1,721,039 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The contribution of the sodium channel subunit Na<sub>V</sub>1.6 to neuronal excitability
No full textThe focus of this work was to elucidate the contribution of a single Na+ channel a-subunit, namely NaV1.6, to the discharge properties of CA1 pyramidal neurons. In the first part of this work, we show that NaV1.6 is strongly aggregated at the axon initial segment. Interestingly, in the absence of NaV1.6 overall Na+ channel density at the axon initial segment remains unchanged, indicating compensation. We find that NaV1.6 displays a hyperpolarized voltage dependence of activation and contributes to persistent and resurgent Na+ currents. As a consequence, loss of NaV1.6 increases action potential threshold and affects spike initiation at the axon initial segment. Furthermore, the absence of NaV1.6 significantly reduces spike gain and spontaneous action potential firing. Utilizing a computational model we characterize the interplay between Na+ channel density and voltage dependence at the axon initial segment in shaping initiation and threshold of action potentials. In the second part, we concentrated on the role of NaV1.6 during status epilepticus induced epileptogenesis in rats. We show that in epileptic CA1 pyramidal neurons the spike afterdepolarization is augmented due to an upregulation of the persistent Na+ current. Utilizing mRNA expression analysis, Western blotting, and immunohistochemistry we demonstrate that the increased excitability is not mediated by upregulation of Na+ channel a-subunits, including NaV1.6. Furthermore, our immunolabellings show that NaV1.6 and total Na+ channel density at axon initial segments are unchanged. In additional experiments, we find that the increased persistent Na+ current in CA1 pyramidal neurons from pilocarpine treated rats is sensitive to high concentrations of the intracellular polyamine spermine. Therefore, we suggest that the generation of a de novo portion of persistent Na+ current, which contributes to the augmented excitability in epilepsy, is mediated by altered polyamine modulation instead of increased Na+ channel expression
Spatial sensitivity of midbrain lateral line units of the goldfish, <em>Carassius auratus</em>
Get PDFThe mechanosensory lateral line system of fish responds to water motions and pressure gradients caused by biotic factors (e.g. prey, predators or conspecifics) or abiotic factors. Theoretical and neurophysiological data show that a stationary vibrating sphere creates a spatial stimulus pattern along the lateral line. This spatial stimulus pattern contains information about the stimulus, i.e. sphere position and sphere vibration direction, and is represented in primary lateral line afferents. Up to now it is not clear how the excitation patterns of primary lateral line afferents are processed along the ascending lateral line pathway. In the medulla, the first nucleus of the ascending lateral line pathway, no representation of the position and/or vibration direction of a stationary vibrating sphere was found. The present study examines if lateral line units in the second nucleus of the ascending lateral line pathway, the torus semicircularis, encode the position and/or vibration direction of a stationary vibrating sphere. To do so, a stationary vibrating sphere (dipole, diameter 10 mm, frequency 50 Hz, duration 500 ms) was positioned at different positions along the rostro-caudal axis of a fish. Sphere vibration directions were 0° (parallel to the long axis of the fish), 45°, 90° (perpendicular to the long axis and the dorso-ventral axis of the fish) and 135°. The maximum peak-to-peak sphere displacement was 124--237 µm. The minimum distances between the fish and the surface of the sphere were 5, 10, 15, 20, 30 or 40 mm. A total of 98 unimodal toral lateral line units were recorded. 16 of these units could be examined with the complete stimulation protocol, that lasted up to four hours. This study examines only the responses of these 16 units. The recording sites of 12 out of these 16 units were verified, they were located in the ventrolateral nucleus of the Torus semicircularis, which is known to receive only lateral line input. The ongoing activity of 14 units was less or euqal 0,44 Hz (mean plus/minus SD 0,44 plus/minus 0,45 Hz, median 0,32 Hz, range 0,01--1,40 Hz). Two units had mean ongoing activities of 12,37~Hz and 51,72~Hz. The responses of one unit were phasic, nine units responded phasic-tonic and six units showed tonic responses. 15 units responded with an increase in evoked neural activity at all sphere positions. One unit showed an increase in evoked neural activity or a decrease in evoked neural activity inhibition, depending on the sphere position. None of the examined toral lateral line units was space sensitive in terms of evoked spike rates or phase locking. In some units a small change (5 mm) in sphere position led to a significant change of the evoked frequency, the phase angle of the response and/or the phase-locking. Similar effects were observed for changes in the direction of sphere vibration. Three units showed siginficant phase-locking at multiple side by side sphere positions. Two of these units responded to only one half of a full wave cycle. One unit, however, responded to both halfs of a full wave cycle. Spatial excitation patterns of three units were independent from sphere vibration direction. The spatial excitation patterns of four units were sytematically and continuously displaced towards the snout of the fish with increasing sphere vibration angles. The spatial excitation patterns of nine units showed no systematic changes to changes of sphere vibration direction. In this study no toral lateral line units were found that single-handedly encode the position and/or vibration direction of a stationary vibrating sphere. I therefore assume that lateral line information on the position and vibration direction of a stationary vibrating sphere is encoded in a population code. If space sensitive lateral line units exist, that encode sphere position and vibration direction, they can possibly be found in the optic tectum (the next level of processing of lateral line information in the ascending lateral line pathway), where computed lateral line maps have been proven in other animals with a lateral line
Experimental quantification and numerical simulation of unsteady flow conditions during free flight maneuvers of insects
No full textThis study aimed to numerically simulate aerodynamic forces produced by wing motion of small fruit flies maneuvering freely inside a flight chamber.
The kinematic data were derived from high-resolution, high-speed video measurements, tracking fluorescent markers on head, body and wings of the animal.
We constructed a geometrical model of the fly and applied the kinematic data to simulate the free flight.
Based on the calculated velocity and pressure fields, we evaluated vorticity and flight forces.
Our numerical simulation confirmed experimentally predicted lift enhancing mechanisms such as the leading edge vortex, rotational circulation and wake capture, and thus appears to be a potent tool to study the impact of body motion on forces and moments during the various forms of flight maneuvers
Vergleichende Untersuchungen zur Neuro- und Verhaltensbiologie infrarotsensitiver pyrophiler Käfer
Get PDFIm Rahmen dieser Arbeit wurden elektrophysiologische und neuroanatomische Untersuchungen an den pyrophilen Käferarten Acanthocnemus nigricans und Melanophila acuminata (bzw. Melanophila cuspidata) durchgeführt. Das Verhalten von A. nigricans wurde zusätzlich im Freiland untersucht. Die drei genannten Käferarten besitzen spezialisierte extraantennale Organe, deren Funktion mit dem ausgeprägten pyrophilen Verhalten in Zusammenhang gebracht wird. A. nigricans besitzt am Prothorax ein paariges scheibenförmiges Organ, auf dem sich bis zu 90 kutikuläre Sensillen befinden. Diese Sensillen gehören einem, morphologisch charakterisierten, neuen Sensillentyp an. In dieser Arbeit wurde erstmals eine breite physiologische Charakterisierung dieser Sensillen vorgenommen. Extrazelluläre Ableitungen zeigen, dass die Sensillen auf thermische Reize reagieren. Der nachgewiesene Schwellenwert für Antworten der Sensillen auf Reizung mit einem Rotlichtlaser (λ= 632,8 nm) liegt zwischen 11 und 25 mW/cm². Die Antworten auf Erwärmung sind phasisch-tonisch. Nach Ende der Reizung folgt eine Phase der Spike-Unterdrückung. Sowohl die Anzahl der ausgelösten Spikes als auch die Dauer der Spike-Unterdrückung sind intensitätsabhängig. Die Sensillen adaptieren auf lange konstante Reize, jedoch nicht vollständig. Die Untersuchungen der zeitlichen Eigenschaften belegen, dass die Grenze des zeitlichen Auflösungsvermögens bei wenigstens 20 Hz liegt. Zusätzlich wurden die neuronalen Projektionen der Afferenzen der kutikulären Sensillen erstmals untersucht. Anterograde Färbungen zeigen ein im Vergleich zu Projektionen anderer sensorischer Systeme ungewöhnliches Verzweigungsmuster: Der Hauptteil der Afferenzen aszendiert bis in das Oberschlundganglion und terminiert dort mit weitreichenden Verzweigungen in der Region des Tritocerebrums posterior zum olfaktorischen Antennallobus. Das Verhalten von A. nigricans wurde auf frischen Brandflächen in Westaustralien beobachtet. A. nigricans sammelt sich gezielt an noch über 100 °C heißen Stellen, den sogenannten „Hot Spots“. Die Käfer landen punktgenau im Randbereich der Hot Spots auf Bereichen mit einer Temperatur zwischen etwa 40 und 50°C. Das Verhalten der Käfer an den Hot Spots wurde mit Hilfe einer Infrarotkamera analysiert. Vermutlich steht es in Zusammenhang mit der Reproduktion von A. nigricans, da beide Geschlechter an den Hot Spots anzutreffen sind und Eiablagen beobachtet wurden. Die Larven entwickeln sich innerhalb weniger Tage und sind während der ersten drei Stadien fleischfressend. Sie ernähren sich vermutlich von Nahrungsressourcen, die durch den Brand entstehen und sind somit an die frische Brandfläche angepasst. Ein Schwerpunkt dieser Arbeit lag darauf, von infrarotsensitiven Zellen im Zentralen Nervensystem von M. acuminata bzw. M. cuspidata abzuleiten. Bei Reizung mit dem Rotlichtlaser konnten reizkorrelierte Potentiale extrazellulär an den thorakalen Konnektiven und im fusionierten Meso-Metathorakalganglion abgeleitetet werden. Erstmalig sollten zentrale Interneurone von M. acuminata bzw. M. cuspidata elektrophysiologisch abgeleitet, gefärbt und charakterisiert werden. Ziel war hier die Identifizierung von infrarotsensitiven Interneuronen. Erstmals gelangen intrazelluläre Ableitungen und Färbungen mehrerer Einzelzellen im fusionierten Meso-Metathorakalganglion. Die abgeleiteten Zellen wurden morphologisch beschrieben und physiologisch grob charakterisiert. Keine dieser Zellen reagierte jedoch auf thermische Reizung der Infrarotorgane. Durch diese Arbeit wurden wichtige Erkenntnisse zur Methode des intrazellulären Ableitens bei M. acuminata (bzw. M. cuspidata) gewonnen. Die Physiologie der Infrarotorgane der beiden Käferarten wird anhand der Ergebnisse dieser Arbeit verglichen und ihre mögliche Funktion im Verhaltenskontext diskutiert. Somit trägt diese Arbeit dazu bei, das Wissen über die infrarotsensorische Sinnessystem pyrophiler Käfer zu erweitern.Comparative studies on the behaviour and the neurobiology of infrared sensitive pyrophilous beetles This study focusses on the infrared sense of the pyrophilous beetle species Acanthocnemus nigricans and Melanophila acuminata (and M. cuspidata, respectively). Both have extraantennal specialized infrared-organs, that probably play an important role in the pyrophilous behaviour. In A. nigricans, one pair of prothoracic, disc-shaped organs has been described that bears up to 90 cuticular sensilla. These sensilla represent a new type of insect sensillum whose morphology and ultra-structure has recently been described. This study provides the first detailed physiological characterisation of the disc sensilla. Extracellular recordings show that the sensilla respond to thermal stimuli. The response threshold was between 11 and 25 mW/cm² for red laser ((λ= 632.8 nm) irradiation. The sensilla showed phasic-tonic responses to irradiation; turning off the irradiation was followed by a spiking pause. The responses and the duration of the spiking pause clearly depended on the irradiation intensity. Sustained stimulation lead to an adaptation of the responses. However, this adaptation was not complete. The lower bound of the time-resolving power of the sensilla was found at a frequency of at least 20 Hz of repeated irradiation. The central-nervous projections of the cuticular sensilla were investigated for the first time by anterograd dye labelling. Most of the fibres ascended into the ipsilateral, anterior connective to terminate in the tritocerebrum of the brain with extensive ramifications. The behaviour of A. nigricans was studied on freshly burnt areas in Western Australia. A. nigricans is known to aggregate close to spots having a surface temperature of more than 100°C. The beetles landed in the periphery of these “Hot Spots” on areas that have a temperature between approx. 40 and 50°C. The behaviour of the beetles was analysed with an infrared camera. It is very likely that this behaviour is connected to the reproduction of A. nigricans as both sexes meet near the Hot Spots and egg depositions have been observed. The larvae developed within only a few days. Laboratory observations indicate that the larvae are most probably carnivorous up to the third stage. It is hypothesised that they feed on ressources created by a fire, and are thus adapted to freshly burnt areas. Infrared-sensitive neurons were recorded with extracellular hook electrodes attached to the thoracic connectives in the central nervous system of M. acuminata and M. cuspidata. Additionally, stimulus-correlated neuronal potentials were recorded from the fused meso-/metathoracic ganglion. One aim of this study was to identify interneurons that respond to thermal stimulation of the infrared organs. Thus, a preparation has been developed, which allows intracellular recordings from single interneurons in Melanophila beetles. To foster the analysis of the thoracic neural networks processing infrared information, several single interneurons in the fused meso-/metathoracic ganglion were recorded and stained intracellularly for the first time. However, none of these cells responded to thermal stimulation. The physiology of the two investigated beetle species is compared and the possible function of the infrared organs is discussed . This study, thus, contributes to the understanding of infrared sensory systems in pyrophilous beetles
From memory and attention to consciousness : Exploring three major aspects of cognitive brain functioning
Get PDFThe present work gives overview and insight into three different areas of cognitive neuroscience, representing exemplary aspects of the diverse spectrum of research areas: Memory, attention and consciousness. Research on memory processes distinguishes between working memory (WM) and long term memory (LTM). According to the classical view, the LTM encoding relies on structures in the MTL including the hippocampus and WM processes rely on the prefrontal and parietal cortices. In contrast to this simple dichotomy, however, recent studies have shown that some WM tasks, e.g. those involving novel stimuli, also activate MTL structures. In the first part the question of whether the maintenance of several items in WM, which activates the MTL, influences the encoding of items into LTM is addressed. It is demonstrated that a simultaneous WM/LTM task results in an interference, which affects memory processing capacities in the MTL and leads to a decrease in the LTM performance when accompanied by a high WM load. Furthermore the parahippocampal cortex (PHC) is revealed as a locus of a memory processing interference between WM and LTM for the first time. Successful information processing requires focusing attention on a certain stimulus property and suppressing irrelevant information. An important paradigm for investigating attentional top-down control in case of interfering stimulus properties is Stroop’s interference task (Stroop, 1935). The second part the neural correlates of a newly developed auditory Stroop task are investigated. Using an event-related functional magnetic resonance imaging (fMRI) design, sound files in a tone-pitch interference task were presented, that required subjects to focus on one stimulus property (pitch or meaning of a spoken word) while ignoring the other one. In contrast to visual Stroop tasks a very posterior part of the anterior cingulate cortex (ACC) was found activated in incongruent phonetic trials (as compared to the incongruent semantic trials), together with common regions such as the pre-supplementary motor area (preSMA) and the dorsolateral prefrontal cortex (DLPFC), areas associated with attentional control. In addition, the integration of these regions into a conflict processing network using functional connectivity was shown. In the context of a theoretical excursus the third part shows within the broad field of consciousness research, how new methods in recoding and analyzing electro-encephalography (EEG) data can lead to a different understanding of the origination of different states of consciousness. The starting point of consideration were recent findings revealing unusual and remarkable alterations in the EEG in meditation experts. Today meditation is considered to be a valuable source deepening our understanding of the neural correlates of consciousness, since meditation experts are usually trained for decades to reach altered states of consciousness. It is suggested that different forms of meditation have similar steps of development, which should be related to similar neurophysiological correlates. Some electrophysiological alterations can be observed on the beginner/student level, which are closely related to non-meditative processes. Others appear to correspond to an advanced/expert level, and seem to be unique for meditation related states of consciousness. Meditation is one possibility of specializing brain/mind functions within the confines of the brain’s neural plasticity. This plasticity is likely supported by certain meditation related EEG patterns, for instance, synchronized gamma oscillations. While it has been formerly postulated that meditation comprises mainly passive relaxation states, recent EEG findings suggest that meditation is associated with active states involving cognitive restructuring and learning.</p
Control of neuronal input-output coupling by recurrent inhibition in the hippocampus
Get PDFDuring different states of hippocampal network activity neurons receive excitatory synaptic input on dendritic compartments and transform it into axonal action potential output. The ensemble output of pyramidal neurons activates local inhibitory microcircuits, which provide recurrent compartment-specific inhibition. In the present study it was observed that neuronal activity patterns that are likely to be present during sharp-waves recruit recurrent inhibition differently than repetitive activity at theta frequency. The observed results suggest that this could adapt the efficacy of input-output conversion to the network-state. In the present study dendritic spikes and their activity-dependent plasticity were identified as specialized signals, which endow correlated excitatory branch input with the ability to withstand recurrent inhibition and to generate precisely timed action potential output independent of the previous activity. These findings suggest that dendritic spikes may provide a cellular correlate for reliable and temporally precise reactivation of behaviorally relevant neuronal assemblies during both exploration and sleep
Shape and Deformation Measurement of Free Flying Birds in Flapping Flight
No full textThis paper describes a new approach for wing shape determination of free fly-ing birds during flapping flight. The optical based measurement method called "image pattern correlation technique" (IPCT) is described as well as modifications of this technique in order to measure wing surfaces formed by feathers. Further-more a newly developed camera driving system is introduced, which enables a movement of the surface measurement system synchronized with a bird. The ap-plication of this system to free flying barn owls is described together with high resolution surface results, obtained during free flapping flight of the bird
- …
