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PubMed1996

Chronopharmacokinetics and chronopharmacodynamics of dextromethamphetamine in man.

Stimulants, in particular the amphetamines, have been studied as countermeasures to fatigue induced by circadian desynchronosis and extended flight operations. To make recommendations concerning the use of dextromethamphetamine for operational tasks, its chronopharmacokinetic and chronopharmacodynamic profiles and influence on circadian rhythms as a countermeasure to performance deficits and fatigue were studied. Ten male volunteers, divided into two groups of five each, were given 30 mg/70 kg of oral dextromethamphetamine during two test sessions one week apart and were evaluated with cognitive (dichotic listening, pattern recognition, and compensatory tracking), subjective (fatigue scale), and physiologic (blood pressure) testing. Session order was counterbalanced with dextromethamphetamine administration at either 8:40 AM or 8:40 PM during session one and a crossover to the other time during session two. Subjective and cognitive testing was begun 1.5 hours before dextromethamphetamine administration and continued every half hour until 12.5 hours after administration. Blood pressure was measured immediately before behavioral testing. Serum and urine were collected at regular intervals for gas chromatography/mass spectrometer analysis of methamphetamine and one of its metabolites, amphetamine. No differences were found in the day-versus-night pharmacokinetic profile of dextromethamphetamine. Cognitive performance and subjective fatigue improved after daytime administration of dextromethamphetamine in comparison to performance before drug administration. This effect was suppressed during the circadian trough, which occurred approximately 8 hours into the night sessions (4:30 AM). No correlations were seen between serum concentration of methamphetamine and measured behavioral parameters.

Adult↗
PubMed1993

Complex spike responses of cerebellar Purkinje cells to constant velocity optokinetic stimuli in the cat flocculus.

In the cat cerebellar flocculus without cerebrum but with intact accessory optic tract, complex spike (CS) responses to horizontal optokinetic stimuli (velocity-step at 2 degrees/s) were investigated. The directionally selective CS responses were present only during the short-duration stimuli but not during the continuous unidirectional stimuli. Following the end of the stimuli during the stationary surround phase, the CS activity was modulated in a manner opposite to the preceding CS response during the stimulation. These CS responses cannot simply be interpreted as sensory responses to the retinal slip input; they may in fact be deeply associated with the motor control command of the eye movement which would be elicited by the retinal slip.

Animals↗
PubMed1993

Direction selective climbing fiber responses to horizontal and vertical optokinetic stimuli in the cat cerebellar flocculus.

In ketamine anesthetized cats, complex spike (CS) responses to movement of a large-field visual surround (optokinetic stimulus) were recorded in the cerebellar flocculus. Two types of Purkinje cells were found. One type showed increased CS activity to optokinetic stimuli directed contralaterally to the recording site and decreased activity to stimuli directed ipsilaterally. The modulation occurred in both monocular (responses to the stimuli for only the ipsilateral eye) and binocular forms (dominant eye, ipsilateral). The other type of cell showed increased CS activity during upward optokinetic stimuli and decreased activity during downward stimuli. The responses occurred only in the binocular form. The dominant eye was either ipsilateral or contralateral with respect to the recording site. Thus, there are two types of Purkinje cells in the cat flocculus: horizontal type cell showing CS modulation during horizontal optokinetic stimuli, and vertical type cell showing CS modulation during vertical optokinetic stimuli.

Animals↗
PubMed2002

A novel paradigm for telemedicine using the personal bio-monitor.

The foray of solid-state technology in the medical field has yielded an arsenal of sophisticated healthcare tools. Personal, portable computing power coupled with the information superhighway open up the possibility of sophisticated healthcare management that will impact the medical field just as much. The full synergistic potential of three interwoven technologies: (1) compact electronics, (2) World Wide Web, and (3) Artificial Intelligence is yet to be realized. The system presented in this paper integrates these technologies synergistically, providing a new paradigm for healthcare. Our idea is to deploy internet-enabled, intelligent, handheld personal computers for medical diagnosis. The salient features of the 'Personal Bio-Monitor' we envisage are: (1) Utilization of the peripheral signals of the body which may be acquired non-invasively and with ease, for diagnosis of medical conditions; (2) An Artificial Neural Network (ANN) based approach for diagnosis; (3) Configuration of the diagnostic device as a handheld for personal use; (4) Internet connectivity, following the emerging bluetooth protocol, for prompt conveyance of information to a patient's health care provider via the World Wide Web. The proposal is substantiated with an intelligent handheld device developed by the investigators for pediatric cardiac auscultation. This device performed accurate diagnoses of cardiac abnormalities in pediatrics using an artificial neural network to process heart sounds acquired by a low-frequency microphone and transmitted its diagnosis to a desktop PC via infrared. The idea of the personal biomonitor presented here has the potential to streamline healthcare by optimizing two valuable resources: physicians' time and sophisticated equipment time. We show that the elements of such a system are in place, with our prototype. Our novel contribution is the synergistic integration of compact electronics' technology, artificial neural network methodology and the wireless web resulting in a revolutionary new paradigm for healthcare management.

Adolescent↗
PubMed1995

Pattern recognition in insects.

After 80 years of research, the field of insect pattern recognition is about to move from the behavioral to the neuronal level. Recent experiments on bees, ants and flies indicate that pattern recognition must be seen as the recruitment of behavioral operations that help the nervous system to solve a task using a small number of potentially simple processing steps. These may now be identified physiologically.

Animals↗
PubMed2004

Hostility and facial affect recognition: effects of a cold pressor stressor on accuracy and cardiovascular reactivity.

The effects of hostility and a cold pressor stressor on the accuracy of facial affect perception were examined in the present experiment. A mechanism whereby physiological arousal level is mediated by systems which also mediate accuracy of an individual's interpretation of affective cues is described. Right-handed participants were classified as high hostile (N = 28) or low hostile (N = 28) using the Cook Medley Hostility Scale. The high-hostile group met joint selection criteria. Only high-hostile participants who showed cardiovascular reactivity to the cold pressor, with systolic BP change exceeding the group mean were included. Groups were further subdivided into cold pressor and non-cold pressor test conditions. It was predicted that high-hostile men, relative to low-hostile men, would show decreased perceptual accuracy when presented with happy, angry, and neutral facial configurations within the left visual field (LVF). Results indicated that high-hostile men were less accurate than low-hostile men in the LVF. Further, pre-stress accuracy scores in the high-hostile men were similar to the post-stress accuracy scores of the low-hostile men. The lateralization of affective function and the role of physiological arousal in affective facial perception are discussed.

Affect↗
PubMed2002

Malalignment: signs and significance.

Malalignment of the vertebrae, in patients suspected of blunt spinal trauma, is the quintessential sign of spinal injury. Malalignment is obvious in displaced fractures and dislocations but is rarely considered in the diagnosis because of the obvious injury. In patients with more subtle injuries such as those limited to ligamentous structures, vertebral malalignment is the only radiographic sign that leads one to the recognition of the injury. Equally important is the fact that vertebral malalignment may be congenital and may be due to physiologic movement as well as radiographic patient positioning. Recognition of the pattern of traumatic malalignment as distinguished from the appearance of non-traumatic malalignment is essential to accurate radiologic diagnosis. Because malalignment is critical to the radiographic assessment of blunt cervical spine injury, this presentation is limited to the cervical spine. The format of the article includes signs of physiologic and traumatic malaignment as seen on antero-posterior and lateral radiographs of the cervico-cranium and the lower cervical spine.

Bone Malalignment↗
PubMed1985

Carbohydrate-structure-dependent recognition of desialylated serum glycoproteins in the liver and leucocytes. Two complementary systems.

Oligosaccharides with four different types of branching were prepared from purified human transferrin, alpha 2-macroglobulin, caeruloplasmin and alpha 1-acid glycoprotein and labelled with NaBH3 3H. Binding of these oligosaccharides to rat liver plasma membrane, rat leucocytes, pig liver plasma membranes and pig leucocyte plasma membranes was investigated. A striking dependence of binding on oligosaccharide branching was observed. The values of apparent association constants Ka at 4 degrees C vary from 10(6) M-1 (biantennary structure) to 10(9) M-1 (tetra-antennary structure) in the liver, whereas in the leucocytes the Ka values were found to be of reversed order, from 1.8 X 10(9) M-1 for biantennary to 2.2 X 10(6) M-1 for tetra-antennary structures. The binding is completely inhibited by 150 mM-D-galactose, but 150 mM-D-mannose has almost no effect on binding. Leucocyte plasma membranes bind preferentially 125I-asialoglycoproteins with biantennary oligosaccharides, thus completing the specificity pattern of the hepatic recognition system for desialylated glycoproteins. Possible physiological roles of these two complementary recognition systems under normal and pathological conditions are discussed.

Animals↗
PubMed1983

Pattern recognition in kittens: performance on Lie patterns.

Despite a vast accumulation of knowledge about the anatomy and physiology of the cat's visual system in recent years, and about its early development, there has been very little experimental study of the development of visual behaviour in this species. This is especially true of the kitten's ability to recognize patterns. Two experiments are reported that aim to remedy some part of this deficiency, and that also serves to examine a particular hypothesis about the basis of pattern analysis in the young organism. This is Hoffman's hypothesis that the orbits of elementary Lie transformation groups (a species of continuous transformation group) represent the basis for coding pattern information.

Age Factors↗
PubMed2005

Magnetoencephalographic correlates of different levels in subjective recognition memory.

In our current study we employed whole-head magnetoencephalography (MEG) to identify neurophysiological correlates (event-related fields, ERFs) of different phenomenologies in human recognition memory. Words which had previously been semantically processed were presented along with previously unstudied words. Via button presses, participants provided subjective indices of three forms of memory: confident recognition, familiarity-based recognition, and misclassification of previously presented items as new (no recognition, misses). Behavioral results revealed a clear distinction between confident recognition (shortest reaction times) and familiarity-based recognition and misses, respectively, and physiological data pointed to bilateral anterior and left anterior/central regions in which magnetic field patterns were directly related to word recognition from approximately 300 ms to 500 ms after word onset. In the context of the prevalent dual process controversy on the roles of familiarity and recollection in recognition memory, we first highlight that two operationalizations of recollection need to be differentiated: We argue that a strategic search for a particular contextual feature stands in clear contrast to the fast and incidental availability of some contextual feature and derive experimental and behavioral indicators for either form of recollection. These indicators are used to select from manifold cognitive neuroscientific work on recognition memory in order to further discuss the neurocognitive characteristics of incidental recollection in contrast to other forms of episodic memory.

Adult↗
PubMed1999

A neural network model of temporal code generation and position-invariant pattern recognition.

Numerous studies have suggested that the brain may encode information in the temporal firing pattern of neurons. However, little is known regarding how information may come to be temporally encoded and about the potential computational advantages of temporal coding. Here, it is shown that local inhibition may underlie the temporal encoding of spatial images. As a result of inhibition, the response of a given cell can be significantly modulated by stimulus features outside its own receptive field. Feedforward and lateral inhibition can modulate both the firing rate and temporal features, such as latency. In this article, it is shown that a simple neural network model can use local inhibition to generate temporal codes of handwritten numbers. The temporal encoding of a spatial pattern has the interesting and computationally beneficial feature of exhibiting position invariance. This work demonstrates a manner by which the nervous system may generate temporal codes and shows that temporal encoding can be used to create position-invariant codes.

Nervous System Physiological Phenomena↗
PubMed2006

Viewpoint dependence in adaptation to facial identity.

We produced morph sequences between identities at a variety of viewpoints, ranging from the three quarter leftward facing view, to the three quarter rightward facing view. We measured the strength of identity adaptation as a function of changing test viewpoint whilst keep the adaptation viewpoint constant, and as a function of adaptation viewpoint whilst keeping test viewpoint constant. Our results show a substantial decrease in adaptation as the angle between adaptation and test viewpoint increases. These findings persisted when we introduced controls for low-level retinotopic adaptation, leading us to conclude that our results show strong evidence for viewpoint dependence in the high-level encoding of facial identity. Our findings support models in which identity is encoded, to a large degree, by viewpoint dependent non-retinotopic neural mechanisms. Functional imaging studies suggest the fusiform gyrus as the most likely location for this mechanism.

Adaptation, Physiological↗
PubMed2001

Orientation-selective adaptation and tilt after-effect from invisible patterns.

Exposure to visual patterns of high contrast (for example, gratings formed by alternating white and black bars) creates after-effects in perception. We become temporarily insensitive to faint test patterns that resemble the pre-exposed pattern (such as gratings of the same orientation), and we require more contrast to detect them. Moreover, if the test pattern is slightly tilted relative to the pre-exposed one, this tilt may be perceptually exaggerated: we experience a tilt after-effect. Here we show that these visual after-effects occur even if the pre-exposed grating is too fine to be perceptually resolved. After looking at a very fine grating, so high in spatial frequency that it was perceptually indistinguishable from a uniform field, observers required more contrast to detect a test grating presented at the same orientation than one presented at the orthogonal orientation. They also experienced a tilt after-effect that depended on the relation of the test pattern's tilt to the unseen orientation of the pre-exposed pattern. Because these after-effects are due to changes in orientation-sensitive mechanisms in visual cortex, our observations imply that extremely fine details, even those too fine to be seen, can penetrate the visual system as far as the cortex, where they are represented neurally without conscious awareness.

Adaptation, Physiological↗
PubMed1993

Color appearance: the effects of illumination and spatial pattern.

The color we perceive at each point in an image depends on information spread across the three spatial arrays of cone photoreceptors. I describe experiments aimed at clarifying how information is integrated across the spatial arrays to yield a color experience. We have found that changes of color appearance due to changes of the ambient illumination and the pattern's spatial frequency can be described by using a simple set of optical and neural transformations. Each transformation can be thought of as having two parts. First, the transformation converts the color representation into a new coordinate frame that is independent of the image contents. Second, the transformation scales the neural responses in the new coordinate frame by a gain factor that depends on the image contents.

Color↗
PubMed2000

Cross axis VOR induced by pursuit training in monkeys: further properties of adaptive responses.

We have shown recently in alert monkeys that repeated interaction between the pursuit and vestibular systems in the orthogonal plane induces adaptive changes in the VOR. To examine further properties of adaptive cross axis VOR induced by pursuit training, sinusoidal whole body rotation was applied either in the pitch or yaw plane while presenting a target spot that moved orthogonally to the rotation plane with either 90 degrees phase-lead or 90 degrees phase-lag to the chair signal. After one hour of training at 0.5 Hz (+/- 10 degrees), considerable phase-shift was observed in orthogonal eye movement responses consistent with the training paradigms by identical chair rotation in complete darkness, with further lead at lower frequencies and lag at higher frequencies. However, gains (eye/chair) induced by phase- shift pursuit training was different during pitch and yaw rotation. Although frequency tuning was maintained during pitch in the phase-shift paradigms, it was not maintained during yaw, resulting in higher gains at lower stimulus frequencies compared to the gains during yaw. This difference may reflect otolith contribution during pitch rotation. To understand further the nature of signals that induce adaptive cross axis VOR, we examined interaction of pursuit, whole field-visual pattern and vestibular stimuli. Magnitudes of the cross axis VOR with a spot alone on one hand and with a spot and pattern moving together in the same plane on the other during chair rotation were similar, and when one of the two visual stimuli was stationary during chair rotation, our well trained monkeys did not induce the cross axis VOR. These results suggest that the cross axis VOR induced by pursuit training shares common mechanisms with the cross axis VOR induced by whole field-slip stimuli and that if conflicting information is given between the two visual stimuli, adaptive changes are inhibited. Horizontal GVPs were recorded in the cerebellar floccular lobe during pitch rotation coupled with horizontal pursuit stimuli. These GVPs did not respond to pitch in the dark before training, but responded after 60 min of pursuit training with eye velocity sensitivities similar to those before training. Adaptive change in the VOR was specific to smooth eye movements but not to saccades in our paradigms.

Adaptation, Physiological↗
PubMed1995

Extraction of discriminant features in post-cardiosurgical intensive care units.

A linear transformation, based on the Karhunen-Loève expansion, is applied to 13 physiological variables, measured in 200 surgical patients, in order to extract a limited number of features well representative of the differences between normal and high-risk classes of subjects. This transformation may be considered as a mapping from the primitive 13-dimensional space to a lower dimensional one, without severely reducing class separability. The efficacy of both transformed and primitive variables in the separation of normal and high-risk subjects is compared using the error probability, i.e. the probability that a patient is assigned to the wrong class. In particular, its upper bound is evaluated through the Kullback divergence and its estimate is computed, from the available samples, by applying a quadratic classifier. The results obtained show that only two transformed variables are able to present a divergence better than the most effective set of eight primitive variables. In agreement with the divergence criterion, the classifier provides a recognition error lower than 5% and greater than 13% when using the two best transformed and the two best primitive variables, respectively. Even though the new variables do not have a direct physiological meaning, this limitation has been partially overcome by calculating the correlation matrix between transformed and primitive variables. The results presented show that the first two transformed variables are strongly related to the most discriminant primitive ones (i.e. cardiac index, oxygen delivery and arterio-venous oxygen difference). In conclusion, the transformation of variables proposed appears to be extremely attractive for practical applications, since it allows recognition systems to be designed which exhibit both high performance and great simplicity.

Algorithms↗