Showing papers by "Ann M. Stowe published in 2013"

Functional near-infrared spectroscopy maps cortical plasticity underlying altered motor performance induced by transcranial direct current stimulation

Abstract: Transcranial direct current stimulation (tDCS) of the human sensorimotor cortex during physical rehabilitation induces plasticity in the injured brain that improves motor performance. Bi-hemispheric tDCS is a noninvasive technique that modulates cortical activation by delivering weak current through a pair of anodal-cathodal (excitation-suppression) electrodes, placed on the scalp and centered over the primary motor cortex of each hemisphere. To quantify tDCS-induced plasticity during motor performance, sensorimotor cortical activity was mapped during an event-related, wrist flexion task by functional near-infrared spectroscopy (fNIRS) before, during, and after applying both possible bi-hemispheric tDCS montages in eight healthy adults. Additionally, torque applied to a lever device during isometric wrist flexion and surface electromyography measurements of major muscle group activity in both arms were acquired concurrently with fNIRS. This multiparameter approach found that hemispheric suppression contralateral to wrist flexion changed resting-state connectivity from intra-hemispheric to inter-hemispheric and increased flexion speed (p<0.05). Conversely, exciting this hemisphere increased opposing muscle output resulting in a decrease in speed but an increase in accuracy (p<0.05 for both). The findings of this work suggest that tDCS with fNIRS and concurrent multimotor measurements can provide insights into how neuroplasticity changes muscle output, which could find future use in guiding motor rehabilitation.

Use of functional near-infrared spectroscopy to monitor cortical plasticity induced by transcranial direct current stimulation

Abstract: Electrical stimulation of the human cortex in conjunction with physical rehabilitation has been a valuable approach in facilitating the plasticity of the injured brain. One such method is transcranial direct current stimulation (tDCS) which is a non-invasive method to elicit neural stimulation by delivering current through electrodes placed on the scalp. In order to better understand the effects tDCS has on cortical plasticity, neuroimaging techniques have been used pre and post tDCS stimulation. Recently, neuroimaging methods have discovered changes in resting state cortical hemodynamics after the application of tDCS on human subjects. However, analysis of the cortical hemodynamic activity for a physical task during and post tDCS stimulation has not been studied to our knowledge. A viable and sensitive neuroimaging method to map changes in cortical hemodynamics during activation is functional near-infrared spectroscopy (fNIRS). In this study, the cortical activity during an event-related, left wrist curl task was mapped with fNIRS before, during, and after tDCS stimulation on eight healthy adults. Along with the fNIRS optodes, two electrodes were placed over the sensorimotor hand areas of both brain hemispheres to apply tDCS. Changes were found in both resting state cortical connectivity and cortical activation patterns that occurred during and after tDCS. Additionally, changes to surface electromyography (sEMG) measurements of the wrist flexor and extensor of both arms during the wrist curl movement, acquired concurrently with fNIRS, were analyzed and related to the transient cortical plastic changes induced by tDCS.

Preconditioning the Neurovascular Unit: Tolerance in the Brain’s Nonneuronal Cells

Abstract: Hypoxia has challenged the homeostatic physiology and survival of cells, tissues, and species over many millennia of evolutionary time. As such, it is not surprising that a brief hypoxic “challenge” serves as a powerful preconditioning stimulus to induce a wide variety of epigenetic changes that promote a transient, robust period of enhanced resistance to injury. Evidence for such “tolerance” is particularly strong in the central nervous system, with hypoxic preconditioning (HPC) paradigms affording both the adult and pediatric brain powerful protection from ischemia and other pathologic insults. In this chapter, we review in vivo and in vitro HPC models and what is currently understood regarding the molecular-genetic basis for the observed protective effects, from the signaling pathways inducing the gene expression changes in response to the hypoxic stress to the effectors that account for the injury-tolerant phenotype. Despite relatively intensive investigation, and the identification of several “hypoxia-mimetic” approaches to pharmacologically induce cerebral ischemic tolerance, the precise mechanisms and mediators of this phenomenon still require considerably more elucidation. We close with a translational perspective highlighting the identified strengths and weaknesses that characterize HPC-induced tolerance, the target subpopulations of patients that could potentially benefit from HPC, and the preclinical studies still needed going forward to help propel HPC-based stroke therapeutics from bench to bedside.