear pattern of LEA for processing of tonal stimuli.

Sex differences in dichotic listening

The present study quantified the magnitude of sex differences in perceptual asymmetries as measured with dichotic listening. This was achieved by means of a meta-analysis of the literature dating back from the initial use of dichotic listening as a measure of laterality. The meta-analysis included 249 effect sizes pertaining to sex differences and 246 effect sizes for the main effect of laterality. The results showed small and homogeneous sex differences in laterality in favor of men ( d = 0.054). The main effect of laterality was of medium magnitude ( d = 0.609) but it was heterogeneous. Homogeneity for the main effect of laterality was achieved through partitioning as a function of task, demonstrating larger asymmetries for verbal ( d = 0.65) than for non-verbal tasks ( d = 0.45). The results are discussed with reference to top-down and bottom-up factors in dichotic listening. The possible influence of a publication bias is also discussed.

Sex-specific effects of postnatal testosterone on lateralization in cichlid fish

Lateralization is a fundamental principle in the organization of brain and behaviour in humans and nonhuman animals. To what extent lateralization is, in addition to genetic factors, under the influence of testosterone, which would also explain sex differences in laterality, is the topic of a long-standing debate. This debate is partly hampered by confusion between organizational and activating effects of testosterone. Here we focused on activating effects, less often studied than organizational effects. Studies on humans have shown ambiguous results and few experimental studies on animals have been conducted. We studied Aequidens rivulatus, a cichlid species in which lateralization of visually guided behaviour has been demonstrated and related to aggressiveness. After treatment with testosterone, lateralization was tested in a rotational preference task where fish had to face a predator. Testosterone induced significant lateralization at the population level. Testosterone-treated fish watched a predator preferentially with the right eye, which is in line with the literature on population-level lateralization of predator viewing in fish. It has been suggested that species differences in laterality of predator escape are related to sociality and we speculate that, within species, testosterone may affect lateralization in relation to a change in sociality. Among the fish of known sex, only males reacted to the treatment; a greater responsiveness of males may explain sex differences in lateralization found in many animal species. This may be caused by sex-specific sensitivity to androgens, perhaps in the habenular area of the brain.

Sex differences in language processing: Functional MRI methodological considerations

To evaluate the influence of both analysis methods and tasks used in the determination of language related sex differences. Previous neuroimaging studies evaluating sex differences in language processing have been inconsistent. The current study compared FMRI activation between men and women on a variety of language tasks using different types of individual (laterality and activation volume) and group analyses to evaluate the effects of task and methodology. Forty subjects completed five language tasks, 19 men and 21 women. Group analyses revealed greater activation for men compared with women in the left pars orbitalis while women showed greater activation within the right insula. With individual analyses, there were no significant sex differences in laterality using two large regions of interest (ROIs) covering the inferior frontal and temporoparietal regions; however, there were significant sex effects within small, specific ROIs (insula, middle temporal and pars opercularis, triangularis, and orbitalis). When holding the task constant, some methods (for example different ROIs within individual analyses) revealed sex differences while others methods did not, indicating a dependence on methodology. The results partly explain why FMRI studies evaluating language related sex effects have been inconsistent.

Is There a Sex Difference in Human Laterality? IV. An Exhaustive Survey of Dual-Task Interference Studies From Six Neuropsychology Journals

The entire contents of six neuropsychology journals (161 volumes, 612 issues) were screened to identify dual-task laterality experiments. Of 112 experiments thus identified, 45.5% provided information about sex differences. Although 23 experiments yielded at least one significant main effect or interaction involving the sex factor, only 5 outcomes represented an unambiguous sex difference in laterality. All 5 of those sex differences support the hypothesis of greater hemispheric specialization in males. The confirmatory outcomes constitute less than 10% of the informative experiments and less than 5% of the total population of experiments. These data alone do not rule out the possibility that sex differences are chance findings (Type I errors). However, when considered along with similar results from perceptual laterality data previously examined, the dual-task data fit the pattern of a small but reliable population-level sex difference in human laterality.

Laterality Effects in the Processing of Syllable Structure

Recent phonological research has shown that the syllable plays a major role in the phonology of German. The present study investigates laterality effects in the processing of syllable structure by means of dichotic presentation of German word pairs that differ in number of syllables, but that differ minimally in the phonemes they comprise (e.g., BREIT and BEREIT). Results showed a sex difference in laterality for the processing of the experimental stimuli, with a greater right-hemispheric lateralization in men and a more bilateral organization in women.

Right-hemispheric superiority in split-brain monkeys for learning and remembering facial discriminations.

Twenty-six split-brain rhesus monkeys learned and remembered 8 go/no-go discriminations of monkey faces significantly better with the right hemisphere than with the left. Four discriminations required differentiating individual identity with expression held constant, and 4 required discriminating facial expression with identity held constant. There was no significant difference in the degree of laterality shown for these 2 types of problems. Female monkeys were more lateralized for learning to discriminate faces than were males. This sex difference in laterality was significant for learning but not for memory. Laterality for the facial discriminations was not significantly related to handedness of the monkeys. Overall, rhesus monkeys, like humans, show a right-hemispheric superiority for facial processing.

Is there a sex difference in human laterality? II. An exhaustive survey of visual laterality studies from six neuropsychology journals.

The contents of six neuropsychology journals (98 volumes, 368 issues) were screened to identify visual half-field (VHF) experiments. Of the 516 experiments identified, 42% provided information about sex differences. Sixty-eight experiments yielded a total of 92 sex differences, 23 of which met stringent criteria for sex differences in laterality. Of the 20 sex differences satisfying stringent criteria and lending themselves to interpretation in terms of the differential lateralization hypothesis, 17 supported the hypothesis of greater hemispheric specialization in males than in females. The 17 confirmatory outcomes represent 7.8% of the informative experiments. When less stringent criteria were invoked, 27 outcomes (12.3% of the informative experiments) were found to be consistent with the differential lateralization hypothesis. Six findings were contrary to the hypothesis. The results, which closely resemble results for auditory laterality studies, are compatible with a population-level sex difference that accounts for 1 to 2% of the variance in laterality.

Is there a sex difference in human laterality? I. An exhaustive survey of auditory laterality studies from six neuropsychology journals.

The entire contents of six neuropsychology journals (98 volumes, 368 issues) were screened to identify auditory laterality experiments. Of the 352 dichotic and monaural listening experiments identified, 40% provided information about sex differences. Among the 49 experiments that yielded at least one significant effect or interaction involving the sex factor, 11 outcomes met stringent criteria for sex differences in laterality. Of those 11 positive outcomes, 9 supported the hypothesis of greater hemispheric specialization in males than in females. The 9 confirmatory outcomes represent 6.4% of the informative experiments. When less stringent criteria were invoked, 21 outcomes (14.9% of the informative experiments) were found to be consistent with the differential lateralization hypothesis. The overall pattern of results is compatible with a weak population-level sex difference in hemispheric specialization.

Generalized and lateralized interference between concurrent tasks performed by children: Effects of age, sex, and skill

Normal right‐handed children in Grades 2–5 engaged in unimanual finger tapping while performing a series of concurrent tasks. In the first of three experiments, recitation and oral reading interfered to a greater degree with right‐hand tapping than with left‐hand tapping, and the asymmetry of interference from reading was greater for poorer readers than for better readers. In Experiment 2, silent reading also interfered asymmetrically with finger tapping, but a visuospatial task generated bilaterally equal interference. Boys outperformed girls on the visuospatial task, and there was a sex difference in the laterality of interference. A similar visuospatial task in Experiment 3 yielded the same sex difference in interference laterality, even though the overall performance of girls and boys did not differ significantly. Age‐related differences in generalized interference occurred for tasks entailing vocalization, but there were no age‐related differences in lateralized interference. The results confirm the ...

Sex differences in the lateralization of language discrimination vs language production

Two tachistoscopic studies employing normal males and females were done to investigate the inconsistency of obtained sex differences on visual laterality tasks to the extent that this inconsistency is task specific. Type of linguistic task (discrimination vs production) and control of attention were manipulated. Results showed that on language discrimination, the sexes were fairly equally lateralized, while on production tasks, females showed greater laterality differences. The attempt to control for attention resulted in higher field differences, but especially so for females. It is suggested that more consideration of task demands in laterality experiments should help clarify the nature of sex differences in laterality.

Sex differences in laterality– meaningfulness versus reliability

Sex differences in laterality– meaningfulness versus reliability

Auditory concept identification as a function of subject sex and stimulus dimensions

Binary stimulus dimensions of duration, laterality, frequency, amplitude, and number were compared for their respective information values in auditory concept identification of males and females. Amplitude, without irrelevant information, was shown to provide significantly less information than the other dimensions with the exception of number. Males performed significantly poorer than females with laterality relevant under conditions of 1, 2, and 3 irrelevant dimensions. Sex differences in laterality were replicated with additional Ss.