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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Analysis and visualization of single-trial event-related potentials

In this study, a linear decomposition technique, independent component analysis (ICA), is applied to single-trial multichannel EEG data from event-related potential (ERP) experiments. Spatial filters derived by ICA blindly separate the input data into a sum of temporally independent and spatially fixed components arising from distinct or overlapping brain or extra-brain sources. Both the data and their decomposition are displayed using a new visualization tool, the "ERP image," that can clearly characterize single-trial variations in the amplitudes and latencies of evoked responses, particularly when sorted by a relevant behavioral or physiological variable. These tools were used to analyze data from a visual selective attention experiment on 28 control subjects plus 22 neurological patients whose EEG records were heavily contaminated with blink and other eye-movement artifacts. Results show that ICA can separate artifactual, stimulus-locked, response-locked, and non-event-related background EEG activities into separate components, a taxonomy not obtained from conventional signal averaging approaches. This method allows: (1) removal of pervasive artifacts of all types from single-trial EEG records, (2) identification and segregation of stimulus- and response-locked EEG components, (3) examination of differences in single-trial responses, and (4) separation of temporally distinct but spatially overlapping EEG oscillatory activities with distinct relationships to task events. The proposed methods also allow the interaction between ERPs and the ongoing EEG to be investigated directly. We studied the between-subject component stability of ICA decomposition of single-trial EEG epochs by clustering components with similar scalp maps and activation power spectra. Components accounting for blinks, eye movements, temporal muscle activity, event-related potentials, and event-modulated alpha activities were largely replicated across subjects. Applying ICA and ERP image visualization to the analysis of sets of single trials from event-related EEG (or MEG) experiments can increase the information available from ERP (or ERF) data. Copyright 2001 Wiley-Liss, Inc.

Non-NASA Center↗
NASA NTRS1993

Effects of microgravity on vestibular ontogeny: direct physiological and anatomical measurements following space flight (STS-29)

Does space flight change gravity receptor development? The present study measured vestibular form and function in birds flown as embryos for 5 days in earth orbit (STS-29). No major changes in vestibular gross morphology were found. Vestibular response mean amplitudes and latencies were unaffected by space flight. However, the results of measuring vestibular thresholds were mixed and abnormal responses in 3 of the 8 flight animals raise important questions.

NASA Discipline Neuroscience↗
NASA NTRS1996

Video-task acquisition in rhesus monkeys (Macaca mulatta) and chimpanzees (Pan troglodytes): a comparative analysis

This study describes video-task acquisition in two nonhuman primate species. The subjects were seven rhesus monkeys (Macaca mulatta) and seven chimpanzees (Pan troglodytes). All subjects were trained to manipulate a joystick which controlled a cursor displayed on a computer monitor. Two criterion levels were used: one based on conceptual knowledge of the task and one based on motor performance. Chimpanzees and rhesus monkeys attained criterion in a comparable number of trials using a conceptually based criterion. However, using a criterion based on motor performance, chimpanzees reached criterion significantly faster than rhesus monkeys. Analysis of error patterns and latency indicated that the rhesus monkeys had a larger asymmetry in response bias and were significantly slower in responding than the chimpanzees. The results are discussed in terms of the relation between object manipulation skills and video-task acquisition.

NASA Discipline Space Human Factors↗
NASA NTRS1990

Characterization and effect of light on the plasma membrane H(+) -ATPase of bean leaves

Proton excretion from bean (Phaseolus vulgaris L.) leaf cells is increased by bright white light. To test whether this could be due, at least in part, to an increase in plasma membrane (PM) ATPase activity, PM vesicles were isolated from primary leaves by phase partitioning and used to characterize PM ATPase activity and changes in response to light. ATPase activity was characterized as magnesium ion dependent, vanadate sensitive, and slightly stimulated by potassium chloride. The pH optimum was 6.5, the Km was approximately 0.30 millimolar ATP, and the activity was about 60% latent. PM vesicles were prepared from leaves of plants grown for 11 days in dim red light (growing slowly) or grown for 10 days in dim red light and then transferred to bright white-light for 1 day (growing rapidly). For both light treatments, ATPase specific activity was approximately 600 to 700 nanomoles per milligram protein per minute, and the latency, Km, and sensitivity to potassium chloride were also similar. PM vesicles from plants grown in complete darkness, however, exhibited a twofold greater specific activity. We conclude that the promotion of leaf growth and proton excretion by bright white light is not due to an increase in ATPase specific activity. Light does influence ATPase activity, however; both dim red light and bright white light decreased the ATPase specific activity by nearly 50% as compared with dark-grown leaves.

NASA Program Space Biology↗
NASA NTRS1988

Inhibition of nitrate transport by anti-nitrate reductase IgG fragments and the identification of plasma membrane associated nitrate reductase in roots of barley seedlings

Membrane associated nitrate reductase (NR) was detected in plasma membrane (PM) fractions isolated by aqueous two-phase partitioning from barley (Hordeum vulgare L. var CM 72) roots. The PM associated NR was not removed by washing vesicles with 500 millimolar NaCl and 1 millimolar EDTA and represented up to 4% of the total root NR activity. PM associated NR was stimulated up to 20-fold by Triton X-100 whereas soluble NR was only increased 1.7-fold. The latency was a function of the solubilization of NR from the membrane. NR, solubilized from the PM fraction by Triton X-100 was inactivated by antiserum to Chlorella sorokiniana NR. Anti-NR immunoglobulin G fragments purified from the anti-NR serum inhibited NO3- uptake by more than 90% but had no effect on NO2- uptake. The inhibitory effect was only partially reversible; uptake recovered to 50% of the control after thorough rinsing of roots. Preimmune serum immunoglobulin G fragments inhibited NO3- uptake 36% but the effect was completely reversible by rinsing. Intact NR antiserum had no effect on NO3- uptake. The results present the possibility that NO3- uptake and NO3- reduction in the PM of barley roots may be related.

NASA Discipline Number 61-10↗
NASA NTRS2001

Compound gravity receptor polarization vectors evidenced by linear vestibular evoked potentials

The utricle and saccule are gravity receptor organs of the vestibular system. These receptors rely on a high-density otoconial membrane to detect linear acceleration and the position of the cranium relative to Earth's gravitational vector. The linear vestibular evoked potential (VsEP) has been shown to be an effective non-invasive functional test specifically for otoconial gravity receptors (Jones et al., 1999). Moreover, there is some evidence that the VsEP can be used to independently test utricular and saccular function (Taylor et al., 1997; Jones et al., 1998). Here we characterize compound macular polarization vectors for the utricle and saccule in hatchling chickens. Pulsed linear acceleration stimuli were presented in two axes, the dorsoventral (DV, +/- Z axis) to isolate the saccule, and the interaural (IA, +/- Y axis) to isolate the utricle. Traditional signal averaging was used to resolve responses recorded from the surface of the skull. Latency and amplitude of eighth nerve components of the linear VsEP were measured. Gravity receptor responses exhibited clear preferences for one stimulus direction in each axis. With respect to each utricular macula, lateral translation in the IA axis produced maximum ipsilateral response amplitudes with substantially greater amplitude intensity (AI) slopes than medially directed movement. Downward caudal motions in the DV axis produced substantially larger response amplitudes and AI slopes. The results show that the macula lagena does not contribute to the VsEP compound polarization vectors of the sacculus and utricle. The findings suggest further that preferred compound vectors for the utricle depend on the pars externa (i.e. lateral hair cell field) whereas for the saccule they depend on pars interna (i.e. superior hair cell fields). These data provide evidence that maculae saccule and utricle can be selectively evaluated using the linear VsEP.

NASA Discipline Developmental Biology↗
NASA NTRS2001

Stimulated single fiber electromyography in the mouse: techniques and normative data

As the number of new transgenic mouse models of human neuromuscular disease continues to increase, the development of sophisticated electrophysiologic techniques for assessing the peripheral nervous system in these models has become important. Neuromuscular junction (NMJ) dysfunction, in particular, is often not detectable by morphologic or other techniques. To enable sensitive testing of murine NMJ function, we developed and tested a method for stimulated single fiber electromyography (S-SFEMG) in the gastrocnemius muscles of anesthetized mice. Jitter was assessed by measuring the mean consecutive latency difference (MCD) of single fiber responses to sciatic nerve stimulation at 2 HZ. Mean MCD values in normothermic mice were in the range of 6-8 micros for different strains, with no MCD values exceeding 25 micros. Reduced core temperature (to 29 degrees--30 degrees C) resulted in increased jitter, whereas intubation and mechanical ventilation of mice did not alter these values. Intraperitoneal and intravenous injection of vecuronium, however, resulted in progressively increased jitter followed by blocking in continuously monitored fibers. These observations validate the utility of S-SFEMG in mice as an index of NMJ function under a variety of physiologic conditions, and suggest that a high safety factor for neuromuscular transmission exists at mouse NMJs. Copyright 2001 John Wiley & Sons, Inc.

Non-NASA Center↗
NASA NTRS2001

Comparing viewer and array mental rotations in different planes

Participants imagined rotating either themselves or an array of objects that surrounded them. Their task was to report on the egocentric position of an item in the array following the imagined rotation. The dependent measures were response latency and number of errors committed. Past research has shown that self-rotation is easier than array rotation. However, we found that imagined egocentric rotations were as difficult to imagine as rotations of the environment when people performed imagined rotations in the midsagittal or coronal plane. The advantages of imagined self-rotations are specific to mental rotations performed in the transverse plane.

NASA Center ARC↗
NASA NTRS2004

Data Grid Management Systems

The "Grid" is an emerging infrastructure for coordinating access across autonomous organizations to distributed, heterogeneous computation and data resources. Data grids are being built around the world as the next generation data handling systems for sharing, publishing, and preserving data residing on storage systems located in multiple administrative domains. A data grid provides logical namespaces for users, digital entities and storage resources to create persistent identifiers for controlling access, enabling discovery, and managing wide area latencies. This paper introduces data grids and describes data grid use cases. The relevance of data grids to digital libraries and persistent archives is demonstrated, and research issues in data grids and grid dataflow management systems are discussed.

Moore, Reagan W.↗
NASA NTRS2000

A dual-task investigation of automaticity in visual word processing

An analysis of activation models of visual word processing suggests that frequency-sensitive forms of lexical processing should proceed normally while unattended. This hypothesis was tested by having participants perform a speeded pitch discrimination task followed by lexical decisions or word naming. As the stimulus onset asynchrony between the tasks was reduced, lexical-decision and naming latencies increased dramatically. Word-frequency effects were additive with the increase, indicating that frequency-sensitive processing was subject to postponement while attention was devoted to the other task. Either (a) the same neural hardware shares responsibility for lexical processing and central stages of choice reaction time task processing and cannot perform both computations simultaneously, or (b) lexical processing is blocked in order to optimize performance on the pitch discrimination task. Either way, word processing is not as automatic as activation models suggest.

Attention↗
NASA NTRS2000

Inducing jet-lag in older people: directional asymmetry

Twenty healthy elderly subjects (12 female, 8 male; mean age 81 years, range 67-87 years) each experienced a 15-day time isolation protocol in which they lived individually in a special laboratory apartment in which sleep and circadian rhythm measures could be taken. There were two experiments: one (6 females, 4 males) involved a 6-h phase advance of the sleep/wake cycle, and the other (6 females, 4 males) a 6-h phase delay. Each started with 5 baseline days, immediately followed by the phase shift. The subject was then held to the phase shifted routine for the remainder of the study. Rectal temperatures were recorded minute-by-minute throughout the entire experiment and each night of sleep was recorded using polysomnography. A directional asymmetry in phase-shift effects was apparent, with significantly more sleep disruption and circadian rhythm amplitude disruption after the phase advance than after the phase delay. Sleep disruption was reflected in reduced time spent asleep, and in changed REM latency, which increased in the phase advance direction but decreased in the phase delay direction. Although the phase advance led to a significant increase in wakefulness in the first half of the night, the phase delay did not lead to an equivalent increase in wakefulness during the second half of the night. Examination of both raw and 'demasked' circadian rectal temperature rhythms confirmed that phase adjustment was slow in both directions, but was less slow (and more monotonic) after the phase delay than after the phase advance. Subjective alertness suffered more disruption after the phase advance than after the phase delay.

NASA Discipline Regulatory Physiology↗
NASA NTRS2000

Horizontal vestibuloocular reflex evoked by high-acceleration rotations in the squirrel monkey. III. Responses after labyrinthectomy

The horizontal angular vestibuloocular reflex (VOR) evoked by high-frequency, high-acceleration rotations was studied in four squirrel monkeys after unilateral labyrinthectomy. Spontaneous nystagmus was measured at the beginning and end of each testing session. During the period that animals were kept in darkness (4 days), the nystagmus at each of these times measured approximately 20 degrees /s. Within 18-24 h after return to the light, the nystagmus (measured in darkness) decreased to 2.8 +/- 1.5 degrees /s (mean +/- SD) when recorded at the beginning but was 20.3 +/- 3.9 degrees /s at the end of the testing session. The latency of the VOR measured from responses to steps of acceleration (3,000 degrees /s(2) reaching a velocity of 150 degrees /s) was 8.4 +/- 0.3 ms for responses to ipsilesional rotations and 7.7 +/- 0.4 ms for contralesional rotations. During the period that animals were kept in darkness after the labyrinthectomy, the gain of the VOR measured during the steps of acceleration was 0.67 +/- 0.12 for contralesional rotations and 0.39 +/- 0.04 for ipsilesional rotations. Within 18-24 h after return to light, the VOR gain for contralesional rotations increased to 0.87 +/- 0.08, whereas there was only a slight increase for ipsilesional rotations to 0.41 +/- 0. 06. A symmetrical increase in the gain measured at the plateau of head velocity was noted after the animals were returned to light. The VOR evoked by sinusoidal rotations of 2-15 Hz, +/-20 degrees /s, showed a better recovery of gain at lower (2-4 Hz) than at higher (6-15 Hz) frequencies. At 0.5 Hz, gain decreased symmetrically when the peak amplitude was increased from 20 to 100 degrees /s. At 10 Hz, gain was decreased for ipsilesional half-cycles and increased for contralesional half-cycles when velocity was raised from 20 to 50 degrees /s. A model incorporating linear and nonlinear pathways was used to simulate the data. Selective increases in the gain for the linear pathway accounted for the recovery in VOR gain for responses at the velocity plateau of the steps of acceleration and for the sinusoidal rotations at lower peak velocities. The increase in gain for contralesional responses to steps of acceleration and sinusoidal rotations at higher frequencies and velocities was due to an increase in the contribution of the nonlinear pathway. This pathway was driven into cutoff and therefore did not affect responses for rotations toward the lesioned side.

NASA Discipline Neuroscience↗
NASA NTRS2000

Simulation studies of vestibular macular afferent-discharge patterns using a new, quasi-3-D finite volume method

A quasi-three-dimensional finite-volume numerical simulator was developed to study passive voltage spread in vestibular macular afferents. The method, borrowed from computational fluid dynamics, discretizes events transpiring in small volumes over time. The afferent simulated had three calyces with processes. The number of processes and synapses, and direction and timing of synapse activation, were varied. Simultaneous synapse activation resulted in shortest latency, while directional activation (proximal to distal and distal to proximal) yielded most regular discharges. Color-coded visualizations showed that the simulator discretized events and demonstrated that discharge produced a distal spread of voltage from the spike initiator into the ending. The simulations indicate that directional input, morphology, and timing of synapse activation can affect discharge properties, as must also distal spread of voltage from the spike initiator. The finite volume method has generality and can be applied to more complex neurons to explore discrete synaptic effects in four dimensions.

NASA Center ARC↗
NASA NTRS2000

The sleep of healthy people--a diary study

To provide baseline data for various research studies at the University of Pittsburgh over a 10-year period, 266 healthy subjects (144 male, 122 female, aged 20-50 years) meeting certain criteria each completed a 14-night sleep diary. For each night, the diary allowed the subjective measurement of bedtime, wake time, time in bed (TIB), sleep efficiency, number of minutes of wake after sleep onset (WASO), alertness on awakening, and percentage of morning needing an alarm (or a person functioning as one). Weeknight versus weekend night differences in TIB (TIBdiff), weekday altertness, and reliance on alarms were examined as possible indicators of sleep debt. In addition, general descriptive data were tabulated. On average, bedtimes were at 23:48 and wake times at 07:23, yielding a mean TIB of 7 hours 35 minutes. As expected, bedtimes and wake times were later on weekend nights than on weeknights. Bedtimes were 26 minutes later, wake times 53 minutes later, yielding a mean weekend TIB increase of 27 minutes. Overall, subjects perceived their sleep latency to be 10.5 minutes, reported an average of one awakening during the night (with an average of 6.4 minutes of WASO), had a diary sleep efficiency of 96.3%, and awoke with an alterness rating of 69.5%. These variables differed little between weeknight and weekend nights. Subjects used an alarm (or a person functioning as an alarm) on 60.9% nights overall, 68.3% on weeknights, 42.5% on weekends. When TIBdiff was used as an estimate of sleep debt (comparing subjects with TIBdiff > 75 minutes with those with a TIBdiff < 30 minutes), the group with more "catch-up sleep" on weekends had shorter weeknight TIB durations (by about 24 minutes) and relied more on an alarm for weekday waking (by about 22%), indicating the possible utility of these variables as sleep debt indices.

NASA Program Biomedical Research and Countermeasur↗
NASA NTRS1999

Horizontal vestibuloocular reflex evoked by high-acceleration rotations in the squirrel monkey. II. Responses after canal plugging

The horizontal angular vestibuloocular reflex (VOR) evoked by high-frequency, high-acceleration rotations was studied in four squirrel monkeys after unilateral plugging of the three semicircular canals. During the period (1-4 days) that animals were kept in darkness after plugging, the gain during steps of acceleration (3, 000 degrees /s(2), peak velocity = 150 degrees /s) was 0.61 +/- 0.14 (mean +/- SD) for contralesional rotations and 0.33 +/- 0.03 for ipsilesional rotations. Within 18-24 h after animals were returned to light, the VOR gain for contralesional rotations increased to 0. 88 +/- 0.05, whereas there was only a slight increase in the gain for ipsilesional rotations to 0.37 +/- 0.07. A symmetrical increase in the gain measured at the plateau of head velocity was noted after animals were returned to light. The latency of the VOR was 8.2 +/- 0. 4 ms for ipsilesional and 7.1 +/- 0.3 ms for contralesional rotations. The VOR evoked by sinusoidal rotations of 0.5-15 Hz, +/-20 degrees /s had no significant half-cycle asymmetries. The recovery of gain for these responses after plugging was greater at lower than at higher frequencies. Responses to rotations at higher velocities for frequencies >/=4 Hz showed an increase in contralesional half-cycle gain, whereas ipsilesional half-cycle gain was unchanged. A residual response that appeared to be canal and not otolith mediated was noted after plugging of all six semicircular canals. This response increased with frequency to reach a gain of 0.23 +/- 0.03 at 15 Hz, resembling that predicted based on a reduction of the dominant time constant of the canal to 32 ms after plugging. A model incorporating linear and nonlinear pathways was used to simulate the data. The coefficients of this model were determined from data in animals with intact vestibular function. Selective increases in the gain for the linear and nonlinear pathways predicted the changes in recovery observed after canal plugging. An increase in gain of the linear pathway accounted for the recovery in VOR gain for both responses at the velocity plateau of the steps of acceleration and for the sinusoidal rotations at lower peak velocities. The increase in gain for contralesional responses to steps of acceleration and sinusoidal rotations at higher frequencies and velocities was due to an increase in the gain of the nonlinear pathway. This pathway was driven into inhibitory cutoff at low velocities and therefore made no contribution for rotations toward the ipsilesional side.

NASA Discipline Developmental Biology↗
NASA NTRS1999

Horizontal vestibuloocular reflex evoked by high-acceleration rotations in the squirrel monkey. I. Normal responses

The horizontal angular vestibuloocular reflex (VOR) evoked by high-frequency, high-acceleration rotations was studied in five squirrel monkeys with intact vestibular function. The VOR evoked by steps of acceleration in darkness (3,000 degrees /s(2) reaching a velocity of 150 degrees /s) began after a latency of 7.3 +/- 1.5 ms (mean +/- SD). Gain of the reflex during the acceleration was 14.2 +/- 5.2% greater than that measured once the plateau head velocity had been reached. A polynomial regression was used to analyze the trajectory of the responses to steps of acceleration. A better representation of the data was obtained from a polynomial that included a cubic term in contrast to an exclusively linear fit. For sinusoidal rotations of 0.5-15 Hz with a peak velocity of 20 degrees /s, the VOR gain measured 0.83 +/- 0.06 and did not vary across frequencies or animals. The phase of these responses was close to compensatory except at 15 Hz where a lag of 5.0 +/- 0.9 degrees was noted. The VOR gain did not vary with head velocity at 0.5 Hz but increased with velocity for rotations at frequencies of >/=4 Hz (0. 85 +/- 0.04 at 4 Hz, 20 degrees /s; 1.01 +/- 0.05 at 100 degrees /s, P < 0.0001). No responses to these rotations were noted in two animals that had undergone bilateral labyrinthectomy indicating that inertia of the eye had a negligible effect for these stimuli. We developed a mathematical model of VOR dynamics to account for these findings. The inputs to the reflex come from linear and nonlinear pathways. The linear pathway is responsible for the constant gain across frequencies at peak head velocity of 20 degrees /s and also for the phase lag at higher frequencies being less than that expected based on the reflex delay. The frequency- and velocity-dependent nonlinearity in VOR gain is accounted for by the dynamics of the nonlinear pathway. A transfer function that increases the gain of this pathway with frequency and a term related to the third power of head velocity are used to represent the dynamics of this pathway. This model accounts for the experimental findings and provides a method for interpreting responses to these stimuli after vestibular lesions.

NASA Program Biomedical Research and Countermeasur↗
NASA NTRS1999

Firing behavior of vestibular neurons during active and passive head movements: vestibulo-spinal and other non-eye-movement related neurons

The firing behavior of 51 non-eye movement related central vestibular neurons that were sensitive to passive head rotation in the plane of the horizontal semicircular canal was studied in three squirrel monkeys whose heads were free to move in the horizontal plane. Unit sensitivity to active head movements during spontaneous gaze saccades was compared with sensitivity to passive head rotation. Most units (29/35 tested) were activated at monosynaptic latencies following electrical stimulation of the ipsilateral vestibular nerve. Nine were vestibulo-spinal units that were antidromically activated following electrical stimulation of the ventromedial funiculi of the spinal cord at C1. All of the units were less sensitive to active head movements than to passive whole body rotation. In the majority of cells (37/51, 73%), including all nine identified vestibulo-spinal units, the vestibular signals related to active head movements were canceled. The remaining units (n = 14, 27%) were sensitive to active head movements, but their responses were attenuated by 20-75%. Most units were nearly as sensitive to passive head-on-trunk rotation as they were to whole body rotation; this suggests that vestibular signals related to active head movements were cancelled primarily by subtraction of a head movement efference copy signal. The sensitivity of most units to passive whole body rotation was unchanged during gaze saccades. A fundamental feature of sensory processing is the ability to distinguish between self-generated and externally induced sensory events. Our observations suggest that the distinction is made at an early stage of processing in the vestibular system.

Non-NASA Center↗
NASA NTRS1999

Immunocytochemical localization of latent transforming growth factor-beta1 activation by stimulated macrophages

Transforming growth factor-beta1 (TGF-beta) is secreted in a latent form consisting of mature TGF-beta noncovalently associated with its amino-terminal propeptide, which is called latency associated peptide (LAP). Biological activity depends upon the release of TGF-beta from the latent complex following extracellular activation, which appears to be the key regulatory mechanism controlling TGF-beta action. We have identified two events associated with latent TGF-beta (LTGF-beta) activation in vivo: increased immunoreactivity of certain antibodies that specifically detect TGF-beta concomitant with decreased immunoreactivity of antibodies to LAP. Macrophages stimulated in vitro with interferon-gamma and lipopolysaccharide reportedly activate LTGF-beta via cell membrane-bound protease activity. We show through dual immunostaining of paraformaldehyde-fixed macrophages that such physiological TGF-beta activation is accompanied by a loss of LAP immunoreactivity with concomitant revelation of TGF-beta epitopes. The induction of TGF-beta immunoreactivity colocalized with immunoreactive betaglycan/RIII in activated macrophages, suggesting that LTGF-beta activation occurs on the cell surface. Confocal microscopy of metabolically active macrophages incubated with antibodies to TGF-beta and betaglycan/RIII prior to fixation supported the localization of activation to the cell surface. The ability to specifically detect and localize LTGF-beta activation provides an important tool for studies of its regulation.

NASA Discipline Radiation Health↗