Reporting to NCEPOD.
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Hospital Mortality↗
Biomedical subjects
H Burton
Publications and source records attributed to H Burton.
Ipsilateral cortical connections of primary somatic sensory cortex in rats.
The organization of ipsilateral cortical connections of the rat primary somatic sensory area (SI) was analyzed following small injections of multiple fluorescent tracers in the same case, into two or three SI body representations identified electrophysiologically. Labeling patterns were studied in tangential cortical sections and in flattened reconstructions from coronal sections. The cytochrome oxidase staining in tangential sections served as a control for injection location and to position labeling patterns found within granular portion of SI. The results show that most connections made with SI are reciprocal. Their topographical organization show different degrees of precision in the different areas. Homotypical and heterotypical connections were defined, the latter being more evident within the granular portion of SI. The findings: (1) were consistent with subdividing rat SI into four distinct areas with each having its own pattern of connections, (2) revealed two topographically organized regions in parietal cortex lateral to SI called second somatosensory (SII) and parietal ventral (PV) areas, (3) confirmed a topographical pattern in motor cortex and suggested an organization for connections between SI and an agranular medial field, and (4) demonstrated three more regions in parietal cortex connected to SI: posterior to SI called parietal medial; lateral to PV called parietal rhinal; posterior to SII called parietal lateral. Differences were noted in the distinctions between and within the maps when label distributions were plotted separately from supra- and infragranular layers. These findings agree with previous parcellations of the rat SI (Chapin et al., '87: J. Comp Neurol 263:326-346), squirrel PV and SII (Krubitzer et al., '86: J. Comp Neurol 250:403-430), and the organization of rat corticospinal neurons in many of the same areas (Li et al., '90: Somat Motor Res 7:315-335).
Animals↗
Topography of connections between primary somatosensory cortex and posterior complex in rat: a multiple fluorescent tracer study.
Thalamocortical connections between ipsilateral thalamus and the first somatic sensory area were traced with simultaneous injections of different fluorescent tracers. Labeled neuronal elements in the antero-medial part (POm) of the posterior nucleus (PO) were topographically organized as an up-right body representation that mirrored a map in the ventroposterior nuclei (VP). No topography was observed in the posterior part of PO. These findings suggest POm in rodents provides precisely organized projections, parallel with those from VP.
Animals↗
Second somatosensory cortical area in macaque monkeys: 2. Neuronal responses to punctate vibrotactile stimulation of glabrous skin on the hand.
Single neuron responses from the second somatosensory cortical area (SII) of macaque monkeys were studied using computer-controlled vibratory stimuli ranging in frequency from 10 to 300 Hz. Results were obtained using chronic recording techniques in awake or lightly tranquilized animals. Most neurons were unable to follow the temporal order of vibrations in excess of 10 Hz. A smaller sample of cells provided faithful reproduction of frequencies up to 50-75 Hz and another responded to low amplitude, high frequency stimulation in excess of 100 Hz. Cells that displayed temporally cohesive responses to lower frequencies demonstrated predictable, time-locked discharges to successive stimulus cycles. Cells activated by higher frequencies showed a lower probability of following successive stimulus cycles. These findings are discussed in reference to the hypothesis that SII may provide a parallel channel for processing high frequency vibrotactile inputs from Pacinian receptors.
Animals↗
Differential effects of GABA and bicuculline on rapidly- and slowly-adapting neurons in primary somatosensory cortex of primates.
In cortical area 3b of monkeys, responses of 71 single neurons to controlled indentations of glabrous skin were recorded before and during iontophoretic application of GABA and bicuculline methiodide (BMI), a GABA receptor antagonist. Constant amplitude indentations were applied to selected sites within the receptive fields of neurons representing the glabrous skin on the digits and palm. Profiles of response magnitudes across stimulation sites were used to quantify receptive field dimensions before and during antagonism of GABAergic inhibition. During administration of BMI, the receptive fields of 26 rapidly-adapting neurons were increased by 3-4 times their original size. Response latencies were substantially longer in the region of expansion than in the original receptive field, suggesting that expansion might be mediated by intracortical connections. The expansion of RFs onto adjacent digits after blockade of GABAergic inhibition suggests that somatotopic reorganization following digit amputations may be subserved by existing excitatory connections. The responses of slowly-adapting neurons were separated into two components, a "dynamic" response corresponding to activity elicited by the initial indenting ramp and a "static" response produced by the sustained indentation. Among 8 slowly-adapting neurons tested with BMI, the receptive fields of the dynamic response component increased to an extent that was similar to the change produced in rapidly-adapting neurons. By contrast, the static response component was rarely altered by BMI. Comparison of the responses to administration of GABA revealed that only 12 of 27 slowly-adapting neurons were inhibited in a dose-dependent manner, whereas 37 of 44 rapidly-adapting neurons exhibited significant reduction of responses in the presence of GABA. Hypotheses are proposed to explain the differential effect of BMI and GABA on slowly- and rapidly-adapting cortical neurons.
Adaptation, Physiological↗
Neuronal activity in the primary somatosensory cortex in monkeys (Macaca mulatta) during active touch of textured surface gratings: responses to groove width, applied force, and velocity of motion.
1. In a descriptive survey of primary somatosensory cortex (SI) responses during active touch, two monkeys (Macaca mulatta) were trained to stroke their fingertips over pairs of gratings with constant ridge (250 microns) and varying groove (500-2,900 microns) width (roughness) and to identify the smoother (smaller groove). Speed of hand motion and applied force level during the stroke were monitored and recorded. Transdural single-unit recordings were obtained from areas 3b and 1 of SI while animals performed the task. 2. The statistical sample consisted of 164 single units. Most cells in the sample responded in some fashion during the stroke, including brief increased or decreased activity to 1-mm ridges (touch strips) placed between surface pairs and at ends of each block to serve as touch sensors. These peristroke response patterns were described briefly. Most cells (153/164) responded to grating contact. Three types of responses to groove width were characterized. 1) Response was proportional to groove width in many cells. There was a vigorous response to roughest and none to smoothest surface. Mean firing rates for these cells appeared linearly related to groove width. 2) Graded responses were seen with smaller response differences to the same groove width range as in 1. Responses of some cells of types 1 and 2 were uncorrelated with variations in applied force and velocity of stroke. 3) There were inverse responses to groove width. Greater responses occurred during contact with smoother surfaces. 3. Many cells were influenced by a combination of changes in groove width, force, and/or velocity. Activity of a small sample of cells in area 1 with slowly adapting (SA) response properties was an almost exclusive positive function of variations in force level. Unlike SAs in 3b, responses of these cells were uncorrelated with alterations in groove width or stroke velocity. Velocity effects were almost always associated with response to groove width. Positive velocity cells coded temporal period. Significant velocity effects were not evident in graded or inverse graded cells. Negative force and velocity effects were due to shifts in behavioral strategy. Periodicity related to the spatial period of the grating was found in autocorrelograms of a small number of cells. Finally, responses of some cells were unaffected by changes in groove width, force, or velocity. Some of these were affected by contact with touch strips. Others responded in undifferentiated fashion to the stroke, and their function remains unresolved. Overall, there was a continuum of response patterns. Subgroups of cells were not distinct.(ABSTRACT TRUNCATED AT 400 WORDS)
Analysis of Variance↗
Tactile discrimination of gratings: psychophysical and neural correlates in human and monkey.
Human and monkey performance on discriminating tactile gratings revealed comparable cross-species Weber functions. Neural data obtained while monkeys performed discriminations revealed some matching of neural and psychometric functions. Nearly constant firing rate differences occurred at discrimination threshold for unequal groove widths. Firing rate differences of some cells decreased on trials preceding discrimination errors, and thus predicted performance.
Animals↗
Neuronal responses in ventroposterolateral nucleus of thalamus in monkeys (Macaca mulatta) during active touch of gratings.
Responses of single neurons were recorded from the ventroposterolateral nucleus (VPL) of the thalamus while a monkey stroked its fingertips over gratings. Monkeys were trained to stroke the gratings with consistent downward applied force and velocity of hand motion. Neurons were selected with receptive fields on the glabrous digits. Average firing rate was computed for a range of grating groove widths; groove width corresponded to roughness. Force and velocity were measured. VPL responses were compared to previously reported responses in primary somatosensory cortex (SI) under identical stimulus conditions, and to reports of peripheral afferent fiber responses to passively applied gratings. VPL responses more closely resembled those of peripheral afferent fibers than those of SI in important respects: lack of independent responses to roughness, force, and velocity; high temporal and force fidelity; and response patterns that closely followed the shape of elevated metal strips used to separate pairs of gratings. The presence in cortex of response patterns not seen in the thalamus, such as response independence and negative correlations to groove width, suggests that they stem from cortical processing.
Afferent Pathways↗
The role of spatially selective attention in the tactile perception of texture.
During manual sensing of object attributes like surface texture, the tactile receptor sheet is conjointly activated at numerous loci. What is the role of spatially selective attention in perception under these conditions? We show that the requirement for spatial focus of attention is minimal in the detection of an abrupt change in texture. In contrast, spatial attention may help in a variety of other tasks of comparable difficulty. These include detecting the absence of a texture change at one of many loci, distinguishing its direction, and discriminating between different textures. Attentional demand appears to vary along a continuum in these tasks, rather than being all-or-none.
Adult↗
Selective attention in vibrotactile tasks: detecting the presence and absence of amplitude change.
Selective spatial attention has a greater effect on detection of the absence of an amplitude change than it has on detection of the presence of such a change. Attention to one of four fingertips was manipulated by an 80% valid tactile cue in two-interval forced-choice tasks. In one task, the target was a vibrotactile amplitude change appearing among constant-amplitude distractors; in the other task, targets of constant amplitude had to be detected amid amplitude changes at the other fingertips. Cuing had a greater effect on the latter task than it did on the former. This asymmetry is consistent with the presence-absence asymmetry found in visual search and does not depend on the difficulty of the two tasks. A statistical model shows that a pooled activity mechanism could account for these experimental results.
Adult↗
Second somatosensory cortical area in macaque monkeys. I. Neuronal responses to controlled, punctate indentations of glabrous skin on the hand.
Responses of 492 single neurons from the second somatosensory cortical area of macaque monkeys were studied using computer controlled ramp indentations. Results were obtained using chronic recording techniques from lightly tranquilized or awake animals. Amongst those cells that were activated by punctate tactile stimuli, various subclasses of responses were identified that included neurons with phasic and sustained adaptation characteristics. In addition, several cells showed unusual firing patterns, such as delayed responses and reverberating afterdischarges. Latency measurements from 90 cells showed a modal latency to ramp stimuli of 34 ms and a second group of cells whose latency exceeded 75 ms. Measurements of response functions to different velocities of indentation revealed that some cells maintained relatively shallow ascending functions but that most cells were insensitive to the velocity variable. The response characteristics of these neurons in primates are discussed in reference to the hypothesis that in the somatosensory cortex, SII occupies a higher order, serially dependent region in a hierarchy from SI to other parts of the brain.
Action Potentials↗
Implantation of cultured sensory neurons and Schwann cells into lesioned neonatal rat spinal cord. II. Implant characteristics and examination of corticospinal tract growth.
The purpose of this study was to test the effectiveness of implants derived from peripheral neural tissue to serve as bridges following interruption of the developing corticospinal tract (CST). Implants prepared from purified populations of cultured dorsal root ganglion neurons (DRGNs) and Schwann cells (SCs) (Kuhlengel et al., J. Comp. Neurol. 293:63-73, 1990) were placed into thoracolumbar regions of neonatal rat spinal cord from which a 2-mm length of dorsal columns had been removed by suction. These cords were examined by a number of techniques 10 days to 6 months later. The implants, recognizable by their DRGN content, filled the vacated dorsal columns and survived the longest periods examined. The most effective method to maintain implant position was dorsal placement of collagen-coated Nitex filter. Implants were inserted either at the time of lesioning or 5 days later. The implant survival rate was better (72% vs. 50%) and meningeal scarring was less with immediate implantation, but delayed implantation resulted in better implant-cord fusion and the implant better filled the lesion cavity. DRGN/SC implants became well vascularized without leptomeningeal cells; this may explain why implant survival was not improved with leptomeningeal cell addition. Particularly well-differentiated implants (full extracellular matrix production and myelination) did not fuse as well with cord as did those less well differentiated. The addition of nerve growth factor to the Nitex filter collagen coating led to improved survival of DRGNs in implants. Electron microscopy showed that astrocytes populated the implant-cord junction region and migrated into implants. Typical SCs related to nonmyelinated and myelinated axons were present in implants. Close proximity of astrocytes and central myelin to SCs and peripheral myelin demonstrated good implant integration with cord. Clusters of SCs, astrocytes, and axons, all enclosed within a common basal lamina, were observed in implants. Immunostaining for GFAP and laminin confirmed our microscopy findings that SCs did not migrate from implant into host but that astrocytes left host tissue to enter implants. Neuroanatomical tracing of CST neurons with HRP-WGA showed that labeled fibers were not present in the implant but were fasciculated just beneath in gray matter. These fibers remained clustered in gray matter underneath the ventral dorsal columns caudal to the lesion. In lesioned but not implanted rats, labeled fibers were only diffusely distributed in gray matter. Delayed implantation led to more variation in fasciculation compared with immediate implantation.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Altered responses to cutaneous stimuli in the second somatosensory cortex following lesions of the postcentral gyrus in infant and juvenile macaques.
Infant macaques recover tactile abilities better than older animals after somatosensory cortical lesions. To investigate the neural basis of this phenomenon, we ablated the hand representation in primary somatosensory cortex (SI) of infant and juvenile Macaca mulatta and recorded in ipsilateral second somatosensory cortex (SII) a year later. We also made tracer injections to verify the lesion boundaries and to study the connections of SII after the lesion of SI. Similar to the report of Pons et al. (Science 237:417-420, '87), we found that substantial portions of the SII hand area were unresponsive to cutaneous stimulation of the hand in both age groups. Particularly, there were no cutaneous receptive fields restricted to the digits. Some responses were elicited in each animal by mechanical stimulation of the hand, including a proportion related to cutaneous receptive fields. This proportion was higher in the infants than in the juveniles, which may explain the greater capacity of the infants for recovery of tactile function after SI lesions. The residual somatic drive in the SII hand area of the juveniles was attributable to sparing of parts of areas 3a and 3b. However, in the infants, this explanation was not tenable since the responses noted in SII occurred even after total ablations of the postcentral gyrus. The pattern of corticocortical connections revealed by injections of HRP into the medial margin of the SI lesion and of Fast Blue into SII in one infant confirmed the absence of SI inputs to the region of SII where responses were recorded from the hand. Representations of body parts other than the hand were normally responsive, and their location was consistent with normal somatotopy in SII.
Animals↗
Persistent arteriolar constriction in microcirculation of the terminal ileum following moderate hemorrhagic hypovolemia and volume restoration.
A stable in vivo preparation of moderate hypovolemia with prompt volume restoration was produced in anesthetized rats. The microcirculation of the terminal ileum was observed in vivo videomicroscopy, and changes in mean arterial pressure (MAP) as well as arteriolar diameters were recorded after a 30-min period in which the MAP was reduced by 50% by bleeding. Volume was restored with shed blood alone (control); dextran 70 alone (dextran); or dextran + hypertonic (7.5%) saline (dextran + HS). A final group of rats was pretreated with allopurinol 5 mg/kg and then treated identically to the control group to assess the role of the xanthine oxidase system in microcirculation changes following hemorrhage. MAP was restored to normal by return of shed blood in control animals, but inflow arterioles (A1) remained significantly constricted. MAP was significantly higher and A1 arteriolar dilation was observed in the dextran + HS group. Responses in allopurinol-pretreated animals were not different from the responses seen in control animals. We conclude that persistent arteriolar constriction is produced by moderate hypovolemia and this effect is ameliorated by volume restoration with dextran + HS.
Allopurinol↗
Southwest Oncology Group Study 8710: trial of cystectomy alone versus neo-adjuvant M-VAC and cystectomy in patients with locally advanced bladder cancer (Intergroup Trial 0080).
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Aged↗
Comparison of magnetic resonance imaging and computed tomography in suspected lesions in the posterior cranial fossa.
OBJECTIVE: To compare computed tomography and magnetic resonance imaging in investigating patients suspected of having a lesion in the posterior cranial fossa. DESIGN: Randomised allocation of newly referred patients to undergo either computed tomography or magnetic resonance imaging; the alternative investigation was performed subsequently only in response to a request from the referring doctor. SETTING: A regional neuroscience centre serving 2.7 million. PATIENTS: 1020 Patients recruited between April 1986 and December 1987, all suspected by neurologists, neurosurgeons, or other specialists of having a lesion in the posterior fossa and referred for neuroradiology. The groups allocated to undergo computed tomography or magnetic resonance imaging were well matched in distributions of age, sex, specialty of referring doctor, investigation as an inpatient or an outpatient, suspected site of lesion, and presumed disease process; the referring doctor's confidence in the initial clinical diagnosis was also similar. INTERVENTIONS: After the patients had been imaged by either computed tomography or magnetic resonance (using a resistive magnet of 0.15 T) doctors were given the radiologist's report and a form asking if they considered that imaging with the alternative technique was necessary and, if so, why; it also asked for their current diagnoses and their confidence in them. MAIN OUTCOME MEASURES: Number of requests for the alternative method of investigation. Assessment of characteristics of patients for whom further imaging was requested and lesions that were suspected initially and how the results of the second imaging affected clinicians' and radiologists' opinions. RESULTS: Ninety three of the 501 patients who initially underwent computed tomography were referred subsequently for magnetic resonance imaging whereas only 28 of the 493 patients who initially underwent magnetic resonance imaging were referred subsequently for computed tomography. Over the study the number of patients referred for magnetic resonance imaging after computed tomography increased but requests for computed tomography after magnetic resonance imaging decreased. The reason that clinicians gave most commonly for requesting further imaging by magnetic resonance was that the results of the initial computed tomography failed to exclude their suspected diagnosis (64 patients). This was less common in patients investigated initially by magnetic resonance imaging (eight patients). Management of 28 patients (6%) imaged initially with computed tomography and 12 patients (2%) imaged initially with magnetic resonance was changed on the basis of the results of the alternative imaging. CONCLUSIONS: Magnetic resonance imaging provided doctors with the information required to manage patients suspected of having a lesion in the posterior fossa more commonly than computed tomography, but computed tomography alone was satisfactory in 80% of cases...
Brain Diseases↗
Quantitative measurements of receptive field changes during antagonism of GABAergic transmission in primary somatosensory cortex of cats.
In cortical area 3b of cats, responses of 76 single neurons to punctate indentations were recorded before and during iontophoretic administration of bicuculline methiodide (BMI), a GABAergic antagonist, at levels that did not affect spontaneous activity. Constant amplitude indentations were applied to selected sites along distal-proximal and radial-ulnar axes that intersected the most sensitive area in the receptive field. Profiles of response magnitudes were used to measure receptive field dimensions before and during antagonism of GABAergic inhibition. Blockade of GABAergic transmission caused receptive field dimensions of 48 rapidly-adapting neurons to increase an average 141%, or nearly 2.5 times their original size. Analysis of the spatial distribution of inhibition indicated that in-field inhibition was larger than surround inhibition. During BMI administration, response latency was significantly longer for response elicited from the expanded territory than for responses elicited from within the original receptive field, suggesting that receptive field expansion might be mediated by multisynaptic intracortical connections. The magnitude of receptive field expansion was independent of receptive field size or peripheral location. In a substantial number of neurons, however, BMI produced asymmetric expansions that extended only in the proximal direction. For 9 slowly-adapting neurons. BMI produced measurable increases in receptive field dimensions, but these changes were significantly smaller than the changes in rapidly-adapting neurons.
Anesthetics↗
Somatotopic organization of the second somatosensory cortical area after lesions of the primary somatosensory area in infant and adult cats.
The somatotopic organization of the second somatosensory cortical area (SII) and receptive fields of multineuron responses to cutaneous stimulation were studied in cats 6-16 months after lesions of the forelimb representation in the primary somatosensory area (SI) at 4 days, 4 weeks of age or in adults. No change was detected in SII. The results contrast with findings of alterations in SII of macaque monkeys following similar ablations of SI.
Aging↗