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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Model of statoconia accumulation in gravireceptors of mollusks

The kinetics of formation and accumulation of statoconia are different for Aplysia californica and Biomphalaria glabrata. In Aplysia californica, the fast growth of statoconia number occurs after the critical size (approximately 45 micrometers) of statocyst is reached; then the increase of statoconia number is proceeding with the nonmonotonic rate during the life of an animal. In Biomphalaria the growth of statoconia number occurs only in the initial phase. Then long-term evolution of statoconia in the absence of their generation is the result of their growth in the cyst lumen. In the case of Aplysia californica it is not clear whether a temporal change of the statoconia size distribution (SSD) is caused by statoconia growth in the cyst lumen similar to that in Biomphalaria (Model 1) or statoconia growth takes place in supporting cells until their release into the cyst lumen occurs. (Model 2). This problem is of practical importance because the majority of experiments related to the development of molluscan gravireceptors in altered gravity dealt with an initial phase of statoconia evolution in Aplysia californica and Biomphalaria glabrata. The purpose of the present work is the application of mathematical modeling to the analysis of mechanisms of statoconia formation by supporting cells.

Non-NASA Center↗
NASA NTRS2003

Afferent innervation of the utricular macula in pigeons

Biotinylated dextran amine (BDA) was used to retrogradely label afferents innervating the utricular macula in adult pigeons. The pigeon utriclar macula consists of a large rectangular-shaped neuroepithelium with a dorsally curved anterior edge and an extended medioposterior tail. The macula could be demarcated into several regions based on cytoarchitectural differences. The striola occupied 30% of the macula and contained a large density of type I hair cells with fewer type II hair cells. Medial and lateral extrastriola zones were located outside the striola and contained only type II hair cells. A six- to eight-cell-wide band of type II hair cells existed near the center of the striola. The reversal line marked by the morphological polarization of hair cells coursed throughout the epithelium, near the peripheral margin, and through the center of the type II band. Calyx afferents innervated type I hair cells with calyceal terminals that contained between 2 and 15 receptor cells. Calyx afferents were located only in the striola region, exclusive of the type II band, had small total fiber innervation areas and low innervation densities. Dimorph afferents innervated both type I and type II hair cells with calyceal and bouton terminals and were primarily located in the striola region. Dimorph afferents had smaller calyceal terminals with few type I hair cells, extended fiber branches with bouton terminals and larger innervation areas. Bouton afferents innervated only type II hair cells in the extrastriola and type II band regions. Bouton afferents innervating the type II band had smaller terminal fields with fewer bouton terminals and smaller innervation areas than fibers located in the extrastriolar zones. Bouton afferents had the most bouton terminals on the longest fibers, the largest innervation areas with the highest innervation densities of all afferents. Among all afferents, smaller terminal innervation fields were observed in the striola and large fields were located in the extrastriola. The cellular organization and innervation patterns of the utricular maculae in birds appear to represent an organ in adaptive evolution, different from that observed for amphibians or mammals.

Non-NASA Center↗
NASA NTRS2003

BDNF heightens the sensitivity of motor neurons to excitotoxic insults through activation of TrkB

The survival promoting and neuroprotective actions of brain-derived neurotrophic factor (BDNF) are well known but under certain circumstances this growth factor can also exacerbate excitotoxic insults to neurons. Prior exploration of the receptor through which BDNF exerts this action on motor neurons deflects attention away from p75. Here we investigated the possibility that BDNF acts through the receptor tyrosine kinase, TrkB, to confer on motor neurons sensitivity to excitotoxic challenge. We blocked BDNF activation of TrkB using a dominant negative TrkB mutant or a TrkB function blocking antibody, and found that this protected motor neurons against excitotoxic insult in cultures of mixed spinal cord neurons. Addition of a function blocking antibody to BDNF to mixed spinal cord neuron cultures is also neuroprotective indicating that endogenously produced BDNF participates in vulnerability to excitotoxicity. We next examined the intracellular signaling cascades that are engaged upon TrkB activation. Previously we found that inhibition of the phosphatidylinositide-3'-kinase (PI3'K) pathway blocks BDNF-induced excitotoxic sensitivity. Here we show that expression of a constitutively active catalytic subunit of PI3'K, p110, confers excitotoxic sensitivity (ES) upon motor neurons not incubated with BDNF. Parallel studies with purified motor neurons confirm that these events are likely to be occuring specifically within motor neurons. The abrogation of BDNF's capacity to accentuate excitotoxic insults may make it a more attractive neuroprotective agent.

Non-NASA Center↗
NASA NTRS2003

Vestibular activation of sympathetic nerve activity

AIM: The vestibulosympathetic reflex refers to sympathetic nerve activation by the vestibular system. Animal studies indicate that the vestibular system assists in blood pressure regulation during orthostasis. Although human studies clearly demonstrate activation of muscle sympathetic nerve activity (MSNA) during engagement of the otolith organs, the role of the vestibulosympathetic reflex in maintaining blood pressure during orthostasis is not well-established. Examination of the vestibulosympathetic reflex with other cardiovascular reflexes indicates that it is a powerful and independent reflex. Ageing, which is associated with an increased risk for orthostatic hypotension, attenuates the vestibulosympathetic reflex. The attenuated reflex is associated with a reduction in arterial pressure. CONCLUSION: These findings suggest that the vestibulosympathetic reflex assists in blood pressure regulation in humans, but future studies examining this reflex in other orthostatically intolerant populations are necessary to address this hypothesis.

Review↗
NASA NTRS2003

Strength training reduces arterial blood pressure but not sympathetic neural activity in young normotensive subjects

The effects of resistance training on arterial blood pressure and muscle sympathetic nerve activity (MSNA) at rest have not been established. Although endurance training is commonly recommended to lower arterial blood pressure, it is not known whether similar adaptations occur with resistance training. Therefore, we tested the hypothesis that whole body resistance training reduces arterial blood pressure at rest, with concomitant reductions in MSNA. Twelve young [21 +/- 0.3 (SE) yr] subjects underwent a program of whole body resistance training 3 days/wk for 8 wk. Resting arterial blood pressure (n = 12; automated sphygmomanometer) and MSNA (n = 8; peroneal nerve microneurography) were measured during a 5-min period of supine rest before and after exercise training. Thirteen additional young (21 +/- 0.8 yr) subjects served as controls. Resistance training significantly increased one-repetition maximum values in all trained muscle groups (P < 0.001), and it significantly decreased systolic (130 +/- 3 to 121 +/- 2 mmHg; P = 0.01), diastolic (69 +/- 3 to 61 +/- 2 mmHg; P = 0.04), and mean (89 +/- 2 to 81 +/- 2 mmHg; P = 0.01) arterial blood pressures at rest. Resistance training did not affect MSNA or heart rate. Arterial blood pressures and MSNA were unchanged, but heart rate increased after 8 wk of relative inactivity for subjects in the control group (61 +/- 2 to 67 +/- 3 beats/min; P = 0.01). These results indicate that whole body resistance exercise training might decrease the risk for development of cardiovascular disease by lowering arterial blood pressure but that reductions of pressure are not coupled to resistance exercise-induced decreases of sympathetic tone.

NASA Discipline Neuroscience↗
NASA NTRS2002

Transcriptional profiling reveals regulated genes in the hippocampus during memory formation

Transcriptional profiling (TP) offers a powerful approach to identify genes activated during memory formation and, by inference, the molecular pathways involved. Trace eyeblink conditioning is well suited for the study of regional gene expression because it requires the hippocampus, whereas the highly parallel task, delay conditioning, does not. First, we determined when gene expression was most regulated during trace conditioning. Rats were exposed to 200 trials per day of paired and unpaired stimuli each day for 4 days. Changes in gene expression were most apparent 24 h after exposure to 200 trials. Therefore, we profiled gene expression in the hippocampus 24 h after 200 trials of trace eyeblink conditioning, on multiple arrays using additional animals. Of 1,186 genes on the filter array, seven genes met the statistical criteria and were also validated by real-time polymerase chain reaction. These genes were growth hormone (GH), c-kit receptor tyrosine kinase (c-kit), glutamate receptor, metabotropic 5 (mGluR5), nerve growth factor-beta (NGF-beta), Jun oncogene (c-Jun), transmembrane receptor Unc5H1 (UNC5H1), and transmembrane receptor Unc5H2 (UNC5H2). All these genes, except for GH, were downregulated in response to trace conditioning. GH was upregulated; therefore, we also validated the downregulation of the GH inhibitor, somatostatin (SST), even though it just failed to meet criteria on the arrays. By during situ hybridization, GH was expressed throughout the cell layers of the hippocampus in response to trace conditioning. None of the genes regulated in trace eyeblink conditioning were similarly affected by delay conditioning, a task that does not require the hippocampus. These findings demonstrate that transcriptional profiling can exhibit a repertoire of genes sensitive to the formation of hippocampal-dependent associative memories.

Non-NASA Center↗
NASA NTRS2002

Does the vestibular system contribute to head direction cell activity in the rat?

Head direction cells (HDC) located in several regions of the brain, including the anterior dorsal nucleus of the thalamus (ADN), postsubiculum (PoS), and lateral mammillary nuclei (LMN), provide the neural substrate for the determination of head direction. Although activity of HDC is influenced by various sensory signals and internally generated cues, lesion studies and some anatomical and physiological evidence suggest that vestibular inputs are critical for the maintenance of directional sensitivity of these cells. However, vestibular inputs must be transformed considerably in order to signal head direction, and the neuronal circuitry that accomplishes this signal processing has not been fully established. Furthermore, it is unclear why the removal of vestibular inputs abolishes the directional sensitivity of HDC, as visual and other sensory inputs and motor feedback signals strongly affect the firing of these neurons and would be expected to maintain their directional-related activity. Further physiological studies will be required to establish the role of vestibular system in producing HDC responses, and anatomical studies are needed to determine the neural circuitry that mediates vestibular influences on determination of head direction.

Review, Tutorial↗
NASA NTRS2002

Neural substrates linking balance control and anxiety

This communication provides an update of our understanding of the neurological bases for the close association between balance control and anxiety. New data suggest that a vestibulo-recipient region of the parabrachial nucleus (PBN) contains cells that respond to body rotation and position relative to gravity. The PBN, with its reciprocal relationships with the extended central amygdaloid nucleus, infralimbic cortex, and hypothalamus, appears to be an important node in a primary network that processes convergent vestibular, somatic, and visceral information processing to mediate avoidance conditioning, anxiety, and conditioned fear responses. Noradrenergic and serotonergic projections to the vestibular nuclei also have parallel connections with anxiety pathways. The coeruleo-vestibular pathway originates in caudal locus coeruleus (LC) and provides regionally specialized noradrenergic input to the vestibular nuclei, which likely mediate effects of alerting and vigilance on the sensitivity of vestibulo-motor circuits. Both serotonergic and nonserotonergic pathways from the dorsal raphe nucleus and the nucleus raphe obscurus also project differentially to the vestibular nuclei, and 5-HT(2A) receptors are expressed in amygdaloid and cortical targets of the PBN. It is proposed that the dorsal raphe nucleus pathway contributes to both (a) a tradeoff between motor and sensory (information gathering) aspects of responses to self-motion and (b) a calibration of the sensitivity of affective responses to aversive aspects of motion. This updated neurologic model continues to be a synthetic schema for investigating the neurological and neurochemical bases for comorbidity of balance disorders and anxiety disorders.

Review↗
NASA NTRS2003

Afferent innervation patterns of the saccule in pigeons

The innervation patterns of vestibular saccular afferents were quantitatively investigated in pigeons using biotinylated dextran amine as a neural tracer and three-dimensional computer reconstruction. Type I hair cells were found throughout a large portion of the macula, with the highest density observed in the striola. Type II hair cells were located throughout the macula, with the highest density in the extrastriola. Three classes of afferent innervation patterns were observed, including calyx, dimorph, and bouton units, with 137 afferents being anatomically reconstructed and used for quantitative comparisons. Calyx afferents were located primarily in the striola, innervated a number of type I hair cells, and had small innervation areas. Most calyx afferent terminal fields were oriented parallel to the anterior-posterior axis and the morphological polarization reversal line. Dimorph afferents were located throughout the macula, contained fewer type I hair cells in a calyceal terminal than calyx afferents and had medium sized innervation areas. Bouton afferents were restricted to the extrastriola, with multi-branching fibers and large innervation areas. Most of the dimorph and bouton afferents had innervation fields that were oriented dorso-ventrally but were parallel to the neighboring reversal line. The organizational morphology of the saccule was found to be distinctly different from that of the avian utricle or lagena otolith organs and appears to represent a receptor organ undergoing evolutionary adaptation toward sensing linear motion in terrestrial and aerial species.

NASA Discipline Neuroscience↗
NASA NTRS2003

Coordinated turn-and-reach movements. II. Planning in an external frame of reference

The preceding study demonstrated that normal subjects compensate for the additional interaction torques generated when a reaching movement is made during voluntary trunk rotation. The present paper assesses the influence of trunk rotation on finger trajectories and on interjoint coordination and determines whether simultaneous turn-and-reach movements are most simply described relative to a trunk-based or an external reference frame. Subjects reached to targets requiring different extents of arm joint and trunk rotation at a natural pace and quickly in normal lighting and in total darkness. We first examined whether the larger interaction torques generated during rapid turn-and-reach movements perturb finger trajectories and interjoint coordination and whether visual feedback plays a role in compensating for these torques. These issues were addressed using generalized Procrustes analysis (GPA), which attempts to overlap a group of configurations (e.g., joint trajectories) through translations and rotations in multi-dimensional space. We first used GPA to identify the mean intrinsic patterns of finger and joint trajectories (i.e., their average shape irrespective of location and orientation variability in the external and joint workspaces) from turn-and-reach movements performed in each experimental condition and then calculated their curvatures. We then quantified the discrepancy between each finger or joint trajectory and the intrinsic pattern both after GPA was applied individually to trajectories from a pair of experimental conditions and after GPA was applied to the same trajectories pooled together. For several subjects, joint trajectories but not finger trajectories were more curved in fast than slow movements. The curvature of both joint and finger trajectories of turn-and-reach movements was relatively unaffected by the vision conditions. Pooling across speed conditions significantly increased the discrepancy between joint but not finger trajectories for most subjects, indicating that subjects used different patterns of interjoint coordination in slow and fast movements while nevertheless preserving the shape of their finger trajectory. Higher movement speeds did not disrupt the arm joint rotations despite the larger interaction torques generated. Rather, subjects used the redundant degrees of freedom of the arm/trunk system to achieve similar finger trajectories with differing joint configurations. We examined finger movement patterns and velocity profiles to determine the frame of reference in which turn-and-reach movements could be most simply described. Finger trajectories of turn-and-reach movements had much larger curvatures and their velocity profiles were less smooth and less bell-like in trunk-based coordinates than in external coordinates. Taken together, these results support the conclusion that turn-and-reach movements are controlled in an external frame of reference.

NASA Discipline Neuroscience↗
NASA NTRS2003

Coordinated turn-and-reach movements. I. Anticipatory compensation for self-generated coriolis and interaction torques

When reaching movements involve simultaneous trunk rotation, additional interaction torques are generated on the arm that are absent when the trunk is stable. To explore whether the CNS compensates for such self-generated interaction torques, we recorded hand trajectories in reaching tasks involving various amplitudes and velocities of arm extension and trunk rotation. Subjects pointed to three targets on a surface slightly above waist level. Two of the target locations were chosen so that a similar arm configuration relative to the trunk would be required for reaching to them, one of these targets requiring substantial trunk rotation, the other very little. Significant trunk rotation was necessary to reach the third target, but the arm's radial distance to the body remained virtually unchanged. Subjects reached at two speeds-a natural pace (slow) and rapidly (fast)-under normal lighting and in total darkness. Trunk angular velocity and finger velocity relative to the trunk were higher in the fast conditions but were not affected by the presence or absence of vision. Peak trunk velocity increased with increasing trunk rotation up to a maximum of 200 degrees /s. In slow movements, peak finger velocity relative to the trunk was smaller when trunk rotation was necessary to reach the targets. In fast movements, peak finger velocity was approximately 1.7 m/s for all targets. Finger trajectories were more curved when reaching movements involved substantial trunk rotation; however, the terminal errors and the maximal deviation of the trajectory from a straight line were comparable in slow and fast movements. This pattern indicates that the larger Coriolis, centripetal, and inertial interaction torques generated during rapid reaches were compensated by additional joint torques. Trajectory characteristics did not vary with the presence or absence of vision, indicating that visual feedback was unnecessary for anticipatory compensations. In all reaches involving trunk rotation, the finger movement generally occurred entirely during the trunk movement, indicating that the CNS did not minimize Coriolis forces incumbent on trunk rotation by sequencing the arm and trunk motions into a turn followed by a reach. A simplified model of the arm/trunk system revealed that additional interaction torques generated on the arm during voluntary turning and reaching were equivalent to < or =1.8 g (1 g = 9.81 m/s(2)) of external force at the elbow but did not degrade performance. In slow-rotation room studies involving reaching movements during passive rotation, Coriolis forces as small as 0.2 g greatly deflect movement trajectories and endpoints. We conclude that compensatory motor innervations are engaged in a predictive fashion to counteract impending self-generated interaction torques during voluntary reaching movements.

NASA Discipline Neuroscience↗
NASA NTRS2003

Balance in a rotating artificial gravity environment

When subjects stand at the center of a fully enclosed room that is rotating at constant velocity, their natural postural sway generates Coriolis forces that destabilize their center of mass and head. We quantitatively assessed how exposure to constant velocity rotation at 10 rpm affected postural control. Twelve subjects stood in a heel-to-toe stance in the rotating room. Each test session involved three phases: (1) pre-rotation, (2) per-rotation, and (3) post-rotation. In each phase, subjects were tested in both eyes open and eyes closed conditions. Four measures were used to characterize center of mass movement and head movement: mean sway amplitude, total power, mean power frequency, and frequency of maximum power. Each measure was computed for anterior-posterior and medial-lateral sway. Both anterior-posterior and medial-lateral head and center of mass sway during rotation had significantly greater mean sway amplitude and total power compared with pre- and post-rotation values. Mean power frequency and frequency of maximum power were little affected. Eyes open conditions were significantly more stable in all test phases than eyes-closed, but vision did not completely suppress the effects of rotation. The greatest effect of rotation was in the eyes-closed condition with mean sway amplitude and total power increasing more than twofold. Inverted pendulum sway was maintained in all phases of both test conditions. No aftereffects of rotation were present after the four 25-s exposures each subject received. We expect that with longer exposure periods and with active generation of body sway subjects would both adapt to rotation and exhibit post-rotary aftereffects.

NASA Discipline Neuroscience↗
NASA NTRS2003

Cross-axis adaptation of torsional components in the yaw-axis vestibulo-ocular reflex

The three pairs of semicircular canals within the labyrinth are not perfectly aligned with the pulling directions of the six extraocular muscles. Therefore, for a given head movement, the vestibulo-ocular reflex (VOR) depends upon central neural mechanisms that couple the canals to the muscles with the appropriate functional gains in order to generate a response that rotates the eye the correct amount and around the correct axis. A consequence of these neural connections is a cross-axis adaptive capability, which can be stimulated experimentally when head rotation is around one axis and visual motion about another. From this visual-vestibular conflict the brain infers that the slow-phase eye movement is rotating around the wrong axis. We explored the capability of human cross-axis adaptation, using a short-term training paradigm, to determine if torsional eye movements could be elicited by yaw (horizontal) head rotation (where torsion is normally inappropriate). We applied yaw sinusoidal head rotation (+/-10 degrees, 0.33 Hz) and measured eye movement responses in the dark, and before and after adaptation. The adaptation paradigm lasted 45-60 min, and consisted of the identical head motion, coupled with a moving visual scene that required one of several types of eye movements: (1) torsion alone (-Roll); (2) horizontal/torsional, head right/CW torsion (Yaw-Roll); (3) horizontal/torsional, head right/CCW torsion (Yaw+Roll); (4) horizontal, vertical, torsional combined (Yaw+Pitch-Roll); and (5) horizontal and vertical together (Yaw+Pitch). The largest and most significant changes in torsional amplitude occurred in the Yaw-Roll and Yaw+Roll conditions. We conclude that short-term, cross-axis adaptation of torsion is possible but constrained by the complexity of the adaptation task: smaller torsional components are produced if more than one cross-coupling component is required. In contrast, vertical cross-axis components can be easily trained to occur with yaw head movements.

Non-NASA Center↗
NASA NTRS2002

Evidence for vestibular regulation of autonomic functions in a mouse genetic model

Physiological responses to changes in the gravitational field and body position, as well as symptoms of patients with anxiety-related disorders, have indicated an interrelationship between vestibular function and stress responses. However, the relative significance of cochlear and vestibular information in autonomic regulation remains unresolved because of the difficulties in distinguishing the relative contributions of other proprioceptive and interoceptive inputs, including vagal and somatic information. To investigate the role of cochlear and vestibular function in central and physiological responses, we have examined the effects of increased gravity in wild-type mice and mice lacking the POU homeodomain transcription factor Brn-3.1 (Brn-3bPou4f3). The only known phenotype of the Brn-3.1(-/-) mouse is related to hearing and balance functions, owing to the failure of cochlear and vestibular hair cells to differentiate properly. Here, we show that normal physiological responses to increased gravity (2G exposure), such as a dramatic drop in body temperature and concomitant circadian adjustment, were completely absent in Brn-3.1(-/-) mice. In line with the lack of autonomic responses, the massive increase in neuronal activity after 2G exposure normally detected in wild-type mice was virtually abolished in Brn-3.1(-/-) mice. Our results suggest that cochlear and vestibular hair cells are the primary regulators of autonomic responses to altered gravity and provide genetic evidence that these cells are sufficient to alter neural activity in regions involved in autonomic and neuroendocrine control.

Non-NASA Center↗
NASA NTRS2002

Differential adaptation of the linear and nonlinear components of the horizontal vestibuloocular reflex in squirrel monkeys

Previous work in squirrel monkeys has demonstrated the presence of linear and nonlinear components to the horizontal vestibuloocular reflex (VOR) evoked by high-acceleration rotations. The nonlinear component is seen as a rise in gain with increasing velocity of rotation at frequencies more than 2 Hz (a velocity-dependent gain enhancement). We have shown that there are greater changes in the nonlinear than linear component of the response after spectacle-induced adaptation. The present study was conducted to determine if the two components of the response share a common adaptive process. The gain of the VOR, in the dark, to sinusoidal stimuli at 4 Hz (peak velocities: 20-150 degrees /s) and 10 Hz (peak velocities: 20 and 100 degrees /s) was measured pre- and postadaptation. Adaptation was induced over 4 h with x0.45 minimizing spectacles. Sum-of-sines stimuli were used to induce adaptation, and the parameters of the stimuli were adjusted to invoke only the linear or both linear and nonlinear components of the response. Preadaptation, there was a velocity-dependent gain enhancement at 4 and 10 Hz. In postadaptation with the paradigms that only recruited the linear component, there was a decrease in gain and a persistent velocity-dependent gain enhancement (indicating adaptation of only the linear component). After adaptation with the paradigm designed to recruit both the linear and nonlinear components, there was a decrease in gain and no velocity-dependent gain enhancement (indicating adaptation of both components). There were comparable changes in the response to steps of acceleration. We interpret these results to indicate that separate processes drive the adaptation of the linear and nonlinear components of the response.

Non-NASA Center↗
NASA NTRS2002

Vestibular convergence patterns in vestibular nuclei neurons of alert primates

Sensory signal convergence is a fundamental and important aspect of brain function. Such convergence may often involve complex multidimensional interactions as those proposed for the processing of otolith and semicircular canal (SCC) information for the detection of translational head movements and the effective discrimination from physically congruent gravity signals. In the present study, we have examined the responses of primate rostral vestibular nuclei (VN) neurons that do not exhibit any eye movement-related activity using 0.5-Hz translational and three-dimensional (3D) rotational motion. Three distinct neural populations were identified. Approximately one-fourth of the cells exclusively encoded rotational movements (canal-only neurons) and were unresponsive to translation. The canal-only central neurons encoded head rotation in SCC coordinates, exhibited little orthogonal canal convergence, and were characterized with significantly higher sensitivities to rotation as compared to primary SCC afferents. Another fourth of the neurons modulated their firing rates during translation (otolith-only cells). During rotations, these neurons only responded when the axis of rotation was earth-horizontal and the head was changing orientation relative to gravity. The remaining one-half of VN neurons were sensitive to both rotations and translations (otolith + canal neurons). Unlike primary otolith afferents, however, central neurons often exhibited significant spatiotemporal (noncosine) tuning properties and a wide variety of response dynamics to translation. To characterize the pattern of SCC inputs to otolith + canal neurons, their rotational maximum sensitivity vectors were computed using exclusively responses during earth-vertical axis rotations (EVA). Maximum sensitivity vectors were distributed throughout the 3D space, suggesting strong convergence from multiple SCCs. These neurons were also tested with earth-horizontal axis rotations (EHA), which would activate both vertical canals and otolith organs. However, the recorded responses could not be predicted from a linear combination of EVA rotational and translational responses. In contrast, one-third of the neurons responded similarly during EVA and EHA rotations, although a significant response modulation was present during translation. Thus this subpopulation of otolith + canal cells, which included neurons with either high- or low-pass dynamics to translation, appear to selectively ignore the component of otolith-selective activation that is due to changes in the orientation of the head relative to gravity. Thus contrary to primary otolith afferents and otolith-only central neurons that respond equivalently to tilts relative to gravity and translational movements, approximately one-third of the otolith + canal cells seem to encode a true estimate of the translational component of the imposed passive head and body movement.

Non-NASA Center↗
NASA NTRS2002

Responses of primate caudal parabrachial nucleus and Kolliker-fuse nucleus neurons to whole body rotation

The caudal aspect of the parabrachial (PBN) and Kolliker-Fuse (KF) nuclei receive vestibular nuclear and visceral afferent information and are connected reciprocally with the spinal cord, hypothalamus, amygdala, and limbic cortex. Hence, they may be important sites of vestibulo-visceral integration, particularly for the development of affective responses to gravitoinertial challenges. Extracellular recordings were made from caudal PBN cells in three alert, adult female Macaca nemestrina through an implanted chamber. Sinusoidal and position trapezoid angular whole body rotation was delivered in yaw, roll, pitch, and vertical semicircular canal planes. Sites were confirmed histologically. Units that responded during rotation were located in lateral and medial PBN and KF caudal to the trochlear nerve at sites that were confirmed anatomically to receive superior vestibular nucleus afferents. Responses to whole-body angular rotation were modeled as a sum of three signals: angular velocity, a leaky integration of angular velocity, and vertical position. All neurons displayed angular velocity and integrated angular velocity sensitivity, but only 60% of the neurons were position-sensitive. These responses to vertical rotation could display symmetric, asymmetric, or fully rectified cosinusoidal spatial tuning about a best orientation in different cells. The spatial properties of velocity and integrated velocity and position responses were independent for all position-sensitive neurons; the angular velocity and integrated angular velocity signals showed independent spatial tuning in the position-insensitive neurons. Individual units showed one of three different orientations of their excitatory axis of velocity rotation sensitivity: vertical-plane-only responses, positive elevation responses (vertical plane plus ipsilateral yaw), and negative elevation axis responses (vertical plane plus negative yaw). The interactions between the velocity and integrated velocity components also produced variations in the temporal pattern of responses as a function of rotation direction. These findings are consistent with the hypothesis that a vestibulorecipient region of the PBN and KF integrates signals from the vestibular nuclei and relay information about changes in whole-body orientation to pathways that produce homeostatic and affective responses.

Non-NASA Center↗
NASA NTRS2002

A quasi-static method for determining the characteristics of a motion capture camera system in a "split-volume" configuration

The purpose of this study was to determine the accuracy, repeatability and resolution of a six-camera Motion Analysis system in a vertical split-volume configuration using a unique quasi-static methodology. The position of a reflective marker was recorded while it was moved quasi-statically over a range of 2.54 mm (0.100 inches) via a linearly-translating table. The table was placed at five different heights to cover both sub-volumes and the overlapping region. Data analysis showed that accuracy, repeatability and resolution values were consistent across all regions of the split-volume, including the overlapping section.

NASA Center JSC↗