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Biomedical subjects

D L Robinson

Publications and source records attributed to D L Robinson.

At least 73 records · Page 4Linked to original sources
PubMed1991

Lateral geniculate neurons in behaving primates. I. Responses to two-dimensional stimuli.

1. Using behaving monkeys, we studied the visual responses of single neurons in the parvocellular layers of the lateral geniculate nucleus (LGN) to a set of two-dimensional black and white patterns. We found that monkeys could be trained to make sufficiently reliable and stable fixations to enable us to plot and characterize the receptive fields of individual neurons. A qualitative examination of rasters and a statistical analysis of the data revealed that the responses of neurons were related to the stimuli. 2. The data from 5 of the 13 "X-like" neurons in our sample indicated the presence of antagonistic center and surround mechanisms and linear summation of luminance within center and surround mechanisms. We attribute the lack of evidence for surround antagonism in the eight neurons that failed to exhibit center-surround antagonism either to a mismatch between the size of the pixels in the stimuli and the size of the receptive field or to the lack of a surround mechanism (i.e., the type II neurons of Wiesel and Hubel). 3. The data from five other neurons confirm and extend previous reports indicating that the surround regions of X-like neurons can have nonlinearities. The responses of these neurons were not modulated when a contrast-reversing, bipartite stimulus was centered on the receptive field, which suggests a linear summation within the center and surround mechanisms. However, it was frequently the case for these neurons that stimuli of identical pattern but opposite contrast elicited responses of similar polarity, which indicates nonlinear behavior. 4. We found a wide variety of temporal patterns in the responses of individual LGN neurons, which included differences in the magnitude, width, and number of peaks of the initial on-transient and in the magnitude of the later sustained component. These different temporal patterns were repeatable and clearly different for different visual patterns. These results suggest that visual information may be carried in the shape as well as in the amplitude of the response waveform.

Animals↗
PubMed1990

Effects of physostigmine on spatial attention in patients with progressive supranuclear palsy.

We tested patients with progressive supranuclear palsy and control subjects on a task of visuopatial attention. Targets preceded by cues on the same side were termed validly cued; and those on the opposite side, invalidly cued. For all subjects, validly cued targets were responded to faster than those that were invalidly cued. The difference between reaction times for invalidly and validly cued targets, which is hypothesized to measure attentional movement, was significantly increased for the patients. The performance of the controls on certain neuropsychological tests was correlated with their attentional ability. These correlations were altered by progressive supranuclear palsy. Physostigmine treatment of the patients induced a speeding of responses to invalidly cued targets as a function of the duration of the disease. These studies show defects in cognition and attention in patients with progressive supranuclear palsy and demonstrate that physostigmine reduces some of the abnormal visual attentional performance.

Aged↗
PubMed1990

Orbital position and eye movement influences on visual responses in the pulvinar nuclei of the behaving macaque.

We studied the influences of eye movements on the visual responses of neurons in two retinotopically organized areas of the pulvinar of the macaque. Cells were recorded from awake, trained monkeys, and visual responses were characterized immediately before and after the animals made saccadic eye movements. A significant proportion of the cells were more responsive to stimuli around the time of eye movements than they were at other intervals. Other cells had response reduction. For some neurons, the change in excitability was associated with orbital position and not the eye movement. For other cells the change was present with eye movements of similar amplitude and direction but with different starting and ending positions. Here it appears that the eye movement is the important parameter. Other cells had effects related to both eye position and eye movements. In all cells tested, the changes in excitability were present when the experiments were conducted in the dark as well as in the light. This suggests that the mechanism of the effect is related to the eye position or eye movement and not visual-visual interactions. For about half of the neurons with modulations, the response showed facilitation for stimuli presented in the most responsive region of the receptive field but not for those at the edge of the field. For the other cells there was facilitation throughout the field. Thus, a gradient of modulation in the receptive field may vary among cells. These experiments demonstrate modulations of visual responses in the pulvinar by eye movements. Such effects may be part of the visual-behavioral improvements at the end of eye movements and/or contribute to spatial constancy.

Animals↗
PubMed1990

Visuospatial attention: effects of age, gender, and spatial reference.

Visual attention is remarkably stable when spatial cuing is used, but non-spatial cues lead to slowing among females and older subjects. Non-spatial cues are associated with poorer performance during the middle stages of the menstrual cycle. Motivation increased overall response speed but not attentional measures, whereas increasing age was associated with generalized slowing and directional asymmetries. Right-eye dominance was correlated with slow responses to downward targets. These data suggest that attentional performance is modified by age, gender, and endocrine status when spatial reference is not present.

Adult↗
PubMed1990

Acute pancreatitis: value of CT in establishing prognosis.

The presence and degree of pancreatic necrosis (30%, 50%, or greater than 50%) was evaluated by means of bolus injection of contrast material and dynamic sequential computed tomography (CT) in 88 patients with acute pancreatitis at initial and follow-up examinations. Pancreatic necrosis was defined as lack of enhancement of all or a portion of the gland. Length of hospitalization, morbidity, and mortality in patients with early or late necrosis (22 patients) were evaluated and compared with the same criteria in the rest of the group. Patients with necrosis had a 23% mortality and an 82% complication rate; patients without necrosis had 0% mortality and 6% morbidity. When only the initial assessment was considered, patients with peripancreatic phlegmons and necrosis had 80% morbidity, compared with 36% morbidity in those with phlegmons and no necrosis. Serious complications occurred in patients who initially had or developed more than 30% necrosis. A CT severity index, based on a combination of peripancreatic inflammation, phlegmon, and degree of pancreatic necrosis as seen at initial CT study, was developed. Patients with a high CT severity index had 92% morbidity and 17% mortality; patients with a low CT severity index had 2% morbidity, and none died.

Abscess↗
PubMed1990

Abnormalities in visual spatial attention in men with mirror movements associated with isolated hypogonadotropic hypogonadism.

We studied spatial attentional performance on a visually cued reaction time task in men with isolated hypogonadotropic hypogonadism. A subset of these patients, who displayed mirror movements, have spatial attentional abnormalities. They were slow to respond to targets in the right visual field and especially slow when those targets followed incorrect or diffuse cues. This slowing was present for at least 500 msec after cue onset. They responded equally to targets in the left visual field independent of the spatial cues. The patient population as a whole was significantly faster than controls across all experimental conditions, although the speed of their attentional movement was normal. These data suggest that patients with isolated hypogonadotropic hypogonadism perform reaction time tasks quickly, that faster reaction times do not reflect superior attentional performance, and that a subset of these patients has a spatial attentional abnormality.

Adult↗
PubMed1989

Influences of lesions of parietal cortex on visual spatial attention in humans.

Several brain areas have been identified with attention, because damage to these regions leads to neglect and extinction. We have tested elements of visual attentional processing in patients with parietal, frontal, or temporal lesions and compared their responses to control subjects. Normal humans respond faster in a reaction time task when the spatial location of a target is correctly predicted by an antecedent stimulus (valid cue) than when the location is incorrectly predicted (invalid cue). The cue is hypothesized to shift attention towards its location and thereby facilitate or impede response latencies. The reaction times of individuals with damage to the parietal lobe are somewhat slowed for targets ipsilateral or contralateral to the side of the lesion if the targets are preceded by valid cues. These same patients are extremely slow in responding to targets in the visual field contralateral to the lesion when the cue has just appeared in the unaffected (ipsilateral) visual field. In addition, these individuals are especially slow in responding to targets in either visual field when the lights are preceded by weak, diffuse illumination of the entire visual field. Patients with lesions of the frontal lobe have very slow reaction times in general and, as is the case for patients with lesions of the temporal lobe, are slow in all conditions for targets in the field contralateral to the lesion. These patterns are probably not associated with attentional defects. For patients with parietal lesions, these studies demonstrate a further deficit in a cued reaction-time task suggesting abnormal visual attention. Since different sites of brain damage yield different patterns of responses, tests such as these could be of analytic and diagnostic value.

Adolescent↗
PubMed1989

Evoked potential augmenting-reducing: a reply to Connolly and Gruzelier.

Connolly and Gruzelier (1982) published a study purporting to evaluate the methods and procedures employed in studies of the Buchsbaum evoked potential (EP) augmenting-reducing effect. Robinson et al. (1984) pointed out that the stimulus intensities employed by Connolly and Gruzelier were much lower than those normally employed by Buchsbaum and his associates. Consequently, the Connolly and Gruzelier data would not really be comparable to the data of Buchsbaum. Connolly and Gruzelier (1986) subsequently criticised the Robinson et al. report. These criticisms are considered in this letter and it is noted that the main points made by Connolly and Gruzelier are based on spurious as well as mathematically incorrect 'conversions' from units of illumination to units of luminance.

Evoked Potentials, Visual↗
PubMed1989

A large-field screen with even texture for vision research.

Studies of the physiology of the central visual system and visual behavior frequently require large tangent screens, and it has been difficult to create a smooth surface with uniform illumination. We have developed a technique for holding drafting paper on a sheet of acrylic so that it can be used as a tangent screen for both front and rear projections. The process utilizes a vacuum system that holds the paper firmly and produces a uniformly smooth surface with good light diffusion; it is simple, flexible, and inexpensive and can be used for any size screens.

Ophthalmology↗
PubMed1989

Competitive Al Inhibition of Net Mg Uptake by Intact Lolium multiflorum Roots : I. Kinetics.

Aluminum impairs uptake of Mg(2+), but the mechanisms of this inhibition are not understood. The depletion technique was used to monitor net Mg(2+) uptake from nutrient solution by intact, 23-day-old plants of ryegrass (Lolium multiflorum Lam., cv Gulf and Wilo). Activities of Mg(2+) and monomeric Al species in nutrient solution were calculated and used as the basis for expressing the results. The kinetics of net Mg(2+) absorption was resolved into (a) a transpiration-dependent uptake component, (b) a metabolically mediated, discontinuous saturable component that is Al(3+) sensitive and p-chloromercuribenzene sulfonic acid (PCMBS) resistant, and (c) a linear, carbonyl cyanide m-chlorophenylhydrazone resistant, Al(3+) sensitive component that might be a type of facilitated diffusion. Lowering the pH from 6.0 to 4.2 exerted a noncompetitive inhibition of net Mg(2+) uptake, while aluminum at 6.6 micromolar Al(3+) activity exerted competitive inhibition of net Mg(2+) uptake at pH 4.2. The Al(3+)-induced effect was obvious after 30 minutes. Cultivar-specific ability to retain a higher affinity for Mg(2+) by postulated transport proteins in the presence of Al(3+) might be one of the mechanisms of differential Al tolerance among ryegrass cultivars.

Journal Article↗
PubMed1989

Management practices to overcome the incidence of grass tetany.

To minimize the incidence of grass tetany, winter pastures should be established on soils containing Mg-rich minerals, drainage should be improved on five-textured soils, legumes should be included in the sward and soil pH should be at least 5.5. Liming acid soils with dolomitic lime increases forage Mg by supplying Mg and by raising soil pH. Calcitic lime applications also can increase Mg availability to plants on soils with adequate Mg. Low rates of application of soluble Mg salts (less than 100 kg/ha of Mg) effectively increase Mg uptake from noncalcareous soils with low cation exchange capacity. Potassium levels in soils and plants should be kept in the lower range of recommended values. Nitrogen application should be regulated to provide the desired level of forage production. Nitrogen fertilizers, especially the nitrate form, stimulate plant Mg uptake if Mg is available in the soil. The most practical and cost-efficient method of supplementing dietary Mg intake is to provide free-choice Mg. Supplements must be palatable and placed in locations frequently used by cow herds. Including a high-energy feed in the supplement may at times increase its preventive effectiveness by increasing Mg absorption and reducing lipolysis. Regardless of the supplement formulation, Mg intake should be monitored on a regular basis, and formulation or management changes should be initiated if Mg consumption is below required levels. In severe grass tetany outbreaks, foliar application of Mg or administration of Mg via the drinking water may be warranted.

Agriculture↗
PubMed1989

The neurophysiological bases of high IQ.

It is suggested that the study of human intelligence must ultimately involve the study of brain processes which limit the availability of information. Consideration of EEG/intelligence studies suggests that inconsistent findings may have arisen partly from the expectation of simple rectilinear relationships where relationships are likely to be curvilinear. There are also theoretical and technical problems such that it is difficult to specify what conventional EEG procedures measure. The EEG evoked potential (EP) data described in this paper were obtained with a new and more powerful analytical procedure based on methods and concepts of systems analysis. With this procedure, EP responses are used to ascertain the relative values of parameters which quantify differences in the transmission characteristics of thalamocortical neuron populations. The results obtained from a study of 48 subjects indicate that high IQ is associated with combinations of neurological parameters which determine an intermediate degree of "arousability" in the cerebral cortex and related structures. This relationship is accounted for in terms of the generally optimal effect that an intermediate degree of arousability would have on different neurophysiological processes mediating the acquisition, retention and utilization of information. Thus, with some important qualifications, middling arousability can be conceived as the neurophysiological basis of high general intelligence or "g".

Adult↗
PubMed1989

The visual superior colliculus and pulvinar.

The data reviewed here suggest several relationships between the superior colliculus, pulvinar and saccadic eye movements. These will be summarized in a series of steps in the visual initiation of saccadic eye movements. Area Pdm of the pulvinar appears to be involved in visual spatial attention. As such it may participate in the earliest decisions to make an eye movement: the shift of attention. This function is suggested by the spatially selective enhancement seen in the activity of individual neurons and the effects of drug injections on attentional performance. The attentional function of area Pdm is probably accomplished in coordination with cortical area 7 and possibly other areas. The spatially non-selective enhancement found in PI and PL may precede or follow the enhancement in Pdm. The next oculomotor function may be played by the visual cells in the superficial layers of the colliculus. Here the enhancement effect appears to be related to target selection which is specifically used with saccadic eye movements. Lesions here lead to animals who are not easily distracted by peripheral events; they do not select saccade targets. Thus the visual regions of the superior colliculus and Pdm may provide separate initiatives to the saccadic system. Once the eye begins to move, there are many relations manifested in both brain areas. Many of the visual collicular cells and those in parts of the pulvinar are unresponsive to visual stimuli during eye movements. In the colliculus, this particular effect may function to minimize erroneous visual targets whereas in the pulvinar the process may be more important perceptually. Finally there is a population of cells in the pulvinar which discharge during and after saccadic eye movements. These cells may have a role in the termination of one attentional scan and the beginning of the next. The pathways through which these effects may be mediated are totally unclear. The visual signal from the superficial layers related to saccade initiation may impinge directly on the cells in the intermediate layers or may reach the oculomotor system through other pathways. The parts of the pulvinar which relate to visual spatial attention are interconnected with posterior parietal cortex and probably function in concert with that area. How those data get to the oculomotor system has yet to be determined. Since the pulvinar is extensively interconnected with the cortex, it is most likely through this route that eye movement information coming from the superior colliculus is brought to higher perceptual areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Pigmented villonodular synovitis presenting as a large lateral knee mass. Case report and review of the literature.

Pigmented villonodular synovitis is characterized by synovial villonodular lesions with hemosiderin pigmentation and a stromal infiltrate of histiocytes. Analogous lesions may occur in joints, bursae, and tendon sheaths. Although the etiology and natural history of pigmented villonodular synovitis remain unknown, it should be considered a benign entity. It usually presents as either diffuse monoarticular involvement with chronic pain and swelling, or a more localized nodular lesion, typically involving the fingers or knees. Although treatment involves excision of the involved tissue, due to its benign behavior, radical surgical procedures are not indicated. A case report of a large, extra-articular mass is described, with histologic and clinical changes consistent with localized PVS.

Aged↗
PubMed1987

Contributions of the pulvinar to visual spatial attention.

Neurons in a subdivision of the pulvinar resemble those in parietal cortex: many respond to visual stimuli, some of these have a spatial selection mechanism, and some have signals about the occurrence of eye movements. These properties suggest a role in visual spatial attention. Injection of GABA-related drugs into this part of the pulvinar alters animals' performance on an attentional task. These data support our hypothesis that the pulvinar contributes to visual spatial attention.

Animals↗