Home About us Contact
|
Home About us Contact | ||
|
|
||
Preferred Direction (prefer + direction)
Selected AbstractsRat anterodorsal thalamic head direction neurons depend upon dynamic visual signals to select anchoring landmark cuesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2004Michaėl B. Zugaro Abstract Head direction cells, which are functionally coupled to ,place' cells of the hippocampus, a structure critically involved in spatial cognition, are likely neural substrates for the sense of direction. Here we studied the mechanism by which head direction cells are principally anchored to background visual cues [M.B. Zugaro et al. (2001) J. Neurosci., 21, RC154,1,5]. Anterodorsal thalamic head direction cells were recorded while the rat foraged on a small elevated platform in a 3-m diameter cylindrical enclosure. A large card was placed in the background, near the curtain, and a smaller card was placed in the foreground, near the platform. The cards were identically marked, proportionally dimensioned, subtended the same visual angles from the central vantage point and separated by 90°. The rat was then disoriented in darkness, the cards were rotated by 90° in opposite directions about the center and the rat was returned. Preferred directions followed either the background card, foreground card or midpoint between the two cards. In continuous lighting, preferred directions shifted to follow the background cue in most cases (30 of the 53 experiments, Batschelet V -test, P < 0.01). Stroboscopic illumination, which perturbs dynamic visual signals (e.g. motion parallax), blocked this selectivity. Head direction cells remained equally anchored to the background card, foreground card or configuration of the two cards (Watson test, P > 0.1). This shows that dynamic visual signals are critical in distinguishing typically more stable background cues which govern spatial neuronal responses and orientation behaviors. [source] Neurons in primary motor cortex engaged during action observationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2010Juliana Dushanova Abstract Neurons in higher cortical areas appear to become active during action observation, either by mirroring observed actions (termed mirror neurons) or by eliciting mental rehearsal of observed motor acts. We report the existence of neurons in the primary motor cortex (M1), an area that is generally considered to initiate and guide movement performance, responding to viewed actions. Multielectrode recordings in monkeys performing or observing a well-learned step-tracking task showed that approximately half of the M1 neurons that were active when monkeys performed the task were also active when they observed the action being performed by a human. These ,view' neurons were spatially intermingled with ,do' neurons, which are active only during movement performance. Simultaneously recorded ,view' neurons comprised two groups: approximately 38% retained the same preferred direction (PD) and timing during performance and viewing, and the remainder (62%) changed their PDs and time lag during viewing as compared with performance. Nevertheless, population activity during viewing was sufficient to predict the direction and trajectory of viewed movements as action unfolded, although less accurately than during performance. ,View' neurons became less active and contained poorer representations of action when only subcomponents of the task were being viewed. M1 ,view' neurons thus appear to reflect aspects of a learned movement when observed in others, and form part of a broadly engaged set of cortical areas routinely responding to learned behaviors. These findings suggest that viewing a learned action elicits replay of aspects of M1 activity needed to perform the observed action, and could additionally reflect processing related to understanding, learning or mentally rehearsing action. [source] An oscillatory interference model of grid cell firingHIPPOCAMPUS, Issue 9 2007Neil Burgess Abstract We expand upon our proposal that the oscillatory interference mechanism proposed for the phase precession effect in place cells underlies the grid-like firing pattern of dorsomedial entorhinal grid cells (O'Keefe and Burgess (2005) Hippocampus 15:853,866). The original one-dimensional interference model is generalized to an appropriate two-dimensional mechanism. Specifically, dendritic subunits of layer II medial entorhinal stellate cells provide multiple linear interference patterns along different directions, with their product determining the firing of the cell. Connection of appropriate speed- and direction- dependent inputs onto dendritic subunits could result from an unsupervised learning rule which maximizes postsynaptic firing (e.g. competitive learning). These inputs cause the intrinsic oscillation of subunit membrane potential to increase above theta frequency by an amount proportional to the animal's speed of running in the "preferred" direction. The phase difference between this oscillation and a somatic input at theta-frequency essentially integrates velocity so that the interference of the two oscillations reflects distance traveled in the preferred direction. The overall grid pattern is maintained in environmental location by phase reset of the grid cell by place cells receiving sensory input from the environment, and environmental boundaries in particular. We also outline possible variations on the basic model, including the generation of grid-like firing via the interaction of multiple cells rather than via multiple dendritic subunits. Predictions of the interference model are given for the frequency composition of EEG power spectra and temporal autocorrelograms of grid cell firing as functions of the speed and direction of running and the novelty of the environment. © 2007 Wiley-Liss, Inc. [source] Synthesis and chiroptical properties of L -valine-containing poly(phenylacetylene)s with (a)chiral pendant terminal groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2006Lo Ming Lai Abstract Poly(phenylacetylene)s containing L -valine residues (P1) with (a)chiral pendant terminal groups R(*) [,(HCC{C6H4CONHCH[CH(CH3)2]COOR(*)})n,]; R(*) = 1-octyl (P1o), (1S,2R,5S)-(+)-menthyl [P1(+)], (1R,2S,5R)-(,)-menthyl [P1(,)] are designed and synthesized. The polymers are prepared by organorhodium catalysts in high yields (yield up to 88%) with high molecular weights (Mw up to ,6.4 × 105). Their structures and properties are characterized by NMR, IR, TGA, UV, and circular dichroism analyses. All the polymers are thermally fairly stable (Td , 320 °C). The chiral moieties induce the poly(phenylacetylene) chains to helically rotate in a preferred direction. The chirality of the pendant terminal groups affects little the helicity of the polymers but their bulkiness stabilizes the helical conformation against solvent perturbation. The backbone conjugation and chain helicity of the polymers can be modulated continuously and reversibly by acid. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2117,2129, 2006 [source] Side-firing sealing caps for hollow optical fibersLASERS IN SURGERY AND MEDICINE, Issue 8 2006Tomonori Watanabe BS Abstract Background and Objectives Hollow optical fibers are useful for delivery of high-energy infrared laser beam such as Er:YAG lasers. We propose side-firing optics for hollow optical fibers for laser endoscopic applications mainly in oto-rhino-laryngology and urology. Study Design/Materials and Methods To produce a circular beam, cone-shaped caps are designed and caps with slanted end are proposed for producing a spot beam in side direction. Both types of caps are fabricated by fusing and polished Pyrex and silica glass tubes. Results For the both of the cone-shaped and slanted-end caps effectively deflect laser beam as designed and these caps show high durability for Er:YAG laser light with pulse energy higher than 100 mJ. Conclusions By choosing the proper shape of the cap ends, these caps deflect an input laser beam to a preferred direction at low insertion losses. By using these side-firing optics, one can easily irradiate the inside of tubular organs. Lasers Surg. Med. 38:792,797, 2006. © 2006 Wiley-Liss, Inc. [source] Asymmetric long and thick dipoles for in-flight telemetry of projectilesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2008L. Bernard Abstract Long and thick dipoles are presented, with a feeding point located off the centre. Parameter studies are performed, showing that asymmetric radiation patterns with a main lobe in a preferred direction can be achieved. Experimental results confirm the feasibility of these antennas and illustrate possible applications. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 508,511, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23105 [source] Measurement of linear polarization in the H, line in solar flaresASTRONOMISCHE NACHRICHTEN, Issue 4 2003Article first published online: 28 MAY 200, P. Kotr Abstract Large solar telescopes built at places with a quite excellent seeing, equipped with a sophisticated optics and control system are too expensive and unique to be used currently in hunting of sudden and short-lasting activity events, e.g. flares and eruptive prominences. For a systematic observation of selected kinds of active phenomena it is still necessary to use smaller or medium-sized telescopes equipped with a special setup of devices. Detection of linear polarization in the H, line emitted in a flare seems to be just a right task and delicate matter for such a systematic observation. This kind of polarization is supposed to be generated by particle beams accelerated in thke corona and directed towards denser chromospheric layers where the particle beams deposit their kinetic energy. As the accelerated particle beams possess a preferred direction of velocity they can produce a linearly polarized light. However, the occurrence of the accelerated particle beams and the related linear polarization in the H, line may have a tendency to appear: 1) at the early beginning of a flare 2) in pulses lasting just a few seconds or even less. To measure the linear polarization in flares regularly we have built an additional branch in the Ond,ejov multichannel flare spectrograph. In this paper we describe the optical system, the detectors, the method used for data recording and reduction and we also briefly discuss the first results. [source] Framing Justice: Using the Concept of Procedural Justice to Advance Political Communication ResearchCOMMUNICATION THEORY, Issue 4 2005John C. Besley Efforts aimed at increasing civic-mindedness must consider both what encourages and what discourages political engagement. Procedural justice argues that individuals care about the fairness of decision-making or deliberative procedures beyond whether the outcome of any future decision goes in their preferred direction. In turn, perceptions of procedural fairness influence participant satisfaction, commitment to the organization, perceived legitimacy of authorities, and willingness to volunteer on an organization's behalf. The concept of procedural justice holds significant promise for addressing questions in political communication research, particularly those examining the impacts of public engagement. Thus, we offer a synthesis of procedural justice research to support a model for studying procedural justice as a type of framing to which individuals are exposed during participation in civic life and, in so doing, try to make more explicit the previously implicit communicative aspects of procedural justice. [source] Rat anterodorsal thalamic head direction neurons depend upon dynamic visual signals to select anchoring landmark cuesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2004Michaėl B. Zugaro Abstract Head direction cells, which are functionally coupled to ,place' cells of the hippocampus, a structure critically involved in spatial cognition, are likely neural substrates for the sense of direction. Here we studied the mechanism by which head direction cells are principally anchored to background visual cues [M.B. Zugaro et al. (2001) J. Neurosci., 21, RC154,1,5]. Anterodorsal thalamic head direction cells were recorded while the rat foraged on a small elevated platform in a 3-m diameter cylindrical enclosure. A large card was placed in the background, near the curtain, and a smaller card was placed in the foreground, near the platform. The cards were identically marked, proportionally dimensioned, subtended the same visual angles from the central vantage point and separated by 90°. The rat was then disoriented in darkness, the cards were rotated by 90° in opposite directions about the center and the rat was returned. Preferred directions followed either the background card, foreground card or midpoint between the two cards. In continuous lighting, preferred directions shifted to follow the background cue in most cases (30 of the 53 experiments, Batschelet V -test, P < 0.01). Stroboscopic illumination, which perturbs dynamic visual signals (e.g. motion parallax), blocked this selectivity. Head direction cells remained equally anchored to the background card, foreground card or configuration of the two cards (Watson test, P > 0.1). This shows that dynamic visual signals are critical in distinguishing typically more stable background cues which govern spatial neuronal responses and orientation behaviors. [source] X-ray birefringence and dichroism obtained from magnetic materialsJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2001S. W. Lovesey In the past decade, synchrotron radiation has triggered a surge in studies of the polarization dependence of X-ray beams passing through non-isotropic materials. A vast range of experimental results concerning polarization-dependent absorption (dichroism) and dispersion (birefringence, for example) are available from materials which are either magnetic or exhibit preferred directions due to the local atomic environment. This article aims to bring together the diversity of modern experiments in this field with established methods of optical calculus, in a way that highlights the simplicity of the underlying physics. A useful framework is formed when observable quantities, in the X-ray case, are related to atomic variables of the sample material. Atomic descriptions of absorption spectra with various levels of complexity are considered, and some well documented sum-rules are encountered. The framework is the most general allowed within the electric dipole approximation. By way of illustration, dichroic X-ray absorption by two materials with highly anisotropic properties and magnetic ions with different valence shells are considered; namely, a 3d -transition ion in ferrous niobate, and a lanthanide ion in dysprosium borocarbide. Both materials display interesting magnetic properties that are challenging to interpret at an atomic level of detail, and it is shown how absorption experiments can contribute to resolving some issues. [source] Connections of eye-saccade-related areas within mesencephalic reticular formation with the optic tectum in goldfishTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 1 2007Maria A. Luque Abstract Physiological studies demonstrate that separate sites within the mesencephalic reticular formation (MRF) can evoke eye saccades with different preferred directions. Furthermore, anatomical research suggests that a tectoreticulotectal circuit organized in accordance with the tectal eye movement map is present. However, whether the reticulotectal projection shifts with the gaze map present in the MRF is unknown. We explored this question in goldfish, by injecting biotin dextran amine within MRF sites that evoked upward, downward, oblique, and horizontal eye saccades. Then, we analyzed the labeling in the optic tectum. The main findings can be summarized as follows. 1) The MRF and the optic tectum were connected by separate axons of the tectobulbar tract. 2) The MRF was reciprocally connected mainly with the ipsilateral tectal lobe, but also with the contralateral one. 3) The MRF received projections chiefly from neurons located within intermediate and deep tectal layers. In addition, the MRF projections terminated primarily within the intermediate tectal layer. 4) The distribution of labeled neurons in the tectum shifted with the different MRF sites in a manner consistent with the tectal motor map. The area containing these cells was targeted by a high-density reticulotectal projection. In addition to this high-density topographic projection, there was a low-density one spread throughout the tectum. 5) Occasionally, boutons were observed adjacent to tectal labeled neurons. We conclude that the organization of the reticulotectal circuit is consistent with the functional topography of the MRF and that the MRF participates in a tectoreticulotectal feedback circuit. J. Comp. Neurol. 500:6,19, 2007. © 2006 Wiley-Liss, Inc. [source] | ||||||||||