Limitations of the Hodgkin-Huxley formalism : effects of single channel kinetics on transmembrane voltage dynamics

A standard membrane model, based on the continuous deterministic Hodgkin-Huxley equations, is compared to an alternative membrane model, based on discrete stochastic ion channel populations represented through Marlcov processes. Simulations explore the relationship between these two levels of description: the behavior predicted by the macroscopic membrane currents versus the behavior predicted by their microscopic ion channels. Discussion considers the extent to which these random events underlying neural signals mediate random events in neural computation

Privilege Can Be Abused: Exploring the Ethical Obligation to Avoid Frivolous Claims of Privilege

Many lawyers believe that ethical duties of confidentiality and zealousness require them to assert attorney-client privilege as aggressively as they assert a criminal defendant’s lack of guilt. They treat client information as if it is “privileged until proven unprivileged,” even though it is the claimant of privilege that has the evidentiary burden of showing that all the legal elements of privilege are met. Ordinarily, the adversary system works well to expose and control frivolous claims, but challenges to frivolous claims of privilege face unique obstacles. Challengers must operate “in the dark,” without the detailed knowledge of the communication needed to determine whether it really is privileged and whether its strategic value justifies the expense of opposition. This has made it easy and advantageous for lawyers to make frivolous claims of attorney-client privilege, despite the threat of court-imposed sanctions. Such abusive claims of privilege decrease the quality of justice by preventing consideration of relevant evidence and increase the cost of litigation by forcing expensive collateral litigation around privilege claims. The strategic advantage of frivolous claims of privilege combined with the inadequacy of the adversary system to discover and sanction such claims suggests that the rules of ethics could serve as a counter-balance. Yet, our existing ethical rules actually seem to encourage lawyers to make frivolous, “knee-jerk” claims of privilege by emphasizing the ethical duties of confidentiality and zealous representation. Against this, I argue that a limit to claims of attorney-client privilege should be understood as implicit in the existing Model Rules of Attorney-Client Privilege and that explicit ethical limits of the kind proposed in the article will not undermine confidentiality. However, an effective ethical limit requires that useful guidance about what constitutes a frivolous claim of privilege can be provided. I condense an analysis of cases in which lawyers have been either legally sanctioned or ethically disciplined for making such claims into a proposed added Comment to Model Rule 3.1 (Meritorious Claims and Contentions)

Psychopathy among pedophilic and non-pedophilic child molesters

Journal ArticleResearch is making increasing clear that, among men who sexually offend against prepubescent children, there are at least two subgroups, pedophiles and non-pedophiles, and that the groups differ in many important respects. Our ability to understand the etiology, nature, and most effective treatment for child molesters will depend, in no small part, on our ability to recognize the differences between these two groups of offenders. This paper reports on two studies which examined possible differences between the groups in psychopathy, a personality dimension long recognized as an important element in sexual offending. Utilizing a validated self-report measure of psychopathy, the Psychopathy Personality Inventory (PPI), both studies found non-pedophilic child molesters to score as significantly more psychopathic than their pedophilic counterparts

Stochastic resonance as a collective property of ion channel assemblies

By use of a stochastic generalization of the Hodgkin-Huxley model we investigate both the phenomena of stochastic resonance (SR) and coherence resonance (CR) in variable size patches of an excitable cell membrane. Our focus is on the challenge how internal noise stemming from individual ion channels does affect collective properties of the whole ensemble. We investigate both an unperturbed situation with no applied stimuli and one in which the membrane is stimulated externally by a periodic signal and additional external noise. For the nondriven case, we demonstrate the existence of an optimal size of the membrane patch for which the internal noise causes a most regular spike activity. This phenomenon shall be termed intrinsic CR. In presence of an applied periodic stimulus we demonstrate that the signal-to-noise ratio (SNR) exhibits SR vs. decreasing patch size, or vs. increasing internal noise strength, respectively. Moreover, we demonstrate that conventional SR vs. the external noise intensity occurs only for sufficiently large membrane patches, when the intensity of internal noise is below its optimal level. Thus, biological SR seemingly is rooted in the collective properties of large ion channel ensembles rather than in the individual stochastic dynamics of single ion channels.Comment: 9 pages, 2 figure

SMC framework in motion control systems

Design of a motion control system should take into account both the unconstrained motion performed without interaction with environment or other system, and the constrained motion where system is in contact with environment or has certain functional interaction with another system. In this paper control systems design approach, based on siding mode methods, that allows selection of control for generic tasks as trajectory and/or force tracking as well as for systems that require maintain some functional relation like bilateral or multilateral systems, establisment of virtual relation among mobile robots or control of haptic systems is presented. It is shown that all basic motion control problems - trajectory tracking, force control, hybrid position/force control scheme and the impedance control - can be treated in the same way while avoiding the structural change of the controller and guarantying stable behavior of the system In order to show applicability of the proposed techniques simulation and experimental results for high precision systems in microsystems assembly tasks and bilateral control systems are presente

Effect of channel block on the spiking activity of excitable membranes in a stochastic Hodgkin-Huxley model

The influence of intrinsic channel noise on the spontaneous spiking activity of poisoned excitable membrane patches is studied by use of a stochastic generalization of the Hodgkin-Huxley model. Internal noise stemming from the stochastic dynamics of individual ion channels is known to affect the collective properties of the whole ion channel cluster. For example, there exists an optimal size of the membrane patch for which the internal noise alone causes a regular spontaneous generation of action potentials. In addition to varying the size of ion channel clusters, living organisms may adapt the densities of ion channels in order to optimally regulate the spontaneous spiking activity. The influence of channel block on the excitability of a membrane patch of certain size is twofold: First, a variation of ion channel densities primarily yields a change of the conductance level. Second, a down-regulation of working ion channels always increases the channel noise. While the former effect dominates in the case of sodium channel block resulting in a reduced spiking activity, the latter enhances the generation of spontaneous action potentials in the case of a tailored potassium channel blocking. Moreover, by blocking some portion of either potassium or sodium ion channels, it is possible to either increase or to decrease the regularity of the spike train.Comment: 10 pages, 3 figures, published 200