Diffusion tractography and neuromotor outcome in very preterm children with white matter abnormalities.

BACKGROUND: Moderate-to-severe white matter abnormality (WMA) in the newborn has been shown to produce persistent disruptions in cerebral connectivity but does not universally result in neurodevelopmental disability in very preterm (VPT) children. The aims of this hypothesis-driven study were to apply diffusion imaging to: (i) examine whether bilateral WMA detected in VPT children in the newborn period can predict microstructural organization at the age of 7 y and (ii) compare corticospinal tract and corpus callosum (CC) measures in VPT children at the age of 7 y with neonatal WMA with normal vs. impaired motor functioning. METHODS: Diffusion parameters of the corticospinal tract and CC were compared between VPT 7-y olds with (n = 20) and without (n = 42) bilateral WMA detected in the newborn period. For those with WMA, diffusion parameters were further examined. RESULTS: Microstructural organization of corticospinal tract and CC tracts at the age of 7 y were altered in VPT children with moderate-to-severe WMA detected at term equivalent age as compared with those without injury. Furthermore, diffusion parameters differed in the CC for children with WMA categorized by motor outcome (n = 8). CONCLUSION: WMA on conventional magnetic resonance imaging at term equivalent age is associated with altered microstructural organization of the corticospinal tract and CC at 7 y of age.

Cutaneous stimulation of the digits and lips evokes responses with different adaptation patterns in primary somatosensory cortex.

Neuromagnetic evoked fields were recorded to compare the adaptation of the primary somatosensory cortex (SI) response to tactile stimuli delivered to the glabrous skin at the fingertips of the first three digits (condition 1) and between midline upper and lower lips (condition 2). The stimulation paradigm allowed to characterize the response adaptation in the presence of functional integration of tactile stimuli from adjacent skin areas in each condition. At each stimulation site, cutaneous stimuli (50 ms duration) were delivered in three runs, using trains of 6 pulses with regular stimulus onset asynchrony (SOA). The pulses were separated by SOAs of 500 ms, 250 ms or 125 ms in each run, respectively, while the inter-train interval was fixed (5s) across runs. The evoked activity in SI (contralateral to the stimulated hand, and bilaterally for lips stimulation) was characterized from the best-fit dipoles of the response component peaking around 70 ms for the hand stimulation, and 8 ms earlier (on average) for the lips stimulation. The SOA-dependent long-term adaptation effects were assessed from the change in the amplitude of the responses to the first stimulus in each train. The short-term adaptation was characterized by the lifetime of an exponentially saturating model function fitted to the set of suppression ratios of the second relative to the first SI response in each train. Our results indicate: 1) the presence of a rate-dependent long-term adaptation effect induced only by the tactile stimulation of the digits; and 2) shorter recovery lifetimes for the digits compared with the lips stimulation.

Modulation, adaptation, and control of orofacial pathways in healthy adults.

UNLABELLED: Although the healthy adult possesses a large repertoire of coordinative strategies for oromotor behaviors, a range of nonverbal, speech-like movements can be observed during speech. The extent of overlap among sensorimotor speech and nonspeech neural correlates and the role of neuromodulatory inputs generated during oromotor behaviors are unknown. The focus of this review is to consider the adaptive capacity of the orofacial substrate, and the neural correlates of kinematic parameter encoding at cortical and subcortical levels subserving oromotor behaviors. Special emphasis is directed toward distributed neural networks that are dynamically modulated by environment and task related demands. LEARNING OUTCOMES: Readers will (1) gain a better understanding of healthy adult orofacial pathways, (2) be able to identify orofacial pathway components that contribute to sensorimotor integration, and (3) better understand the flexible connectivity among distributed neural networks subserving oromotor behavior.