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D Burke

Publications and source records attributed to D Burke.

At least 199 records · Page 11Linked to original sources
PubMed1994

The contribution of one-dimensional motion mechanisms to the perceived direction of drifting plaids and their after effects.

When motion aftereffects (MAEs) are measured by adapting to a drifting plaid (simultaneous adaptation) or by adapting to the plaid's component gratings in alternation (alternating adaptation), it has been shown that the velocity and duration of the MAE are smaller in the latter case [Wenderoth, P., Bray, R. & Johnstone, S. (1988) Perception, 17, 81-91; Burke, D. & Wenderoth, P. (1993) Vision Research, 33, 351-359]. However, Burke and Wenderoth additionally reported that the directions of MAEs induced by simultaneous and alternating adaptation were identical, an apparent inconsistency if the differences in duration and velocity were due to the presence of "blobs" at the component grating intersects in the simultaneous case. Presumably, the direction of the "blobs" should also affect perceived plaid direction during adaptation and, hence, the MAE direction. In five experiments, we have measured both perceived adapting plaid and MAE direction, tested with both alternating and simultaneous adaptation, measured interocular transfer of plaid-induced MAEs and obtained MAE and plaid direction judgments under monocular and binocular viewing conditions. All of the data indicate that there is a blob tracking mechanism which is preferentially stimulated by plaids whose component gratings have high spatial frequency, low temporal frequency and high contrast. Differences between simultaneous and alternating adaptation emerge only when more optimal blobs are used, thus accounting for Burke and Wenderoth's failure to find a difference. The data also support Burke and Wenderoth's claim that the blob tracking mechanism is monocular: alternating and simultaneous adaptation produce identical MAEs under interocular transfer conditions, even using plaids with more optimal blobs. We also report the unexpected finding that plaids with more- and less-optimal blobs appear to drift in directions 20 degrees apart yet their aftereffects differ in direction by only 3-5 degrees. That is, more optimal blob plaids--compared with less optimal blob plaids--change both perceived plaid direction during adaptation and subsequent perceived MAE direction but the latter change is much more modest. Possible explanations of this dissociation are considered.

Adaptation, Ocular↗
PubMed1994

The role of the blobs in determining the perception of drifting plaids and their motion aftereffects.

Motion aftereffects (MAEs) can be induced by adaptation to a pair of differently oriented drifting gratings whether the gratings are presented simultaneously, as a coherent plaid, or in alternation. The fact that the former MAEs were generally larger than the latter led to the suggestion that simultaneous adaptation involved higher-level extrastriate processes not involved in the alternating effects. In the past few years evidence has accumulated that the difference is in fact due to a low-level monocular process which can be termed the 'blob-tracking mechanism'. A review is presented of the evidence on MAEs induced by simultaneous and alternating adaptation, the evidence for the monocularity of the blob-tracking mechanism, the data which implicate the blob mechanism in the determination of MAE magnitude, perceived plaid drift direction, and in perceived plaid coherence.

Humans↗
PubMed1994

Differences in behaviour of sensory and motor axons following release of ischaemia.

The changes in excitability and supernormality of sensory and motor axons of the median (or ulnar) nerve were tracked during and following ischaemia at the wrist for periods of 5-20 min in normal human volunteers. Supernormality was defined as the fractional increase in excitability produced by a maximal conditioning stimulus, 10 ms before the test stimulus. With relatively brief periods of ischaemia (< 10 min), sensory and motor axons behaved similarly, with an increase in excitability (producing a decrease in threshold) and a decrease in supernormality during ischaemia and a long-lasting decrease in excitability (and increase in supernormality) following release of ischaemia. Most subjects reported paraesthesiae during brief periods of ischaemia but not after its release. No one experienced fasciculation. The threshold changes were generally similar during longer periods of ischaemia, but in the post-ischaemic phase the behaviour of sensory and motor axons diverged. After a rapid post-ischaemic increase, the threshold of sensory axons decreased, approaching the pre-ischaemic level, before rising again and then slowly returning to the control level. Sensory axons of different threshold behaved in a qualitatively similar manner, with no evidence of a bimodal distribution of thresholds in the post-ischaemic phase (as occurs with motor axons when the ischaemia is sufficient to produce fasciculation; see Bostock et al. J. Physiol (Lond) 1991; 441: 537-57). The 'notch' on the threshold plot for sensory axons lasted 20-40 min and was accompanied by a relatively small but appropriate change in supernormality. No such 'notch' was seen with motor axons. The changes in latency were generally similar for sensory and motor axons, largely paralleling the supernormality plots, except at the time of the 'notch'. To test the hypothesis that the differences in behaviour of sensory and motor axons resulted from differences in inward rectification activated by hyperpolarization, the changes in threshold produced by long-lasting (300 ms) depolarizing and hyperpolarizing current pulses were compared for sensory and motor axons. In seven of eight subjects, there was evidence of more inward rectification in sensory axons. In the eighth subject, motor axons behaved similarly to sensory axons. It is concluded that a difference in inward rectification contributes to but is insufficient by itself to account for the differences in behaviour of sensory and motor axons and that the greater propensity of sensor y axons to discharge ectopically cannot be attributed to a single factor.

Action Potentials↗
PubMed1994

Acyclovir in the treatment of recurrent respiratory papillomatosis. A pilot study.

Six patients with severe, recalcitrant, juvenile-onset recurrent respiratory papillomatosis were treated with 7 independent trials of acyclovir. In 2 trials, patients received acyclovir in place of interferon-alpha; the remaining 5 trials were in patients not otherwise receiving chemotherapy. Quantitative analysis of overall disease extent, laryngeal involvement, and degree of glottic obstruction for the 6 months prior to acyclovir administration and during acyclovir administration demonstrated a statistically significant decrease in all parameters evaluated in those patients who were otherwise unmediated. The 2 patients who discontinued interferon-alpha immediately prior to beginning acyclovir demonstrated worsening disease, consistent with the well-recognized rebound phenomenon associated with stopping interferon. This study suggests that acyclovir decreases the extent of respiratory papillomatosis in patients with recalcitrant disease. The beneficial effect of acyclovir appears to be insufficient to counteract the rebound of disease when interferon is stopped abruptly.

Acyclovir↗
PubMed1993

Microneurography, impulse conduction, and paresthesias.

It is possible to learn more about peripheral nerve function in human subjects than is obtainable with routine nerve conduction studies, and thereby to study the basis of "positive" symptoms, such as paresthesias. Using microneurography, ectopic impulse activity in cutaneous afferents has been recorded in patients suffering from neurologic disorders and in normal subjects in whom paresthesias were provoked by hyperventilation, prolonged tetanization of cutaneous nerves and ischemia. Using relatively simple modifications of standard nerve conduction techniques, the increases in axonal excitability responsible for this ectopic activity have been documented in human volunteers. Hyperventilation increases axonal excitability but does not change supernormality, probably because Na+ channels are activated by the decrease in [Ca2+] on the axonal membrane. Prolonged tetanic stimulation and ischemia probably share similar mechanisms. At least in motor axons, postischemic ectopic activity occurs when the hyperpolarization that results from activation of the Na+/K+ pump lowers the membrane potential below the equilibrium potential for K+. A high extracellular [K+] can then result in an inward current producing depolarization and possibly triggering regenerative processes.

Axons↗
PubMed1993

Postoperative pain-related morbidity: video-assisted thoracic surgery versus thoracotomy.

One hundred thirty-eight consecutive, nonrandomized patients, with equivalent demographic and preoperative physiologic parameters, underwent either a video-assisted thoracic surgical (VATS) approach (n = 81) or a limited lateral thoracotomy (LLT) approach (n = 57) to accomplish pulmonary resection for peripheral lung lesions (< or = 3 cm in diameter). Wedge resection was done in 74 VATS patients and 19 LLT patients. Seven patients underwent VATS lobectomy and 38 patients had lobectomy performed through an LLT. Pain was quantitated by postoperative narcotic requirements, the need for intercostal/epidural analgesia, and patient perception of pain index scoring. Shoulder and pulmonary function (forced expiratory volume in 1 second) were measured preoperatively, 3 days postoperatively, and at 3 weeks of follow-up. Patients undergoing VATS experienced significantly less postoperative pain. No patients undergoing VATS required intercostal block/epidural analgesia; 31 LLT patients (54%) required this treatment for breakthrough pain (p = 0.001). Narcotic requirements were less (p = 0.05) among VATS patients, which correlated with lower perception of pain index after operation for VATS patients. Shoulder girdle strength was equally impaired at day 3, but function was more improved in VATS patients at 3 weeks (p = 0.01). Patients undergoing wedge resection alone by LLT had greater impairment in early (day 3) pulmonary function (forced expiratory volume in 1 second) (p = 0.002); this difference from VATS was not sustained at 3 weeks. Video-assisted thoracic surgery is associated with reduced pain, shoulder dysfunction, and early pulmonary impairment compared with LLT for select patients requiring pulmonary resection.

Humans↗
PubMed1993

The effect of interactions between one-dimensional component gratings on two-dimensional motion perception.

Ferrera and Wilson [(1990) Vision Research, 30, 273-287] reported veridical perception of the direction of motion of Type I plaids, whose component gratings span the resultant direction, but marked misperception of the direction of motion of Type II plaids, whose component gratings both lie on one side of the resultant direction. Because they failed to find any effect of component direction (angular) separation on this misperception, Ferrera and Wilson concluded that the misperception was not due to perceptual repulsion of component directions. We report that component direction repulsion does occur, that plaid direction misperception is tuned to component separation, with larger repulsions for smaller angles. It is concluded that there is no fundamental difference in direction coding for Type I and Type II plaids, and that Ferrera and Wilson failed to find a direction separation effect because the range of separations they used was insufficiently broad to detect the slope of the angular function.

Humans↗
PubMed1993

Determinants of two-dimensional motion aftereffects induced by simultaneously- and alternately-presented plaid components.

Wenderoth, Bray and Johnstone [(1988) Perception, 17, 81-91] measured motion aftereffects induced on stationary vertical sine-wave gratings by horizontally drifting two-dimensional patterns (plaids). The adapting plaid component gratings were simultaneously or alternately presented and were oriented left and right of vertical by 15, 45 or 75 degrees. It was found that aftereffects decreased linearly in the alternating conditions as the plaid component orientations changed but this was not the case in the simultaneous adaptation conditions, a finding taken to be consistent with the hypothesis that one-dimensional aftereffects have a low level site (possibly V1) whereas two-dimensional effects have a higher level site (possibly MT). In three experiments, we have examined in more detail the determinants of aftereffects induced by simultaneous and alternating plaid components. The data suggest that the mechanisms involved are more complex than those put forward by Wenderoth et al. and that plaid perception utilizes both higher and lower level processes which can be referred to, respectively, as an intersection of constraints algorithm and a moving "blob" detector.

Adaptation, Ocular↗
PubMed1993

Force and displacement-controlled tendon vibration in humans.

This study investigated how the mechanical characteristics of tendon vibration influence the responses of human muscle receptors. In this study, we used a tendon vibrator in which the force, displacement and frequency of vibration were precisely controlled. The tendon vibrator could produce large amplitude displacements, so it was also used to impose ramp-and-hold stretches to the tendon to help classify muscle spindle afferents. In normal human subjects, we recorded microneurographically from single muscle afferents during tendon vibration to determine how afferent responses are influenced by the force and the displacement applied to the tendon and how these influences of force and displacement change with vibration frequency. Our results indicate that the sensitivity of muscle spindle afferents to tendon vibration is enhanced by increasing force and displacement and decreased by increasing frequency. It is concluded that, in order to predict the afferent response to vibration, the mechanical characteristics of tendon vibration must be controlled. Controlling the mechanical characteristics of tendon vibration and understanding the effect of vibration on afferent discharge will be useful for furthering our understanding of the peripheral control of movement.

Adult↗
PubMed1993

Association of interleukin-6 in the pathogenesis of acutely fatal SIVsmm/PBj-14 in pigtailed macaques.

Infection with a variant of simian immunodeficiency virus (SIVsmm/PBj-14) causes death in juvenile pigtailed macaques within 8 days of infection. The primary pathology is localized to the lymphoid tissues of the gut and spleen. Although the virus is present, the lesions are most consistent with acute reactive inflammation. We studied the serum and tissues for evidence of acute cytokine production often associated with acute inflammation. One factor, IL-6, was found to be significantly increased (> 1000-fold) over all other measured cytokines in all the pigtailed macaques who died acutely. Increased levels of IL-6 were found both in the serum and in the inflamed tissues. mRNA for IL-6 was found in the tissues with the highest protein levels of IL-6. The marked increase in IL-6 and IL-6 mRNA correlated with the virus levels in the tissues and serum as determined by viral isolation, immunohistochemistry, and Northern blot analysis. These findings suggest that the underlying pathogenesis of primary tissue damage, necrosis, and death by PBj-14 is the induction of cytokine production. Although the presence of the virus may be critical for the initiation of these events, the intense inflammatory reaction is associated with the cause of death.

Animals↗
PubMed1993

Direct comparison of corticospinal volleys in human subjects to transcranial magnetic and electrical stimulation.

1. The effects of graded transcranial magnetic and anodal electrical stimulation of the human motor cortex were compared in human subjects undergoing orthopaedic operations on the spine, before and after withdrawal of volatile anaesthesia. Corticospinal volleys were recorded from the spinal cord in the low-cervical and low-thoracic regions (six subjects) or the mid-thoracic region (two subjects) using bipolar electrodes inserted into the epidural space. 2. Electrical stimuli were delivered using anode at the vertex and cathode 7 cm laterally. The corticospinal volley at threshold consisted of a single deflection with a mean latency to peak of 4.17 ms at the rostral recording site. With further increases in stimulus strength the latency of this D wave shortened in two steps, first by 0.89 ms (seven subjects) and then by a further 0.8 ms (two subjects), indicating that the site of activation of some corticospinal neurones had shifted to deep subcortical sites. 3. When volatile anaesthetics were given, a corticospinal volley could not be defined in three subjects with magnetic stimuli of 70, 80 and 100% maximal stimulator output with the coil at the vertex (Novametrix Magstim 200, round coil, external diameter 14 cm). In the remaining five subjects, the component of lowest threshold was a D wave recorded at the rostral site at 4.0 ms when stimulus intensity was, on average, 70%. With stimuli of 90-100% a total of five small I waves could be defined in the five subjects (i.e. on average one I wave per subject). 4. After cessation of volatile anaesthetics in seven subjects, the thresholds for D and I waves were lower and their amplitudes were greater. The D wave remained the component of lowest threshold in all subjects, appearing at the low-cervical level with magnetic stimuli of 50%. However, in three subjects I waves also appeared at D wave threshold, and the D wave was smaller than with electrical stimulation at I wave threshold. There was no consistent change in latency of the magnetic D wave as stimulus intensity was increased to 100%. 5. These findings suggest that the previously reported difference in latency of the EMG potentials produced in upper-limb muscles by anodal stimulation and magnetic stimulation of the human motor cortex is not because the corticospinal volley induced by magnetic stimulation lacks a D wave.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1993

Motoneuronal output and gradation of effort in attempts to contract acutely paralysed leg muscles in man.

1. The study was designed to determine the degree to which normal subjects can control motoneurones innervating a leg muscle when acutely deprived of muscle afferent feedback. Microneurographic recordings were made from eighteen motor fascicles in the common peroneal nerve, of which thirteen innervated tibialis anterior and five toe dorsiflexor muscles. The nerve was then blocked completely at a distal site near the fibular head with local anaesthetic. A sequence of tests was performed with each fascicle to determine the degree to which the subject could control the motoneuronal drive to the paralysed muscle. 2. During a complete distal block of the common peroneal nerve, motoneurones innervating tibialis anterior were frequently activated during weak attempted contraction of the synergist toe extensors and vice versa. 3. When subjects attempted contractions of the paralysed muscles at a constant effort, pressure applied to the dorsum of the foot caused relatively small changes in the level of neural output, producing a small increase in motoneuronal drive to tibialis anterior, but no consistent change in the drive to toe extensor fascicles. 4. Subjects were able to increase the motoneuronal drive to the paralysed tibialis anterior in five steps of effort each lasting 10 s. The level of motor output increased linearly with step number, but declined as the step was maintained, more so when auditory feedback was withdrawn. 5. There was hysteresis in the relationship between motoneuronal output and force (measured on the contralateral side) during attempts to make slowly increasing then decreasing ramps of effort on both sides over 20-120 s. Motor drive to the paralysed muscle increased disproportionately rapidly compared with contralateral force when subjects attempted bilaterally symmetrical increasing efforts. 6. Subjects attempted to activate the paralysed muscle group maximally for 20-30 s with auditory feedback of the neurogram and verbal encouragement. There was a small statistically significant reduction in the motoneuronal output 5-10 s into the 30 s effort but, with further encouragement, it recovered towards the end of the effort. 7. When compared directly in the same recording sequences, attempts to make rapid brief maximal efforts (2-3 s duration) produced the same motoneuronal output as attempts to make sustained efforts. 8. Similar results occurred when the motoneuronal output to tibialis anterior was recorded during a selective distal block of tibialis anterior sparing toe dorsiflexors.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1993

The firing rates of human motoneurones voluntarily activated in the absence of muscle afferent feedback.

1. To quantify the net influence of muscle afferent feedback on the firing rates of human motoneurones, the discharge frequencies of single motor axons in the common peroneal nerve were recorded during sustained voluntary efforts performed in the absence of feedback from the target muscle. These data were compared with the firing rates of single motor units in the intact tibialis anterior muscle. In five subjects, recordings were made from fifty-two motor axons innervating tibialis anterior during acute deafferentation and paralysis of the dorsiflexor muscles produced by anaesthetic block of the nerve distal to the recording site. 2. Maximal sustainable firing rates were determined for twenty-four motoneurons, twelve of which were classified as relatively low threshold (estimated recruitment level < or = 10% maximal) and six as high threshold. Mean firing rates of the low-threshold motoneurones (21.7 +/- 2.7 Hz; +/- S.E.M.) were significantly higher than those of the high-threshold motoneurones (14.0 +/- 4.4 Hz). The mean firing rate of the twenty-four deafferented motoneurones during maximal efforts to contract the paralysed muscle was 18.6 +/- 1.9 Hz, significantly lower than the maximal firing rates of single motor units recorded from the normally innervated tibialis anterior muscle (28.2 +/- 0.6 Hz). 3. During half-maximal efforts, the mean firing rate of eight deafferented motoneurones (10.8 +/- 1.1 Hz) was significantly lower than that of intact motor units (16.5 +/- 0.2 Hz). A similar finding was apparent during minimal efforts; the mean discharge frequency of seven deafferented motoneurones during weak voluntary efforts was 6.0 +/- 0.9 Hz, compared with 7.3 +/- 0.13 Hz for intact motor units. Overall, the range of motoneurone firing rates (from minimal to maximal levels of voluntary effort) was significantly affected by the acute deafferentation, but was shifted significantly to lower rates. 4. During sustained maximal voluntary efforts of at least 30 s duration the firing rate of deafferented motoneurones decreased over the first 5 s but was then maintained, i.e. there was no progressive decline as occurs with normally innervated motor units during fatiguing contractions. This observation supports a reflex origin for the normal decline in motoneurone discharge. 5. It is concluded that muscle afferents in the common peroneal nerve provide a net facilitation to the tibialis anterior motoneurone pool, reflexly increasing the motor output at all levels of voluntary drive by approximately one-third.

Action Potentials↗
PubMed1993

Culture negative cytotoxin positive stools in community acquired diarrhoea.

In a significant proportion of cases of community acquired diarrhoea no recognised pathogen is detected. Verocytotoxin producing Escherichia coli (VTEC) are associated with haemorrhagic colitis and the haemolytic uraemic syndrome but their role in community acquired diarrhoea is not fully understood. Using a method of toxin enhancement in mixed faecal culture, 175 stools negative on culture for recognised pathogens were tested for the presence of cytotoxin and 28% were found to be positive. Nine were neutralised by anti-VT1, 29 by anti-VT2, and eight by neither. No control stool samples yielded any cytotoxin. VTEC should be considered as a causative agent in sporadic community acquired diarrhoea.

Adolescent↗
PubMed1992

Limitations of laser treatment for malignant dysphagia.

Of 86 patients with inoperable malignant dysphagia, 68 (79 per cent) underwent successful palliation by endoscopic laser therapy, of whom 24 remained well palliated until the time of death. In 18 patients laser treatment was unsuccessful and nine of these underwent intubation, eight successfully. After successful laser therapy, dysphagia recurred in 44 patients a mean of 7.8 weeks later. Of these, 31 received palliation until death by dilatation with or without laser therapy, and 13 required intubation. The overall laser-related complication rate was 12 per cent with a mortality rate of 4 per cent. The intubation-related mortality rate was 9 per cent.

Adenocarcinoma↗
PubMed1992

The function of large and small nerve fibers in renal failure.

Previous clinical and neurophysiological studies of uremic neuropathy have focused almost exclusively on the function of large sensory and motor axons. The sensations of heat and cold depend on the function of unmyelinated afferents and small myelinated afferents, respectively, and these sensations can be quantified using a standardized psychophysical technique. Thermal thresholds were measured in 20 patients with end-stage renal failure to determine the extent of small afferent fiber involvement and to compare this with the clinical and electrophysiological evidence of large fiber involvement. Whereas abnormalities of standard nerve conduction studies were found in 16 patients, abnormal thermal thresholds were found in only 6 patients. In the nerve conduction studies, the amplitudes of nerve potentials were reduced more than their conduction velocities, consistent with an axonopathy. This study found little evidence of significant dysfunction of small afferent fibers in end-stage renal failure and, when such changes occurred, they did not correlate with the clinical evidence of polyneuropathy. The functional sparing of axons of small diameter is consistent with the relative sparing of these axons in pathological studies.

Electromyography↗