Dynamic changes in area 1 somatosensory cortex during transient sensory deprivation: a preliminary study.
ABSTRACT To investigate the neural plasticity in the somatosensory cortex, changes in somatosensory evoked potentials (SSEPs) during finger ischemia were evaluated and compared with those affected by touch or movement interference. Somatosensory evoked potentials were recorded in the vicinity of the central sulcus in four patients with intractable epilepsy. During electrical stimulation to a selected finger, ischemic anesthesia was induced in another finger. Effects of tactile or movement interference were examined during electrical stimulation to the selected finger by applying tactile stimulation to or inducing voluntary movement of the other finger. Dynamic SSEPs were recorded during varying levels of sensory deprivation and different types of interference, and the dynamic nature of the SSEP changes within an individual was studied in detail. Somatosensory evoked potential changes appeared during finger ischemia and tended to persist during the postischemic stage, which is indicative of sensory plasticity and the maintenance of new conditioning. Amplitudes of the early and late cortical components increased when complete finger anesthesia was induced-a sign of the unmasking phenomenon. Amplitudes of early cortical SSEPs decreased when ischemic anesthesia was incomplete, similar to the findings when tactile or movement interference was applied. Surrounding inhibition, therefore, may become dominant before the unmasking phenomenon appears in early cortical SSEPs.
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ABSTRACT: To determine the characteristics of high-frequency oscillations (HFOs) of cortical somatosensory evoked potentials (SEPs), the effect of general anesthesia on HFOs and low-frequency primary cortical responses was studied. The authors recorded SEPs elicited by median nerve stimulation directly from human brains of seven patients who underwent implantation of subdural electrodes before surgical treatment of intractable epilepsy. Recordings were made before and during general anesthesia. Changes in the number of HFOs and amplitude ratios of HFOs/primary cortical responses were analyzed. Under general anesthesia, the number of HFO peaks and the amplitude ratios were significantly decreased. General anesthesia induced remarkably decreased HFO activities when compared to low-frequency SEPs, suggesting that each of those originated from different generators. Possible relations between gamma-amino-butyric acid (GABA)ergic inhibitory interneurons and HFOs are discussed.Journal of Clinical Neurophysiology 11/2006; 23(5):426-30. DOI:10.1097/01.wnp.0000186217.15904.99 · 1.60 Impact Factor
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ABSTRACT: Injury to the cervical spinal cord results in complete or partial loss of arm and hand function, severely limiting the performance of daily activities. Deficits in hand function in individuals with cervical spinal cord injury (SCI) are primarily due to a loss of descending motor pathways that are vital for fine control of the hand and fingers. In addition to these deficits, secondary plastic reorganization may create further loss of function. This thesis will explore the following questions: 1. What are the similarities and differences between cortical organization of muscles affected by a cervical SCI to those not affected by the injury?; 2. Do individuals with cervical SCI improve in hand function and cortical organization after an intensive hand training intervention?; 3. Which physical therapy intervention provides the optimal conditions by which to improve hand function following cervical SCI? In chapter 2 we compare cortical motor maps of transcranial magnetic stimulation (TMS) evoked responses of muscles rostral and caudal to the injury to those of ND individuals. The cortical maps of the biceps brachii or the thenar muscles were constructed, and compared between ND individuals and individuals with SCI. The motor threshold (MT) for the thenar muscles in individuals with SCI was significantly higher than ND individuals. The purpose of the study described in chapter 3 was to compare the functional and cortical changes associated with two different interventions: unimanual or bimanual massed practice training, both combined with somatosensory stimulation. There was a significant difference between pre- and post-intervention scores on tests measuring unimanual hand function, bimanual hand function, and sensory function. This difference was associated with a difference between pre- and post-intervention cortical map area. The purpose of the study described in chapter 4 was to compare clinical and cortical changes associated with either a delayed intervention control period or a combined intervention of massed practice training with electrical stimulation. Participants were randomly assigned to one of two groups: delayed intervention control group or immediate intervention group. Participants were also randomly assigned to one of four groups: unimanual training with somatosensory stimulation, bimanual training with somatosensory stimulation, unimanual training with functional electrical stimulation, or bimanual training with functional electrical stimulation. There was a significant difference between the control and immediate intervention group on the test measuring unimanual hand function. Participants in the bimanual group performed significantly better on the test measuring bimanual hand function. There was a significant difference between the control group and immediate intervention group in cortical map area. In chapter 5 we discuss the clinical relevance of the results of the studies described in three prior chapters. Conclusions drawn include the idea that cortical maps of muscles caudal to the level of injury in individuals with SCI have higher motor thresholds than ND participants. Individuals with tetraplegia can improve in hand function and sensation with a physical therapy intervention of massed practice training combined with somatosensory stimulation. Finally, the type of training (unimanual massed practice or bimanual massed practice) influences the type of improvements gained, however the type of electrical stimulation does not influence the clinical outcome.
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ABSTRACT: To review the principles of neural plasticity and make recommendations for research on the neural bases for rehabilitation of neurogenic speech disorders. A working group in speech motor control and disorders developed this report, which examines the potential relevance of basic research on the brain mechanisms involved in neural plasticity and discusses possible similarities and differences for application to speech motor control disorders. The possible involvement of neural plasticity in changes in speech production in normalcy, development, aging, and neurological diseases and disorders was considered. This report focuses on the appropriate use of functional and structural neuroimaging and the design of feasibility studies aimed at understanding how brain mechanisms are altered by environmental manipulations such as training and stimulation and how these changes might enhance the future development of rehabilitative methods for persons with speech motor control disorders. Increased collaboration with neuroscientists working in clinical research centers addressing human communication disorders might foster research in this area. It is hoped that this article will encourage future research on speech motor control disorders to address the principles of neural plasticity and their application for rehabilitation.Journal of Speech Language and Hearing Research 03/2008; 51(1):S240-58. DOI:10.1044/1092-4388(2008/019) · 1.93 Impact Factor