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Biomedical subjects

W A Roberts

Publications and source records attributed to W A Roberts.

At least 37 records · Page 2Linked to original sources
PubMed1991

Peripherally evoked single unit responses in ventroposterolateral nucleus in the absence of the dorsal column nuclei in rat.

The present experiments were designed to determine the effects of removing the dorsal column nuclei on the evoked responses of the ventroposterolateral nucleus (VPL) neurons in the rat. Previously, we have observed inhibitory interactions between forelimb and hindlimb inputs to VPL (Roberts and Wells 1990), and have also observed a synaptic recovery process within VPL following dorsal column nuclei (DCN) lesions (Wells and Tripp 1987). In an attempt to describe any changes in VPL responses that correlate with the synaptic recovery in VPL following lesions to the DCN, we have studied the incidence of the inhibition process in VPL, the latency of activation of single unit VPL responses to peripheral nerve stimulation, the number of evoked unit responses observed per track studied and the somatotopy of responses in VPL. Dorsal column nuclei lesions did not alter the incidence or duration of the inhibitory interaction between forelimb and hindlimb inputs to VPL. Following DCN lesions, there was a significant increase in the latency to activation of VPL neurons by both forelimb and hindlimb inputs. This increase in latency returned to a non-significant difference from control over the same interval of time that is required for the structural recovery in VPL. There was a significant reduction in the number of evoked unit responses observed per track studied in the deafferented group at the twenty day post-lesion time course. This difference was no longer statistically significant in the sixty-four day post-lesion group. Finally, we have observed little change in the overall anatomic distribution of responses to forelimb or hindlimb stimulation in VPL following DCN lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Extensive dual innervation and mutual inhibition by forelimb and hindlimb inputs to ventroposterolateral nucleus projection neurons in the rat.

The stimulation of brachial plexus and sciatic nerve resulted in a precisely timed, synchronous volley of inputs to ventroposterolateral (VPL) neurons from either forelimb or hindlimb. Such stimulation activated sensory fibers of all modalities and was therefore modality-nonspecific. Extracellular recordings of modality-nonspecific single-unit evoked responses from VPL showed that 13% of VPL projection neurons responded to both forelimb and hindlimb inputs. We also demonstrated mutually inhibitory interactions between inputs from forelimb and hindlimb in 45% of VPL units. Unlike the somatotopic map produced by others using modality-specific inputs, the modality-nonspecific evoked response map of VPL had a broadly overlapping distribution of evoked responses. This was especially true for the more caudal aspects of VPL. When the delivery of stimuli was appropriately timed, forelimb inputs caused the inhibition of responses to forelimb stimulation; similarly, hindlimb inputs inhibited responses to forelimb stimulation. The inhibition had a variable duration that may reflect a combination of processes, including recurrent inhibitory collateral input from the thalamic reticular nucleus (TRN) or an intrinsic hyperpolarizing inhibitory afterpotential of the VPL neuron. The presence of an extensive converging input on VPL neurons and an inhibitory correlate to this overlapping of inputs may explain the shifting of VPL maps following lesions of peripheral nerve, spinal cord, or dorsal column nuclei (DCN).

Action Potentials↗
PubMed1989

Memory deficit caused by compressed air equivalent to 36 meters of seawater.

Twenty-four students from a diving school undertook a hyperbaric chamber dive to a pressure equal to 36 m of seawater. Tests of cognitive function and manual dexterity, performed in the chamber during the 35-min bottom time and before, or after, the dive included immediate and delayed free recall of words presented as 7 lists of 15 each, recognition of previously presented words, number identification, and a forceps pickup of ball bearings. Delayed free recall and immediate free recall (primacy region) were significantly impaired, whereas manual dexterity and recognition memory were not. These are in keeping with previously reported findings but indicate that significant impairment of memory may occur in experienced divers at operational depths for air diving. Lack of effect on recognition memory suggests that cueing strategies might be useful for debriefing divers.

Adolescent↗
PubMed1989

Central-place foraging by Rattus norvegicus on a radial maze.

We studied central-place foraging in rats (Rattus norvegicus) by placing food items that varied in size and weight at the ends of a 4-arm radial maze. In Experiments 1-3, rats increasingly tended to carry food to the center of the maze as the size of those items increased. Very large food items often were hoarded in the center. Rats consumed food faster on the arms than in the center, and rats traveled faster when carrying food than when not. Blocking arm entrances increased travel time between the center and the arms and decreased food carrying at every item weight except the largest. In Experiments 4-6, important conditions that influence the degree of food-carrying behavior were discovered; these were the intersection of maze arms, the presence of a conspecific, and the use of open vs. closed maze arms.

Animals↗
PubMed1989

Timing multimodal events in pigeons.

The peak procedure was used in two experiments to study pigeons' ability to time multimodal events. In the first experiment, birds were trained to time a single event consisting of a 9-s tone or light followed by a 21-s fixed interval associated with a signal of light or tone (signal of the other modality). On occasional empty trials, different lengths of the first signal were followed by a long period of the second signal. Peak response times as a function of the duration of the first signal were linear and had a slope of close to one in all birds. This indicates that the birds were timing only the second signal. In a second experiment, two complex events were used in training. One consisted of a 9-s tone or light followed by a 21-s fixed interval associated with a light or tone. The other consisted of a 21-s tone or light followed by a 9-s fixed interval associated with a light or tone. Different durations of the first signal were again used on empty trials. Peak response times as a function of the duration of the first signal were again linear in all birds. The slope of the function was less than one but greater than zero for 3 birds. This indicates that these birds were partly timing the entire complex event of 30-s duration and partly timing only the second signal of the event. A model is proposed in which the bird takes as a criterion for timing a weighted average of different target criteria. Comparisons with the performance of rats are made.

Journal Article↗
PubMed1989

Timing light and tone signals in pigeons.

Pigeons' ability to time light and tone stimuli was examined in four experiments. In Experiment 1, two groups of pigeons were trained to discriminate between 2- and 8-s durations of lights or tones and then were transferred to reversal or nonreversal discriminations in the alternate modality. Pigeons learned the light discrimination faster than the tone discrimination and showed immediate positive intermodal transfer from tone to light but not from light to tone. In Experiments 2-4, the peak procedure was used to study birds' timing of 15- and 30-s fixed-interval light and tone signals. Peak times on empty trials under baseline conditions closely approximated the length of fixed-interval signals. When pigeons were tested with time-outs and intermodal switches introduced midway through an empty trial, they tended to reset the timing mechanism and begin timing again from 0 s. With both estimation and production procedures, pigeons were less accurate when timing the tone stimuli than when timing the light stimuli. A comparison of these data with data from timing experiments with rats suggests several possible differences in timing processes between pigeons and rats.

Animals↗
PubMed1987

Localized endophthalmitis: a newly described cause of the so-called toxic lens syndrome.

We report five cases of post-extracapsular cataract extraction infection in which subsequent pathologic analyses identified the organisms and found the infection to be localized or confined to the lens capsular sac. The most common offending organisms were gram-positive pleomorphic bacilli. In one case, we were able to identify the bacteria as Propionibacterium acnes. We designate this condition a localized endophthalmitis. It should be considered any time a persistent, smoldering, postoperative inflammation occurs, and in the differential diagnosis of phacoanaphylactic endophthalmitis. The condition itself is not new, but undoubtedly many such cases have gone unrecognized or have been misdiagnosed as the so-called toxic lens syndrome. In localized endophthalmitis, a clinically visible inflammatory process may occur even when multiple diagnostic taps are negative, although when the cases first appeared, the surgeons were not aware of the entity and anaerobic cultures were not always obtained. A negative tap may be explained by the fact that metabolic products from the organisms are released from the bag into the anterior segment and vitreous. A synergistic reaction may occur between these organisms and retained lens cortical remnants that may cause or exacerbate a hypersensitivity reaction. The condition may be worsened by Nd:YAG capsulotomy. The pathogenesis of localized endophthalmitis has nothing to do with the type of intraocular lens fixation (lens capsular sac or ciliary sulcus); rather, the simple presence of a capsular sac after extracapsular cataract extraction is the prerequisite for the clinical condition.

Aged↗
PubMed1985

Short-term memory for simultaneously presented visual and auditory signals in the pigeon.

A series of divided-attention experiments in which matching to the visual or auditory component of a tone-light compound was compared with matching to visual or auditory elements as sample stimuli were carried out. In 0-s delayed and simultaneous matching procedures, pigeons were able to match visual signals equally well when presented alone or with a tone; tones were matched at a substantially lower level of accuracy when presented with light signals than when presented as elements. In further experiments, it was demonstrated that the interfering effect of a signal light on tone matching was not related to the signaling value of the light, and that the prior presentation of light proactively interfered with auditory delayed matching. These findings indicate a divided attention process in which auditory processing is strongly inhibited in the presence of visual signals.

Animals↗
PubMed1984

Osteomalacia of very-low-birth-weight infants.

Neonatal osteomalacia has received scant attention in the orthopedic literature, despite a reported incidence of 13-32% in very-low-birth-weight infants. This retrospective study focused on the calcium, phosphorus, and vitamin D metabolism of 10 surviving infants up to 28 weeks old born over a 30-month period. Clinical and radiologic evidence of osteomalacia appeared to be related to the intake of calcium and phosphorus. The lower the amount of mineral intake, the more severe was the clinical appearance of rickets. The amount of vitamin D intake, although low, did not correlate with the degree of clinical or radiographic abnormalities noted in these infants. There was an orderly appearance of radiographic changes that were dependent on the amount of mineral depletion. Recognition and identification of the early radiographic findings may lead to the early diagnosis and treatment of osteomalacia in the very-low-birth-weight infant. Prevention of fractures resulting from calcium, phosphorus, or vitamin D deficiency is the goal of early therapy.

Calcium, Dietary↗
PubMed1983

Marital disturbance and child problems: a cautionary note regarding hyperactive children.

In previous work, investigators have found a relationship between marital discord and childhood conduct problems (aggression) in clinic samples. Given the wide variability of aggression found among hyperactive children, it would follow from previous work that child aggression may be associated with marital discord in a hyperactive population. This hypothesis was tested in a sample of 23 boys (ages 5 to 8) diagnosed as attention deficit with hyperactivity. Aggressive behaviors were tracked by the children's teachers for 12 school days. Parental and teacher ratings of conduct problems were also obtained. Additionally, the auditory version of the laboratory Continuous Performance Test was administered. Marital adjustment, overt hostility, and conflict tactics, as reported by the mothers, were not significantly correlated with any of the measures of aggression or conduct problems. In other words, marital discord in families with a hyperactive boy did not explain differential rates of aggressive behavior despite definite variability in both the marital and child behavioral measures. Marital discord was marginally related to severity of attentional deficit on the Continuous Performance Test. The results underscore the need for caution in attempting to extend findings from a general population (i.e., undifferentiated clinic-referred children) to a specific diagnostic subgroup (i.e., attention-deficit hyperactive children).

Aggression↗
PubMed1982

Some observations of the effects of intertrial interval and delay on delayed matching to sample in pigeons.

Accuracy of delayed matching to sample was studied in pigeons at different combinations of length of intertrial interval and length of delay. When intertrial interval and delay were varied between sessions in Experiments 1 and 2, accuracy increased monotonically with intertrial interval and decreased monotonically with delay. Evidence was found for constancy of performance at equivalent ratios of intertrial interval to delay, and percentage of correct choices was linearly related to the log of this ratio. In Experiments 3 and 4, intertrial interval was manipulated as a within-sessions variable. In contrast to the effect of this variable when manipulated between sessions, accuracy improved only from the shortest interval to the next shortest interval and remained constant at all longer intervals. In Experiment 4, it was found that performance improved as a direct function of the mean intertrial interval for sessions and that this relation was not affected by the degree of intertrial interval variability within sessions. These findings resemble the effects of temporal variables on autoshaping, and the possibility is discussed that some common processes are involved in delayed matching and autoshaping.

Animals↗
PubMed1980

Distribution of trials and intertrial retention in delayed matching to sample with pigeons.

On the basis of the notion that the events of a delayed matching to sample (DMTS) trial would be forgotten over a long intertrial interval (ITI), it was predicted that a 20-sec ITI would lead to better performance than a 1-sec ITI with a random order of DMTS trials but that a 1-sec ITI would be superior to a 20-sec ITI with a homogeneous order of DMTS trials. Contrary to this prediction, it was found in Experiments 1 and 2 that a 20-sec ITI led to a higher accuracy than a 1-sec ITI with both random and homogeneous orders. In Experiment 3, daily reversal learning was used to show that varying the ITI was directly opposite effects on DMTS with homogeneous orders of trials and on simultaneous discrimination learning; a 1-sec ITI facilitated discrimination learning and hindered DMTS, relative to a 20-sec ITI. Analyses of two-trial sequences within the first three experiments indicated that memories of Trial n - 1 influenced performance on Trial n; pigeons' choice on Trial n reflected a preference for the pattern presented on or for the position of the key most recently pecked on Trial n - 1 regardless of the outcome (reinforced or nonreinforced) of Trial n - 1. In Experiment 4, performance on homogeneous DMTS trials embedded within random DMTS trials, using stimuli from another dimension, was studied. Performance on embedded trials was equally good with massed and spaced distribution of trials and was superior to performance on control trials. It is suggested that the carry-over of memory of preceding trials provides information necessary for successful performance in discrimination learning but acts to interfere with processing of the sample stimulus in DMTS.

Animals↗