The 1987-1988 NASA space/gravitational biology accomplishments

Individual technical summaries of research projects of the NASA Space/Gravitational Biology Program, for research conducted during the period January 1987 to April 1988 are presented. This Program is concerned with using the characteristics of the space environment, particularly microgravity, as a tool to advance knowledge in the biological sciences; understanding how gravity has shaped and affected life on earth; and understanding how the space environment affects both plant and animal species. The summaries for each project include a description of the research, a list of the accomplishments, an explanation of the significance of the accomplishments, and a list of publications

Detection thresholds of macaque otolith afferents

The vestibular system is our sixth sense and is important for spatial perception functions, yet the sensory detection and discrimination properties of vestibular neurons remain relatively unexplored. Here we have used signal detection theory to measure detection thresholds of otolith afferents using 1 Hz linear accelerations delivered along three cardinal axes. Direction detection thresholds were measured by comparing mean firing rates centered on response peak and trough (full-cycle thresholds) or by comparing peak/trough firing rates with spontaneous activity (half-cycle thresholds). Thresholds were similar for utricular and saccular afferents, as well as for lateral, fore/aft, and vertical motion directions. When computed along the preferred direction, full-cycle direction detection thresholds were 7.54 and 3.01 cm/s(2) for regular and irregular firing otolith afferents, respectively. Half-cycle thresholds were approximately double, with excitatory thresholds being half as large as inhibitory thresholds. The variability in threshold among afferents was directly related to neuronal gain and did not depend on spike count variance. The exact threshold values depended on both the time window used for spike count analysis and the filtering method used to calculate mean firing rate, although differences between regular and irregular afferent thresholds were independent of analysis parameters. The fact that minimum thresholds measured in macaque otolith afferents are of the same order of magnitude as human behavioral thresholds suggests that the vestibular periphery might determine the limit on our ability to detect or discriminate small differences in head movement, with little noise added during downstream processing

The 1988-1989 NASA Space/Gravitational Biology Accomplishments

This report consists of individual technical summaries of research projects of NASA's space/gravitational biology program, for research conducted during the period May 1988 to April 1989. This program is concerned with using the unique characteristics of the space environment, particularly microgravity, as a tool to advance knowledge in the biological sciences; understanding how gravity has shaped and affected life on Earth; and understanding how the space environment affects both plant and animal species. The summaries for each project include a description of the research, a list of the accomplishments, an explanation of the significance of the accomplishments, and a list of publications

Models of Causal Inference in the Elasmobranch Electrosensory System: How Sharks Find Food

We develop a theory of how the functional design of the electrosensory system in sharks reflects the inevitability of noise in high-precision measurements, and how the Central Nervous System may have developed an efficient solution to the problem of inferring parameters of stimulus sources, such as their location, via Bayesian neural computation. We use Finite Element Method to examine how the electrical properties of shark tissues and the geometrical configuration of both the shark body and the electrosensory array, act to focus weak electric fields in the aquatic environment, so that the majority of the voltage drop is signalled across the electrosensory cells. We analyse snapshots of two ethologically relevant stimuli: localized prey-like dipole electric sources, and uniform electric fields resembling motion-induced and other fields encountered in the ocean. We demonstrated that self movement (or self state) not only affects the measured field, by perturbing the self field, but also affects the external field. Electrosensory cells provide input to central brain regions via primary afferent nerves. Inspection of elasmobranch electrosensory afferent spike trains and inter-spike interval distributions indicates that they typically have fairly regular spontaneous inter-spike intervals with skewed Gaussian-like variability. However, because electrosensory afferent neurons converge onto secondary neurons, we consider the convergent input a "super afferent" with the pulse train received by a target neuron approaching a Poisson process with shorter mean intervals as the number of independent convergent spike trains increases. We implement a spiking neural particle filter which takes simulated electrosensory "super afferent" spike trains and can successfully infer the fixed Poisson parameter, or the equivalent real world state, distance to a source. The circuit obtained by converting the mathematical model to a network structure bears a striking resemblance to the cerebellar-like hindbrain circuits of the dorsal octavolateral nucleus. The elasmobranchs’ ability to sense electric fields down to a limit imposed by thermodynamics seems extraordinary. However we predict that the theories presented here generalize to other sensory systems, particularly the other octavolateralis senses which share cerebellar-like circuitry, suggesting that the cerebellum itself also plays a role in dynamic state estimation

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 380)

This bibliography lists 192 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during Oct. 1993. Subject coverage includes: aerospace medicine and physiology, life support systems and man/system technology, protective clothing, exobiology and extraterrestrial life, planetary biology, and flight crew behavior and performance

The 1989-1990 NASA space biology accomplishments

Individual technical summaries of research projects on NASA's Space Biology Program for research conducted during the period May 1989 to April 1990 are presented. This program is concerned with using the unique characteristics of the space environment, particularly microgravity, as a tool to advance the following: (1) knowledge in the biological sciences; (2) understanding of how gravity has shaped and affected life on the Earth; and (3) understanding of how the space environment affects both plants and animals. The summaries for each project include a description of the research, a list of accomplishments, an explanation of the significance of the accomplishments, and a list of publications

Orbiting Frog Otolith experiment (OFO-A): Data reduction and control experimentation

The OFO-A mission was prepared as a part of a special program of vestibular physiology with the purpose of studying in which way the lack of the gravity pull will affect the functioning of that part of the labyrinth which controls balance. The gravitational components corresponded to the different head positions, namely, the gravity sensitive or positioning receptors. It is evident that in weightlessness the gravity sensitive receptors are deprived of their primary input

Biophysical Properties of Zebrafish Hair Cells

Hair cells are specialized mechanosensory receptors in vertebrates that detect and process auditory and vestibular information with remarkable precision, fidelity and efficiency (Schwander et al., 2010). Most of our knowledge about these cells stems from in vitro preparations using isolated tissue, which creates the need for a relatively simple in vivo vertebrate model to study hair cells. The zebrafish (Danio rerio) is being increasingly used to study the genetic basis of hearing and deafness but also the function and physiology of hair cells (Nicolson, 2005). However, the use of the zebrafish as an in vivo model to study hair cell function is currently limited by our poor understanding of their biophysical properties. The aim of this study was to provide a detailed description of the biophysical properties of zebrafish hair cells both in the lateral line as well as inner ear during early and mature stages of fish development. I have used single cell patch-clamp electrophysiology to measure potassium currents and synaptic transmission in hair cells. I found that hair cells from the lateral line and inner ear show different current types, the expression of which depends upon the position of the cell within the lateral line neuromast or inner ear macula. Moreover, I found that the abundance of hair cell types in the lateral line changes over time, which potentially reflects adaptations to a changing sensory environment for the fish. The synaptic machinery of the lateral line hair cells is comparable in terms of efficiency to its mammalian counterpart, but less sensitive. Lastly, I have also developed an approach to study hair cell properties in vivo in the juvenile fish

Precision and reliability of cochlear nerve response in mice lacking functional synaptic ribbons

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 87-99).Synaptic ribbons are electron-dense structures surrounded by vesicles and anchored to the presynaptic membrane of photoreceptors, retinal bipolar cells and hair cells. Ribbon synapses are characterized by sustained exocytosis that is graded with stimulus intensity and can achieve high release rates. Leading hypotheses implicate the ribbon in maintenance of a large readily releasable pool (RRP) of presynaptic vesicles which enables rapid and precisely-timed exocytosis that supports instantaneous discharge rates of well over 1000 spikes per second. To gain insight into the function of this specialized presynaptic molecular machinery, we characterized the response properties of single auditory nerve (AN) fibers in a mouse with targeted deletion of a presynaptic scaffolding gene, bassoon, in which ribbons are no longer anchored to the active zone. Since each mammalian AN fiber usually receives input from a single inner hair cell active zone to which a single ribbon is typically anchored, single-fiber recordings from bassoon mutants and control mice offer a sensitive functional metric of the contribution of individual ribbons to neural function. Response properties of mutant AN fibers were similar, in many respects, to wild-type. Spike intervals remained irregular, thresholds were unaffected, dynamic range was unchanged, spike synchronization to(cont.) stimulus phase was unimpaired, the time course of post-onset adaptation and recovery from adaptation were normal, and the ability to sustain discharge throughout a long-duration stimulus was unaffected. These data indicate that the presynaptic mechanisms which regulate precise timing of exocytosis, graded release rates and sustained neurotransmitter release were not impaired by loss of the ribbon. However, reductions were seen in spontaneous and sound-evoked AN fiber discharge rates, coinciding with an increased variance of first spike timing to stimulus onset. Unlike fibers from wild-type mice, mutants failed to show increased peak rate as stimulus onset became more abrupt. The reduction of peak rates and increased first spike variance likely result from degraded reliability of discharge to stimulus onset via a mechanism such as reduced RRP size. Thus, the ribbon appears to support a large RRP that enables the rapid onset rates necessary for the auditory system to resolve stimulus features key for many perceptual tasks.by Bradley N. Buran.Ph.D