Can the Archaeology of Manual Specialization Tell Us Anything About Language Evolution? A Survey of the State of Play

In this review and position paper we explore the neural substrates for manual specialization and their possible connection with language and speech. We focus on two contrasting hypotheses of the origins of language and manual specialization: the language-first scenario and the tool-use-first scenario. Each one makes specific predictions about hand-use in non-human primates, as well as about the necessity of an association between speech adaptations and population-level right-handedness in the archaeological and fossil records. The concept of handedness is reformulated for archaeologists in terms of manual role specialization, using Guiard's model asymmetric bimanual coordination. This focuses our attention on skilled bimanual tasks in which both upper limbs play complementary roles. We review work eliciting non-human primate hand preferences in co-ordinated bimanual tasks, and relevant archaeological data for estimating the presence or absence of a population-level bias to the right hand as the manipulator in extinct hominin species and in the early prehistory of our own species

Regional and Hemispheric Determinants of Language Laterality: Implications for Preoperative fMRI

Language is typically a function of the left hemisphere but the right hemisphere is also essential in some healthy individuals and patients. This inter-subject variability necessitates the localization of language function, at the individual level, prior to neurosurgical intervention. Such assessments are typically made by comparing left and right hemisphere language function to determine “language lateralization” using clinical tests or fMRI. Here, we show that language function needs to be assessed at the region and hemisphere specific level, because laterality measures can be misleading. Using fMRI data from 82 healthy participants, we investigated the degree to which activation for a semantic word matching task was lateralized in 50 different brain regions and across the entire cortex. This revealed two novel findings. First, the degree to which language is lateralized across brain regions and between subjects was primarily driven by differences in right hemisphere activation rather than differences in left hemisphere activation. Second, we found that healthy subjects who have relatively high left lateralization in the angular gyrus also have relatively low left lateralization in the ventral precentral gyrus. These findings illustrate spatial heterogeneity in language lateralization that is lost when global laterality measures are considered. It is likely that the complex spatial variability we observed in healthy controls is more exaggerated in patients with brain damage. We therefore highlight the importance of investigating within hemisphere regional variations in fMRI activation, prior to neuro-surgical intervention, to determine how each hemisphere and each region contributes to language processing. Hum Brain Mapp, 2010. © 2010 Wiley-Liss, Inc

Handedness and Sleep

Introduction Restorative sleep is crucial for cognitive, emotional and behavioral performance and general human well-being. Handedness has been discussed as one factor affecting sleep among various others including age, body mass index (BMI) and sex. Being the preferred use of one hand over the other, handedness has been linked to physiological traits like memory function and pathological conditions like psychiatric disorders. While several studies investigated potential associations between handedness and (mostly subjective) sleep, large-scale studies including a broad age span of participants and studies analyzing women and men separately are lacking. In addition, there are only few studies determining objective sleep. These studies provided inconsistent results. Objectives Therefore, the aim of this study was to examine associations between handedness and both objective and subjective sleep in a large cohort with a broad age range from 18 to 80 years. In addition, the aim was to address potential endocrine effects by comparing associations in women and men as well as in premenopausal and postmenopausal women. Methods A subset of the approximately 10,000 participants from the population-based study “LIFE-Adult” (Leipzig Research Center for Civilization Diseases – adult group) was analyzed with regard to their handedness, objective and subjective sleep and important co-factors. Objective sleep data were determined using at-home actigraphy from 1764 healthy participants (18 to 80 years, 908 women), averaging five consecutive nights. 1024 individuals receiving acticraphy had been previously excluded for not meeting any of the in- and exclusion criteria. Only data collected in nights prior to work days were used. In addition, subjective sleep-related data were captured by self-report diaries, the Pittsburgh Sleep Quality Index (PSQI), the Epworth Sleepiness Scale (ESS) and the Morningness-Eveningness-Questionnaire (MEQ). Handedness was determined using the Edinburgh Handedness Inventory (EHI). The EHI provides information on the direction (i.e. left vs right) and the degree of handedness (i.e. strong vs weak). To address potential endocrine effects, premenopausal women (≤45 years) and postmenopausal women (≥55 years) were analyzed separately. This was also done for men, leaving four subgroups: young females (N=190), young males (N=137), female seniors (N=511) and male seniors (N=519) in order to compare pre- and postmenopausal age groups. Subgroups were compared using t-Test and correlations between sleep parameters and handedness were calculated using Spearman rank correlations. Results The degree and direction of handedness were correlated with “wake after sleep onset” (WASO) in the total sample and all women (the more right-handed/lateralized the shorter WASO). In postmenopausal women, additionally, time in bed (TIB) and total sleep time (TST) were positively correlated with right-handedness/higher lateralization. There were no other significant associations between an objective sleep variable and handedness. In both premenopausal women and >55-year-old men subjective quality of sleep (PSQI) was correlated with direction and degree of handedness, i.e. the more right-handed/lateralized the better. In the total sample and postmenopausal women, the degree and the direction of handedness were negatively correlated with daytime sleepiness, i.e. the less right-handed/lateralized the higher the daytime sleepiness. The chronotype was not associated with handedness in any group. 91% of participants were classified as RH with a very high degree of lateralization that was lower in non-RH participants. 5.4% of the women and 4.1% of the men were lefthanded, 3.6% of the women and 4.8% of the men were ambidextrous as defined by the EHI-Score (EHI > 50 as RH, EHI < -40 as LH). Discussion To my knowledge, this is by far the largest study investigating the association between handedness and objective and subjective sleep. Most essential findings are, that righthandedness and higher lateralization both are associated with the following: a) less WASO in the whole group, all women and postmenopausal women b) more TIB and TST in postmenopausal women c) better subjective quality of sleep in premenopausal women and >55-year old men d) less daytime sleepiness in the total group and postmenopausal women Thus, overall, while associations were not consistently found in all groups, righthandedness tended to be associated with better sleep and less daytime sleepiness. Overall, associations were weak, though. The finding, that direction and degree of handedness showed similar correlations, is plausible, since the vast majority of participants were right handed and showed a high degree of lateralization. Results of this study are met by a relatively small body of literature, as only 11 studies were conducted on the association between handedness and sleep so far. Out of these, four used objective measuring techniques on young participants exclusively (mean ages from 20.5 to 22.4 years), delivering a rather inconsistent picture. For example, while longer or shorter TST was found to be associated with right-handedness, other studies could not find an association at all. Also findings from our study do not show a homogenous picture. Overall, however, direction and degree of handedness (the more right-handed and the more lateralized) were associated with better objective sleep, being roughly in line with most of the studies. In contrast to these, however, our study is the first one to include participants over 30 years of age. Comparably, out of the seven studies focusing on subjective sleep, all but one included participants younger than 30 years. Findings here mostly indicated, that righthandedness or higher lateralization are associated with better subjective sleep (e.g. longer TST, less WASO, fewer sleep problems). The only study targeting older participants did not find differences in the proportion of individuals agreeing to the question, whether they “can get enough rest and sleep”. Thus, our study is overall in line with the studies in younger adults. Importantly, our study is the first to explore the relationship between handedness and daytime sleepiness. Here, right-handedness and higher lateralization were associated with less daytime sleepiness. This finding is in line with the idea that it may be more stressful and exhausting for non-RH coping in a right-handed world. While we did not find striking differences between women and men or between preand postmenopausal women, several indications might suggest endocrine influences: For example, TIB and TST were positively correlated in postmenopausal but negatively in premenopausal women. Such findings warant further research on the influence of sex hormones on both handedness and sleep. Conclusion Although associations found in this study were not consistent in all subgroups, a trend towards right-handedness and higher lateralization being associated with aspects of better objective and subjective sleep as well as less daytime sleepiness became apparent. Seemingly differing associations between women and men are in line with endocrine interactions. Degree and direction of handedness seem to be equally important and should both be considered in future research

Handedness and Sleep

Introduction Restorative sleep is crucial for cognitive, emotional and behavioral performance and general human well-being. Handedness has been discussed as one factor affecting sleep among various others including age, body mass index (BMI) and sex. Being the preferred use of one hand over the other, handedness has been linked to physiological traits like memory function and pathological conditions like psychiatric disorders. While several studies investigated potential associations between handedness and (mostly subjective) sleep, large-scale studies including a broad age span of participants and studies analyzing women and men separately are lacking. In addition, there are only few studies determining objective sleep. These studies provided inconsistent results. Objectives Therefore, the aim of this study was to examine associations between handedness and both objective and subjective sleep in a large cohort with a broad age range from 18 to 80 years. In addition, the aim was to address potential endocrine effects by comparing associations in women and men as well as in premenopausal and postmenopausal women. Methods A subset of the approximately 10,000 participants from the population-based study “LIFE-Adult” (Leipzig Research Center for Civilization Diseases – adult group) was analyzed with regard to their handedness, objective and subjective sleep and important co-factors. Objective sleep data were determined using at-home actigraphy from 1764 healthy participants (18 to 80 years, 908 women), averaging five consecutive nights. 1024 individuals receiving acticraphy had been previously excluded for not meeting any of the in- and exclusion criteria. Only data collected in nights prior to work days were used. In addition, subjective sleep-related data were captured by self-report diaries, the Pittsburgh Sleep Quality Index (PSQI), the Epworth Sleepiness Scale (ESS) and the Morningness-Eveningness-Questionnaire (MEQ). Handedness was determined using the Edinburgh Handedness Inventory (EHI). The EHI provides information on the direction (i.e. left vs right) and the degree of handedness (i.e. strong vs weak). To address potential endocrine effects, premenopausal women (≤45 years) and postmenopausal women (≥55 years) were analyzed separately. This was also done for men, leaving four subgroups: young females (N=190), young males (N=137), female seniors (N=511) and male seniors (N=519) in order to compare pre- and postmenopausal age groups. Subgroups were compared using t-Test and correlations between sleep parameters and handedness were calculated using Spearman rank correlations. Results The degree and direction of handedness were correlated with “wake after sleep onset” (WASO) in the total sample and all women (the more right-handed/lateralized the shorter WASO). In postmenopausal women, additionally, time in bed (TIB) and total sleep time (TST) were positively correlated with right-handedness/higher lateralization. There were no other significant associations between an objective sleep variable and handedness. In both premenopausal women and >55-year-old men subjective quality of sleep (PSQI) was correlated with direction and degree of handedness, i.e. the more right-handed/lateralized the better. In the total sample and postmenopausal women, the degree and the direction of handedness were negatively correlated with daytime sleepiness, i.e. the less right-handed/lateralized the higher the daytime sleepiness. The chronotype was not associated with handedness in any group. 91% of participants were classified as RH with a very high degree of lateralization that was lower in non-RH participants. 5.4% of the women and 4.1% of the men were left-handed, 3.6% of the women and 4.8% of the men were ambidextrous as defined by the EHI-Score (EHI > 50 as RH, EHI < -40 as LH). Discussion To my knowledge, this is by far the largest study investigating the association between handedness and objective and subjective sleep. Most essential findings are, that right-handedness and higher lateralization both are associated with the following: a) less WASO in the whole group, all women and postmenopausal women b) more TIB and TST in postmenopausal women c) better subjective quality of sleep in premenopausal women and >55-year old men d) less daytime sleepiness in the total group and postmenopausal women Thus, overall, while associations were not consistently found in all groups, right-handedness tended to be associated with better sleep and less daytime sleepiness. Overall, associations were weak, though. The finding, that direction and degree of handedness showed similar correlations, is plausible, since the vast majority of participants were right handed and showed a high degree of lateralization. Results of this study are met by a relatively small body of literature, as only 11 studies were conducted on the association between handedness and sleep so far. Out of these, four used objective measuring techniques on young participants exclusively (mean ages from 20.5 to 22.4 years), delivering a rather inconsistent picture. For example, while longer or shorter TST was found to be associated with right-handedness, other studies could not find an association at all. Also findings from our study do not show a homogenous picture. Overall, however, direction and degree of handedness (the more right-handed and the more lateralized) were associated with better objective sleep, being roughly in line with most of the studies. In contrast to these, however, our study is the first one to include participants over 30 years of age. Comparably, out of the seven studies focusing on subjective sleep, all but one included participants younger than 30 years. Findings here mostly indicated, that right-handedness or higher lateralization are associated with better subjective sleep (e.g. longer TST, less WASO, fewer sleep problems). The only study targeting older participants did not find differences in the proportion of individuals agreeing to the question, whether they “can get enough rest and sleep”. Thus, our study is overall in line with the studies in younger adults. Importantly, our study is the first to explore the relationship between handedness and daytime sleepiness. Here, right-handedness and higher lateralization were associated with less daytime sleepiness. This finding is in line with the idea that it may be more stressful and exhausting for non-RH coping in a right-handed world. While we did not find striking differences between women and men or between pre- and postmenopausal women, several indications might suggest endocrine influences: For example, TIB and TST were positively correlated in postmenopausal but negatively in premenopausal women. Such findings warant further research on the influence of sex hormones on both handedness and sleep. Conclusion Although associations found in this study were not consistent in all subgroups, a trend towards right-handedness and higher lateralization being associated with aspects of better objective and subjective sleep as well as less daytime sleepiness became apparent. Seemingly differing associations between women and men are in line with endocrine interactions. Degree and direction of handedness seem to be equally important and should both be considered in future research

Age-Related Attenuation of Dominant Hand Superiority

The decline of motor performance of the human hand-arm system with age is well-documented. While dominant hand performance is superior to that of the non-dominant hand in young individuals, little is known of possible age-related changes in hand dominance. We investigated age-related alterations of hand dominance in 20 to 90 year old subjects. All subjects were unambiguously right-handed according to the Edinburgh Handedness Inventory. In Experiment 1, motor performance for aiming, postural tremor, precision of arm-hand movement, speed of arm-hand movement, and wrist-finger speed tasks were tested. In Experiment 2, accelerometer-sensors were used to obtain objective records of hand use in everyday activities

Brain reorganization as a function of walking experience in 12-month-old infants: implications for the development of manual laterality

Hand preference in infancy is marked by many developmental shifts in hand use and arm coupling as infants reach for and manipulate objects. Research has linked these early shifts in hand use to the emergence of fundamental postural–locomotor milestones. Specifically, it was found that bimanual reaching declines when infants learn to sit; increases if infants begin to scoot in a sitting posture; declines when infants begin to crawl on hands and knees; and increases again when infants start walking upright. Why such pattern fluctuations during periods of postural–locomotor learning? One proposed hypothesis is that arm use practiced for the specific purpose of controlling posture and achieving locomotion transfers to reaching via brain functional reorganization. There has been scientific support for functional cortical reorganization and change in neural connectivity in response to motor practice in adults and animals, and as a function of crawling experience in human infants. In this research, we examined whether changes in neural connectivity also occurred as infants coupled their arms when learning to walk and whether such coupling mapped onto reaching laterality. Electroencephalogram (EEG) coherence data were collected from 43 12-month-old infants with varied levels of walking experience. EEG was recorded during quiet, attentive baseline. Walking proficiency was laboratory assessed and reaching responses were captured using small toys presented at mid-line while infants were sitting. Results revealed greater EEG coherence at homologous prefrontal/central scalp locations for the novice walkers compared to the prewalkers or more experienced walkers. In addition, reaching laterality was low in prewalkers and early walkers but high in experienced walkers. These results are consistent with the interpretation that arm coupling practiced during early walking transferred to reaching via brain functional reorganization, leading to the observed developmental changes in manual laterality

Neonatal White Matter Maturation Is Associated With Infant Language Development

Background: While neonates have no sophisticated language skills, the neural basis for acquiring this function is assumed to already be present at birth. Receptive language is measurable by 6 months of age and meaningful speech production by 10-18 months of age. Fiber tracts supporting language processing include the corpus callosum (CC), which plays a key role in the hemispheric lateralization of language; the left arcuate fasciculus (AF), which is associated with syntactic processing; and the right AF, which plays a role in prosody and semantics. We examined if neonatal maturation of these fiber tracts is associated with receptive language development at 12 months of age. Methods: Diffusion-weighted imaging (DWI) was performed in 86 infants at 26.6 ± 12.2 days post-birth. Receptive language was assessed via the MacArthur-Bates Communicative Development Inventory at 12 months of age. Tract-based fractional anisotropy (FA) was determined using the NA-MIC atlas-based fiber analysis toolkit. Associations between neonatal regional FA, adjusted for gestational age at birth and age at scan, and language development at 12 months of age were tested using ANOVA models. Results: After multiple comparisons correction, higher neonatal FA was positively associated with receptive language at 12 months of age within the genu (p < 0.001), rostrum (p < 0.001), and tapetum (p < 0.001) of the CC and the left fronto-parietal AF (p = 0.008). No significant clusters were found in the right AF. Conclusion: Microstructural development of the CC and the AF in the newborn is associated with receptive language at 12 months of age, demonstrating that interindividual variation in white matter microstructure is relevant for later language development, and indicating that the neural foundation for language processing is laid well ahead of the majority of language acquisition. This suggests that some origins of impaired language development may lie in the intrauterine and potentially neonatal period of life. Understanding how interindividual differences in neonatal brain maturity relate to the acquisition of function, particularly during early development when the brain is in an unparalleled window of plasticity, is key to identifying opportunities for harnessing neuroplasticity in health and disease

The Construct of Personality and Hemispheric Usage

Studies on the differential contributions of the cerebral hemispheres to human experience and behavior have demonstrated that the hemispheres are lateralized for cognitive strategies and, possibly, for emotional valance. Recently researchers have demonstrated that the hemispheres may also be lateralized for certain personality disorders and personality traits. Using lateral eye movements as a measure of hemispheric activation, Dawson, Tucker, and Swenson (in preparation) have shown that certain self-description questionnaires may serve to discriminate subjects who characteristically utilize one hemisphere over the other, regardless of the relative adaptiveness of the cognitive strengths of that hemisphere for the task at hand. This study replicated the findings of the Dawson et al. study, using brain wave activity as an index of lateralized activation. Separating subjects on the basis of their scores on self-description personality measures, it was discovered that subjects who were unrealistically favorable in their self-descriptions (deniers) evidenced greater right hemisphere activation, regardless of the task being performed. Subjects who were overly critical in their self-descriptions (critics) evidenced symmetrical hemispheric activation with a tendency toward greater left hemispheric activation, particularly evident during the baseline and spatial tasks. These findings were evidenced in both the theta and alpha bands for average power, with comparisons in the theta band demonstrating the clearest personality related effects. Analyses on coherence data were performed and described without interpretation. The results of this study were used to provide support for a theory of hemispheric personality. A model is built on the research findings on lateralized cognition and then extended to address some of the recent controversies in the lateralization literature. Implications for further research are discussed and suggestions of how such a model might be used in psychological/medical treatment and diagnoses are discussed

Investigating brain responses to section endings in tonal, classical and rhythmic music : an fMRI study

Our overall aim was to examine brain responses to different experiences of time in music with a particular focus on the question of how we experience large-scale music form. The present experiment was aimed at investigating the neural correlates to experiencing section endings in teleological (goal-directed) music as well as in rhythmic (groove-based) music. We used functional magnetic resonance imaging (fMRI) on 14 human participants. Comparing transition points to continuous sections of the music we found that there was more neural activity in both musical genres at the transition points. Additionally we saw stronger blood-oxygen-level dependent (BOLD) fMRI activations at transition points in the rhythmical piece than in the classical piece. We did four region-of-interest (ROI) analyses, based on a priori expectations about the likely involvement of different brain areas in our task; the ventrolateral prefrontal cortex (VLPFC), the posterior temporal cortex (PTC), the dorsolateral prefrontal cortex (DLPFC) and the posterior parietal cortex (PPC). PTC was the only region that showed activations strong enough to survive the correction for multiple comparisons

Quantifying interictal intracranial EEG to predict focal epilepsy

Intracranial EEG (IEEG) is used for 2 main purposes, to determine: (1) if epileptic networks are amenable to focal treatment and (2) where to intervene. Currently these questions are answered qualitatively and sometimes differently across centers. There is a need for objective, standardized methods to guide surgical decision making and to enable large scale data analysis across centers and prospective clinical trials. We analyzed interictal data from 101 patients with drug resistant epilepsy who underwent presurgical evaluation with IEEG. We chose interictal data because of its potential to reduce the morbidity and cost associated with ictal recording. 65 patients had unifocal seizure onset on IEEG, and 36 were non-focal or multi-focal. We quantified the spatial dispersion of implanted electrodes and interictal IEEG abnormalities for each patient. We compared these measures against the 5 Sense Score (5SS), a pre-implant estimate of the likelihood of focal seizure onset, and assessed their ability to predict the clinicians choice of therapeutic intervention and the patient outcome. The spatial dispersion of IEEG electrodes predicted network focality with precision similar to the 5SS (AUC = 0.67), indicating that electrode placement accurately reflected pre-implant information. A cross-validated model combining the 5SS and the spatial dispersion of interictal IEEG abnormalities significantly improved this prediction (AUC = 0.79; p<0.05). The combined model predicted ultimate treatment strategy (surgery vs. device) with an AUC of 0.81 and post-surgical outcome at 2 years with an AUC of 0.70. The 5SS, interictal IEEG, and electrode placement were not correlated and provided complementary information. Quantitative, interictal IEEG significantly improved upon pre-implant estimates of network focality and predicted treatment with precision approaching that of clinical experts.Comment: 25 pages, 4 Figures, 1 tabl