1,919 research outputs found
Adaptation in chemoreception cells II: The effects of cross-adapting backgrounds depend on spectral tuning.
No full text1. The cross-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using NH4 receptor cells, of known spectral tuning, from the lobster (Homarus americanus). 2. Spectrum experiments: The spectral tuning of NH4 receptor cells was investigated using NH4Cl and 7 other compounds selected as the most stimulatory non-best compounds for NH4 cells from a longer list of compounds tested in previous studies. Based on their responses to the compounds tested, 3 spectral subpopulations of NH4 cells were revealed: NH4-Glu cells which responded second-best to Glutamate (Glu); NH4- Bet cells which responded second-best to Betaine (Bet); and 'pure' NH4 cells, which responded to NH4C1 only (Fig. 1). 3. Cross-adaptation experiments: Overall, cross-adaptation with Glu and Bet backgrounds caused suppression of response of NH4 receptor cells to various concentrations of NH4Cl. However, the different subpopulations of NH4 cells were affected differently: (a) The stimulus-response functions of NH4-Glu cells were significantly suppressed by both a 3 μM (G3) and 300 μM (G300) Glu backgrounds, (b) The stimulus-response functions of NH4-Bet cells was not affected by a 3 μM (B3), but significantly suppressed by a 300 μM (B300) Bet background. (c) The stimulus-response functions of pure NH4 cells were not affected by any of the Glu or Bet backgrounds (Figs. 3, 4). 4. The stimulus-response functions of 5 cells from all different subpopulations were enhanced by cross-adaptation with the G300 and B300 backgrounds (Fig. 4, Table 1). 5. Whereas self-adaptation caused parallel shifts in stimulus-response functions (Borroni and Atema 1988), cross-adaptation caused a decrease in slope of stimulus-response functions. Implications of the results from cross- and self-adaptation experiments on NH4 receptor cells, for a receptor cell model are discussed
Effects of limb position on motor resonance
No full textAim: Observation of hand or foot flexion-extension movements executed by others evokes in limb-specific spinal motor pathways of the observer a “motor resonant” response (MR) with the same time course and muscular activation pattern as used in the observed movements. Changing the position of the hand (prone to supine) produces the same effects on the timing of both subliminal resonant response during observation and muscular contractions during movement, presumably by a different partitioning of the motor command to flexor and extensor muscles depending on hand kinaesthetic afferences (Borroni et al. 2005). Here we continue this line of investigation by studying the effects of changes in position of the foot, during observation of foot oscillation movements.
Methods: Modulation of the H-reflex in the right Soleus muscle was recorded in human observers sitting in a chair with their feet either suspended or in full contact with the ground (n=9 and n=10 respectively). Subjects observed a 1Hz sinusoidal oscillation of the suspended right foot performed by another subject sitting in front of them.
Results: In both foot positions, observation induced a significant (p<0.0001) H-reflex modulation which could be fitted by a sinusoidal function with the same period as the observed movement. The common fit of the H-reflex modulations from all subjects was phase-shifted with respect to movement ( by 66° (average 66° ± 15) when the foot was suspended and by 159° (average = 152° ± 41) when it was resting on the ground. Average values are significantly different (p<0.001, Watson-Williams test).
Conclusion: With the foot suspended, the time course of MR reflects the temporal relations between muscular activation and the flexion-extension movement at 1Hz. With the foot on the ground, the shift in and its greater variability (p<0.025, Mann-Whitney test on angular distances) may reflect an attempt to reproduce a movement similar but not identical to the observed one. In fact, in this position afferent input informs the observer that the flexion-extension movement cannot be executed
What you see is what you get : motor resonance in peripheral vision
No full textObservation of others’ actions evokes a motor resonant (MR) response, mediated by the mirror neuron system, which reflects the motor program encoding the observed actions. Presumably factors internal (attention, motivation, emotion) or external (location, salience) to observers, can modulate MR responses. We have started a series of studies evaluating the role of some of these factors, such as attention (Cerri et al. 2010) and emotion (Borroni et al. 2012). Here we explore the importance of location of the action in the visual field of observers.
A grasping action was presented in the near peripheral vision of subjects (10° from fixation point), who were asked to maintain their gaze on a fixation point in the left lower corner of a computer screen while, on the right, a short video showed an avatar hand grasping a ball. Motor-evoked potentials (MEPs) were elicited in the right Opponens Pollicis by transcranial magnetic stimulation of primary motor cortex, at different delays during the observed action. Two different grasping actions were shown to two different groups of 20 subjects: a normal (palmar finger flexion) or an impossible grasping (dorsal finger flexion). After the experiment, subjects were questioned about the action they had observed.
All subjects, whether they had observed the normal or the impossible action, reported seeing a normal grasping movement. Consistently, the same response was recorded in both conditions: MEPs were significantly larger at all dynamic delays compared to baseline for both normal and impossible actions. Thus motor responses were elicited by observation of an action in peripheral vision, though the corresponding motor program was grossly imprecise. We propose two complementary interpretations: 1. peripheral vision did not provide enough visual information to evoke distinct MR responses in the different conditions and delays, and 2. the action that was explicitly perceived influenced the shape of responses
Adaptation in chemoreception cells I: Self-adapting backgrounds determine threshold and cause parallel shift of response function.
No full text1. The self-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using lobster (Homarus americanus) NH4 receptor cells. 2. These receptors responded for several seconds to the onset of the backgrounds, and then returned to their initial level of spontaneous activity (usually zero). The strongest response always occurred only during the steepest concentration change; the response then decayed back to zero or to the earlier spontaneous firing level, while the background concentration was still rising, and remained silent during the entire time that the background was maintained constant (20-30 min) (Fig. 2). 3. Exposure to constant self-adapting backgrounds eliminated the responses of NH4 receptor cells to stimuli of concentration lower than the background, and reduced the responses to all higher stimulus concentrations tested by a nearly equal amount. This resulted in a parallel shift of the stimulus-response function to the right along the abscissa (Figs. 3 and 4). 4. Since the response threshold was completely re-set by adaptation to backgrounds, NH4 receptors seem to function mostly as detectors of relative rather than absolute stimulus intensity across their entire dynamic range: the response to a given stimulus-to-background ratio remained the same over 3 log step increases of background concentration (Fig. 6). 5. As in other sensory modalities, a parallel shift of response functions appears to be an important property of chemoreceptor cells, allowing for this sensory system to function over a wider stimulus intensity range than the instantaneous dynamic range of individual receptor cells
A Comparative Survey on Islamic Riba and Western Usury
No full textThe article addresses the theme of usury taking into account various viewpoints and traditions, pausing in particular on the Western and Islamic notions of lending at interest, in order to outline its distinctive features in the present days as well as throughout its historical evolution. The author applies a comparative research method, examining both the differences and similarities between the Western and Muslim concept of usury so to present an accurate picture of the phenomenon. In fact, the article aims at answering the latest questions concerning the possibility for the Muslim model to be a valuable resource in overcoming the keep going financial crisis
Iranian Festivals and Political Discourse under the Abbasids
No full textCelebrations of the two main festivals of the Iranian calendar, Nawrūz and Mihraǧān, are part of the general phenomenon of presence of Iranian strands in social and political culture of the Abbasid centuries. Through a critical approach to the sources, the author verifies the assumption that Iranian festivals were a politically relevant element of Abbasid culture and customs. The political relevance of Nawrūz and Mihraǧān is then discussed with regard to its relations with contemporary Islamic political discourse as a whole, in order to verify two recent interpretations of Islamic political theory and practice in the formative centuries. Sources hereby considered lead to the conclusion that Nawrūz and Mihraǧān are clearly embedded into Abbasid political discourse. Those festivals, in fact, concurred to the construction of a hierarchic legitimacy. At the same time, incompatibility or competition between them and Islamic political theory remained merely exceptional
La risoluzione extragiudiziale controversie in materia bancaria: caratterizzazione funzionale e pro!li procedimentali dell’Arbitro Bancario Finanziario
No full textNeural compensation for mechanical differences between hand and foot during coupled oscillations of the two segments
No full text(1) Rhythmic flexion-extensions of the hand and foot on one side were performed by ten male and nine female subjects. Limbs were rotated in the same direction (in-phase) or in opposite directions (anti-phase). Oscillation frequency ranged from 0.6 to 3.2 Hz for in-phase and to 2.2 Hz for anti-phase movements. In both genders, movement synchrony was more strictly maintained during anti-phase than during in-phase coupling. (2) EMG recordings showed that, in males, movement synchrony was achieved by activating hand movers in advance of foot movers. This phase advance increased as the oscillation frequency increased. In females, instead, muscles of the two limbs were activated almost simultaneously over most of the frequency range. Since the different timing of muscle activation in the two genders suggests that their limbs have different mechanical characteristics, the frequency response of each limb was estimated in either gender. The frequency response between 0.6 and 3.2 Hz was evaluated in five males and five females by measuring the phase delay between the onset of the EMG activity and the onset of the related movement, both when the limbs were moved in isolation and when they were coupled. (3) In uncoupled conditions, the hand and foot curves were roughly parallel in females, the phase delay being about 45°larger in the hand than in the foot. In males, the curves were also separated by 45°at the lowest frequencies but they further diverged when the frequency was raised, because of a faster increase in the phase delay in the hand than in the foot. These results indicate that, when the extremities have to be coupled, a nervous compensation is necessary and that it must be different in the two genders. (4) Analysis of the phase-response when limbs were coupled showed that synchrony was approached by two mechanisms: (a) an earlier EMG activation of the hand movers, preferentially utilised by males during in-phase coupling; and (b) a change in the viscoelastic properties of one extremity, which reduces (or eliminates) the difference between their frequency responses as well as between the EMG onsets of hand and foot movers. This second mechanism was utilised by both genders during anti-phase coupling
Studio della distribuzione della radioattività naturale e del radiocesio conseguente all'incidente di Chernobyl in un suolo dell'Appennino Settentrionale
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