Biomedical subjects

T W Kjaer

Publications and source records attributed to T W Kjaer.

12 recordsLinked to original sources

PubMed2001

Precuneus-prefrontal activity during awareness of visual verbal stimuli.

Awareness is a personal experience, which is only accessible to the rest of world through interpretation. We set out to identify a neural correlate of visual awareness, using brief subliminal and supraliminal verbal stimuli while measuring cerebral blood flow distribution with H(2)(15)O PET. Awareness of visual verbal stimuli differentially activated medial parietal association cortex (precuneus), which is a polymodal sensory cortex, and dorsolateral prefrontal cortex, which is thought to be primarily executive. Our results suggest participation of these higher order perceptual and executive cortical structures in visual verbal awareness.

Adult↗

PubMed2000

Neonatal treatment with beta-cell stimulatory agents reduces the incidence of diabetes in BB rats.

The aim of the study was to investigate whether various beta-cell stimulatory drugs, given neonatally, influence the incidence of diabetes in BB rats. Newborn BB rats were treated twice daily for 6 days and diabetes development was observed during the following 200-day study period. Compared to a diabetes incidence of 63.8% in 163 control BB rats which received saline or were untreated, the percentage of experimental BB rats that developed diabetes was as follows in the different subgroups: arginine-glucose: 47% (n = 73, p < 0.02); glucagon: 37% (n = 93, p < 0.0001); tolbutamide-glucose: 36% (n = 58, p < 0.0005); and theophylline-glucose: 39% (n = 41, p < 0.005). A long-term arginine-glucose treatment was not superior to the shorter neonatal treatment. Histological examination revealed a higher degree of insulitis in diabetic than in non-diabetic animals but no difference according to the kind of treatment was observed. Finally, we found that the diabetes incidence in BB rats was higher in the first litter compared to subsequent litters (p = 0.04). Thus, neonatal treatment with various beta-cell stimulatory agents reduces diabetes incidence in BB rats. The theory behind the study, that the treatment accelerates beta-cell maturation leading to increased immunological tolerance towards beta cells, is discussed.

Animals↗

PubMed1999

A 15O-H2O PET study of meditation and the resting state of normal consciousness.

The aim of the present study was to examine whether the neural structures subserving meditation can be reproducibly measured, and, if so, whether they are different from those supporting the resting state of normal consciousness. Cerebral blood flow distribution was investigated with the 15O-H20 PET technique in nine young adults, who were highly experienced yoga teachers, during the relaxation meditation (Yoga Nidra), and during the resting state of normal consciousness. In addition, global CBF was measured in two of the subjects. Spectral EEG analysis was performed throughout the investigations. In meditation, differential activity was seen, with the noticeable exception of V1, in the posterior sensory and associative cortices known to participate in imagery tasks. In the resting state of normal consciousness (compared with meditation as a baseline), differential activity was found in dorso-lateral and orbital frontal cortex, anterior cingulate gyri, left temporal gyri, left inferior parietal lobule, striatal and thalamic regions, pons and cerebellar vermis and hemispheres, structures thought to support an executive attentional network. The mean global flow remained unchanged for both subjects throughout the investigation (39+/-5 and 38+/-4 ml/100 g/min, uncorrected for partial volume effects). It is concluded that the (H2)15O PET method may measure CBF distribution in the meditative state as well as during the resting state of normal consciousness, and that characteristic patterns of neural activity support each state. These findings enhance our understanding of the neural basis of different aspects of consciousness.

Adult↗

PubMed1997

Insensitivity of V1 complex cell responses to small shifts in the retinal image of complex patterns.

An important role for neurons in the early visual system is to convey information about the structure of visual stimuli. However, neuronal responses show substantial variation across presentations of the same stimulus. In awake monkeys, it has been assumed that a great deal of this variation is related to the scatter in eye position (inducing scatter in the retinal position of the stimulus). Here we investigate the implied consequence of this assumption, i.e., that the scatter variation in eye position degrades the decodability of the neural response. We recorded from 50 complex cells in primary visual cortex of fixating monkeys while different complex stimuli were presented. Three types of retinal shifts were considered: natural scatter in the fixation, systematic fixation point shift, and systematic stimulus position shift. The stimulus pattern accounts for >50% of the response variance, always six times that accounted for by the scatter in eye position during fixation. The retinal location of a stimulus had to be shifted by 10-12 min of arc, an amount almost two times larger than the smallest picture element, before the responses changed systematically. Nonetheless, changes of the stimulus at the single pixel level often gave rise to discriminable responses. Thus complex cells convey information about the spatial structure of a stimulus, independent of rigid stimulus displacements on the order of the receptive field size or smaller.

Animals↗

PubMed1996

Latency: another potential code for feature binding in striate cortex.

1. We recorded the responses of 37 striate cortical complex cells in fixating monkeys while presenting a set of oriented stimuli that varied in contrast. 2. The two response parameters of strength and latency can be interpreted as a code: the strength defines the stimulus form (here the orientation), and the latency is more a function of the stimulus contrast. 3. Synchronization based on latency could make a strong contribution to the process of organizing the neural responses to different objects, i.e., binding.

Animals↗

PubMed1995

Information flow and temporal coding in primate pattern vision.

We perform time-resolved calculations of the information transmitted about visual patterns by neurons in primary visual and inferior temporal cortices. All measurable information is carried in an effective time-varying firing rate, obtained by averaging the neuronal response with a resolution no finer than about 25 ms in primary visual cortex and around twice that in inferior temporal cortex. We found no better way for a neuron receiving these messages to decode them than simply to count spikes for this long. Most of the information tends to be concentrated in one or, more often, two brief packets, one at the very beginning of the response and the other typically 100 ms later. The first packet is the most informative part of the message, but the second one generally contains new information. A small but significant part of the total information in the message accumulates gradually over the entire course of the response. These findings impose strong constraints on the codes used by these neurons.

Animals↗

PubMed1994

Decoding cortical neuronal signals: network models, information estimation and spatial tuning.

We have studied the encoding of spatial pattern information by complex cells in the primary visual cortex of awake monkeys. Three models for the conditional probabilities of different stimuli, given the neuronal response, were fit and compared using cross-validation. For our data, a feed-forward neural network proved to be the best of these models. The information carried by a cell about a stimulus set can be calculated from the estimated conditional probabilities. We performed a spatial spectroscopy of the encoding, examining how the transmitted information varies with both the average coarseness of the stimulus set and the coarseness differences within it. We find that each neuron encodes information about many features at multiple scales. Our data do not appear to allow a characterization of these variations in terms of the detection of simple single features such as oriented bars.

Animals↗

PubMed1992

Interleukins increase surface ganglioside expression of pancreatic islet cells in vitro.

This experiment was conducted in order to investigate whether expression of gangliosides on islet cell surface in vitro is influenced by cytokines, especially interleukin 1. Islets from adult Lewis rats were incubated with different concentrations of recombinant-derived human cytokines. Following dispase treatment, the single cells were labeled with monoclonal antiganglioside antibodies A2B5 or R2D6, and conjugate. Both are directed against beta cells; A2B5 is recognized to bind specifically to pancreatic islet cells, while R2D6 is shown to bind no other pancreatic cells than beta cells. Surface labeling was evaluated in blind trials using a fluorescence microscope and a fluorescence-activated cell sorter (FACS). A2B5 staining demonstrated a significantly higher number of labeled cells after incubation with interleukin 1 alpha (14.9% +/- 2.8; p less than 0.005), interleukin 1 beta (23.2% +/- 4.2; p less than 0.0005) or TNF alpha (16.1% +/- 4.0; p = 0.005) compared to endotoxin controls (4.1% +/- 1.1). Interleukin 1 beta (9.5% +/- 1.5; p less than 0.005) showed a significantly increased number of R2D6-stained cells (control: 2.3% +/- 1.3). A similar but not significant effect was seen with interleukin 1 alpha and TNF alpha. Interleukin 6 had no effect on the antigen expression. The intensity of labeling was elevated among interleukin 1 beta-incubated cells compared to control samples. Thus, treatment of islets with different cytokines, especially interleukin 1 beta, increases surface antigen expression. We suggest that this mechanism of action in vitro may be of importance for the putative diabetogenic effect of interleukin 1.

Animals↗

PubMed1991

Reduction of diabetes incidence in NOD mice by neonatal glucose treatment.

The aim of this study was to investigate whether neonatal glucose treatment influences the incidence of diabetes in NOD mice. Thirty-nine NOD mice (19 males, 20 females) were treated with 8 g glucose/kg BW/day administered by subcutaneous injections twice a day for the first six days of life. Thirty-six untreated NOD mice (20 males, 16 females) served as a control group. In the glucose-treated group, 33% became diabetic compared with 58% in the control group (X2 = 5.3, p = 0.021). Among the glucose-treated males, 16% became diabetic compared with 50% of the untreated males (X2 = 5.5, p = 0.019), whereas 50% of the glucose-treated females became diabetic compared with 69% of the untreated females (X2 = 1.1, NS). We conclude that neonatal glucose treatment can reduce the diabetes incidence in NOD mice. These results could have implications for the prevention of type 1 diabetes mellitus in humans.

Animals↗

PubMedDate not supplied

Adjacent visual cortical complex cells share about 20% of their stimulus-related information.

The responses of adjacent neurons in inferior temporal (IT) cortex carry signals that are to a large degree independent (Gawne and Richmond, 1993). Adjacent primary visual cortical neurons have similar orientation tuning (Hubel and Wiesel, 1962, 1968), suggesting that their responses might be more redundant than those in IT. We recorded the responses of 26 pairs of adjacent complex cells in the primary visual cortex of two awake monkeys while using both a set of 16 bar-like stimuli, and a more complex set of 128 two-dimensional patterns. Linear regression showed that 40% of the signal variance of one neuron was related to that of the other when the responses to the bar-like stimuli were considered. However, when the responses to the two-dimensional stimuli were included in the analysis, only 19% of the signal variance of one neuron was related to that of the adjacent one, almost exactly the same results as found in IT. An information theoretic analysis gave similar results. We hypothesize that this trend toward independence of information processing by adjacent cortical neurons is a general organizational strategy used to maximize the amount of information carried in local groups.

Action Potentials↗

PubMedDate not supplied

Cranial base angulation and prognathism related to cranial and general skeletal maturation in human fetuses.

The purpose of the present study was to describe normal midsagittal craniofacial morphology in second trimester human fetuses. Measurements of the cranial base angle and the prognathism of the maxilla and the mandible were performed on radiographs of cranial midsagittal tissue blocks of 52 fetuses with a gestational age from 13 to 27 weeks. Special procedures were developed for the definitions of the nasion and sella reference points on the radiographs in the early stages of fetal development. Mean data were reported for stages of crown rump length (CRL) and maturation of the fetal cranial base (MSS), usable as reference in assessment of pathological fetal crania in reports and autopsy procedures. Regression equations were determined for the regression of the angular values on CRL, MSS, and general skeletal maturation (TNO). The cranial base angle was found to decrease significantly, and the angles of prognathism to increase significantly with increasing CRL, TNO, and MSS values. It was suggested that these simultaneous and similar changes in the three angles could be accounted for by the upwards movement of the sella point produced by a cranial displacement of the pituitary fossa caused by local cartilagenous growth and bony remodelling during the period of study. The study thus reflects the influence of cranial skeletal maturation on the early development in shape of the craniofacial complex.

Cephalometry↗

PubMedDate not supplied

Ossification sequence of occipital bone and vertebrae in human fetuses.

The aim of this radiographic study of human fetuses was to examine the pattern and sequence of ossification in the occipital bone and the spinal vertebrae. Together with previous studies of ossification of the human fetal basal cranium, this study can serve as a reference for normalcy in future studies of fetuses with neural tube defects and associated pathological development of the axial skeleton. Thirty-nine normal fetuses aborted between 9 and 14 weeks of gestation were examined. Based on the appearance of ossification centers in the bones under study, the fetuses could be grouped in four well-defined developmental stages, which were named occipito-spinal stages I-IV (OS I-IV). The OS stage was closely related to gestational age, crown-rump length, foot length, and degree of ossification in the hands and feet.

Embryonic and Fetal Development↗