Search PubMed⌕ Search

Biomedical subjects

H Burton

Publications and source records attributed to H Burton.

118 records · Page 7Linked to original sources
PubMed1970

Acetabularia chloroplast DNA: electron microscopic visualization.

Isolated chloroplasts of Acetabularia mediterranea, lysed by osmotic shock in a protein monolayer, released large amounts of supercoiled DNA. In some cases, the DNA radiated in large loops from centers of organization. The amount of DNA per chloroplast may be similar to that of a bacterium.

Centrifugation, Density Gradient↗
PubMedDate not supplied

Functional MRI in human somatosensory cortex activated by touching textured surfaces.

MRI revealed activation foci in human somatosensory cortex during protocols involving stimulation of the fingertips with a textured surface. A 2D T2*-weighted gradient echo sequence was used to acquire images. The imaging protocol included acquiring images while subjects performed specific tactile stimulation paradigms (activation scans) or rested. Three different paradigms were used to produce functional activation using a textured surface to rub the fingertips of one hand. First, motor sensory activation was produced by rubbing the textured surface held in one hand against the fingertips of the opposite hand only during the activation scans. Second, the hand holding the textured surface moved throughout the experiment but touched the fingertips of the opposite hand only during the activation scans. Third, subjects remained still in the magnet throughout the entire study while an investigator rubbed the textured surface against the subjects' fingertips during the activation scans. Images were postprocessed using a cross-correlation scheme. The results revealed multiple foci of motor sensory activation near the central sulcus, postcentral sulcus, and prefrontal cortex.

Adult↗
PubMedDate not supplied

Multiple foci in parietal and frontal cortex activated by rubbing embossed grating patterns across fingerpads: a positron emission tomography study in humans.

Somatosensory representations occupy parietal postcentral gyral (S1) and lateral sulcal-opercular cortex (S2). To address the issue of possible multiple activation foci in these regions and possible differences due to stimulating skin directly or through an imposed tool, we studied changes in cerebral blood flow with positron emission tomography during passive tactile stimulation of one or two fingertips. Restrained fingers were rubbed with embossed gratings using a rotating drum stimulator in 11 subjects. For different scans, gratings touched the skin directly for optimal stimulation of cutaneous receptors (called skin mode stimulation) or indirectly through an imposed guitar plectrum snugly fitted to the same fingers (called tool mode stimulation). The latter was expected to stimulate deep receptors better. Subjects estimated roughness after each scan. Direct skin contact activated statistically validated foci in both hemispheres. On the contralateral side these foci occurred in the anterior and posterior limbs of the postcentral gyrus and on the ipsilateral side only in the posterior limb. Tool mode stimulation activated one contralateral focus that was in the posterior limb of the postcentral gyrus. These results suggest at least two maps for distal fingertips in S1 with the anterior and posterior foci corresponding, respectively, to activations in area 3b and the junction between areas 1 and 2. In contralateral S2, skin mode stimulation activated a peak that was anterior and medial to a focus associated with tool mode stimulation. The magnitude of PET counts contralateral to stimulation was greater in the anterior S1 and the S2 regions during initial scans but reversed to more activation in the posterior S1 during later scans. These short-term practice effects suggest changes in neural activity with stimulus novelty.

Adult↗
PubMedDate not supplied

Tactile attention tasks enhance activation in somatosensory regions of parietal cortex: a positron emission tomography study.

We used positron emission tomography to study cortical regions mediating tactile attention. Cues selectively directed subjects to attend to the roughness or duration of contact with embossed gratings that rubbed against a single fingertip with controlled speed and force. The task required discriminating between paired gratings that differed in tactile features of roughness and/or length. For different blocks of trials, cues directed attention to one tactile feature or indicated a divided attention strategy to a change in either feature. All attention conditions unambiguously activated several somatosensory foci in the parietal cortex, including somatotopically appropriate portions of the primary somatosensory cortex in the postcentral gyrus (S1) and the secondary somatosensory region (S2) within parietal opercular regions. There was no evidence for separate processing foci for selective and divided attention strategies, or for selectively attending to roughness versus stimulus duration. We observed a greater magnitude blood flow change in S2 versus S1 during attention tasks, which suggests that S2 might actually influence S1 activity. Despite these differences, modulation of S1 and S2 supports concepts of early selection in tactile attention. There were also examples of non-sensory foci in frontal cortex, anterior cingulate gyrus and bilateral superior parietal regions at the fundus of the postcentral sulcus. Posterior parietal regions observed in this study did not overlap foci seen in studies of visual attention. Thus, the posterior parietal region may be subdivided into modality-specific subregions, each of which processes information needed to attend to a specific modality. These non-sensory areas may constitute a network that provides a source of modulating influences on the earlier stage, sensory areas.

Adolescent↗
PubMedDate not supplied

A multicenter study of short hour dialysis using AN69S. Preliminary results.

A multicenter prospective study of short hour (SH, less than or equal to 3 hr) dialysis using a high flux membrane (AN69S) plus volumetric control (VC), versus conventional (greater than or equal to 4 hr) (CNV) cellulosic non-VC dialysis, is ongoing. The study hypothesizes that SH treatment over 1 year will provide adequate dialysis, will not increase morbidity, and may improve quality of life. To date, 112 patients have been entered, and 54 have completed 6 months, 30 by SH. There were no differences in biophysiologic parameters at 6 months. Mean hospitalization was 5.24 days per patient. The SH group had a higher (p = 0.0374) hospitalization rate because of two patients. Quality of life was similar in SH and CNV groups. The study indicates that SH dialysis is feasible, safe, and as comfortable as CNV.

Acrylic Resins↗