Biomedical subjects

Carolyn W-H Wu

Publications and source records attributed to Carolyn W-H Wu.

5 recordsLinked to original sources

PubMed2005

Effects of somatosensory stimulation on use-dependent plasticity in chronic stroke.

BACKGROUND AND PURPOSE: There is a need to develop strategies to enhance the beneficial effects of motor training, including use-dependent plasticity (UDP), in neurorehabilitation. Peripheral nerve stimulation (PNS) modulates motor cortical excitability in healthy humans and could influence training effects in stroke patients. METHODS: We compared the ability of PNS applied to the (1) arm, (2) leg, and (3) idle time to influence training effects in the paretic hand in 7 chronic stroke patients. The end point measure was the magnitude of UDP. RESULTS: UDP was more prominent with arm stimulation (increased by 22.8%) than with idle time (by 2.9%) or leg stimulation (by 6.4%). CONCLUSIONS: PNS applied to the paretic limb paired with motor training enhances training effects on cortical plasticity in stroke patients.

Aged↗

PubMed2005

Enduring representational plasticity after somatosensory stimulation.

Somatosensory stimulation (SS), leading to increases in motor cortical excitability, influences motor performance in patients with brain lesions like stroke. The mechanisms by which SS modulates motor function are incompletely understood. Here, we used functional magnetic resonance imaging (fMRI, blood-oxygenation-level-dependent (BOLD), and perfusion imagings simultaneously acquired in a 3 T magnet) to assess the effects of SS on thumb-movement-related activation in three regions of interest (ROI) in the motor network: primary motor cortex (M1), primary somatosensory cortex (S1), and dorsal premotor cortex (PMd) in healthy volunteers. Scans were obtained in different sessions before and after 2-h electrical stimulation applied to the median nerve at the wrist (MNS), to the skin overlying the shoulder deltoid muscle (DMS), and in the absence of stimulation (NOSTIM) in a counterbalanced design. We found that baseline perfusion intensity was comparable within and across sessions. MNS but not DMS nor NOSTIM led to an increase in signal intensity and number of voxels activated by performance of median nerve-innervated thumb movements in M1, S1, and PMd for up to 60 min. Task-related fMRI activation changes were most prominent in M1 followed by S1 and to a lesser extent in PMd. MNS elicited a displacement of the center of gravity for the thumb movement representation towards the other finger representations within S1. These results indicate that MNS leads to an expansion of the thumb representation towards other finger representations within S1, a form of plasticity that may underlie the influence of SS on motor cortical function, possibly supporting beneficial effects on motor control.

Adult↗

PubMed2005

Somatosensory areas S2 and PV project to the superior colliculus of a prosimian primate, Galago garnetti.

As part of an effort to describe the connections of the somatosensory system in Galago garnetti, a small prosimian primate, injections of tracers into cortex revealed that two somatosensory areas, the second somatosensory area (S2) and the parietal ventral somatosensory area (PV), project densely to the ipsilateral superior colliculus, while the primary somatosensory area (S1 or area 3b) does not. The three cortical areas were defined in microelectrode mapping experiments and recordings were used to identify appropriate injection sites in the same cases. Injections of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) were placed in S1 in different mediolateral locations representing body regions from toes to face in five galagos, and none of these injections labeled projections to the superior colliculus. In contrast, each of the two injections in the face representation of S2 in two galagos and three injections in face and forelimb representations of PV in three galagos produced dense patches of labeled terminations and axons in the intermediate gray (layer IV) over the full extent of the superior colliculus. The results suggest that the higher-order somatosensory areas, PV and S2, are directly involved in the visuomotor functions of the superior colliculus in prosimian primates, while S1 is not. The somatosensory inputs appear to be too widespread to contribute to a detailed somatotopic representation in the superior colliculus, but they may be a source of somatosensory modulation of retinotopically guided oculomotor instructions.

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PubMed2004

Prefrontal cortex asymmetry for memory encoding of words and abstract shapes.

Previous work suggested a differential contribution of prefrontal cortex (PFC) to successful encoding depending on the stimulus material. Here, we tested the hypothesis that encoding of words preferentially involves the left PFC, while encoding of nonverbal items (abstract shapes) relies on the right PFC. We used an experimental design that evaluated encoding of both words and abstract shapes in the same healthy volunteers. A transient virtual lesion of the left or the right PFC was elicited with transcranial magnetic stimulation (TMS) while subjects memorized verbal and nonverbal items. We found that encoding of verbal material was disrupted by left PFC stimulation, whereas encoding of nonverbal material was disrupted by right PFC stimulation. These results demonstrate a functionally relevant lateralization of prefrontal contribution for verbal and nonverbal memory encoding.

Adult↗

PubMed2003

Somatosensory cortex of prosimian Galagos: physiological recording, cytoarchitecture, and corticocortical connections of anterior parietal cortex and cortex of the lateral sulcus.

Compared with our growing understanding of the organization of somatosensory cortex in monkeys, little is known about prosimian primates, a major branch of primate evolution that diverged from anthropoid primates some 60 million years ago. Here we describe extensive results obtained from an African prosimian, Galago garnetti. Microelectrodes were used to record from large numbers of cortical sites in order to reveal regions of responsiveness to cutaneous stimuli and patterns of somatotopic organization. Injections of one to several distinguishable tracers were placed at physiologically identified sites in four different cortical areas to label corticortical connections. Both types of results were related to cortical architecture. Three systematic representations of cutaneous receptors were revealed by the microelectrode recordings, S1 proper or area 3b, S2, and the parietal ventral area (PV), as described in monkeys. Strips of cortex rostral (presumptive area 3a) and caudal (presumptive area 1-2) to area 3b responded poorly to tactile stimuli in anesthetized galagos, but connection patterns with area 3b indicated that parallel somatosensory representations exist in both of these regions. Area 3b also interconnected somatotopically with areas S2 and PV. Areas S2 and PV had connections with areas 3a, 3b, 1-2, each other, other regions of the lateral sulcus, motor cortex (M1), cingulate cortex, frontal cortex, orbital cortex, and inferior parietal cortex. Connection patterns and recordings provided evidence for several additional fields in the lateral sulcus, including a retroinsular area (Ri), a parietal rostral area (PR), and a ventral somatosensory area (VS). Galagos appear to have retained an ancestral preprimate arrangement of five basic areas (S1 proper, 3a, 1-2, S2, and PV). Some of the additional areas suggested for lateral parietal cortex may be primate specializations.

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