Neuromorphic analogue VLSI

Neuromorphic systems emulate the organization and function of nervous systems. They are usually composed of analogue electronic circuits that are fabricated in the complementary metal-oxide-semiconductor (CMOS) medium using very large-scale integration (VLSI) technology. However, these neuromorphic systems are not another kind of digital computer in which abstract neural networks are simulated symbolically in terms of their mathematical behavior. Instead, they directly embody, in the physics of their CMOS circuits, analogues of the physical processes that underlie the computations of neural systems. The significance of neuromorphic systems is that they offer a method of exploring neural computation in a medium whose physical behavior is analogous to that of biological nervous systems and that operates in real time irrespective of size. The implications of this approach are both scientific and practical. The study of neuromorphic systems provides a bridge between levels of understanding. For example, it provides a link between the physical processes of neurons and their computational significance. In addition, the synthesis of neuromorphic systems transposes our knowledge of neuroscience into practical devices that can interact directly with the real world in the same way that biological nervous systems do

Bioinspired engineering of exploration systems for NASA and DoD

A new approach called bioinspired engineering of exploration systems (BEES) and its value for solving pressing NASA and DoD needs are described. Insects (for example honeybees and dragonflies) cope remarkably well with their world, despite possessing a brain containing less than 0.01% as many neurons as the human brain. Although most insects have immobile eyes with fixed focus optics and lack stereo vision, they use a number of ingenious, computationally simple strategies for perceiving their world in three dimensions and navigating successfully within it. We are distilling selected insect-inspired strategies to obtain novel solutions for navigation, hazard avoidance, altitude hold, stable flight, terrain following, and gentle deployment of payload. Such functionality provides potential solutions for future autonomous robotic space and planetary explorers. A BEES approach to developing lightweight low-power autonomous flight systems should be useful for flight control of such biomorphic flyers for both NASA and DoD needs. Recent biological studies of mammalian retinas confirm that representations of multiple features of the visual world are systematically parsed and processed in parallel. Features are mapped to a stack of cellular strata within the retina. Each of these representations can be efficiently modeled in semiconductor cellular nonlinear network (CNN) chips. We describe recent breakthroughs in exploring the feasibility of the unique blending of insect strategies of navigation with mammalian visual search, pattern recognition, and image understanding into hybrid biomorphic flyers for future planetary and terrestrial applications. We describe a few future mission scenarios for Mars exploration, uniquely enabled by these newly developed biomorphic flyers

Astigmatism and Pseudoaccommodation in Pseudophakic Eyes

noAdvanced IOLs with circumferential zones of different power provide pseudoaccommodation. We investigated the potential for power variation with meridian, namely astigmatism, to provide pseudo-accommodation. With appropriate power and axis orientations, acceptable pseudo-accommodation can be achieved

Searching for collective behavior in a network of real neurons

Maximum entropy models are the least structured probability distributions that exactly reproduce a chosen set of statistics measured in an interacting network. Here we use this principle to construct probabilistic models which describe the correlated spiking activity of populations of up to 120 neurons in the salamander retina as it responds to natural movies. Already in groups as small as 10 neurons, interactions between spikes can no longer be regarded as small perturbations in an otherwise independent system; for 40 or more neurons pairwise interactions need to be supplemented by a global interaction that controls the distribution of synchrony in the population. Here we show that such "K-pairwise" models--being systematic extensions of the previously used pairwise Ising models--provide an excellent account of the data. We explore the properties of the neural vocabulary by: 1) estimating its entropy, which constrains the population's capacity to represent visual information; 2) classifying activity patterns into a small set of metastable collective modes; 3) showing that the neural codeword ensembles are extremely inhomogenous; 4) demonstrating that the state of individual neurons is highly predictable from the rest of the population, allowing the capacity for error correction.Comment: 24 pages, 19 figure

A `bright zone' in male hoverfly (Eristalis tenax) eyes and associated faster motion detection and increased contrast sensitivity

Eyes of the hoverfly Eristalis tenax are sexually dimorphic such that males have a fronto-dorsal region of large facets. In contrast to other large flies in which large facets are associated with a decreased interommatidial angle to form a dorsal `acute zone' of increased spatial resolution, we show that a dorsal region of large facets in males appears to form a `bright zone' of increased light capture without substantially increased spatial resolution. Theoretically, more light allows for increased performance in tasks such as motion detection. To determine the effect of the bright zone on motion detection, local properties of wide field motion detecting neurons were investigated using localized sinusoidal gratings. The pattern of local preferred directions of one class of these cells, the HS cells, in Eristalis is similar to that reported for the blowfly Calliphora. The bright zone seems to contribute to local contrast sensitivity; high contrast sensitivity exists in portions of the receptive field served by large diameter facet lenses of males and is not observed in females. Finally, temporal frequency tuning is also significantly faster in this frontal portion of the world, particularly in males, where it overcompensates for the higher spatial-frequency tuning and shifts the predicted local velocity optimum to higher speeds. These results indicate that increased retinal illuminance due to the bright zone of males is used to enhance contrast sensitivity and speed motion detector responses. Additionally, local neural properties vary across the visual world in a way not expected if HS cells serve purely as matched filters to measure yaw-induced visual motion

Exploiting Photoisomerization: Spectroscopy on a Carotenoid Sensor and Retinal Proteins

Light-based methodologies enjoy popularity due to their non-invasive nature. In particular in the field of optogenetics, where genetic targeting of neurons permits not only simultaneous imaging of a large number of cells but also optical control of neuronal activity. For this, ion channels or pumps are inserted into the membrane which are activated by light. A deep biophysical understanding of the optogenetic systems is key for their successful application. In this thesis, I present a new member in the family of organic voltage sensors. I demonstrate that in a single lipid bilayer environment, the carotenoid Zeaxanthin has a linear and reversible spectral Raman response to an electric field applied across the membrane. The underlying mechanism is an increased photoisomerization rate resulting in a higher 13-cis population which is detected via a characteristic vibrational band at 1130 cm−1. Channelrhodopsin-2 (ChR2) is a frequently used protein in optogenetics to silence neuronal activity. By variation of amino acid side chains, we found experimental evidence for ground-state heterogeneity in the hydrogen bond interactions of the retinal protonated Schiff base (PSB). We have identified with Raman spectroscopy two spectral components of the C=N–H mode of the PSB at 1661 and 1665 cm−1, representing hydrogen bonds to different amino acid side chains. These two interactions of the PSB could be essential for a voltage-sensing mechanism in ChR2. In a pioneering approach we combined time-resolved absorption spectroscopy with serial femtosecond X-ray crystallography to scrutinize mechanistic details of sodium pumping in Krokinobacter eikastus rhodopsin 2 (KR2). Using an infrared-emitting quantum cascade laser (QCL), we verified that crystalline KR2 exhibits reaction kinetics similar to those observed in its detergent solubilized form. Hereupon, we have identified a previously proposed transient sodium binding site during the O intermediate where the sodium is coordinated by the amino acid side chains of N112 and D251. The findings regarding the ion transport mechanism in KR2 will facilitate the design of protein variants for an optogenetic application. Bistable G-protein coupled receptors (GPCRs) have two thermally stable conformations and are a promising class of rhodopsins which have the potential to serve as an optogenetic switch. We were able to conduct a first biophysical characterization of the invertebrate jumping spider rhodopsin-1 (JSR1). We propose a model of the two-photon reaction based on spectroscopic results. During these reactions, the Schiff base stays protonated implying that a deprotonation is not a prerequisite for the function of bistable GPCRs. A proposed mediating water molecule as part of the counterion complex in the inactive conformation is identified by Raman spectroscopy and later confirmed by an X-ray crystallographic structure. In conclusion, this thesis provides insights into the mechanistic details of established and upcoming optogenetic tools. These results will help to adapt their biophysical properties better suiting the needs of application.Lichtbasierende Methoden erfreuen sich aufgrund ihrer nicht-invasiven Eigenschaft großer Beliebtheit. Im Besonderen in der Optogenetik, wo Neuronen genetisch modifiziert werden um nicht nur die simultane Beobachtung einer großen Anzahl von Neuronen, sondern auch optische Kontrolle von neuronaler Aktivität zu ermöglichen. Hierzu werden Ionenkanäle oder -pumpen in die Membran gebracht, die durch Licht aktiviert werden können. Ein tiefes Verständnis von optogenetischen Systemen ist eine Schlüsselvoraussetzung für eine erfolgreiche Anwendung. In dieser Arbeit präsentiere ich einen Neuzugang in die Familie der organischen Spannungssensoren. Ich demonstriere, dass das Karotenoid Zeaxanthin, eingebracht in eine einzelne Lipiddoppelschicht, eine lineare und reversible Reaktion zeigt, wenn ein elektrisches Feld über die Membran angelegt wird. Der zugrunde liegende Mechanismus ist eine größere Population an 13-cis Isomeren, hervorgerufen durch eine erhöhte Photoisomerationsrate. Dies führt zu einem Anwachsen einer charakteristischen Vibrationsbande bei 1130 cm−1. Kanalrhodopsin-2 (ChR2) wird regelmäßig in der Optogentik genutzt um neuronale Aktivität zu verhindern. Durch Variation von Aminosäurenseitenketten liefern wir Beweise für eine Heterogenität in der Wasserstoffbrückeninteraktion der protonierten Schiffschen Base (PSB) im Grundzustand. Wir konnten mit Raman Spektroskopie zwei spektrale Komponenten in der PSB Vibrationsmode (C=N–H) bei 1661 und 1665 cm−1 identifizieren, die jeweils eine Wasserstoffbrücke zu einer anderen Aminosäurenseitenkette darstellen. Diese zwei Interaktionen könnten von Bedeutung für einen Spannungsmessungsmechanismus in ChR2 sein. Um den Natriumpumpmechanismus von Krokinobacter eikastus rhodopsin 2 (KR2) zu untersuchen, haben wir in einer Pionierarbeit zeitaufgelöste Absorbtionspektroskopie mit Röntgenkristallographie kombiniert. Die Benutzung eines Quantumkaskadenlasers (QCL) ermöglichte es uns sicher zu stellen, dass kristallines KR2 vergleichbare Reaktionskinetiken aufweist als in Detergens gelost. Wir konnten daraufhin eine im Vorfeld postulierte vorübergehende Natriumbindungsstelle während des O Intermediats zwischen den Seitenketten von N112 und D251 identifizieren. Die Ergebnisse über den Ionentransportmechanismus werden die Konzipierung von Proteinvarianten für eine optogenetische Anwendung erleichtern. Bistabile G-Protein-gekoppelte Rezeptoren (GPCRs) haben zwei thermisch stabile Konformationen und sind eine vielversprechende Klasse von Rhodopsinen für einen optogentischen Schalter. Wir konnten eine erste biophysikalische Charakterisierung von jumping spider rhodopsin-1 (JSR1) durchführen. Wir schlagen, basierend auf spektroskopischen Ergebnissen, ein Model einer zwei-Photonen Reaktion vor. Während dieser Reaktionen bleibt die SB protoniert. Dies impliziert, dass eine Deprotonierung keine Voraussetzung für die Funktion von bistabilen GPCRs ist. Ein angenommenes Wassermolekül als Teil des Konterionennetzwerks konnte mit Raman Spektroskopie detektiert werden, was später durch eine Röntgenstruktur bestätigt wurde. Zusammenfassend bietet diese Arbeit Einblicke in die Mechanismen von etablierten sowie neuen optogenetischen Werkzeugen. Die Resultate werden dazu beitragen, ihre biophysikalischen Eigenschaften an die Erfordernisse der Anwendung anzupassen

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 128, May 1974

This special bibliography lists 282 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1974

Combined Self-consistent-field And Spin-flip Tamm-dancoff Density Functional Approach To Potential Energy Surfaces For Photochemistry

We present a new approach to calculating potential energy surfaces for photochemical reactions by combining self-consistent-field calculations for single-reference ground and excited states with symmetry-corrected spin-flip Tamm-Dancoff approximation calculations for multireference electronic states. The method is illustrated by an application with the M05-2X exchange-correlation functional to cis-trans isomerization of the penta-2,4-dieniminium cation, which is a model (with three conjugated double bonds) of the protonated Schiff base of retinal. We find good agreement with multireference configuration interaction-plus-quadruples (MRCISD+Q) wave function calculations along three key paths in the strong-interaction region of the ground and first excited singlet states