Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session M6: Multi-Scale Aspects and Dynamical Networks in Integrated Physiologic Systems |
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Sponsoring Units: DBP Chair: Plamen Ivanov, Boston University Room: LACC 502A |
Tuesday, March 22, 2005 5:30PM - 6:06PM |
M6.00001: Universality in complex-network synchronization Invited Speaker: Heterogeneity in the degree (connectivity) distribution has been shown to suppress synchronization in networks of symmetrically coupled oscillators with uniform coupling strength. In this contribution we uncover a condition for enhanced synchronization in weighted networks with asymmetric coupling. It is shown that in the optimum regime synchronizability is solely determined by the average degree and does not depend on the system size and the details of the degree distribution. In scale-free networks, where the average degree may increase with heterogeneity, while the overall cost involved in the network coupling is significantly reduced as compared to the case of unweighted coupling. Consequences for metabolic networks will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 6:06PM - 6:42PM |
M6.00002: Multimodal signal integration in the nervous system: from ion channels to neurons to networks - and reverse. Invited Speaker: Signal encoding in single neurons and neuronal nets can drastically change depending on their actual dynamical state. Dynamic state transitions are of particular relevance when different types of signals have to be simultaneously integrated because each signal can modify the transduction characteristics of each other signal due to the system's inherent non-linearities. Nonlinear, multimodal signal encoding can already be seen at the single neuron level [Braun et al. 1994, Nature 367: 270-273] and is an essential characteristic of integrative brain functions [Wollweber et al. 2004, J Thermal Biol, 29: 345-350]. However, signal encoding and neuromodulation takes place at a still lower level, namely by alterations of voltage- or ligand-gated ion channels. Nevertheless, to avoid an overwhelming complexity, the dynamics at the lower levels are often neglected when higher levels are examined, e.g. neuronal network analysis generally does not consider the details of ion channel gating. Hodgkin-Huxley type computer simulations shall elucidate which simplifications can be made without loss of essential functional properties and which state transitions at lower levels can become of functional relevance for the higher level dynamics [Sosnovtseva et al. 2004, FNL 4:L521-L533]. [Preview Abstract] |
Tuesday, March 22, 2005 6:42PM - 7:18PM |
M6.00003: Imaging Collective Dynamics in the Neocortex Invited Speaker: Central to understanding collective neural dynamics is the problem of \textit{obtaining spatiotemporal data} which reveals the collective behavior of neural ensembles; this can be done either through multi-contact recordings or through various imaging modalities. As an example of both the power and limitations of imaging techniques, we consider the onset, spread, and termination of focal seizures, imaged using the intrinsic optical signal (IOS). The IOS is a change in light reflectance from neural tissue that correlates with the underlying electrophysiological activity. With incident light in the green range, the IOS reflects changes in blood volume (CBV signal); for incident light in the orange range, the IOS shows a change in the oxygenation state of hemoglobin (Hbr signal), and can be correlated with the BOLD (blood oxygen level dependent) fMRI signal; for incident red light, the IOS reflects changes in cell volume and/or light scattering (LS signal). Using the IOS to image the spread of focal neocortical seizures induced by 4-aminopyridine in the rat, we found that the CBV, Hbr and LS signals were equally useful in localizing the ictal onset. We found a focal, profound dip in hemoglobin oxygenation (Hbr signal) during the entire seizure duration, implying that brain perfusion is inadequate to meet the metabolic demands of an epileptic focus. We observed significant variability in the spatial distribution of the active region during seizure termination. However, the IOS was unable to resolve electrophysiologically distinct patterns of seizure onset and the signal, at all incident wavelengths, persisted long after seizure termination. [Preview Abstract] |
Tuesday, March 22, 2005 7:18PM - 7:54PM |
M6.00004: Circadian clock and cardiac vulnerability: A time stamp on multi-scale neuroautonomic regulation Invited Speaker: Cardiovascular vulnerability displays a 24-hour pattern with a peak between 9AM and 11AM. This daily pattern in cardiac risk is traditionally attributed to external factors including activity levels and sleep-wake cycles. However,influences from the endogenous circadian pacemaker independent from behaviors may also affect cardiac control. We investigate heartbeat dynamics in healthy subjects recorded throughout a 10-day protocol wherein the sleep/wake and behavior cycles are desynchronized from the endogenous circadian cycle,enabling assessment of circadian factors while controlling for behavior-related factors. We demonstrate that the scaling exponent characterizing temporal correlations in heartbeat dynamics over multiple time scales does exhibit a significant circadian rhythm with a sharp peak at the circadian phase corresponding to the period 9-11AM, and that this rhythm is independent from scheduled behaviors and mean heart rate. Our findings of strong circadian rhythms in the multi-scale heartbeat dynamics of healthy young subjects indicate that the underlying mechanism of cardiac regulation is strongly influenced by the endogenous circadian pacemaker. A similar circadian effect in vulnerable individuals with underlying cardiovascular disease would contribute to the morning peak of adverse cardiac events observed in epidemiological studies. [Preview Abstract] |
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