Enhanced pre-frontal functional-structural networks to support postural control deficits after traumatic brain injury in a pediatric population

Traumatic brain injury (TBI) affects the structural connectivity, triggering the re-organization of structural-functional circuits in a manner that remains poorly understood. We focus here on brain networks re-organization in relation to postural control deficits after TBI. We enrolled young participants who had suffered moderate to severeTBI, comparing them to young typically developing control participants. In comparison to control participants, TBI patients (but not controls) recruited prefrontal regions to interact with two separated networks: 1) a subcortical network including part of the motor network, basal ganglia, cerebellum, hippocampus, amygdala, posterior cingulum and precuneus; and 2) a task-positive network, involving regions of the dorsal attention system together with the dorsolateral and ventrolateral prefrontal regions

REPIMPACT - a prospective longitudinal multisite study on the effects of repetitive head impacts in youth soccer

Repetitive head impacts (RHI) are common in youth athletes participating in contact sports. RHI differ from concussions; they are considered hits to the head that usually do not result in acute symptoms and are therefore also referred to as \textquotedblsubconcussive\textquotedbl head impacts. RHI occur e.g., when heading the ball or during contact with another player. Evidence suggests that exposure to RHI may have cumulative effects on brain structure and function. However, little is known about brain alterations associated with RHI, or about the risk factors that may lead to clinical or behavioral sequelae. REPIMPACT is a prospective longitudinal study of competitive youth soccer players and non-contact sport controls aged 14 to 16~years. The study aims to characterize consequences of exposure to RHI with regard to behavior (i.e., cognition, and motor function), clinical sequelae (i.e., psychiatric and neurological symptoms), brain structure, function, diffusion and biochemistry, as well as blood- and saliva-derived measures of molecular processes associated with exposure to RHI (e.g., circulating microRNAs, neuroproteins and cytokines). Here we present the structure of the REPIMPACT Consortium which consists of six teams of clinicians and scientists in six countries. We further provide detailed information on the specific aims and the design of the REPIMPACT study. The manuscript also describes the progress made in the study thus far. Finally, we discuss important challenges and approaches taken to overcome these challenges

Cross-site harmonization of multi-shell diffusion MRI measures based on rotational invariant spherical harmonics (RISH)

Quantification methods based on the acquisition of diffusion magnetic resonance imaging (dMRI) with multiple diffusion weightings (e.g., multi-shell) are becoming increasingly applied to study the in-vivo brain. Compared to single-shell data for diffusion tensor imaging (DTI), multi-shell data allows to apply more complex models such as diffusion kurtosis imaging (DKI), which attempts to capture both diffusion hindrance and restriction effects, or biophysical models such as NODDI, which attempt to increase specificity by separating biophysical components. Because of the strong dependence of the dMRI signal on the measurement hardware, DKI and NODDI metrics show scanner and site differences, much like other dMRI metrics. These effects limit the implementation of multi-shell approaches in multicenter studies, which are needed to collect large sample sizes for robust analyses. Recently, a post-processing technique based on rotation invariant spherical harmonics (RISH) features was introduced to mitigate cross-scanner differences in DTI metrics. Unlike statistical harmonization methods, which require repeated application to every dMRI metric of choice, RISH harmonization is applied once on the raw data, and can be followed by any analysis. RISH features harmonization has been tested on DTI features but not its generalizability to harmonize multi-shell dMRI. In this work, we investigated whether performing the RISH features harmonization of multi-shell dMRI data removes cross-site differences in DKI and NODDI metrics while retaining longitudinal effects. To this end, 46 subjects underwent a longitudinal (up to 3 time points) two-shell dMRI protocol at 3 imaging sites. DKI and NODDI metrics were derived before and after harmonization and compared both at the whole brain level and at the voxel level. Then, the harmonization effects on cross-sectional and on longitudinal group differences were evaluated. RISH features averaged for each of the 3 sites exhibited prominent between-site differences in the frontal and posterior part of the brain. Statistically significant differences in fractional anisotropy, mean diffusivity and mean kurtosis were observed both at the whole brain and voxel level between all the acquisition sites before harmonization, but not after. The RISH method also proved effective to harmonize NODDI metrics, particularly in white matter. The RISH based harmonization maintained the magnitude and variance of longitudinal changes as compared to the non-harmonized data of all considered metrics. In conclusion, the application of RISH feature based harmonization to multi-shell dMRI data can be used to remove cross-site differences in DKI metrics and NODDI analyses, while retaining inherent relations between longitudinal acquisitions

Testing Multiple Coordination Constraints with a Novel Bimanual Visuomotor Task

The acquisition of a new bimanual skill depends on several motor coordination constraints. To date, coordination constraints have often been tested relatively independently of one another, particularly with respect to isofrequency and multifrequency rhythms. Here, we used a new paradigm to test the interaction of multiple coordination constraints. Coordination constraints that were tested included temporal complexity, directionality, muscle grouping, and hand dominance. Twenty-two healthy young adults performed a bimanual dial rotation task that required left and right hand coordination to track a moving target on a computer monitor. Two groups were compared, either with or without four days of practice with augmented visual feedback. Four directional patterns were tested such that both hands moved either rightward (clockwise), leftward (counterclockwise), inward or outward relative to each other. Seven frequency ratios (3∶1, 2∶1, 3∶2, 1∶1, 2∶3. 1∶2, 1∶3) between the left and right hand were introduced. As expected, isofrequency patterns (1∶1) were performed more successfully than multifrequency patterns (non 1∶1). In addition, performance was more accurate when participants were required to move faster with the dominant right hand (1∶3, 1∶2 and 2∶3) than with the non-dominant left hand (3∶1, 2∶1, 3∶2). Interestingly, performance deteriorated as the relative angular velocity between the two hands increased, regardless of whether the required frequency ratio was an integer or non-integer. This contrasted with previous finger tapping research where the integer ratios generally led to less error than the non-integer ratios. We suggest that this is due to the different movement topologies that are required of each paradigm. Overall, we found that this visuomotor task was useful for testing the interaction of multiple coordination constraints as well as the release from these constraints with practice in the presence of augmented visual feedback

Bimanual motor control: functional and structural brain measures in healthy subjects and traumatic brain injury patients

Summary In daily life, a large number of activities require the integrated use of both hands. For instance, bimanual motor control is needed to tie your shoelaces, to open a jar, to drive a car or to ride a bike. In order to accurately time and execute such movements, communication between both hemispheres via the corpus callosum (CC) is required. Therefore, an important element of the present thesis was the exploration of the specific role of the CC in bimanual coordination. In addition, bimanual motor control was studied in patients with traumatic brain injury (TBI). TBI patients often experience damage to the CC due to its specific location and composition, and generally demonstrate persistent motor control deficits for years following the injury. Here, we wanted to gain insights into injury-related bimanual coordination deficits as well as concomitant alterations in (sub)cortical motor systems. In part oneof the present thesis we first included a literature survey. This extensive overview revealed an essential role of the CC in bimanual coordination performance, and to some extent made it possible to map specific bimanual task characteristics onto different CC subregions, particularly regarding the type of sensory modality involved. In this literature reviewour first experimental study was included in which the microstructural organization of 7 CC subregions of healthy young adults was correlated with performance on a complex bimanual coordination task, performed either with or without augmented visual feedback. Diffusion tensor imaging (DTI) results demonstrated that bimanual coordination skills, particularlyin the absence of augmented visual feedback, were related to microstructural properties of the CC subsections connecting bilateral primary motor and bilateral occipital cortices. We concluded that in a group of healthy young adults, brain structure can predict variation in bimanual coordination performance. Subsequently, in the same group of healthy subjects, the added value of diffusion kurtosis imaging (DKI; providing a more complete picture of the white matter microstructural organization) relative to DTI was explored in relating white matter microstructure to bimanual performance. Although DKI resulted in higher absolute values of diffusion, and lower absolute values of anisotropy, associations between bimanual performance and white matter organization were comparable for bothdiffusion models. In the second part of the present thesis the focus shifted from the healthy brain to the traumatically injured brain. On the one hand we investigated TBI-induced grey matter volumetric alterations, and on the other hand TBI-induced functional (sub)cortical reorganization, both in relation to bimanual task performance. Structural imaging revealed enlarged ventricles and atrophy in overall and regional subcortical grey matter volume in TBI patients relative to controls. Behaviorally, TBI patients demonstrated poorer (i.e., slower and less accurate) bimanual performance than controls, which was significantly related to volume reductions in subcortical motor-related grey matter structures.Finally, we examined whether these bimanual coordination deficits were accompanied with altered brain function. Compared with controls, functional magnetic resonance imaging (fMRI) findings in TBI revealed reduced (sub)cortical activations during the planning phase of the movement, followed by more widespread and increased neural activity during the execution phase. It was suggested that TBI-induced altered planning-related activations might be interrelated with the nonselective recruitment of brain areas during execution, as well as with impaired motor control. In conclusion, the present doctoral thesis provided evidence for the important and rather specific role of the corpus callosum in bimanual coordination. With the introduction of new neuroimaging techniques, such as diffusion-weighted imaging, this brain structure-function relationship can now be described at a microstructural level, resulting in increased specificity. In addition, we demonstrated that TBI-induced persistent impairments in bimanual motor control were related to subcortical grey matter loss, and were accompanied by altered functional activations, as evidenced by fMRI. Ultimately, these findings may contribute indirectly to the improvement and establishment of new motor rehabilitation approaches following traumatic brain injury.status: publishe

Interactions between brain structure and behavior: the corpus callosum and bimanual coordination

Bimanual coordination skills are required for countless everyday activities, such as typing, preparing food, and driving. The corpus callosum (CC) is the major collection of white matter bundles connecting both hemispheres that enables the coordination between the two sides of the body. Principal evidence for this brain-behavior relationship in humans was first provided by research on callosotomy patients, showing that sectioning (parts of) the CC affected interactions between both hands directly. Later, new noninvasive in vivo imaging techniques, such as diffusion tensor imaging, have energized the study of the link between microstructural properties of the CC and bimanual performance in normal volunteers. Here we discuss the principal factors (such as age, pathology and training) that mediate the relationship between specific bimanual functions and distinct anatomical CC subdivisions. More specifically, the question is whether different bimanual task characteristics can be mapped onto functionally distinct CC subregions. We review the current status of this mapping endeavor, and propose future perspectives to inspire research on this unique link between brain structure and behavior.publisher: Elsevier articletitle: Interactions between brain structure and behavior: The corpus callosum and bimanual coordination journaltitle: Neuroscience & Biobehavioral Reviews articlelink: http://dx.doi.org/10.1016/j.neubiorev.2014.03.008 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.status: publishe

Brain activation patterns for preparing and performing internally and externally guided bimanual movements in Traumatic Brain Injury

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Callosal contributions to bimanual coordination: influence of task complexity and sensory feedback

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Neural predictors of motor control and impact of visuo-proprioceptive information in youth

For successful motor control, the central nervous system is required to combine information from the environment and the current body state, which is provided by vision and proprioception respectively. We investigated the relative contribution of visual and proprioceptive information to upper limb motor control and the extent to which structural brain measures predict this performance in youth (n = 40; age range 9-18 years). Participants performed a manual tracking task, adopting in-phase and anti-phase coordination modes. Results showed that, in contrast to older participants, younger participants performed the task with lower accuracy in general and poorer performance in anti-phase than in-phase modes. However, a proprioceptive advantage was found at all ages, that is, tracking accuracy was higher when proprioceptive information was available during both in- and anti-phase modes at all ages. The microstructural organization of interhemispheric connections between homologous dorsolateral prefrontal cortices, and the cortical thickness of the primary motor cortex were associated with sensory-specific accuracy of tracking performance. Overall, the findings suggest that manual tracking performance in youth does not only rely on brain regions involved in sensorimotor processing, but also on prefrontal regions involved in attention and working memory. Hum Brain Mapp, 2017. © 2017 Wiley Periodicals, Inc.status: publishe