<p> The dissertation consists of three parts. The first part is a systematic review of the literature regarding transcranial direct current stimulation (tDCS) and its effects on lower extremity motor behaviors and corticospinal excitability of the lower extremity representation of the motor cortex in healthy subjects. The second part investigates how different electrode montages and electrode conductance mediums affect corticospinal excitability of the tibialis anterior (TA) representation of the motor cortex in healthy subjects. The third part studies how different electrode montage and electrode conductance medium combinations affect ankle tracking accuracy in healthy subjects regarding the dominant lower extremity.</p><p>

<p> BACKGROUND AND PURPOSE: While it is well known that sensory impairment is indicative of poor outcome following stroke, we do not know its true prevalence nor do we understand how brain lesions influence sensory impairment or how sensory impairment influences functional status. The current project analyzed an existing de-identified database to address three specific aims: 1) To determine the prevalence of impairments of absolute and just noticeable difference sensory thresholds in chronic stroke, 2) To determine the relationship of specific lesion characteristics to impaired sensory thresholds in chronic stroke, and 3) To determine the correlation between impaired sensory thresholds and functional status in the chronic phase of stroke. METHODS: Absolute and just noticeable difference sensory thresholds were assessed for eleven perceptual continua spanning five sensory domains in 110 subjects (76 normal controls, 21 with right hemisphere lesions, 13 with left hemisphere lesions). Lesion volume and subtraction analysis were performed with the MRIcroN software. RESULTS: Subjects with right hemisphere lesions had a greater percentage of failures on threshold assessments that subjects with left hemisphere lesions (p=0.004) and normal control subjects (p&lt;0.0001). Subjects with right hemisphere lesions had greater severity of impairment on threshold assessments than subjects with left hemisphere lesions (p=0.003) and normal control subjects (p&lt;0.0001). Lesion volume was not correlated with impaired sensory thresholds, instead lesions of the caudate nucleus were common to subjects with a high percentage of failures on threshold assessments. Impaired sensory thresholds correlated with stroke severity as defined by the NIHSS (r=0.39, p&lt;0.03) and transfer scores on the Barthel Index (r=-0.55, p=0.02).</p>