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Search Results: 1 - 10 of 169055 matches for " Kathleen E. Cullen "
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The neural encoding of self-generated and externally applied movement: implications for the perception of self-motion and spatial memory
Kathleen E. Cullen
Frontiers in Integrative Neuroscience , 2013, DOI: 10.3389/fnint.2013.00108
Abstract: The vestibular system is vital for maintaining an accurate representation of self-motion. As one moves (or is moved) toward a new place in the environment, signals from the vestibular sensors are relayed to higher-order centers. It is generally assumed the vestibular system provides a veridical representation of head motion to these centers for the perception of self-motion and spatial memory. In support of this idea, evidence from lesion studies suggests that vestibular inputs are required for the directional tuning of head direction cells in the limbic system as well as neurons in areas of multimodal association cortex. However, recent investigations in monkeys and mice challenge the notion that early vestibular pathways encode an absolute representation of head motion. Instead, processing at the first central stage is inherently multimodal. This minireview highlights recent progress that has been made towards understanding how the brain processes and interprets self-motion signals encoded by the vestibular otoliths and semicircular canals during everyday life. The following interrelated questions are considered. What information is available to the higher-order centers that contribute to self-motion perception? How do we distinguish between our own self-generated movements and those of the external world? And lastly, what are the implications of differences in the processing of these active versus passive movements for spatial memory?
In vivo Conditions Induce Faithful Encoding of Stimuli by Reducing Nonlinear Synchronization in Vestibular Sensory Neurons
Adam D. Schneider,Kathleen E. Cullen,Maurice J. Chacron
PLOS Computational Biology , 2011, DOI: 10.1371/journal.pcbi.1002120
Abstract: Previous studies have shown that neurons within the vestibular nuclei (VN) can faithfully encode the time course of sensory input through changes in firing rate in vivo. However, studies performed in vitro have shown that these same VN neurons often display nonlinear synchronization (i.e. phase locking) in their spiking activity to the local maxima of sensory input, thereby severely limiting their capacity for faithful encoding of said input through changes in firing rate. We investigated this apparent discrepancy by studying the effects of in vivo conditions on VN neuron activity in vitro using a simple, physiologically based, model of cellular dynamics. We found that membrane potential oscillations were evoked both in response to step and zap current injection for a wide range of channel conductance values. These oscillations gave rise to a resonance in the spiking activity that causes synchronization to sinusoidal current injection at frequencies below 25 Hz. We hypothesized that the apparent discrepancy between VN response dynamics measured in in vitro conditions (i.e., consistent with our modeling results) and the dynamics measured in vivo conditions could be explained by an increase in trial-to-trial variability under in vivo vs. in vitro conditions. Accordingly, we mimicked more physiologically realistic conditions in our model by introducing a noise current to match the levels of resting discharge variability seen in vivo as quantified by the coefficient of variation (CV). While low noise intensities corresponding to CV values in the range 0.04–0.24 only eliminated synchronization for low (<8 Hz) frequency stimulation but not high (>12 Hz) frequency stimulation, higher noise intensities corresponding to CV values in the range 0.5–0.7 almost completely eliminated synchronization for all frequencies. Our results thus predict that, under natural (i.e. in vivo) conditions, the vestibular system uses increased variability to promote fidelity of encoding by single neurons. This prediction can be tested experimentally in vitro.
The Vestibular System Implements a Linear–Nonlinear Transformation In Order to Encode Self-Motion
Corentin Massot,Adam D. Schneider,Maurice J. Chacron,Kathleen E. Cullen
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1001365
Abstract: Although it is well established that the neural code representing the world changes at each stage of a sensory pathway, the transformations that mediate these changes are not well understood. Here we show that self-motion (i.e. vestibular) sensory information encoded by VIIIth nerve afferents is integrated nonlinearly by post-synaptic central vestibular neurons. This response nonlinearity was characterized by a strong (~50%) attenuation in neuronal sensitivity to low frequency stimuli when presented concurrently with high frequency stimuli. Using computational methods, we further demonstrate that a static boosting nonlinearity in the input-output relationship of central vestibular neurons accounts for this unexpected result. Specifically, when low and high frequency stimuli are presented concurrently, this boosting nonlinearity causes an intensity-dependent bias in the output firing rate, thereby attenuating neuronal sensitivities. We suggest that nonlinear integration of afferent input extends the coding range of central vestibular neurons and enables them to better extract the high frequency features of self-motion when embedded with low frequency motion during natural movements. These findings challenge the traditional notion that the vestibular system uses a linear rate code to transmit information and have important consequences for understanding how the representation of sensory information changes across sensory pathways.
The Vestibular System Implements a Linear–Nonlinear Transformation In Order to Encode Self-Motion
Corentin Massot,Adam D. Schneider,Maurice J. Chacron,Kathleen E. Cullen
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1001365
Abstract: Although it is well established that the neural code representing the world changes at each stage of a sensory pathway, the transformations that mediate these changes are not well understood. Here we show that self-motion (i.e. vestibular) sensory information encoded by VIIIth nerve afferents is integrated nonlinearly by post-synaptic central vestibular neurons. This response nonlinearity was characterized by a strong (~50%) attenuation in neuronal sensitivity to low frequency stimuli when presented concurrently with high frequency stimuli. Using computational methods, we further demonstrate that a static boosting nonlinearity in the input-output relationship of central vestibular neurons accounts for this unexpected result. Specifically, when low and high frequency stimuli are presented concurrently, this boosting nonlinearity causes an intensity-dependent bias in the output firing rate, thereby attenuating neuronal sensitivities. We suggest that nonlinear integration of afferent input extends the coding range of central vestibular neurons and enables them to better extract the high frequency features of self-motion when embedded with low frequency motion during natural movements. These findings challenge the traditional notion that the vestibular system uses a linear rate code to transmit information and have important consequences for understanding how the representation of sensory information changes across sensory pathways.
Head Movements Evoked in Alert Rhesus Monkey by Vestibular Prosthesis Stimulation: Implications for Postural and Gaze Stabilization
Diana E. Mitchell, Chenkai Dai, Mehdi A. Rahman, Joong Ho Ahn, Charles C. Della Santina, Kathleen E. Cullen
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0078767
Abstract: The vestibular system detects motion of the head in space and in turn generates reflexes?that are vital for our daily activities. The eye movements produced by the vestibulo-ocular reflex (VOR) play an essential role in stabilizing the visual axis (gaze), while vestibulo-spinal reflexes ensure the maintenance of head and body posture. The neuronal pathways from the?vestibular periphery to the cervical spinal cord potentially serve a dual role, since they function to stabilize the head relative to inertial space and could thus contribute to gaze (eye-in-head + head-in-space) and posture stabilization. To date, however, the functional significance of vestibular-neck pathways in alert primates remains a matter of debate. Here we used a vestibular prosthesis to 1) quantify vestibularly-driven head movements in primates, and 2) assess whether these evoked head movements make a significant contribution to gaze as well as postural stabilization. We stimulated electrodes implanted in the horizontal semicircular canal of alert rhesus monkeys, and measured the head and eye movements evoked during a 100ms time period for which the contribution of longer latency voluntary inputs to the neck would be minimal. Our results show that prosthetic stimulation evoked significant head movements with latencies consistent with known vestibulo-spinal pathways. Furthermore, while the evoked head movements were substantially smaller than the coincidently evoked eye movements, they made a significant contribution to gaze stabilization, complementing the VOR to ensure that the appropriate gaze response is achieved. We speculate that analogous compensatory head movements will be evoked when implanted prosthetic devices are transitioned to human patients.
TeV Strings and Collider Probes of Large Extra Dimensions
Schuyler Cullen,Maxim Perelstein,Michael E. Peskin
Physics , 2000, DOI: 10.1103/PhysRevD.62.055012
Abstract: Arkani-Hamed, Dimopoulos, and Dvali have proposed that the fundamental gravitational scale is close to 1 TeV, and that the observed weakness of gravity at long distances is explained by the presence of large extra compact dimensions. If this scenario is realized in a string theory of quantum gravity, the string excited states of Standard Model particles will also have TeV masses. These states will be visible to experiment and in fact provide the first signatures of the presence of a low quantum gravity scale. Their presence also affects the more familiar signatures due to real and virtual graviton emission. We study the effects of these states in a simple string model.
Contribution of the Local RAS to Hematopoietic Function: A Novel Therapeutic Target
Kathleen E. Rodgers
Frontiers in Endocrinology , 2013, DOI: 10.3389/fendo.2013.00157
Abstract: The renin-angiotensin system (RAS) has long been a known endocrine system that is involved in regulation of blood pressure and fluid balance. Over the last two decades, evidence has accrued that shows that there are local RAS that can affect cellular activity, tissue injury, and tissue regeneration. There are locally active ligand peptides, mediators, receptors, and signaling pathways of the RAS in the bone marrow (BM). This system is fundamentally involved and controls the essential steps of primitive and definitive blood-cell production. Hematopoiesis, erythropoiesis, myelopoiesis, thrombopoiesis, formation of monocytic and lymphocytic lineages, as well as stromal elements are regulated by the local BM RAS. The expression of a local BM RAS has been shown in very early, primitive embryonic hematopoiesis. Angiotensin-converting enzyme (ACE-1, CD143) is expressed on the surface of hemangioblasts and isolation of the CD143 positive cells allows for recovery of all hemangioblast activity, the first endothelial and hematopoietic cells, forming the marrow cavity in the embryo. CD143 expression also marks long-term blood-forming CD34+ BM cells. Expression of receptors of the RAS is modified in the BM with cellular maturation and by injury. Ligation of the receptors of the RAS has been shown to modify the status of the BM resulting in accelerated hematopoiesis after injury. The aim of the present review is to outline the known functions of the local BM RAS within the context of primitive and definitive hematopoiesis as well as modification of BM recovery by administration of exogenous ligands of the RAS. Targeting the actions of local RAS molecules could represent a valuable therapeutic option for the management of BM recovery after injury as well as neoplastic disorders.
Self efficacy for fruit, vegetable and water intakes: Expanded and abbreviated scales from item response modeling analyses
Tom Baranowski, Kathleen B Watson, Christine Bachman, Janice C Baranowski, Karen W Cullen, Debbe Thompson, Anna-Maria Siega Riz
International Journal of Behavioral Nutrition and Physical Activity , 2010, DOI: 10.1186/1479-5868-7-25
Abstract: Cross sectional assessment. Items were modified to have easy, moderate and difficult levels of self efficacy. Classical test theory and item response modeling were applied.One middle school at each of seven participating sites (Houston TX, Irvine CA, Philadelphia PA, Pittsburg PA, Portland OR, rural NC, and San Antonio TX).714 6th grade students.Adding items to reflect level (low, medium, high) of self efficacy for fruit and vegetable intake achieved scale reliability and validity comparable to existing scales, but the distribution of items across the latent variable did not improve. Selecting items from among clusters of items at similar levels of difficulty along the latent variable resulted in an abbreviated scale with psychometric characteristics comparable to the full scale, except for reliability.The abbreviated scale can reduce participant burden. Additional research is necessary to generate items that better distribute across the latent variable. Additional items may need to tap confidence in overcoming more diverse barriers to dietary intake.Fruit and vegetable (FV) consumption among children is generally considered health promoting. Self efficacy (SE), a person's confidence in being able to perform a behavior (e.g. eat FV), originated in Bandura's Social Cognitive Theory [1] and has been incorporated into several theories [2-4] predicting behavior. Inconsistencies exist across studies with children as to whether SE was related to FV intake [5,6], and when detected, the relationships were low [2,7,8]. There has been concern for high response burden [2], however, when only one or two SE items were used, the expected relationships were not detected [2]. Characteristics of the existing full scale may account for the inconsistencies and low correlations. Although classical test theory reliability was acceptable for the original scale (alpha = 0.88) [9], item response modeling (IRM), a psychometric procedure that fits a latent variable to items, was also used to
Ten Simple Rules for Doing Your Best Research, According to Hamming
Thomas C Erren ,Paul Cullen,Michael Erren,Philip E Bourne
PLOS Computational Biology , 2007, DOI: 10.1371/journal.pcbi.0030213
Abstract:
STAKCERT Worm Relational Model for Worm Detection
Madihah Mohd Saudi,Andrea J Cullen,Mike E Woodward
Lecture Notes in Engineering and Computer Science , 2010,
Abstract:
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