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Biomedical subjects

H Burton

Publications and source records attributed to H Burton.

At least 19 recordsLinked to original sources
PubMed2006

Reading embossed capital letters: an fMRI study in blind and sighted individuals.

Reading Braille activates visual cortex in blind people [Burton et al., J Neurophysiol 2002;87:589-611; Sadato et al., Nature 1996;380:526-528; Sadato et al., Brain 1998;121:1213-1229]. Because learning Braille requires extensive training, we had sighted and blind people read raised block capital letters to determine whether all groups engage visual cortex similarly when reading by touch. Letters were passively rubbed across the right index finger at 30 mm/s using an MR-compatible drum stimulator. Age-matched sighted, early blind (lost sight 0-5 years), and late blind (lost sight >5.5 years) volunteers performed three tasks: stating an identified letter, stating a verb containing an identified letter, and feeling a moving smooth surface. Responses were voiced immediately after the drum stopped moving across the fingertip. All groups showed increased activity in visual areas V1 and V2 during both letter identification tasks. Blind compared to sighted participants showed greater activation increases predominantly in the parafoveal-peripheral portions of visuotopic areas and posterior parts of BA 20 and 37. Sighted participants showed suppressed activity in most of the same areas except for small positive responses bilaterally in V1, left V5/MT+, and bilaterally in BA 37/20. Blind individuals showed suppression of the language areas in the frontal cortex, while sighted individuals showed slight positive responses. Early blind showed a more extensive distribution of activity in superior temporal sulcal multisensory areas. These results show cross-modal reorganization of visual cortex and altered response dynamics in nonvisual areas that plausibly reflect mechanisms for adaptive plasticity in blindness.

Adaptation, Physiological↗
PubMed2005

Diffusion tensor imaging reveals white matter reorganization in early blind humans.

Multiple functional methods including functional magnetic resonance imaging, transcranial magnetic stimulation, and positron emission tomography have shown cortical reorganization in response to blindness. We investigated microanatomical correlates of this reorganization using diffusion tensor imaging and diffusion tensor tractography (DTT). Five early blind (EB) were compared with 7 normally sighted (NS) persons. DTT showed marked geniculocalcarine tract differences between EB and NS participants. All EB participants showed evidence of atrophy of the geniculocortical tracts. Connections between visual cortex and the orbital frontal and temporal cortices were relatively preserved in the EB group. Importantly, no additional tracts were found in any EB participant. Significant alterations of average diffusivity and relative anisotropy were found in the white matter (WM) of the occipital lobe in the EB group. These observations suggest that blindness leads to a reorganization of cerebral WM and plausibly support the hypothesis that visual cortex functionality in blindness is primarily mediated by corticocortical as opposed to thalamocortical connections.

Adult↗
PubMed2005

Mapping changes in surgical mortality over 9 years by peer review audit.

BACKGROUND: There is increasing public scrutiny of deaths among surgical patients. This analysis sought evidence of changes in practice over time in the management of patients who died under surgical care. METHODS: The surgeons and anaesthetists in National Health Service hospitals providing the care of all surgical patients in Scotland participated in the Scottish Audit of Surgical Mortality (SASM). Data from peer review audit, critical event analysis and individual feedback of deaths while in surgical care over 9 years (1994-2002) were examined for trends over time. RESULTS: Over a 9-year period, 40,448 patients died while in surgical care. Consultant surgeon and anaesthetist involvement in decision making and operating increased significantly (P < 0.001), and death after elective surgery declined to 0.27 per cent of elective operations. Adverse events were more frequently due to failures of hospital systems or process than to individual clinician errors. Fewer adverse events were identified as having contributed to or caused the death of patients over time (P < 0.001). Failure to use deep vein thrombosis (DVT) prophylaxis and failure to use high-dependency or intensive therapy units (HDU/ITU) became less common, once highlighted by the SASM. CONCLUSION: Through continuous peer review audit, the SASM has mapped and may have contributed to changes in surgical and anaesthetic practice over a 9-year period, indicating that the rate of adverse events can be decreased by changing clinician practice (DVT prophylaxis) and provision of facilities (HDU/ITU). Similar approaches should be considered by other medical specialties.

Aged↗
PubMed2004

Default brain functionality in blind people.

We studied whether default functionality of the human brain, as revealed by task-independent decreases in activity occurring during goal-directed behaviors, is functionally reorganized by blindness. Three groups of otherwise normal adults were studied: early blind, adventitiously blind, and normally sighted. They were imaged by using functional MRI during performance of a word association task (verb generation to nouns) administered by using auditory stimuli in all groups and Braille reading in blind participants. In sighted people, this task normally produces robust task-independent decreases relative to a baseline of quiet wakefulness with eyes closed. Our functional MRI results indicate that task-independent decreases are qualitatively similar across all participant groups in medial and dorsal prefrontal, lateral parietal, anterior precuneus, and posterior cingulate cortices. Similarities in task-independent decreases are consistent with the hypothesis that functional reorganization resulting from the absence of a particular sensory modality does not qualitatively affect default functionality as revealed by task-independent decreases. More generally, these results support the notion that the brain largely operates intrinsically, with sensory information modulating rather than determining system operations.

Blindness↗
PubMed2003

Dissociating cortical regions activated by semantic and phonological tasks: a FMRI study in blind and sighted people.

Previous neuroimaging studies of language processing in blind individuals described cortical activation of primary (V1) and higher tier visual areas, irrespective of the age of blindness onset. Specifically, participants were given nouns and asked to generate an associated verb. These results confirmed the presence of adaptations in the visual cortex of blind people and suggested that these responses represented linguistic operations. The present functional magnetic resonance imaging study attempted to further characterize these responses as being preferential for semantic or phonological processing. Three groups of participants (sighted, early onset, and late-onset blind) heard lists of related words and attended to either a common meaning (semantic task) or common rhyme (phonological task) that linked the words. In all three groups, the semantic task elicited stronger activity in the left anterior inferior frontal gyrus and the phonological task evoked stronger activity bilaterally in the inferior parietal cortex and posterior aspects of the left inferior frontal gyrus. Only blind individuals showed activity in occipital, temporal, and parietal components of visual cortex. The spatial extent of visual cortex activity was greatest in early blind, who exhibited activation in all ventral and dorsal visual cortex subdivisions (V1 through MT) for both tasks. Preferential activation appeared for the semantic task. Late blind individuals exhibited responses in ventral and dorsal V1, ventral V2, VP and V8, but only for the semantic task. Our findings support prior evidence of visual cortex activity in blind people engaged in auditory language processing and suggest that this activity may be related to semantic processing.

Acoustic Stimulation↗
PubMed2003

Primary open angle glaucoma. The need for a consensus case definition.

Primary open angle glaucoma is an important cause of visual impairment and blindness in the United Kingdom. This paper gives a brief overview of the condition and its management. It presents evidence of the continued absence of a consensus case definition for this condition. This has resulted in considerable uncertainty about what is diagnosed and treated as primary open angle glaucoma. The important negative effects of this situation are outlined. These include the impact on the person wrongly diagnosed with the condition, the uncertainties both for commissioning and provision of clinical healthcare services, and the lack of a firm basis for research into the condition. It is argued that there is an urgent need to resolve this problem to improve the health of the population.

Adult↗
PubMed2002

Prevalence of primary open angle glaucoma in general ophthalmic practice in the United Kingdom.

AIM: To estimate the predicted prevalence of primary open angle glaucoma (POAG) from the activity of a local ophthalmology department. METHOD: Using clinic audit data, the local incidence and prevalence of POAG in the registered population of two primary care trusts were calculated. RESULTS: The local derived prevalence estimate for POAG was 978 per 100 000 people aged 40-89 years (95% CI 753 to 1272) compared with the expected prevalence from a published model of 1230 people per 100 000 people aged 40-89 years. CONCLUSION: The derived prevalence was not statistically significantly different from that predicted. Based on the published evidence that about half of the POAG cases are undetected, it would have been expected that local audit figures would have yielded figures about 50% lower than the epidemiological model. The main reason for this higher prevalence is thought to be differences in the diagnostic criteria used. This lack of consensus on the case definition for POAG is a deficit, which will hamper future needs assessment.

Adult↗
PubMed2002

Adaptive changes in early and late blind: a FMRI study of verb generation to heard nouns.

Literacy for blind people requires learning Braille. Along with others, we have shown that reading Braille activates visual cortex. This includes striate cortex (V1), i.e., banks of calcarine sulcus, and several higher visual areas in lingual, fusiform, cuneus, lateral occipital, inferior temporal, and middle temporal gyri. The spatial extent and magnitude of magnetic resonance (MR) signals in visual cortex is greatest for those who became blind early in life. Individuals who lost sight as adults, and subsequently learned Braille, still exhibited activity in some of the same visual cortex regions, especially V1. These findings suggest these visual cortex regions become adapted to processing tactile information and that this cross-modal neural change might support Braille literacy. Here we tested the alternative hypothesis that these regions directly respond to linguistic aspects of a task. Accordingly, language task performance by blind persons should activate the same visual cortex regions regardless of input modality. Specifically, visual cortex activity in blind people ought to arise during a language task involving heard words. Eight early blind, six late blind, and eight sighted subjects were studied using functional magnetic resonance imaging (fMRI) during covert generation of verbs to heard nouns. The control task was passive listening to indecipherable sounds (reverse words) matched to the nouns in sound intensity, duration, and spectral content. Functional responses were analyzed at the level of individual subjects using methods based on the general linear model and at the group level, using voxel based ANOVA and t-test analyses. Blind and sighted subjects showed comparable activation of language areas in left inferior frontal, dorsolateral prefrontal, and left posterior superior temporal gyri. The main distinction was bilateral, left dominant activation of the same visual cortex regions previously noted with Braille reading in all blind subjects. The spatial extent and magnitude of responses was greatest on the left in early blind individuals. Responses in the late blind group mostly were confined to V1 and nearby portions of the lingual and fusiform gyri. These results confirm the presence of adaptations in visual cortex of blind people but argue against the notion that this activity during Braille reading represents somatosensory (haptic) processing. Rather, we suggest that these responses can be most parsimoniously explained in terms of linguistic operations. It remains possible that these responses represent adaptations which initially are for processing either sound or touch, but which are later generalized to the other modality during acquisition of Braille reading skills.

Adaptation, Physiological↗
PubMed2002

Adaptive changes in early and late blind: a fMRI study of Braille reading.

Braille reading depends on remarkable adaptations that connect the somatosensory system to language. We hypothesized that the pattern of cortical activations in blind individuals reading Braille would reflect these adaptations. Activations in visual (occipital-temporal), frontal-language, and somatosensory cortex in blind individuals reading Braille were examined for evidence of differences relative to previously reported studies of sighted subjects reading print or receiving tactile stimulation. Nine congenitally blind and seven late-onset blind subjects were studied with fMRI as they covertly performed verb generation in response to reading Braille embossed nouns. The control task was reading the nonlexical Braille string "######". This study emphasized image analysis in individual subjects rather than pooled data. Group differences were examined by comparing magnitudes and spatial extent of activated regions first determined to be significant using the general linear model. The major adaptive change was robust activation of visual cortex despite the complete absence of vision in all subjects. This included foci in peri-calcarine, lingual, cuneus and fusiform cortex, and in the lateral and superior occipital gyri encompassing primary (V1), secondary (V2), and higher tier (VP, V4v, LO and possibly V3A) visual areas previously identified in sighted subjects. Subjects who never had vision differed from late blind subjects in showing even greater activity in occipital-temporal cortex, provisionally corresponding to V5/MT and V8. In addition, the early blind had stronger activation of occipital cortex located contralateral to the hand used for reading Braille. Responses in frontal and parietal cortex were nearly identical in both subject groups. There was no evidence of modifications in frontal cortex language areas (inferior frontal gyrus and dorsolateral prefrontal cortex). Surprisingly, there was also no evidence of an adaptive expansion of the somatosensory or primary motor cortex dedicated to the Braille reading finger(s). Lack of evidence for an expected enlargement of the somatosensory representation may have resulted from balanced tactile stimulation and gross motor demands during Braille reading of nouns and the control fields. Extensive engagement of visual cortex without vision is discussed in reference to the special demands of Braille reading. It is argued that these responses may represent critical language processing mechanisms normally present in visual cortex.

Adaptation, Physiological↗
PubMed2001

Neural correlates for roughness choice in monkey second somatosensory cortex (SII).

This experiment explored the relationship between neural firing patterns in second somatosensory cortex (SII) and decisions about roughness of tactile gratings. Neural and behavioral data were acquired while monkeys made dichotomous roughness classifications of pairs of gratings that differed in groove width (1.07 vs. 1.90 and 1.42 vs. 2.53 mm). A computer-controlled device delivered the gratings to a single immobilized finger pad. In one set of experiments, three levels of contact force (30, 60, and 90 g) were assigned to these gratings at random. In another set of experiments, three levels of scanning speed (40, 80, and 120 mm/s) were assigned to these gratings at random. Groove width was the intended variable for roughness. Force variation disrupted the monkeys' groove-width (roughness) classifications more than did speed variation. A sample of 32 SII cells showed correlated changes in firing (positive or negative effects of both variables) when groove width and force increased. While these cells were recorded, the monkeys made roughness classification errors, confusing wide groove-width gratings at low force with narrow groove-width gratings at high force. Three-dimensional plots show how some combinations of groove width and force perturbed the monkeys' trial-wise classifications of grating roughness. Psychometric functions show that errors occurred when firing rates failed to distinguish gratings. A possible interpretation is that when asked to classify grating roughness, the monkeys based classifications on the firing rates of a subset of roughness-sensitive cells in SII. Results support human psychophysical data and extend the roughness range of a model of the effects of groove width and force on roughness. One monkey's SII neural sample (21 cells) showed significant correlation between firing rate response functions for groove width and speed (both correlations either positive or negative). Only that monkey showed a statistically significant interaction between groove width and speed on roughness classification performance. This additional finding adds weight to the argument that SII cell firing rates influenced monkey roughness classifications.

Animals↗
PubMed2000

Field immobilisation of southern elephant seals with intravenous tiletamine and zolazepam.

Southern elephant seals (Miroungo leonina) were immobilised with a mixture of tiletamine and zolazepam administered intravenously at a mean (sd) dose rate of 0.46 (0.08) mg/kg. This dose provided a satisfactory degree of anaesthesia with no side effects, and the induction, duration and recovery times were short. The mean (sd) induction time was 26 (9) seconds and the mean level of anaesthesia was 4.4 units on an eight-point scale. Male seals were given less drug than female seals, remained immobilised for shorter periods and recovered sooner. The mean (sd) dose of drug administered to males was 0.44 (0.06) mg/kg and to females 0.48 (0.08) mg/kg, and the mean (sd) duration times were 14.9 (4.5) minutes and 16.1 (5.3) minutes. The mean (sd) time taken to recover from immobilisation was 14.5 (4.6) minutes for males and 15.7 (5.3) minutes for females. Physiological condition and size significantly affected the duration of anaesthesia. Thin seals remained immobilised for 18 (7) minutes whereas fatter seals remained immobilised for 15 (4) minutes (P<0.0001).

Anesthetics, Dissociative↗
PubMed2000

Effects on discrimination performance of selective attention to tactile features.

This study examined selective attention to tactile dimensions by combining a selective cueing paradigm with a test of integrality. In Experiment 1, subjects selectively attended to changes in the frequency or duration of pairs of vibrotactile stimuli and identified the higher frequency or longer duration stimulus. In Experiment 2, using surface gratings in an identical experimental procedure, subjects identified the rougher or longer duration stimulus. In both experiments, greater performance accuracy was found on trials where the cue correctly (valid) predicted the changing dimension, vs incorrectly (invalid) cued or no-cue (neutral) trials. More errors on the invalidly vs neutrally cued trials show the cost of focal attention. Increases in performance on validly vs neutrally cued trials show a benefit of filtering irrelevant stimuli in the cued conditions. Results effectively demonstrate focal attention to tactile features. Tests of integrality, in terms of the effects of correlated change in both dimensions, showed no redundancy gain for either vibrotactile or grating tasks, suggesting that frequency and roughness are separable from stimulus duration. Interference of negative correlated change for frequency but not roughness discriminations may be explained by differences in task difficulty.

Adult↗
PubMed2000

Tactile-spatial and cross-modal attention effects in the primary somatosensory cortical areas 3b and 1-2 of rhesus monkeys.

Neuronal responses in somatosensory cortical areas 3b and 1-2 (S1) were recorded during an attention task involving cue directed selection of one of three simultaneous stimuli: dual sinewave shaped vibrotactile stimuli applied to mirror sites on both hands or a similarly timed auditory tone. The cued stimulus occurred with one of two equally probable patterns: a constant amplitude vibration or the latter with a superimposed brief sinewave amplitude pulse midway during stimulation. Uncued stimuli always contained amplitude pulses. Two monkeys signaled the absence or presence of an amplitude pulse by appropriately moving a foot pedal up or down. Cues initiated trials by marking the location where the monkey had to discriminate the stimulus pattern. Cue location and stimulus pattern varied randomly per trial. Approximately 50% of cells (44/77 in 3b and 39/77 in 1-2) had significantly different firing rates to stimulation cued to the contralateral hand relative to spatially cuing the ipsilateral hand or cross-modally the auditory stimulus. Relatively suppressed firing rates during times prior to the epoch containing amplitude pulses improved signal-to-noise ratios for responses to amplitude pulses. Instances of significant enhanced activity during and after intervals with amplitude pulses were rare and relative to suppressed activity when cues directed attention to the ipsilateral hand or auditory stimulus. The present findings suggest that attention influences even the earliest stage somatosensory cortical processing. Findings were more modest in S1 than those previously seen in S2 (Burton et al., Somatosens Mot Res 14: 237-267, 1997), which supports the concept of multistage attention processes for touch.

Acoustic Stimulation↗
PubMed2000

Attending to and remembering tactile stimuli: a review of brain imaging data and single-neuron responses.

Clinical and neuroimaging observations of the cortical network implicated in tactile attention have identified foci in parietal somatosensory, posterior parietal, and superior frontal locations. Tasks involving intentional hand-arm movements activate similar or nearby parietal and frontal foci. Visual spatial attention tasks and deliberate visuomotor behavior also activate overlapping posterior parietal and frontal foci. Studies in the visual and somatosensory systems thus support a proposal that attention to the spatial location of an object engages cortical regions responsible for the same coordinate referents used for guiding purposeful motor behavior. Tactile attention also biases processing in the somatosensory cortex through amplification of responses to relevant features of selected stimuli. Psychophysical studies demonstrate retention gradients for tactile stimuli like those reported for visual and auditory stimuli, and suggest analogous neural mechanisms for working memory across modalities. Neuroimaging studies in humans using memory tasks, and anatomic studies in monkeys support the idea that tactile information relayed from the somatosensory cortex is directed ventrally through the insula to the frontal cortex for short-term retention and to structures of the medial temporal lobe for long-term encoding. At the level of single neurons, tactile (such as visual and auditory) short-term memory appears as a persistent response during delay intervals between sampled stimuli.

Animals↗
PubMed2000

Response patterns in second somatosensory cortex (SII) of awake monkeys to passively applied tactile gratings.

This experiment explored the effects of controlled manipulations of three parameters of tactile gratings, groove width (1.07-2.53 mm), contact force (30-90 g), and scanning speed (40-120 mm/s), on the responses of cells in second somatosensory cortex (SII) of awake monkeys that were performing a groove-width classification task with passively presented stimuli. A previous experiment involving an active touch paradigm demonstrated that macaque SII cells code groove-width and hand-movement parameters in their average firing rates. The present study used a passive-touch protocol to remove somatosensory activation related to hand movements that accompany haptic exploration of surfaces. Monkeys maintained a constant hand position while a robotic device delivered stimulation with tactile gratings to a single stabilized finger pad. Single-unit recordings isolated 216 neurons that were retrospectively assigned to SII on histological criteria. Firing patterns for 86 of these SII cells were characterized in detail, while monkeys classified gratings as rough (1.90 and 2.53 mm groove widths) or smooth (1.07 and 1.42 mm groove widths), with trial-wise random, parametric manipulation of force or speed; the monkeys compared 1.07 versus 1.90 mm and 1.42 versus 2.53 mm in alternating blocks of trials. We studied 33 cells with systematic variation of groove width and force, 49 with groove width and speed, and four with all three variables. Sixty-three cells were sensitive to groove width, 43 to force (effects of random force in speed experiments contributed to N), and 34 to speed. Relatively equal numbers of cells changed mean firing rates as positive or negative functions of increasing groove width, force, and/or speed. Cells typically changed mean firing rates for two or three of the independent variables. Effects of groove width, force, and speed were additive or interactive. The variety of response functions was similar to that found in a prior study of primary somatosensory cortex (SI) that used passive touch. The SII sample population showed correlated changes (both positive and negative) in firing rates with increasing groove width and force and to a lesser degree, with increasing groove width and speed. This correlation is consistent with human psychophysical studies that found increasing groove width and force increase perceived roughness magnitude, and it strengthens the argument for SII's direct involvement in roughness perception.

Action Potentials↗
PubMed2000

Deaths following hernia surgery: room for improvement.

BACKGROUND: Abdominal wall herniae are common and may well lead to death. The aim of this study was to examine the deaths of patients with an inguinal, femoral or incisional hernia to identify aspects of management which could be improved upon. METHOD: Data collected by the Scottish Audit of Surgical Mortality 1994-1997 was analysed by interrogation of the database for all deaths on a surgical ward or within 30 days of surgery where the principle diagnosis was inguinal, fermoral or incisional hernia. RESULTS: There were 133 deaths out of 31,525 operations over the 4-year period. Mortality was highest among femoral hernia operations in women (37 deaths/1184 operations; 3.1%) and 59% of femoral hernia surgery was performed outwith normal working hours. The 133 patients were elderly (mean age 79 years) and unfit, but less than half the operations involved consultant anaesthetists or consultant surgeons. Delay in referral contributed to death in 15/133 patients and adverse factors in management, particularly in the perioperative period, caused the death of 2 patients and contributed to the death of a further 29/133. CONCLUSIONS: Herniae carry a significant mortality in elderly, unfit patients who require close attention to perioperative management. These patients should be anaesthetised and operated upon by consultant staff during the normal working day.

Adult↗