Intersubject Differences Research Articles

Multi-Atlas Brain Parcellation Using Squeeze-and-Excitation Fully Convolutional Networks

Multi-atlas parcellation (MAP) is carried out on a brain image by propagating and fusing labelled regions from brain atlases. Typical nonlinear registration-based label propagation is time-consuming and sensitive to inter-subject differences. Recently, deep learning parcellation (DLP) has been proposed to avoid nonlinear registration for better efficiency and robustness than MAP. However, most existing DLP methods neglect using brain atlases, which contain high-level information (e.g., manually labelled brain regions), to provide auxiliary features for improving the parcellation accuracy. In this paper, we propose a novel multi-atlas DLP method for brain parcellation. Our method is based on fully convolutional networks (FCN) and squeeze-and-excitation (SE) modules. It can automatically and adaptively select features from the most relevant brain atlases to guide parcellation. Moreover, our method is trained via a generative adversarial network (GAN), where a convolutional neural network (CNN) with multi-scale l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> loss is used as the discriminator. Benefiting from brain atlases, our method outperforms MAP and state-of-the-art DLP methods on two public image datasets (LPBA40 and NIREP-NA0).

Neural Modulation Transmission Is a Marker for Speech Perception in Noise in Cochlear Implant Users.

Cochlear implants (CIs) restore functional hearing in persons with a severe hearing impairment. Despite being one of the most successful bionic prosthesis, performance with CI (in particular speech understanding in noise) varies considerably across its users. The ability of the auditory pathway to encode temporal envelope modulations (TEMs) and the effect of degenerative processes associated with hearing loss on TEM encoding is assumed to be one of the reasons underlying the large intersubject differences in CI performance. The objective of the present study was to investigate how TEM encoding of the stimulated neural ensembles of human CI recipients is related to speech perception in noise (SPIN). We used electroencephalography as a noninvasive electrophysiological measure to assess TEM encoding in the auditory pathway of CI users by means of the 40-Hz electrically evoked auditory steady state response (EASSR). Nine CI users with a wide range of SPIN outcome were included in the present study. TEM encoding was assessed for each stimulation electrode of each subject and new metrics; the CI neural modulation transmission difference (CIMTD) and the CI neural modulation transmission index (CIMTI) were developed to quantify the amount of variability in TEM encoding across the stimulated neural ensembles of the CI electrode array. EASSR patterns varied across the CI electrode array and subjects. We found a strong correlation (r = 0.89, p = 0.001) between the SPIN outcomes and the variability in EASSR amplitudes across the array as assessed with CIMTD/CIMTI. The results of the present study show that the 40-Hz EASSR can be used to objectively assess the neural encoding of TEMs in human CI recipients. Overall reduced or largely variable TEM encoding of the neural ensembles across the electrode array, as quantified with the CIMTD/CIMTI, is highly correlated with speech perception in noise outcome with a CI.

Understanding Inter-Individual Variability in Monoclonal Antibody Disposition.

Monoclonal antibodies (mAbs) are currently the largest and most dominant class of therapeutic proteins. Inter-individual variability has been observed for several mAbs; however, an understanding of the underlying mechanisms and factors contributing to inter-subject differences in mAb disposition is still lacking. In this review, we analyze the mechanisms of antibody disposition and the putative mechanistic determinants of inter-individual variability. Results from in vitro, preclinical, and clinical studies were reviewed evaluate the role of the neonatal Fc receptor and Fc gamma receptors (expression and polymorphism), target properties (expression, shedding, turnover, internalization, heterogeneity, polymorphism), and the influence of anti-drug antibodies. Particular attention is given to the influence of co-administered drugs and disease, and to the physiological relevance of covariates identified by population pharmacokinetic modeling, as determinants of variability in mAb pharmacokinetics.

Individually Rate Corrected QTc Intervals in Children and Adolescents

Accurate evaluation of the appearance of QTc sex differences during childhood and adolescence is intricate. Inter-subject differences of individual QT/RR patterns make generic heart rate corrections inaccurate because of fast resting heart rates in children. The study investigated 527 healthy children and adolescents aged 4–19 years (268 females, 50.9%). All underwent continuous ECG 12-lead monitoring while performing postural changes during a 70-min investigative protocol to obtain QT interval measurements at different heart rates. On average, more than 1200 ECG measurements (QT interval and its 5-min history of preceding RR intervals) were made in each subject. Curvilinear QT/RR regression involving intra-individual correction for QT/RR hysteresis were calculated in each subject. The projection of the QT/RR regressions to the heart rate of 60 beats per minute defined individually corrected QTc intervals. In males, gradual QTc shortening by about 15 ms appeared during the ages of 13–19 years synchronously with the incidence of secondary sex signs (p = 0.016). On the contrary, whilst gradual QTc prolongation by about 10 ms appeared in females, it occurred only during ages 16–19 years and was not related to the incidence of secondary sex signs (p = 0.18). The study also showed that in children and adolescents, linear QT/RR models fit the intra-subject data significantly more closely than the log-linear models (p < 0.001). The study speculates that hormonal shifts during puberty might be directly responsible for the QTc shortening in males but that QTc prolongation in females is likely more complex since it was noted to follow the appearance of secondary sex signs only after a considerable delay.

Representative 3D shape of the distal femur, modes of variation and relationship with abnormality of the trochlear region

The anatomy of the distal femur has a predominant influence on the mechanics of both patello- and tibio-femoral joints. Especially, the morphological degeneration of the trochlear region dramatically affects the overall knee biomechanics and, from a clinical point of view, the staging of such a degeneration is fundamental to tailor the optimal therapeutic solution. The description of morphological variability and pathological inter-subject differences of the trochlea can be achieved by means of statistical shape modeling of a set of three-dimensional surfaces. This representation encodes information, spread into the dataset, in terms of modes of variations that model global, regional and even local morphological features. In view of that, the aim of this study was to develop a statistical shape model of the distal femur to capture the variability of the trochlear region into specific modes of variation and to study the interplay between the variation of the trochlea and the condylar regions. Using CT scans of patients affected by different levels of abnormality of the trochlear region, the distal femur geometries were co-registered to a reference shape using the pair-wise correspondence approach and principal component analysis provided the key modes of variation (MoVs). Apart from the first two MoVs, which described the global magnitude of the femur and the shaft length, the main following ones showed high correlation with sulcus depth (r2=0.70), sulcus angle (r2=0.70), lateral trochlear inclination (r2=0.66), and height of the two condylar facets in the anterior direction (r2=0.66), whose abnormal variations are typical signs of trochlear degeneration. High interplay between trochlear abnormalities and notch width (r2=0.71), lateral condylar size (r2=0.67), and medial condylar size (r2=0.99) was found. Interestingly, the model predicted morphological associations not included in the training dataset, nonetheless difficult to demonstrate physiologically. Interestingly from a biomechanical point of view, the distribution of some MoVs was found statistically different across the patients featuring physiological and pathological ranges of hip-knee-ankle alignment, femoral internal-external rotation and tibial slope. However, no linear correlation was found between the angular indexes and such MoVs. As a result, we can assert that statistical modeling of the distal femur are to date an effective way to visualize and quantify abnormalities of the trochlear regions supporting the introduction of advanced analysis, diagnostic and treatment support tools to elucidate physiologic and pathological variability in the morphology, to drive the staging and assist the selection of the optimal treatment option tailored to the patient.

Comparing school-leaving tests across nine subjects in China and England: task granularity and scoring objectivity

ABSTRACTPrevious research suggests that knowledge in different subjects varies in terms of objectivity and ‘granularity’ (division of knowledge content into smaller chunks). It has also been suggested that subject objectivity and granularity vary across different educational systems, due to resource differences. This study measures knowledge objectivity and granularity manifested in school-leaving assessments across nine subjects and two educational systems—China and England. While previous studies have investigated assessments using vague operationalisations such as ‘essay’ or ‘short answer’ questions, this study presents a ratio variable to measure granularity: the implied time allocated to individual items. Objectivity is operationalised by coding the item scoring guides as consisting of entirely response content and thus being objective, or as including descriptive content and thus being subjective. It is found that, across both educational systems, STEM subjects have finer granularity and higher objectivity. China assesses with finer granularity and higher objectivity than England (except in mathematics, where granularity is similar and all items objective). England shows significantly greater variation in both variables. The findings offer empirical corroboration of claims about inter-subject differences across different national contexts. They suggest that finer granularity, higher objectivity, and less variation are adopted to cope with resource constraints.

A CONVOLUTIONAL AUTOENCODER APPROACH TO LEARN VOLUMETRIC SHAPE REPRESENTATIONS FOR BRAIN STRUCTURES.

We propose a novel machine learning strategy for studying neuroanatomical shape variation. Our model works with volumetric binary segmentation images, and requires no preprocessing such as the extraction of surface points or a mesh. The learned shape descriptor is invariant to affine transformations, including shifts, rotations and scaling. Thanks to the adopted autoencoder framework, inter-subject differences are automatically enhanced in the learned representation, while intra-subject variances are minimized. Our experimental results on a shape retrieval task showed that the proposed representation outperforms a state-of-the-art benchmark for brain structures extracted from MRI scans.

Neuroanatomical Basis of Individuality in Muscle Tuning Function: Neural Correlates of Muscle Tuning.

In a conventional view of motor control, the human brain might employ an optimization principle that leads a stereotypical motor behavior which we observe as an averaged behavioral data over subjects. In this scenario, the inter-individual motor variability is considered as an observation noise. Here, we challenged this view. We considered a motor control task where the human participants manipulated arm force by coordinating shoulder and elbow torques and investigated the muscle-tuning function that represents how the brain distributed the ideal joint torques to multiple muscles. In the experimental data, we observed large inter-individual variability in the profile of a muscle-tuning function. This contradicts with a well-established optimization theory that is based on minimization of muscle energy consumption and minimization of motor variability. We then hypothesized the inter-subject differences in the structure of the motor cortical areas might be the source of the across-subjects variability of the motor behavior. This was supported by a voxel-based morphometry analysis of magnetic resonance imaging; The inter-individual variability of the muscle tuning profile was correlated with that of the gray matter volume in the premotor cortex which is ipsilateral to the used arm (i.e., right hemisphere for the right arm). This study suggests that motor individuality may originate from inter-individual variation in the cortical structure.

Effect of Crystalline Lens Aberrations on Adaptive Optics Simulation of Intraocular Lenses.

To evaluate the impact of the lens aberrations on the adaptive optics visual simulation of pseudophakic intraocular lens (IOL) profiles. In 20 right phakic eyes, lens higher order aberrations (HOAs) were calculated as the whole eye minus the corneal aberrations. Visual simulation using low and high contrast corrected distance visual acuity (CDVA) testing was carried out with the VAO instrument (Voptica, SL, Murcia, Spain), considering three optical conditions of the lens: removing HOA (no lens-HOA), removing spherical aberration (no lens-SA), and with lens HOA (natural condition). In addition, a through-focus visual simulation of a trifocal diffractive IOL profile with high contrast CDVA was also measured in two conditions: no lens-HOA and natural condition. Three different pupil sizes (3, 4.5, and 6 mm) were tested for all conditions. There were no significant intersubject differences between the three optical conditions and in the IOL simulation for all pupil sizes (P > .05). For 4.5- and 6-mm pupils, mean VA values of the no-lens SA and no lens-HOA conditions were similar and slightly worse than those of the natural condition. Individual differences between the no lens-HOA condition and the other two optical conditions, estimated as 95% limits of agreement, were acceptable for 3-mm pupil but worse as pupil diameter increased. The effect of lens aberrations on visual simulation is imperceptible for a small pupil diameter of 3 mm. Although the increment of pupil size increases the probability of patients with significant visual impact of lens HOAs, the mean intersubject VA differences are negligible. [J Refract Surg. 2019;35(2):126-131.].

Molecular characterization of intact cell-derived and cell-free bacterial DNA from carious dentine samples

Microbial analyzes of carious dentine samples, especially in terms of interventions, represent a challenge due to difficulties in carious dentine sampling particularly with small bacterial DNA contents. Therefore, information about the quantitative reduction of bacterial DNA as well as microbial shifts and differences in diversity correlating with treatment interventions are scarce. In this study, carious dentine samples were collected in a first step in the course of a selective caries excavation at two different deep dentine caries lesions in three patients. Second, after selective caries excavation and sampling of carious dentine, an intervention was performed by applying dental materials onto the remaining carious dentine followed by a restoration of the study teeth with composite fillings. After 8 weeks, remaining carious dentine was sampled and analyzed as described above. The microbial community before and after therapy was analyzed by conventional culture compared to bacterial DNA analyses using 16S rRNA gene based real-time PCR and terminal restriction fragment length polymorphism (T-RFLP) for fingerprinting community changes within carious dentine samples. An ultra-pure workflow allowed the valid comparison of even small carious dentine samples with low DNA contents and the differentiation between intact cell-derived and cell-free bacterial DNA. Intra- and inter-subject related differences in the bacterial DNA content and its composition in deep dentine caries were determined considering the first visits. The ratio of cell-free bacterial DNA and DNA from intact cells decreased in two of three subjects included in the current study from visit 1 to visit 2 with the test substance (1:200 to 1:17) and the control substance (1:82 to 1:7). T-RFLP revealed changes in the bacterial diversity and composition shifts after treatment as well as between cell-free bacterial DNA and DNA derived from intact cells.The approach of differentiation and quantification of cell-free and intact cell-derived bacterial DNA is reasonable within the investigation of carious dentine samples, especially when considering the effect of an intervention. T-RFLP is principally suitable for the analysis of microbial shifts within carious dentine samples.

How Best to Present Complex Ecosystem Information in Stated Preference Studies?

This study examines the most effective way to present complex information in the context of ecosystem service-based assessments of landscape-level decision-making, using choice consistency as a way of measuring what is “most effective”. The experiment compares a verbal presentation of information with a variety of visualisations of the same information in a discrete choice experiment about a catchment management plan in New Zealand. The analysis uses a scale heterogeneity model to identify inter-subject differences in choice consistency, measured as the relative weight of the deterministic and random components of utility. The results indicate that choice consistency is reduced when information is presented visually rather than verbally. Radar graphs reduce choice consistency more than histograms or colour maps. The time required to complete the choice tasks also increased when information was not verbal, suggesting that cognitive processing of verbal and visual information occurs quite differently.

Elevation in lung volume and preventing catastrophic airway closure in asthmatics during bronchoconstriction.

BackgroundAsthma exacerbations cause lung hyperinflation, elevation in load to inspiratory muscles, and decreased breathing capacity that, in severe cases, may lead to inspiratory muscle fatigue and respiratory failure. Hyperinflation has been attributed to a passive mechanical origin; a respiratory system time-constant too long for full exhalation. However, because the increase in volume is also concurrent with activation of inspiratory muscles during exhalation it is unclear whether hyperinflation in broncho-constriction is a passive phenomenon or is actively controlled to avoid airway closure.MethodsUsing CT scanning, we measured the distensibility of individual segmental airways relative to that of their surrounding parenchyma in seven subjects with asthma and nine healthy controls. With this data we tested whether the elevation of lung volume measured after methacholine (MCh) provocation was associated with airway narrowing, or to the volume required to preventing airway closure. We also tested whether the reduction in FVC post-MCh could be attributed to gas trapped behind closed segmental airways.FindingsThe changes in lung volume by MCh in subjects with and without asthma were inversely associated with their reduction in average airway lumen. This finding would be inconsistent with hyperinflation by passive elevation of airway resistance. In contrast, the change in volume of each subject was associated with the lung volume estimated to cause the closure of the least stable segmental airway of his/her lungs. In addition, the measured drop in FVC post MCh was associated with the estimated volume of gas trapped behind closed segmental airways at RV.ConclusionsOur data supports the concept that hyperinflation caused by MCh-induced bronchoconstriction is the result of an actively controlled process where parenchymal distending forces on airways are increased to counteract their closure. To our knowledge, this is the first imaging-based study that associates inter-subject differences in whole lung behavior with the interdependence between individual airways and their surrounding parenchyma.

High-throughput elucidation of thrombus formation reveals sources of platelet function variability.

In combination with microspotting, whole-blood microfluidics can provide high-throughput information on multiple platelet functions in thrombus formation. Based on assessment of the inter- and intra-subject variability in parameters of microspot-based thrombus formation, we aimed to determine the platelet factors contributing to this variation. Blood samples from 94 genotyped healthy subjects were analyzed for conventional platelet phenotyping: i.e. hematologic parameters, platelet glycoprotein (GP) expression levels and activation markers (24 parameters). Furthermore, platelets were activated by ADP, CRP-XL or TRAP. Parallel samples were investigated for whole-blood thrombus formation (6 microspots, providing 48 parameters of adhesion, aggregation and activation). Microspots triggered platelet activation through GP Ib-V-IX, GPVI, CLEC-2 and integrins. For most thrombus parameters, inter-subject variation was 2-4 times higher than the intra-subject variation. Principal component analyses indicated coherence between the majority of parameters for the GPVI-dependent microspots, partly linked to hematologic parameters, and glycoprotein expression levels. Prediction models identified parameters per microspot that were linked to variation in agonist-induced αIIbβ3 activation and secretion. Common sequence variation of GP6 and FCER1G, associated with GPVI-induced αIIbβ3 activation and secretion, affected parameters of GPVI-and CLEC-2-dependent thrombus formation. Subsequent analysis of blood samples from patients with Glanzmann thrombasthenia or storage pool disease revealed thrombus signatures of aggregation-dependent parameters that were subject-dependent, but not linked to GPVI activity. Taken together, this high-throughput elucidation of thrombus formation revealed patterns of inter-subject differences in platelet function, which were partly related to GPVI-induced activation and common genetic variance linked to GPVI, but also included a distinct platelet aggregation component.

Coil model comparison for cerebellar transcranial magnetic stimulation

Objective. Transcranial magnetic stimulation (TMS) has been increasingly used for investigating the function of different areas of the cerebellum. Experimental studies have shown variable effectiveness of different types of coils in cerebellar TMS. Our objective is to systematically investigate the effects of coil type on the electric field (E-field) induced in the cerebellum. Approach. Induced E-fields of cerebellar TMS were modelled using individualised head models of 15 subjects. A double-cone, a figure-of-8 and a round coil were modelled, and E-field measurements were performed to validate the coil models. The E-fields induced in anatomical models are statistically analysed to investigate the effects of the coil type and placement on the stimulation strength, depth and focality. Main results. The E-field measurements showed that the applied thin-wire approximation is valid and useful for computational modelling of TMS coils. Inter-subject analysis of the induced E-fields showed that the round coil systematically produced the weakest E-fields. The difference between the double-cone and figure-of-8 coils was not systematic; instead, the most efficient coil type depended on the targeted region of the cerebellum. Further, despite inter-subject differences, the double-cone coil appeared more suitable for stimulating deeper regions of the cerebellum, whereas the figure-of-8 coil produces more focal stimulation, hence providing precise stimulation of regions closer to the scalp surface. Significance. The double-cone, round and figure-of-8 coils have different advantages over each other in different situations. The choice of the coil geometry and placement should be made with care for the desired stimulation outcome. Moreover, inter-subject anatomical differences affect the E-field induced in the cerebellum, and anatomical modelling using magnetic resonance imaging data can enhance the precision of cerebellar TMS.

Human manual control precision depends on vestibular sensory precision and gravitational magnitude.

Precise motion control is critical to human survival on Earth and in space. Motion sensation is inherently imprecise, and the functional implications of this imprecision are not well understood. We studied a "vestibular" manual control task in which subjects attempted to keep themselves upright with a rotational hand controller (i.e., joystick) to null out pseudorandom, roll-tilt motion disturbances of their chair in the dark. Our first objective was to study the relationship between intersubject differences in manual control performance and sensory precision, determined by measuring vestibular perceptual thresholds. Our second objective was to examine the influence of altered gravity on manual control performance. Subjects performed the manual control task while supine during short-radius centrifugation, with roll tilts occurring relative to centripetal accelerations of 0.5, 1.0, and 1.33 GC (1 GC = 9.81 m/s2). Roll-tilt vestibular precision was quantified with roll-tilt vestibular direction-recognition perceptual thresholds, the minimum movement that one can reliably distinguish as leftward vs. rightward. A significant intersubject correlation was found between manual control performance (defined as the standard deviation of chair tilt) and thresholds, consistent with sensory imprecision negatively affecting functional precision. Furthermore, compared with 1.0 GC manual control was more precise in 1.33 GC (-18.3%, P = 0.005) and less precise in 0.5 GC (+39.6%, P < 0.001). The decrement in manual control performance observed in 0.5 GC and in subjects with high thresholds suggests potential risk factors for piloting and locomotion, both on Earth and during human exploration missions to the moon (0.16 G) and Mars (0.38 G). NEW & NOTEWORTHY The functional implications of imprecise motion sensation are not well understood. We found a significant correlation between subjects' vestibular perceptual thresholds and performance in a manual control task (using a joystick to keep their chair upright), consistent with sensory imprecision negatively affecting functional precision. Furthermore, using an altered-gravity centrifuge configuration, we found that manual control precision was improved in "hypergravity" and degraded in "hypogravity." These results have potential relevance for postural control, aviation, and spaceflight.

Guiding Ketogenic Diet with Breath Acetone Sensors.

Ketogenic diet (KD; high fat, low carb) is a standard treatment for obesity, neurological diseases (e.g., refractory epilepsy) and a promising method for athletes to improve their endurance performance. Therein, the level of ketosis must be regulated tightly to ensure an effective therapy. Here, we introduce a compact and inexpensive breath sensor to monitor ketosis online and non-invasively. The sensor consists of Si-doped WO3 nanoparticles that detect breath acetone selectively with non-linear response characteristics in the relevant range of 1 to 66 ppm, as identified by mass spectrometry. When tested on eleven subjects (five women and six men) undergoing a 36-h KD based on the Johns Hopkins protocol, this sensor clearly recognizes the onset and progression of ketosis. This is in good agreement to capillary blood β-hydroxybutyrate (BOHB) measurements. Despite similar dieting conditions, strong inter-subject differences in ketosis dynamics were observed and correctly identified by the sensor. These even included breath acetone patterns that could be linked to low tolerance to that diet. As a result, this portable breath sensor represents an easily applicable and reliable technology to monitor KD, possibly during medical treatment of epilepsy and weight loss.

Variability of Foveal Avascular Zone Metrics Derived From Optical Coherence Tomography Angiography Images.

PurposeTo characterize sources of inter- and intrasubject variability in quantitative foveal avascular zone (FAZ) metrics.MethodsTwo 3×3-mm optical coherence tomography angiography scans (centered on the fovea) were acquired in both eyes of 175 subjects. An image of the superficial plexus was extracted from each scan and segmented twice by a single observer. Four quantitative FAZ morphology metrics (area, axis ratio, acircularity, major horizontal axis angle) were calculated, and a variance components analysis was performed.ResultsMean (±SD) age was 27.9 ± 11.9 years, and 55% were female. Area had the largest amount of variance resulting from intersubject differences (93.1%). In contrast, there was large interocular variance for axis ratio, acircularity, and major horizontal axis angle (55.0%, 53.7%, 70.7%, respectively), though only axis ratio showed significant asymmetry between fellow eyes (P < 0.05). Neither repeated images from the same eye nor repeated segmentation on the same image were significant sources of variance.ConclusionsMetrics of FAZ morphology show excellent repeatability and reliability. Excluding FAZ area, there was a high amount of variance attributed to interocular differences for the other FAZ metrics; therefore, the fellow eye should not be considered a control for FAZ studies when using these metrics.Translational RelevanceVision scientists must be prudent when choosing FAZ metrics, as they display varying degrees of within-subject differences relative to between-subject differences. It seems likely that different metrics will be best suited for different tasks, such as monitoring small changes over time within a single subject or assessing whether a given FAZ is abnormal.

Seasonal variation of spontaneous blink rate and beta EEG activity

Seasonal variations of the photoperiod have been shown to regulate biological and behavioral functions, with also effects on clinical symptom and course of several psychiatric conditions. Although melatonin is considered the principal signal used to transmit informations about the light and dark cycle, a dopamine (DA) role in regulating seasonal changes has been suggested. Few studies have addressed a seasonal pattern of dopamine, and human studies have been conducted on inter-subject differences, comparing measures obtained during fall-winter with those of spring-summer. We studied within-subject seasonal changes of blink rate (BR), a indirect marker of central DA activity, in 26 normal subjects (15 females and 11 males, mean age: 24.7 ± 4.0) during winter, spring, summer and fall. Occipital EEG activity and subjective measures of vigilance and mood were also assessed to account for variations on arousal and fatigue. A significant seasonal effect was found for BR, with higher rate in summer, and for EEG beta activity, with higher activity in spring and summer. Subjective fatigue was found higher in winter. According to our data, it is possible that higher BR and increased EEG beta activity result by an arousal activation sustained by dopamine systems during the months with a long photoperiod.

ACC Sulcal Patterns and Their Modulation on Cognitive Control Efficiency Across Lifespan: A Neuroanatomical Study on Bilinguals and Monolinguals.

The anterior cingulate cortex (ACC) is a key structure implicated in the regulation of cognitive control (CC). Previous studies suggest that variability in the ACC sulcal pattern-a neurodevelopmental marker unaffected by maturation or plasticity after birth-is associated with intersubject differences in CC performance. Here, we investigated whether bilingual experience modulates the effects of ACC sulcal variability on CC performance across the lifespan. Using structural MRI, we first established the distribution of the ACC sulcal patterns in a large sample of healthy individuals (N = 270) differing on gender and ethnicity. Second, a participants' subsample (N = 157) was selected to test whether CC performance was differentially affected by ACC sulcation in bilinguals and monolinguals across age. A prevalent leftward asymmetry unaffected by gender or ethnicity was reported. Sulcal variability in the ACC predicted CC performance differently in bilinguals and monolinguals, with a reversed pattern of structure-function relationship: asymmetrical versus symmetrical ACC sulcal patterns were associated with a performance advantage in monolinguals and a performance detriment to bilinguals and vice versa. Altogether, these findings provide novel insights on the dynamic interplay between early neurodevelopment, environmental background and cognitive efficiency across age.

Passive Wrist Stiffness: The Influence of Handedness.

This paper reports on the quantification of passive wrist joint stiffness and investigates the potential influence of handedness and gender on stiffness estimates. We evaluated the torque-angle relationship during passive wrist movements in 2 degrees of freedom (into flexion-extension and radial-ulnar deviation) in 13 healthy subjects using a wrist robot. Experimental results determined intrasubject differences between dominant and nondominant wrist and intersubject differences between male and female participants. We found differences in the magnitude of passive stiffness of left- and right-hand dominant males and right-hand dominant females suggesting that the dominant hand tends to be stiffer than the nondominant hand. Left-hand stiffness magnitude was found to be 37% higher than the right-hand stiffness magnitude in the left-handed male group and the right-hand stiffness magnitude was 11% and 40% higher in the right-handed male and female groups, respectively. Other joint stiffness features such as the orientation and the anisotropy of wrist stiffness followed the expected pattern from previous studies. The observed difference in wrist stiffness between the dominant and nondominant limb is likely due to biomechanical adaptations to repetitive asymmetric activities (such as squash, tennis, basketball, or activities of daily living such as writing, teeth brushing, etc.). Understanding and quantifying handedness influence on stiffness may have critical implication for the optimization of surgical and rehabilitative interventions.