Somatosensory mismatch negativity in healthy children.

AIM: Event-related potentials (ERPs) obtained when focused attention is kept away from the stimulus (unnoticed stimulation) are possibly linked to automatic mismatch-detection mechanisms, and could be a useful tool to investigate sensory discrimination ability. By considering the high impact of impaired somatosensory integration on many neurological disturbances in children, we aimed to verify whether mismatch-related responses to somatosensory stimulation could be obtained in healthy children. METHOD: Eleven healthy participants (age range 6-11y, mean 8y 2mo, SD 1y 7mo; seven males, four females) underwent 'oddball' electrical stimulation of the right hand (80% frequent stimuli delivered to the thumb, 20% deviant stimuli delivered to the fifth finger). Data were compared with those obtained when the frequent stimuli to the thumb were omitted ('standard-omitted' protocol). ERPs were recorded at frontal, central, and parietal scalp locations. Children's overt attention was engaged by a demanding video game. RESULTS: In the oddball protocol, deviant stimulation elicited a left central negativity at about 160ms latency, followed by a left frontal negative response at about 220ms latency. Standard-omitted traces showed only a left parietal negative response spreading to right parietal regions. INTERPRETATION: Mismatch-related somatosensory responses can be reliably obtained in children, providing that appropriate technical contrivances are used. In clinical use, the frontal components, which are present only during the oddball protocol, could be a reliable and unequivocal neurophysiological marker of the automatic mismatch-detection mechanism.

Dissociated effects of quiet stance on standard and high-frequency (600 Hz) lower limb somatosensory evoked potentials.

OBJECTIVE: To verify whether standing can modulate somatosensory input from lower limb to the cortex. Somatosensory afferents have been evaluated not only by means of somatosensory evoked potentials recorded by means of classical wide-bandpass filtering (standard SEPs), but also by high-frequency somatosensory evoked potentials (HF-SEPs), which probably play a role in the processing of rapid adaptive changes. METHODS: Eight healthy subjects underwent right posterior tibial nerve (PTN) stimulation in two different conditions (standing and lying supine). Standard SEPs reflecting the activity of both subcortical and cortical generators further underwent digital filtering (300-800 Hz), in order to enhance HF-SEP components. RESULTS: Stance significantly reduces the P40 cortical component of standard SEPs. By contrast, HF-SEPs did not show any significant change between the two conditions. CONCLUSIONS: The lack of any gating effect on HF-SEPs lends further substance to the hypothesis that HF-SEPs play a pivotal role in the processing of somatosensory inputs related to rapid adaptive changes. SIGNIFICANCE: Our data confirm that standard and HF-SEPs reflect two distinct mechanisms with strongly different functional significance. Further studies are needed to definitively establish whether this dissociation is merely caused by the activation of anatomically different neuronal pools, or by the involvement of distinct functional mechanisms.

Visual and vestibular functioning, and age and surgery effects on postural control in healthy children with vertical strabismus.

PURPOSE: To describe visual and vestibular functioning and the effects of age and surgery effects on postural control in healthy children with vertical strabismus. DESIGN: This is a comparative case series. METHODS: We evaluated participants at the Scientific Institute Eugenio Medea during routine clinical activities. We enrolled 30 consecutive children/adolescents (age range 4-13 years) with isolated vertical strabismus, with and without corrective surgery. Participants were split into four subgroups according to age (4-8 years versus 9-13 years) and ocular surgery (surgery versus no surgery). The clinical protocol included ophthalmological, orthoptic, neurological, physiatrical, otolaryngological, and vestibular evaluations, and the instrumental protocol included ocular cyclotorsions assessment, posturography, and vestibular myogenic-evoked potentials. Main outcome measures of the study were the prevalence of study-relevant orthopedic, ocular, vestibular, and posturographic abnormalities. RESULTS: Among the overall largely variable findings across patients' groups, we found some interesting trends: larger binocular vision and convergence disorders in younger children, smaller prevalence of asymmetric vestibular-evoked potentials in operated children, less posturographic abnormalities in younger children. No clear-cut beneficial effect of surgery was found on all clinical and instrumental parameters considered, despite good re-alignment of the eyes. CONCLUSION: The pathophysiology of postural control in vertical strabismus is extremely complex and above the potential of this study design and should be specifically addressed in deeper experimental studies.

MRI predicts efficacy of constraint-induced movement therapy in children with brain injury.

Using resting state (RS) functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), we identified the predictors of clinical improvement following constraint-induced movement therapy (CIMT) in pediatric patients with chronic hemiplegia.From 14 children with congenital or acquired brain injury and 10 sex- and age-matched healthy controls, brain dual-echo, DTI and RS fMRI sequences were acquired before CIMT. The Quality of Upper Extremities Skills Test and the Gross Motor Function Measure (GMFM) were administered at baseline, at the end of CIMT (10 weeks), and after 6 months. Mean diffusivity and fractional anisotropy (FA) were measured in the lesion responsible for the clinical symptomatology, the affected and unaffected corticospinal tract (CST), motor transcallosal fibers, and uncinate fasciculus (as an internal control). Independent component analysis was used to identify the sensorimotor RS network. The ability of baseline MRI variables to predict clinical changes over time was assessed using multivariate linear models. At baseline, patients had increased mean diffusivity in the symptomatic lesion and decreased FA in the symptomatic lesion, affected corticospinal tract, and motor transcallosal fibers. A reduced RS functional connectivity was found in the bilateral cerebellum, left precentral gyrus, and right secondary sensorimotor cortex. At follow up, Quality of Upper Extremities Skills Test and GMFM scales improved significantly. Baseline average lesion FA predicted clinical improvement at week 10, and baseline functional connectivity of the right secondary sensorimotor cortex and cerebellum predicted GMFM improvement at month 6. DTI and RS fMRI offer promising and objective markers to predict clinical outcomes following CIMT in pediatric patients with congenital or acquired hemiplegia.