The diagnostic value of cerebellar-vestibular tests in detecting learning disabilities, dyslexia, and attention deficit disorder

Postural Instability in Children with ADHD Is Improved by Methylphenidate

HIGHLIGHTS

Both spatial and temporal analyses of the Center of Pressure demonstrate that children with ADHD have poorer postural control than typically developing sex-, age-, and IQ-matched children.

Poor sensory integration in postural control could partially explained the deficits in postural stability in children with ADHD.

MPH treatment improves postural performance in both spatial and temporal domains in children with ADHD.

MPH improves postural control specifically when visual and proprioceptive inputs are misleading.

Such improvement could be due to MPH effects on neurons, facilitating cerebellar processing of postural control.

The aim of this study was to examine postural control in children with ADHD and explore the effect of methylphenidate (MPH), using spatial and temporal analyses of the center of pressure (CoP). Thirty-eight children with ADHD (mean age 9.82 ± 0.37 years) and 38 sex- age- and IQ-matched children with typically development were examined. Postural stability was evaluated using the Multitest Equilibre machine (Framiral®) at inclusion and after 1 month of MPH in children with ADHD. Postural stability was assessed by recording under several conditions: with eyes open and fixed on a target, with eyes closed and with vision perturbed by optokinetic stimulation, on stable and unstable platforms. At inclusion, we observed poor spatial and temporal postural stability in children with ADHD. The spectral power index was higher in children with ADHD than in controls. Canceling time was shorter at low and medium frequencies of oscillation and longer at higher frequencies in children with ADHD. After 1 month of MPH, the surface area and mean velocity of the CoP decreased significantly under the most complex conditions (unstable platform in the absence of proprioceptive and visual inputs). The spectral power index decreased significantly after MPH while the canceling time did not change. Poor postural control in children with ADHD supports the hypothesis of cerebellar dysfunction in this disorder. Postural control could be improved by a more efficient processing of sensory inputs (a high-level process), as suggested by the decrease in spectral power index after MPH without changes in the canceling time (a low-level process).

Toward Defining the Neural Substrates of ADHD: A Controlled Structural MRI Study in Medication-Naïve Adults

OBJECTIVE

We assessed the neural correlates of adult ADHD in treatment-naïve participants, an approach necessary for identifying neural substrates unconfounded by medication effects.

METHOD

The sample consisted of 24 medication-naïve adults with Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV) diagnosed ADHD and 24 healthy controls, comparable on age, sex, handedness, reading achievement, IQ, and psychiatric comorbidity. All participants were assessed with structured diagnostic interviews. Magnetic resonance imaging (MRI)-based regional voxel-based morphometry (r-VBM) was used to assess volumetric differences in a priori defined brain regions of interest.

RESULTS

VBM analysis revealed group differences in the hypothesized cortical and subcortical areas; however, only cerebellar volume reductions in ADHD retained significance (p < .05) after corrections for multiple comparisons.

CONCLUSION

These results support the notion that medication-naïve ADHD as expressed in adulthood, manifests subtle brain volume reductions from normal in the cerebellum, and possibly in other syndrome-congruent gray-matter structures. Larger samples are required to confirm these findings.

Distinct regions of the cerebellum show gray matter decreases in autism, ADHD, and developmental dyslexia

Differences in cerebellar structure have been identified in autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), and developmental dyslexia. However, it is not clear if different cerebellar regions are involved in each disorder, and thus whether cerebellar anatomical differences reflect a generic developmental vulnerability or disorder-specific characteristics. To clarify this, we conducted an anatomic likelihood estimate (ALE) meta-analysis on voxel-based morphometry (VBM) studies which compared ASD (17 studies), ADHD (10 studies), and dyslexic (10 studies) participants with age-matched typically-developing (TD) controls. A second ALE analysis included studies in which the cerebellum was a region of interest (ROI). There were no regions of significantly increased gray matter (GM) in the cerebellum in ASD, ADHD, or dyslexia. Data from ASD studies revealed reduced GM in the inferior cerebellar vermis (lobule IX), left lobule VIIIB, and right Crus I. In ADHD, significantly decreased GM was found bilaterally in lobule IX, whereas participants with developmental dyslexia showed GM decreases in left lobule VI. There was no overlap between the cerebellar clusters identified in each disorder. We evaluated the functional significance of the regions revealed in both whole-brain and cerebellar ROI ALE analyses using Buckner and colleagues' 7-network functional connectivity map available in the SUIT cerebellar atlas. The cerebellar regions identified in ASD showed functional connectivity with frontoparietal, default mode, somatomotor, and limbic networks; in ADHD, the clusters were part of dorsal and ventral attention networks; and in dyslexia, the clusters involved ventral attention, frontoparietal, and default mode networks. The results suggest that different cerebellar regions are affected in ASD, ADHD, and dyslexia, and these cerebellar regions participate in functional networks that are consistent with the characteristic symptoms of each disorder.

Impaired Cerebellar Learning in Children with Prenatal Alcohol Exposure: A Comparative Study of Eyeblink Conditioning in Children with ADHD and Dyslexia

Neuroanatomical and behavioral evidence indicate that the cerebellum is particularly vulnerable to the toxic effects of prenatal alcohol exposure. Recent research has shown impairments in eyeblink conditioning in rats following binge-like neonatal ethanol exposure. The neural substrates of eyeblink conditioning have been localized to the cerebellum and related brainstem mechanisms. The present study considered whether heavy prenatal alcohol exposure would result in similar impairments in eyeblink conditioning in children. A related purpose was to determine if eyeblink conditioning could discriminate between children with prenatal alcohol exposure and children diagnosed with attention deficit hyperactive disorder or developmental dyslexia. Fifty-three age-matched children [10 prenatal alcohol exposure (FAE), 16 attention deficit hyperactive disordered (ADHD), 14 children with dyslexia (DYS), 13 normal controls] were assessed on eyeblink conditioning in the delay paradigm. Children in the FAE and DYS groups failed to learn the conditioned response, producing longer latencies and poorly timed responses to the conditioning stimulus. Children with ADHD were impaired on measures of adaptively timed responses, although conditioned responses matched normal controls. The results suggest that children prenatally exposed to alcohol have deficits in cerebellar processing similar to those with dyslexia, and that these functional deficits are related to disabilities in learning.

Egocentric mental rotation in Hungarian dyslexic children

A mental rotation task was given to 27 dyslexic children (mean age 9 years, 2 months) and to 28 non-dyslexic children (mean age 8 years, 8 months). Pictures of right and left hands were shown at angles of 0, 50, 90 and 180 degrees, and the subjects were required to indicate whether what was shown was a right hand or a left hand. It was found that, in this task, the dyslexics did not show the normal pattern of response times at different angles, and also, that they made more errors than the controls. It is argued that this result is compatible with hypothesis that, in typical cases of dyslexia, there is a malfunctioning in the posterior parietal area.

Physiological and behavioral effects of an antivertigo antihistamine in adults

12 neurologically normal adults were tested before and after administration of meclizine, an over-the-counter medication for motion sickness. A battery of four tests was used: (1) distortion-product otoacoustic emissions, (2) the Repeated Evoked Potentials version of the Auditory Brainstem Response, (3) quantitative electroencephalography measured over the left and right sides of the auditory cortex, and (4) a hand-eye coordination task. The battery required approximately 1.5 hr. to complete. Each subject was tested with the battery in each of eight longitudinal sessions: three times on a control day (9 am, 1 pm, 3 pm--no medication); the same times on a second day one week later (medication at approximately 11:30 am), and 24- and 48-hr. check-up sessions following the medication day. Analysis indicated changes in all components, with details suggesting the site(s) of action of this type of antihistamine. The cross-section of the auditory system yielded by this battery makes it possible to observe effects at the periphery, in the brainstem, and in the cortex, including evidence linking otoacoustic emissions with central auditory physiology. Implications range from cautions regarding the use of antihistamines to physiological support for employing such medications to enhance patients' response to vestibular rehabilitation as well as to improve performance in learning-disordered children.

Time estimation deficits in developmental dyslexia: evidence of cerebellar involvement

In addition to their language-related difficulties, dyslexic children suffer problems in motor skill, balance, automatization and speeded performance. Given the recent evidence for cerebellar involvement in the acquisition of language fluency, these problems suggest cerebellar deficit. To test the hypothesis of cerebellar dysfunction in dyslexia, a time estimation task considered to be a sensitive index of cerebellar function was administered to matched groups of dyslexic and control children. The dyslexic children showed the predicted deficit on time estimation (among the most severe obtained in our research programme) but not on a control, loudness estimation, task. Cerebellar dysfunction, therefore, provides a parsimonious account of otherwise disparate data on deficits in dyslexia.

Cognitive and neuropsychological characteristics of attention deficit hyperactivity disorder children receiving stimulant medications

10 children receiving stimulant medication for Attention Deficit Hyperactivity Disorder were compared to normal children on cognitive and neuropsychological dimensions in a pilot study. When compared with 10 normal children the ADHD children showed significant differences on cognitive measures, including the Wechsler Developmental Index, the Bender Visual-motor Gestalt Test, and the Benton Revised Visual Retention Test. Elevated levels of polyspike EEG activity were also noted for these children. Analysis suggested that ADHD children receiving stimulant medications may have persisting neuropsychological difficulty. Further research on the neuropsychological correlates of ADHD seems warranted.

Automatisation deficits in balance for dyslexic children

Traditional theories of dyslexia have focused on components of the reading process. The Dyslexic Automatisation Deficit hypothesis takes a broader view, attributing deficits to an inability to become completely fluent in cognitive and motor skills. A series of experiments compared the balance of 15-yr.-old and 11-yr.-old groups of dyslexic children and normal children matched for age and IQ under single-task and dual-task conditions. There were no group differences in the single-task conditions. However, introduction of a concurrent secondary task led to a dissociation in that, whereas the balance of normal children was unaffected, the dyslexic children's balance was significantly impaired. It was concluded that the normal children balanced automatically whereas the dyslexic children did not. These results directly support the proposed framework.

Dramatic favorable responses of children with learning disabilities or dyslexia and attention deficit disorder to antimotion sickness medications: four case reports

Responses of four learning disabled children who showed dramatic improvements to one or more antimotion-sickness-antihistamines and -stimulants are described qualitatively. These cases were selected from a prior quantitative study in which three antihistamines (meclizine, cyclizine, dimenhydrinate) and three stimulants (pemoline, methylphenidate, dextroamphetamine) were tested in variable combinations (using a specific clinical method) for favorable responses by 100 children characterized by diagnostic evidence of learning disabilities and cerebellar-vestibular dysfunctioning. Pending validation in double-blind controlled studies, these qualitative results suggest that the "cerebellar-vestibular (CV) stabilizing" antimotion-sickness medications, Piracetam included, and their combinations may be shown to be therapeutically useful in treating children with learning disabilities or dyslexia and attention deficit disorder.