Unilateral Damage Research Articles

Insula and sensory insular cortex and somatosensory control in patients with insular stroke

In functional imaging studies, the insular cortex (IC) has been identified as an essential part of the processing of a whole spectrum of multimodal sensory input. However, there are no lesion studies including a sufficient number of patients, which would reinforce the functional imaging data obtained from healthy subjects. Such lesion studies should examine how damage to the IC affects sensory perception. We chose acute stroke patients with lesions affecting the IC in order to fill this gap. A comprehensive sensory profiling by applying a quantitative sensory testing protocol was performed and a voxel-lesion behaviour mapping analysis in 24 patients with acute unilateral cortical damage was applied. Our data demonstrate that patients with lesions of the posterior IC have deficits in temperature perception, but did not show other sensory deficits such as hot or cold pain perception associated with specific lesion locations. Our data allow the conclusion that the posterior IC may represent the major region responsible for encoding warm and cold perception in the brain. To what extent focal IC lesions may also impair pain processing or induce post-stroke pain has to be addressed in future studies including more patients.

Optic Ataxia: From Balint’s Syndrome to the Parietal Reach Region

Optic ataxia is a high-order deficit in reaching to visual goals that occurs with posterior parietal cortex (PPC) lesions. It is a component of Balint's syndrome that also includes attentional and gaze disorders. Aspects of optic ataxia are misreaching in the contralesional visual field, difficulty preshaping the hand for grasping, and an inability to correct reaches online. Recent research in nonhuman primates (NHPs) suggests that many aspects of Balint's syndrome and optic ataxia are a result of damage to specific functional modules for reaching, saccades, grasp, attention, and state estimation. The deficits from large lesions in humans are probably composite effects from damage to combinations of these functional modules. Interactions between these modules, either within posterior parietal cortex or downstream within frontal cortex, may account for more complex behaviors such as hand-eye coordination and reach-to-grasp.

MAS 기반 피난시뮬레이션을 이용한 분산대피 비교 연구

Smoke is one of the most critical factor when escaping from the fire since it reduces visibility and interrupts finding emergency exit lights. Therefore, it is recommended that an evacuation simulation program should incorporate the smoke factor. In addition, it is suggested that the program should include not only the unilateral damage by the smoke but also the detour evacuation by risk communication. In this study, MAS (Multi Agent System)-based simulation program which incorporates the reduced walking speed by smoke and adopts the dispersion evacuation logic during escaping from the fire. To make comparison, a commercial evacuation program, Pathfinder was used. It was found that the simulation results of MAS (Multi Agent System)-based program is better than Pathfinder in terms of safe evacuation. It means that evacuation simulation need a additional evaluation categories that include not only quick evacuation time but also safe evacuee number.

Examination and Treatment of Patients With Unilateral Vestibular Damage, With Focus on the Musculoskeletal System: A Case Series

Persistent dizziness and balance problems have been reported in some patients with unilateral vestibular pathology. The purpose of this case series was to address the examination and treatment of musculoskeletal dysfunction in patients with unilateral vestibular hypofunction. The musculoskeletal system was evaluated with the Global Physiotherapy Examination, dynamic balance was measured during walking with triaxial accelerometers positioned on the lower and upper trunk, and symptoms and functional limitations were assessed with standardized self-report measures. The 4 included patients had symptoms of severe dizziness that had lasted more than 1 year after the onset of vestibular dysfunction and a moderate level of perceived disability. Musculoskeletal abnormalities typically included postural misalignment, restricted abdominal respiration, restricted trunk movements, and tense muscles of the upper trunk and neck. The patients attended a modified vestibular rehabilitation program consisting of body awareness exercises addressing posture, movements, and respiration. After the intervention, self-reported symptoms and perceived disability improved. Improvements in mobility and positive physical changes were found in the upper trunk and respiratory movements. The attenuation of mediolateral accelerations (ie, body oscillations) in the upper trunk changed; a relatively more stable upper trunk and a concomitantly more flexible lower trunk were identified during walking in 3 patients. The recovery process may be influenced by self-inflicted rigid body movements and behavior strategies that prevent compensation. Addressing physical dysfunction and enhancing body awareness directly and dizziness indirectly may help patients with unilateral vestibular hypofunction break a self-sustaining cycle of dizziness and musculoskeletal problems. Considering the body as a functional unit and including both musculoskeletal and vestibular systems in examination and treatment may be important.

The ear craves the familiar: Pragmatic repetition in left and right cerebral damage

Background: Repetition occurs plentifully in normal conversation, but empirical studies of the pragmatic use of repetition are rare and pragmatic repetition, defined as verbal repetition in conversational use, in disordered language has not been systematically investigated. Applying a method of analysis that was piloted utilising normal discourse, discourse samples from persons with left and right brain damaged were examined for incidence and charcteristics of repetition.Aims: The purpose of this exploratory study was to examine verbal repetition following cerebral hemispheric damage. From previous studies of hemispheric influences on communicative competence, it was hypothesised that unilateral damage would affect verbal repetition differently. Following earlier results for hemispheric effects on proportion of formulaic expressions, overall more verbal repetition was predicted in persons with left hemisphere damage than those with right hemisphere damage or healthy speakers. Furthermore, previous studies led to a prediction of more repetition of formulaic (than novel, propositional) expressions following left hemisphere damage than the other two study groups. We explored whether characteristics and functions of repetition, developed as part of a new method for quantifying repetition in spontaneous speech, differed systematically between groups.Methods & Procedures: Transcripts of discourse by persons diagnosed with a single cerebral vascular accident and from age- and education-comparable healthy control (HC) participants were analysed. A method was developed for quantifying verbal repetition and identifying five factors, specifically localness (immediate, delayed, or distant), preservation of the original target (identical or altered), source (self or other), grammatical unit of speech (word, phrase, clause, or sentence), and phrase type (formulaic or novel), and three functions (maintaining form, enhancing content, and socialisation).Outcomes & Results: Results revealed significantly higher use of repetition by left hemisphere (28%) than right hemisphere-damaged (RHD) participants (19%) or the HC group (18%). The proportion of formulaic expression repeated by the left hemisphere group was significantly higher (57%) than the right hemisphere group (30%). Fewer repetitions were used by the left hemisphere group (25%) for the function of enhancing the content of talk as compared to the HC group (40%), whereas the RHD group used the least repetition for socialisation (15%).Conclusions: Pragmatic repetition is to be distinguished from rote repetition (on command) in aphasia diagnosis and from pathological repetition behaviours, including perseveration, following brain damage. The method described here allows for the measurement of pragmatic repetition and its characteristics in normal and disordered language. The findings support previous results for pragmatic and formulaic language behaviours in these populations. This study provides new information on the roles of repetition in normal conversation and on the impact of neurological damage on this function. Identification and measurement of repetition will inform perspectives on evaluation and rehabilitation of conversational speech.

Praxis, language, and handedness: A tricky triad

Department of Experimental Psychology, Ghent University, BelgiumOn several occasions in his excellent monograph on apraxia,Georg Goldenberg points at the relation between apraxia,aphasia, and handedness (Goldenberg, 2013b). The co-occurrences of these manifestations are believed to shedlight on their cerebral organization as well as on their mutual(in)dependence.InmycommentIwouldliketoemphasizethedifficulties associated with claims regarding relations be-tween cognitive functions and their neural correlates, inparticular when it comes to their hemispheric co-lateralization. First I will outline the stance taken by Golden-berg, then I will provide some empirical and theoretical in-sights that might hint at an alternative reading of the clinicaldata.In several chapters the question is raised whether there ex-ists an obligatory relation between apraxia and aphasia, as inright handers these symptoms occur most often followingleft hemispheric lesions. Clearly, many studies have reporteda strong association between symptoms of apraxia andaphasia and their co-occurrence even increases in clinicalstudies that use dichotomous categorizations or focus onsevere types of aphasia such as global aphasia (Duffy D Goldenberg, Hartmann, & Schlott, 2003,Goldenberg, Hermsdorfer, Glindemann, Rorden, & Karnath,2007; Wang & Goodglass, 1992). Although it seems fromthese data that most patients suffering from aphasia alsotend to show apraxia, the relation is not mandatory, anddissociations are believed to be more prominent in left-handed patients. Goldenberg devotes a separate chapter toapraxia in left handers. According to his view “the absence ofright handedness leads to a reshuffling of asymmetric brainfunctions resulting in a random distribution of their later-ality” (p. 185). This experiment of nature offers the opportu-nity to investigate what functions ‘go together’ and form anobligatory link, and what functions are independent. Gold-enberg states that if two such functions “are in fact sub-components of one overarching function, they will always belocated in the same hemisphere” (p. 186). Subsequentexploration of clinical data of left-handed patients withapraxia is taken to suggest that most left-handers do notexhibit a more symmetric organization of apraxia, but revealbilateral disturbances following unilateral lesions, just likeright-handers. Goldenberg continues to demonstrate thatleft-handed patients suffer from apraxia as a consequence ofleft or right unilateral brain damage that may or may not beaccompanied by aphasia (Goldenberg, 2013a, 2013b). Heconcludes that neither the relation between apraxia andaphasia nor between apraxia and handedness is obligatoryand that “.the laterality of apraxia can vary independentlyfrom aphasia or handedness.” (p. 190).As Goldenberg elegantly demonstrates, apraxia is not amonolithic construct but consists of several (at least partiallydissociated) symptoms flagging disturbances of an over-arching cognitivefunction calledpraxis. The same can be saidfor aphasia with respect to language. In addition to thecomposed nature of these cognitive concepts, neuroimaginghas unveiled that in normal participants tasks of praxis andlanguage typically activate clusters of regions whose laterali-zation depends on the particular subcomponent and regionunder investigation. Handedness is a multifaceted concepttoo, that varies with the method of assessment and theapplied categorization. Dividing individuals in right and lefthanders might not do justice to the complex influence of thistrait, in particular when relating handedness to asymmetry ofcognitive function. Very few right handers show right hemi-spheric language dominance, but considerably more lefthanders do. As a result, left handed groups are more likely tocontain some individuals with atypical functional asymme-tries, resulting in lower mean asymmetry scores in behavioraland functional imaging studies. Given the complexity of the

Intranigral lipopolysaccharide induced anxiety and depression by altered BDNF mRNA expression in rat hippocampus

It is known that lipopolysaccharide (LPS) treatment induces neuroinflammation and memory deterioration. One of the mechanisms may be the interference with brain-derived neurotrophic factor (BDNF) gene expression and function. Lipopolysaccharide (3 μg/kg and 10 μg/kg) was unilaterally injected into the substantia nigra of adult male Wistar rats. Pergolide-induced rotational behavior test was employed to validate unilateral damage to the dopamine nigrostriatal neurons. Anxiety-depression-like behaviors were studied by means of elevated plus-maze task and forced swimming test, as animal models of anxiety and depression. Rats given LPS exhibited the following: decrease of the percentage of the time spent and the number of entries in the open arm within elevated plus-maze test and decrease of swimming and increase of immobility times within forced swimming test. In addition, these behaviors are associated with decreased BDNF mRNA expression in rat hippocampus. Taken together, these data indicate that intranigral LPS infusion influences the induction of BDNF mRNA expression within hippocampus which contributes to observed behavioral responses in rats, with relevance for Parkinson's disease conditions.

Motion perception within the blind hemifield

BackgroundHomonymous visual field deficit is a common clinical problem, most frequently caused by stroke or traumatic brain injury. After 3 months, the visual field loss is generally considered to be permanent. In certain cases, however, information within the blind hemifield can influence behaviour despite the individual often having no conscious awareness of the stimulus. The mechanism and extent of this function remains poorly understood, especially in cases of adult-onset injury. We aimed to investigate the ability of patients with primary visual cortex damage sustained in adulthood to detect and discriminate direction of low-luminance moving targets within the blind visual field. Our hypothesis was that individuals will retain some ability beyond chance, optimally for speeds between 8°/s and 30°/s. MethodsParticipants were recruited from ophthalmological or stroke services in three UK centres. Testing was done at the John Radcliffe Hospital, Oxford. Of 14 participants recruited, two were excluded after structural imaging showed almost complete damage to the occipital lobe, extending to parietal and temporal lobes including subcortical nuclei. Cases with additional non-correctable visual impairment, or previous neurological disease, were also excluded. All patients had sustained unilateral damage to the primary visual cortex (V1), causing homonymous visual field loss recorded by Humphrey perimetry. Pathological changes had been caused by posterior circulation stroke in 11 patients, or by benign tumour resection in three patients, at least 6 months previously. Psychophysical testing was conducted with a 60Hz monitor at a distance of 68 cm. Visual stimuli consisted of moving black dots (8 dots per deg2) in an aperture of 5° or 8° diameter. Stimulus location was restricted to the scotoma, on a grey background. Each stimulus appeared for 500 ms with jittered onset while the participant fixated on a central black cross. In experiment 1, participants indicated whether a stimulus appeared in the first or second time-interval. If they saw nothing, they were instructed to guess. In experiment 2, participants reported horizontal or vertical direction of motion. In both experiments, stimulus speed was altered parametrically: 4°/s, 8°/s, 20°/s, 32°/s, with 20 trials per condition. Fixation was recorded with an eye tracker, and any trials containing eye movements were removed from analysis. All patients underwent high-resolution structural MRI on the day of testing. Primary outcome was whether patients could demonstrate significant detection or discrimination of visual stimuli above chance. Secondary analysis considered how accuracy altered as a function of stimulus speed. Statistical testing was modelled with a binomial distribution. Written and verbal consent was given by all participants. Ethics approval was provided by the Oxford Research Ethics Committee (ref B 08/H0605/156). FindingsEight patients showed significant detection above chance (patient [P] 1 94%, p<0·01; P2 55%, p=0·04; P3 57%, p=0·03; P4 58·8%, p=0·02; P5 55·8%, p=0·04; P6 67·3%, p=0·01; P7 69·9%, p=0·001; P8 100%, p<0·001), and three patients correctly discriminated direction of motion (P4 75%, p=0001; P6 60%, p=0·018; P7 58·7%, p=0·026). Group analysis revealed an inverted-U pattern of accuracy as a function of speed across both experiments. Performance was best at 20°/s (mean detection 60·3% [SE 3·1], p<0·001, with patients 1 and 8 excluded from analysis because of performance at ceiling; mean discrimination 56·0% [SE 2·6], p=0·01), and also significantly above chance at 4°/s and 8°/s, but not 32°/s. InterpretationThis study is one of the few to assess visual performance in patients with homonymous visual field deficit due to primary visual cortex damage in adulthood. We have shown that even low-contrast complex motion can elicit blindsight in most patients, with optimum detection and discrimination at speeds of 20°/s. In some cases, particularly for direction discrimination, differences in performance can be subtle. Such trends become more apparent at a group level, or perhaps if patients were to undertake a greater number of trials. Performance as a function of speed echoes research into motion processing in area MT+/V5, where an optimum response is seen for intermediate speeds. It provides further evidence for a direct, perhaps subcortical route to this region when V1 is damaged, which may be present in most patients with these areas intact. That slow motion (postulated to depend upon V1 processing) was discriminated above chance, though small, warrants further investigation. FundingRoyal Society, Wellcome Trust, NIHR Oxford Biomedical Research Centre.

Dual-task method unveils the presence of hemispatial neglect after several years from stroke

Event Abstract Back to Event Dual-task method unveils the presence of hemispatial neglect after several years from stroke Mario Bonato1* 1 Ghent University, Department of Experimental Psychology, Belgium Background After unilateral brain damage several stroke patients show neglect, a deficit of awareness for the space opposite to the lesioned hemisphere. Evidence shows that neglect depends on task difficulty but also that it either disappears or stabilizes within few months from stroke. Here I tried to reconcile these apparently contradictory findings by showing that the disappearance of neglect after few months from stroke partially reflects the insensitivity of the testing methods adopted rather than a full recovery of the deficit. Method A right-hemisphere stroke patient (GB) who did not present any deficit at standard paper-and-pencil tests for neglect diagnosis was longitudinally tested for 3.5 years through a computer-based task with different levels of difficulty. Briefly-presented, lateralized targets had to be reported either in isolation or while concurrently processing additional, visual or auditory, stimuli. Results From month 12 to 30 after stroke the patient detected all targets presented in the contralesional hemispace (perfect performance). At month 30, following the administration of a more difficult version of the task with reduced target diameter, the patient showed more than 80% of omissions for the contralesional hemispace. The vast majority of omissions occurred under dual-tasking, that is when the patient had to pay attention not only to stimuli location but also to additional information, either visual or auditory. Discussion A new diagnostic method based on dual-tasking allowed to unveil and modulate the presence and the degree of neglect for more than three years after stroke. It allows to conclude that not only the presence but also the time course of neglect is closely dependent on the testing method difficulty. This new and sensitive approach revealed an unexpectedly long-lasting (neuro)functional plasticity which might also be advantageous for the implementation of more effective rehabilitation policies. Relevance A new computer-based method allowed to obtain a strikingly more sensitive measure of neglect (a disabling disorder of spatial processing). The clinical relevance of this approach is straightforward: Undiagnosed residual neglect in the chronic phases after stroke constitutes a major threat for the personal safety of patients and of other people (e.g. when crossing the road and/or driving) and results in the impossibility in accessing specific rehabilitation. This method mimics every-day life cognitive demands thereby reducing the gap between performance in neuropsychological tests and in complex everyday contexts. Acknowledgements Supported by a FWO-Marie Curie Pegasus Fellowship Keywords: Attention, spatial awareness, hemispatial neglect, computer-based assessment, Neuropsychological Tests, Stroke, stroke rehabilitation Conference: Belgian Brain Council 2014 MODULATING THE BRAIN: FACTS, FICTION, FUTURE, Ghent, Belgium, 4 Oct - 4 Oct, 2014. Presentation Type: Poster Presentation Topic: Clinical Neuroscience Citation: Bonato M (2014). Dual-task method unveils the presence of hemispatial neglect after several years from stroke. Conference Abstract: Belgian Brain Council 2014 MODULATING THE BRAIN: FACTS, FICTION, FUTURE. doi: 10.3389/conf.fnhum.2014.214.00055 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 01 Jul 2014; Published Online: 13 Jul 2014. * Correspondence: Dr. Mario Bonato, Ghent University, Department of Experimental Psychology, Ghent, Belgium, B9000, Belgium, mario.bonato@unipd.it Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Mario Bonato Google Mario Bonato Google Scholar Mario Bonato PubMed Mario Bonato Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Why Bilateral Damage Is Worse than Unilateral Damage to the Brain

Human and animal lesion studies have shown that behavior can be catastrophically impaired after bilateral lesions but that unilateral damage often produces little or no effect, even controlling for lesion extent. This pattern is found across many different sensory, motor, and memory domains. Despite these findings, there has been no systematic, computational explanation. We found that the same striking difference between unilateral and bilateral damage emerged in a distributed, recurrent attractor neural network. The difference persists in simple feedforward networks, where it can be understood in explicit quantitative terms. In essence, damage both distorts and reduces the magnitude of relevant activity in each hemisphere. Unilateral damage reduces the relative magnitude of the contribution to performance of the damaged side, allowing the intact side to dominate performance. In contrast, balanced bilateral damage distorts representations on both sides, which contribute equally, resulting in degraded performance. The model's ability to account for relevant patient data suggests that mechanisms similar to those in the model may operate in the brain.

Hypoxia and spermatogenesis

This review mainly focuses on our understanding of spermatogenesis in physiological and pathological hypoxic condition. Real hypoxia is closely related to vascular changes and an increase in testicular temperature. Both induce a reduction in sperm count and can be related to the increase in germ cell apoptosis. On the other hand, change in the temperature, and oxygen levels in the microenvironment have influence on spermatogonial stem cell function and differentiation. The initial connection between hypoxia and a factor critical for stem cell maintenance is alteration in Oct-4 expression, and these data may be a useful strategy for modulating stem cell function. Unilateral testicular ischemia-induced cell death can be accompanied by an increase in germ cell apoptosis in the contralateral testis. The injury of contralateral testis following unilateral testicular damage is controversial, and it can contribute to the reduction in fertility.

Pathophysiological mechanisms of impaired limb use and repair strategies for motor systems after unilateral injury of the developing brain

The corticospinal tract (CST) is important for limb control. In humans, it begins developing prenatally but CST connections do not have a mature pattern until about 6 months of age and its capacity to evoke muscle contraction does not mature until mid-adolescence. An initially bilateral projection is subsequently refined, so that most ipsilateral CST connections are eliminated. Unilateral brain damage during refinement leads to bilateral developmental impairments. The damaged side develops sparse and weak contralateral spinal connections and the non-involved hemisphere maintains its ipsilateral projection to develop an aberrant bilateral spinal projection. In a kitten model of unilateral spastic cerebral palsy, we replicate key features of the CST circuit changes: robust bilateral CST projections from the non-involved hemisphere, sparse contralateral connections from the affected hemisphere, and motor impairments. We discuss the role of activity-dependent synaptic competition in development of bilateral CSTs and consider several experimental strategies for restoring a more normal pattern of CST connections from the damaged and non-involved sides. We highlight recent results stressing the importance of combined repair of CST axons, restoration of a more normal motor cortex motor representation, and key involvement of spinal cholinergic interneurons in restoring skilled motor function.

Impact of bubble size in a rat model of cerebral air microembolization

BackgroundCerebral air microembolization (CAM) is a frequent side effect of diagnostic or therapeutic interventions. Besides reduction of the amount of bubbles, filter systems in the clinical setting may also lead to a dispersion of large gas bubbles and therefore to an increase of the gas–liquid-endothelium interface. We evaluated the production and application of different strictly defined bubble diameters in a rat model of CAM and assessed functional outcome and infarct volumes in relation to the bubble diameter.MethodsGas emboli of defined number and diameter were injected into the carotid artery of rats. Group I (n = 7) received 1800 air bubbles with a diameter of 45 μm, group II (n = 7) 40 bubbles of 160 μm, controls (n = 6) saline without gas bubbles; group I and II yielded the same total injection volume of air with 86 nl. Functional outcome was assessed at baseline, after 4 h and 24 h following cerebral MR imaging and infarct size calculation.ResultsComputer-aided evaluation of bubble diameters showed high constancy (group I: 45.83 μm ± 2.79; group II: 159 μm ± 1.26). Animals in group I and II suffered cerebral ischemia and clinical deterioration without significant difference. Infarct sizes did not differ significantly between the two groups (p = 0.931 u-test).ConclusionsWe present further development of a new method, which allows reliable and controlled CAM with different bubble diameters, producing neurological deficits due to unilateral cerebral damage. Our findings could not display a strong dependency of stroke frequency and severity on bubble diameter.

Multiple sessions of transcranial direct current stimulation to the intact hemisphere improves visual function after unilateral ablation of visual cortex

Damage to cerebral systems is frequently followed by the emergence of compensatory mechanisms, which serve to reduce the effects of brain damage and allow recovery of function. Intrinsic recovery, however, is rarely complete. Non-invasive brain stimulation technologies have the potential to actively shape neural circuits and enhance recovery from brain damage. In this study, a stable deficit for detecting and orienting to visual stimuli presented in the contralesional visual hemifield was generated by producing unilateral brain damage of the right posterior parietal and contiguous visual cortical areas. A long regimen of inhibitory non-invasive transcranial direct-current stimulation (cathodal tDCS, 2mA, 20min) was applied to the contralateral (intact) posterior parietal cortex over 14weeks (total of 70 sessions, one per day, 5days per week) and behavioral outcomes were periodically assessed. In three out of four stimulated cats, lasting recovery of visuospatial function was observed. Recovery started after 2-3weeks of stimulation, and recovered targets were located first in the periphery, and moved to more central visual field locations with the accrual of stimulation sessions. Recovery for moving tasks followed a biphasic pattern before reaching plateau levels. Recovery did not occur for more difficult visual tasks. These findings highlight the ability of multiple sessions of transcranial direct-current stimulation to produce recovery of visuospatial function after unilateral brain damage.

Posttraumatic Vertigo and Dizziness

Dizziness and vertigo are common symptoms following minor head trauma. Although these symptoms resolve within a few weeks in many patients, in some the symptoms may last much longer and impede ability to return to work and full functioning. Causes of persisting or recurrent dizziness may include benign paroxysmal positional vertigo, so-called labyrinthine concussion, unilateral vestibular nerve injury or damage to the utricle or saccule, perilymphatic fistula, or less commonly traumatic endolymphatic hydrops. Some dizziness after head trauma is due to nonlabyrinthine causes that may be related to structural or microstructural central nervous system injury or to more complicated interactions between migraine, generalized anxiety, and issues related to patients self-perception, predisposing psychological states, and environmental and stress-related factors. In this article, the authors review both the inner ear causes of dizziness after concussion and also the current understanding of chronic postconcussive dizziness when no peripheral vestibular cause can be identified.

On structural computations until fracture based on an anisotropic and unilateral damage theory

This paper describes the formulation and numerical implementation of a family of anisotropic and unilateral damage models for the prediction of damage and final rupture in engineering structures. The damage can be load oriented, microstructure oriented, or (for the first time within this modeling framework) softening. The local equations are solved using a combination of fixed-point and Newton–Raphson algorithms, whose efficiencies are drastically improved through Aitken’s relaxation and BFGS approximation. A delay-effect method is used to control the localization of damage, which leads to an objective calculation of the final rupture of structures.

Continuum Damage Mechanics (CDM) Based Local Approach to the Sheet-Bulk Metal Formability Prediction

Since sheet-bulk metal forming processes inherit properties of both sheet and bulk metal forming processes, their analysis requires on one side following certain methods conventionally devised in these process classes analyses whereas on the other side leaving certain customs out. For instance, inherent anisotropy of the rolled sheet has to be taken into account whereas due to non-vanishing out of plane stress component, analysis with thin shells using the plane stress state assumption is no more applicable. Similarly, methods based on necking instabilities, i.e. forming limit diagrams, which are typically used in sheet metal formability assessment; fall short in sheet-bulk metal formability prediction. In the present study, we propose a local approach to fracture, more specifically a phenomenologically based Lemaitre variant CDM model, devised frequently in bulk metal forming analysis, as an alternative. For this purpose, a combined nonlinear isotropic-kinematic hardening plasticity with Hill48 type initial anisotropy is fully coupled with isotropic damage. Together with the concept of effective stress and equivalent strain principle, quasi-unilateral damage evolution is used, where the energetic contribution of the compressive stress state to the damage driving force is scaled with a so-called crack closure parameter, . For the quasi unilateral damage evolution is inactive whereas for it is fully active which completely suppresses the development of damage under compressive stress states. The framework devises state coupling between elasticity and damage and kinematic coupling between plasticity and damage which increases the relative effect of on the eventual damage development. To this end, a direct extension to the finite strains for metal forming analysis is realized using a corotational formulation and the developed framework is implemented as a VUMAT subroutine for ABAQUS Explicit. For evaluation of the predictive capability of the model, teeth forming process results for DC04 reported in Soyarslan et al. 2011, An Experimental and Numerical Assessment of Sheet-Bulk Formability of Mild Steel DC04, Journal of Manufacturing Science and Engineering, Vol. 133 6, (2011) S. (061008) 1-9, are used. Mechanical material characterization studies are realized using a hybrid experimental-numerical procedure. This methodology relies on minimizing the difference between the experimentally handled global clamp force demand diagrams and the diagrams from the simulations at the complete range of the experiments involving fracture. As known finite element solutions with softening material models are prone to pathological mesh dependence. For this fact, a crack band method is used where the minimum element size, as a controlling parameter of the localization size, is also fitted through the characterization studies and identically used in the process simulations. The simulations show that a correct prediction of the zone and time of fracture is possible for the selected process whereas since the teeth formation process is mainly a compressive process, once the quasi-unilateral damage development is not used, i.e. for , a premature crack prediction is recorded which is not compatible with the experimental findings.

Atypical retinotopic organization of visual cortex in patients with central brain damage: congenital and adult onset.

It remains unclear to what extent retinotopic maps can undergo large-scale plasticity following damage to human visual cortex. The literature has predominately focused on retinotopic changes in patients with retinal pathologies or congenital brain malformations. Yet, damage to the adult visual cortex itself is common in cases such as stroke, tumor, or trauma. To address this issue, we used a unique database of fMRI vision maps in patients with adult-onset (n=25) and congenital (n=2) pathology of the visual cortex. We identified atypical retinotopic organization in three patients (two with adult-onset, and one with congenital pathology) consisting of an expanded ipsilateral field representation that was on average 3.2 times greater than healthy controls. The expanded representations were located at the vertical meridian borders between visual areas such as V1/V2. Additionally, two of the three patients had apparently an ectopic (topographically inconsistent) representation of the ipsilateral field within lateral occipital cortex that is normally associated with visual areas V3/V3A (and possibly other areas). Both adult-onset cases had direct damage to early visual cortex itself (rather than to the afferent drive only), resulting in a mostly nonfunctional hemisphere. The congenital case had severe cortical malformation of the visual cortex and was acallosal. Our results are consistent with a competitive model in which unilateral damage to visual cortex or disruption of the transcallosal connections removes interhemispheric suppression from retino-geniculate afferents in intact visual cortex that represent the vertical meridian and ipsilateral visual field.

An isotropic unilateral damage model coupled with frictional sliding for quasi-brittle materials

In this paper, we present an original extension of an isotropic damage model for quasi-brittle materials and assess its predictive capabilities. The proposed model accounts not only for unilateral behavior related to the opening and closure of microcracks but also for inelastic strains reflecting the frictional sliding along closed microcracks. More importantly, owing to its careful mathematical formulation with a particular attention paid to the continuous differentiability of the underlined thermodynamic potential, the model ensures the continuity of the inelastic stress–strain response. First applications show that it is able to predict the asymmetric behavior and hysteretic response of microcracked materials such as concrete and some rocks

Intranigral lipopolysaccharide administration induced behavioral deficits and oxidative stress damage in laboratory rats: Relevance for Parkinson's disease

In the present study, we examined whether oxidative stress in the hippocampus contributes to memory deficits induced by unilateral injections of two different doses of lipopolysaccharide (3μg/kg and 10μg/kg) into the substantia nigra of adult male Wistar rats. Pergolide-induced rotational behavior test was employed to validate unilateral damage to the dopamine nigrostriatal neurons. Lipopolysaccharide-induced memory impairments were observed, as measured by the Y-maze and radial arm-maze tasks. Decreased activities of superoxide dismutase and glutathione peroxidase were observed in the rat hippocampal homogenates of lipopolysaccharide-treated animals as compared with control. Production of malondialdehyde (lipid peroxidation) significantly increased in the rat hippocampal homogenates of lipopolysaccharide-treated animals as compared with control, as a consequence of impaired antioxidant enzymes activities. Additionally, only within Y-maze, significant correlations between behavioral deficits and indicators of oxidative stress were found.However, further studies are necessary in order to elucidate the effects of intranigral lipopolysaccharide administration on memory performance and oxidative stress status and also the possible correlation that might exist between these aspects.