Postural Control during the Stroop Test in Dyslexic and Non Dyslexic Teenagers

Postural control in quiet stance although simple still requires some cognitive resources; dual cognitive tasks influence further postural control. The present study examines whether or not dyslexic teenagers experience postural instability when performing a Stroop dual task for which their performances are known to be poor. Fifteen dyslexics and twelve non-dyslexics (14 to 17 years old) were recruited from the same school. They were asked to perform three tasks: (1) fixate a target, (2) perform an interference Stroop test (naming the colour or the word rather than reading the word), (3) performing flexibility Stroop task: the subject performed the interference task as in (2) except when the word was in a box, in which case he had to read the word. Postural performances were measured with a force platform. The results showed a main task effect on the variance of speed of body sway only: such variance was higher in the flexibility task than for the other two tasks. No group effect was found for any of the parameters of posture (surface, mediolateral and anteroposterior sway, variance of speed). Further wavelet analysis in the time-frequency domain revealed an increase in the spectral power of the medium frequency range believed to be related to cerebellum control; an accompanying increase in the cancellation time of the high frequency band related to reflexive loops occurred for non-dyslexics only. These effects occurred for the flexibility task and could be due to its high cognitive difficulty. Dyslexics displayed shorter cancellation time for the medium frequency band for all tasks, suggesting less efficient cerebellar control, perhaps of eye fixation and attention influencing body sway. We conclude that there is no evidence for a primary posture deficit in 15 year old teenagers who come from the general population and who were recruited in schools

Postural Hypo-Reactivity in Autism is Contingent on Development and Visual Environment: A Fully Immersive Virtual Reality Study

Although atypical motor behaviors have been associated with autism, investigations regarding their possible origins are scarce. This study assessed the visual and vestibular components involved in atypical postural reactivity in autism. Postural reactivity and stability were measured for younger (12–15 years) and older (16–33 years) autistic participants in response to a virtual tunnel oscillating at different frequencies. At the highest oscillation frequency, younger autistic participants showed significantly less instability compared to younger typically-developing participants; no such group differences were evidenced for older participants. Additionally, no significant differences in postural behavior were found between all 4 groups when presented with static or without visual information. Results confirm that postural hypo-reactivity to visual information is present in autism, but is contingent on both visual environment and development

The pathophysiology of restricted repetitive behavior

Restricted, repetitive behaviors (RRBs) are heterogeneous ranging from stereotypic body movements to rituals to restricted interests. RRBs are most strongly associated with autism but occur in a number of other clinical disorders as well as in typical development. There does not seem to be a category of RRB that is unique or specific to autism and RRB does not seem to be robustly correlated with specific cognitive, sensory or motor abnormalities in autism. Despite its clinical significance, little is known about the pathophysiology of RRB. Both clinical and animal models studies link repetitive behaviors to genetic mutations and a number of specific genetic syndromes have RRBs as part of the clinical phenotype. Genetic risk factors may interact with experiential factors resulting in the extremes in repetitive behavior phenotypic expression that characterize autism. Few studies of individuals with autism have correlated MRI findings and RRBs and no attempt has been made to associate RRB and post-mortem tissue findings. Available clinical and animal models data indicate functional and structural alterations in cortical-basal ganglia circuitry in the expression of RRB, however. Our own studies point to reduced activity of the indirect basal ganglia pathway being associated with high levels of repetitive behavior in an animal model. These findings, if generalizable, suggest specific therapeutic targets. These, and perhaps other, perturbations to cortical basal ganglia circuitry are mediated by specific molecular mechanisms (e.g., altered gene expression) that result in long-term, experience-dependent neuroadaptations that initiate and maintain repetitive behavior. A great deal more research is needed to uncover such mechanisms. Work in areas such as substance abuse, OCD, Tourette syndrome, Parkinson’s disease, and dementias promise to provide findings critical for identifying neurobiological mechanisms relevant to RRB in autism. Moreover, basic research in areas such as birdsong, habit formation, and procedural learning may provide additional, much needed clues. Understanding the pathophysioloy of repetitive behavior will be critical to identifying novel therapeutic targets and strategies for individuals with autism

Aging and vestibular system: specific tests and role of melatonin in cognitive involvement

Balance disorders are frequent with aging. They are particularly important because they decrease social autonomy of the aged subjects and they often provoke falls. The cause is always multifactorial. There is evidence that aging affects multiple sensory inputs, as well as the muscoloskeletal system and central nervous system ability to perform sensorimotor integration. For the evaluation of decreased balance skills in elderly, a specific questionnaire has been prepared, in order to identify high risk of falling called falling risk inventory (FRI) questionnaire, and a complex psycho-sensory-motor test has been studied by means of posturography, in order to detect specific vestibular impairment. Regarding ethiopathogenesis of balance disorders in aged subjects, because the decline of behavioral and cognitive performances are due also to decline of biological rhythm control, the role of melatonin (the hormone regulating circadian rhythms, being strictly connected with cerebellar function, and it is well known that cerebellum acts in elderly both at motor and cognitive regulation. The goals of the present paper are: (i) To present a self-administered FRI questionnaire aimed at identifying possible causes of falls and quantifying falling risk in aged. (ii) To validate posturography as a specific test to investigate vestibular involvement in elderly in correlation with FRI. (iii) To present a complex behavioral test (NT) aimed at evaluating both spatial orientation and spatial memory in elderly, factors involved into the genesis of complex dizziness and unsteadiness. (iv) To evaluate the role of melatonin in cognitive involvement in dizzy, old subjects due to the functional correlations between circadian rhythms, cerebellum balance disturbances and cognitive disorders. General conclusions are: FRI correlates with falling risk. Posturography identifies specific vestibular impairments correlated to balance disorders and elderly falls. Spatial orientation is altered in about 40% of dizzy patients but no significant differences are revealed in melatonin rhythm. Spatial memory is highly altered only in subjects with inversion of circadian melatonin rhythm it is possible to hypothesize that the alteration of the normal circadian melatonin rhythm plays some role in the genesis of dizziness in a subpopulation of patients

Visual Feedback Postural Control Re-education

Maintaining postural stability is a complex process [1] involving the coordinated actions of biomechanical, sensory, motor, and central nervous system components. A relatively simple biomechanical definition for postural stability can be formulated in terms of the position of the body center of gravity relative to the base of support. The body movements used to maintain postural stability, however, are complex because of the number of joint systems and muscles involved. The center of gravity (CoG) is the point at which the whole weight of a body may be considered to act. In humans who are standing quietly and vertically erect, the CoG is located at the level of the hips and slightly forward of the ankle joints. CoG height is 0.5527 of total height. CoG and center of mass (CoM) are equivalent points in space when the gravitational field is uniform and gravity is the only force under consideration