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Mathematical models of neurobehavioral function are useful both for understanding the underlying physiology and for predicting the effects of rest-activity-work schedules and interventions on neurobehavioral function. In a symposium titled Modeling Human Neurobehavioral Performance I: Uncovering Physiologic Mechanisms at the 2006 Society for Industrial and Applied Mathematics/Society for Mathematical Biology (SIAM/SMB) Conference on the Life Sciences, different approaches to modeling the physiology of human circadian rhythms, sleep, and neurobehavioral performance and their usefulness in understanding the underlying physiology were examined. The topics included key elements of the physiology that should be included in mathematical models, a computational model developed within a cognitive architecture that has begun to include the effects of extended wake on information-processing mechanisms that influence neurobehavioral function, how to deal with interindividual differences in the prediction of neurobehavioral function, the applications of systems biology and control theory to the study of circadian rhythms, and comparisons of these methods in approaching the overarching questions of the underlying physiology and mathematical models of circadian rhythms and neurobehavioral function. A unifying theme was that it is important to have strong collaborative ties between experimental investigators and mathematical modelers, both for the design and conduct of experiments and for continued development of the models., Sponsored in part by Air Force Office of Scientific Research (AFOSR) Grants nos. FA9550-05-1-0086 and FA9550-06-0080; by Air Force Research Laboratory Grant no. 04HE02COR; National Institutes of Health (NIH) Grants nos. K02-HD045459 and GM078993; and National Space Biomedical Research Institute (NSBRI) Grant no. HPF00405. Prepared in collaboration with the Division of Applied Sciences, Harvard University, Cambridge, MA; Air Force Research Laboratory, Mesa, AZ; Sleep and Performance Research Center, Washington State University, Spokane, WA; and Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, CA. Published in the Journal of Biological Rhythms, v22 n3 p233-245, Jun 2007.

Circadian rhythms are endogenous rhythms with a cycle length of approximately 24 h. Rhythmic production of specific proteins within pacemaker structures is the basis for these physiological and behavioral rhythms. Prior work on mathematical modeling of molecular circadian oscillators has focused on the fruit fly, Drosophila melanogaster. Recently, great advances have been made in our understanding of the molecular basis of circadian rhythms in mammals. Mathematical models of the mammalian circadian oscillator are needed to piece together diverse data, predict experimental results, and help us understand the clock as a whole. Our objectives are to develop mathematical models of the mammalian circadian oscillator, generate and test predictions from these models, gather information on the parameters needed for model development, integrate the molecular model with an existing model of the influence of light and rhythmicity on human performance, and make models available in BioSpice so that they can be easily used by the general community. Two new mammalian models have been developed, and experimental data are summarized. These studies have the potential to lead to new strategies for resetting the circadian clock. Manipulations of the circadian clock can be used to optimize performance by promoting alertness and physiological synchronization., info:eu-repo/semantics/published

The luminance and red-green chromatic detection mechanisms respond to, respectively, the sum and difference of the long-wave (L) and middle-wave (M) zone contrast signals. The most-detectable stimulus is not a small patch of luminance drifting grating, as suggested by others, but rather a small, foveal red-green chromatic flash. Even at the smallest test size examined, 2.3' diameter, the red-green mechanism i~s more sensitive than the luminance mechanism, which has profound implication for visual physiology. When a suprathreshold luminance flash (a pedestal) occurs coincidentally with a red-green chromatic flash, detection of color is facilitated ~2-fold, regardless of spot size, as shown by forced-choice results, and this constant facilitation contrasts with the much larger facilitation reported earlier for small flashes. The lack of chromatic masking by suprathreshold luminance pedestals supports the view of separable luminance and red-green detectors. Isolation of the red-green mechanism with large test flashes on different colored backgrounds showed that the red-green mechanism responds to an equally-weighted difference of L and M cone contrast on each background. Even for fields as low as 400 trolands, sensitivity is controlled by cone-selective adaptation (as well as second-site adaptation), which is surprising in view of recent physiological recordings suggesting that light adaptation in cones is insignificant below 2000 trolands. Motion mechanisms receiving L and M cone signals were studied with 1 cpd, flickering and drifting gratings. At low velocity, a spectrally-opponent (SPO) motion mechanism is more sensitive than the luminance (LUM) mechanism, which summates L and M signals. The SPO mechanism has equal L and M contrast weights at low velocity but is L-cone dominated at intermediate and high velocity, whereas the LUM mechanism shows the reverse pattern of weights. The SPO motion mechanism appears distinct frown a red-green hue mechanism, for the latter

When a suprathreshold luminance flash, presented as an increment on a large background field, accompanies a coincident equiluminant flash, the chromatic threshold is reduced. Early studies suggested that the chromatic facilitation grows large at small test size. We have measured detection thresholds for test spots with diameters from 5 min - 1 degree. Even for the smallest size the chromatic red-green sensitivity (specified in cone-contrast coordinates) is greater than luminance sensitivity, which has important implication for what the eye sees best. Facilitation by the luminance flash remains constant at 2x for all sizes contrary to other earlier studies. Further work with 1 degree flashes indicates that the facilitation results from a demarcation of the chromatic region by luminance features, and is not due to simple reduction of detection uncertainty. We also studied how the L and M cone signals combine in detecting motion.

When a suprathreshold luminance flash, presented as an increment on a larger background field, accompanies a circular equiluminant chromatic flash at the same spatial location, the chromatic threshold is reduced by about two-fold. This facilitation results from the clearly-visible edges of the luminance flash (the 'pedestal') serving to demarcate the test region, segregating it from its surround. Signal detection experiments show that this facilitation does not occur because the contour reduces the spatio-temporal detection uncertainty of the observer. Partial and incomplete luminance contours produce partial facilitation. An illusory contour pattern can produce the full facilitation effect, measured with a forced-choice method. Recent experiments show that a thin luminance line which bisects the test region produces weak facilitation, the amount of which varies slightly with line length. This result poses a challenge to simple models of the facilitation mechanism, since the line does not demarcate two differently colored regions. The facilitation effect can be used as a rigorous means of probing the way in which low-level visual attributes (edges, color) interact at higher levels. Keywords: Psychophysiology; Visual perception.

When a suprathreshold luminance flash, presented as an increment on a larger background field, accompanies a circular isoluminant chromatic flash at the same spatial location, chromatic threshold is reduced by about two-fold. This facilitation results from the clearly-visible edges of the luminance flash (the pedestal ) serving to demarcate the test region, segregating it from its surround. Recent signal detection experiments show that this facilitation does not occur as a result of the contour's reducing the spatio-temporal detection uncertainty of the observer; instead of merely directing the observer's attention, the pedestal must alter the properties of chromatic detectors (by changing the extent of spatial integration, for instance). A thin luminance ring can be used to create the facilitating contour. Displacing the ring relative to the test causes the facilitation to decline sharply, as if the visual system integrated uniformly within the demarcated region. However, the contour does not have to enclose the test region: small segments of the ring presented on the test circumference have about half the maximum facilitatory effect, while 180 deg of arcs produces the whole effect. These results can be used as a rigorous means of probing the way in which low-level visual attributes (edges, color) interact at higher levels.

Masking provides information about spatial-temporal tuning of detectors. The detectability of a test sine-wave grating was measured in the presence of a mask of one or more sine-wave gratings. Patterns varied in spatial frequency, orientation and velocity. Conclusions of 4 studies are: 1) Orientation and spatial frequency tuning are not separable: changing relative mask-test spatial frequency changes orientation tuning. 2) Patterns moving in opposite directions are not detected independently; right and left moving patterns mask each other and are detected by opponent-motion mechanisms sensitive to opposite velocities. At threshold, opposite directions may be detected independently. 3) Masking of a wide range of tests by a vertical mask of 4cpd, moving left or right at 4 hz, showed: a) asymmetry wherein low spatial and temporal tests were strongly masked and high spatial frequencies were facilitated; b) non-separability of the three tuning variable of spatial and temporal frequency and orientation, ruling out simple explanation. 4) A mask consisting of a small group of spectral components (simulating bandlimited 2D noise) produced strong masking by obscuring beats that would otherwise occur (and aid detection) when a single sine-wave test grating is added to a single sine-wave mask. Keywords: Human vision, Psychophysics, and Masking.

Respiration was monitored with magnetometers in 12 healthy supine young adults at sea level, and in an altitude chamber at simulated high altitudes ooof 8,000, 9,000, 11,000 and 14,000 feet. Periodic breathing which was strong enough to include apnea at the time of minimum ventilation was seen in all subjects at high altitude. The cycle time of periodic breathing ranged from 12 to 34 seconds. On average across the population the incidence of periodic breathing increased with altitude. The cycle time of the periodic pattern increased as the strength of the pattern increased. After normalizing to a standard pattern strength, cycle time decreased as altitude increased. The study was repeated 3 weeks later on 7 of the subjects. The standard cycle time at 14,000 feet of each subject in the second series was the same as in the first series to within, on the average, 6%. Each subject studied at 11,000 feet in both series reproduced his cycle time to within, on the average, 9%. The variation of standard cycle time for a given subject is less than the variation across the population, indicating characteristic cycle times for some individuals (one-way ANOVA, P less than 0.025).