Showing papers by "Christoph Braun published in 2000"
TL;DR: The same series of prolonged repetitive stimulations produced two different opposite effects on the spatial relationship of the cortical representations of the digits, suggesting that differential activation in the same region of somatosensory cortex is specific to different tasks.
Abstract: Maps of the body surface in somatosensory cortex have been shown to be highly plastic, altering their configuration in response to changes in use of body parts. The current study investigated alterations in the functional organization of the human somatosensory cortex resulting from massed practice. Over a period of 4 weeks, subjects were given synchronous tactile stimulation of thumb (D1) and little finger (D5) for 1 hr/d. They had to identify the orientation of the stimuli. Neuroelectric source localization based on high-resolution EEG revealed that, when subjects received passive tactile stimulation of D1 or D5, the representations of the fingers in primary somatosensory cortex were closer together after training than before. There was also an apparently correlative tendency to anomalously mislocalize near-threshold tactile stimuli equally to the distant finger costimulated during training rather than preferentially to the finger nearest to the finger stimulated in a post-training test. However, when the stimulus discrimination had to be made, neuroelectric source imaging revealed that the digital representations of D1 and D5 were further apart after training than before. Thus, the same series of prolonged repetitive stimulations produced two different opposite effects on the spatial relationship of the cortical representations of the digits, suggesting that differential activation in the same region of somatosensory cortex is specific to different tasks.
133 citations
TL;DR: Sensitivity of the fingers of the two hands to faint tactile stimuli were tested in eight healthy subjects with a von Frey hair in a forced choice point localization test, showing a higher frequency of mislocalizations to the neighboring fingers than to more distant fingers.
Abstract: Sensitivity of the fingers of the two hands to faint tactile stimuli were tested in eight healthy subjects with a von Frey hair in a forced choice point localization test. Frequencies of correct responses were higher on the left than on the right hand, consistent with a right hemispheric advantage for spatial processing. Within the hands, stimulations of the ring fingers resulted in the highest percentage of correct localizations and stimulations of the thumbs in the fewest correct responses. This superiority of the ring fingers is probably related to a higher point pressure sensitivity and does not reflect the relative size of the representational area of the different fingers in the somatosensory cortex. Mislocalizations, i.e., stimuli that were not correctly attributed to the stimulation site, were located in the vicinity of the stimulation site within the finger as well as across fingers. The distribution of mislocalization across fingers deviates from a distribution expected by chance, showing a higher frequency of mislocalizations to the neighboring fingers than to more distant fingers. This observation in humans matches well with electrophysiological evidence from animal studies that some primary somatosensory cortex neurons have receptive fields that are not restricted to a single digit, but rather cover neighboring digits.
67 citations
TL;DR: The pattern of activation in the somatosensory cortex adapts dynamically to the spatio-temporal characteristics of the stimuli, resulting in integrated, overlapping cortical representations whereas asynchronous stimulation leads to segregated representations.
Abstract: Long-term synchronous tactile stimulation of two sites of the body results in integrated, overlapping cortical representations whereas asynchronous stimulation leads to segregated representations. To investigate the cortical capacity to adapt dynamically to stimulation properties 22 subjects were stimulated at digits 1, 3 and 5 of both hands in either random or fixed order. Changes in the functional organization of the somatosensory cortex were inferred by neuromagnetic source analysis based on somatosensory evoked magnetic fields. Compared to the stimulation in random sequence, the stimulation in fixed order revealed a reduction in distance between the cortical representation of D1 and D3. We conclude that the pattern of activation in the somatosensory cortex adapts dynamically to the spatio-temporal characteristics of the stimuli.
30 citations
01 Jan 2000
TL;DR: Chronic pain patients have experienced years of persistent noxious stimulation in the lumbar region, and cortical reogranization should be present in an area of the somatosensory cortex that represents the back, but not in unrelated areas of somatosENSory cortex, such as those representing the finger.
Abstract: Does the persistent noxious stimulation experienced by patients suffering from chronic back pain lead to cortical reorganization? Previous research has shown that changes in sensory inputs lead to changes in the cortical representation of the relevant somatic structures. Cessation of peripheral input leads to the reduction in size of the cortical representation of the corresponding area, while adjacent cortical areas expand [1]. If a body part is used extensively, however, the corresponding representation in somatosensory cortex expands [2]. Chronic pain patients have experienced years of persistent noxious stimulation in the lumbar region. Cortical reogranization should thus be present in an area of the somatosensory cortex that represents the back, but not in unrelated areas of somatosensory cortex, such as those representing the finger.