1,748 research outputs found
Potential mechanisms for imperfect synchronization in parkinsonian basal ganglia
Neural activity in the brain of parkinsonian patients is characterized by the
intermittently synchronized oscillatory dynamics. This imperfect
synchronization, observed in the beta frequency band, is believed to be related
to the hypokinetic motor symptoms of the disorder. Our study explores potential
mechanisms behind this intermittent synchrony. We study the response of a
bursting pallidal neuron to different patterns of synaptic input from
subthalamic nucleus (STN) neuron. We show how external globus pallidus (GPe)
neuron is sensitive to the phase of the input from the STN cell and can exhibit
intermittent phase-locking with the input in the beta band. The temporal
properties of this intermittent phase-locking show similarities to the
intermittent synchronization observed in experiments. We also study the
synchronization of GPe cells to synaptic input from the STN cell with
dependence on the dopamine-modulated parameters. Dopamine also affects the
cellular properties of neurons. We show how the changes in firing patterns of
STN neuron due to the lack of dopamine may lead to transition from a lower to a
higher coherent state, roughly matching the synchrony levels observed in basal
ganglia in normal and parkinsonian states. The intermittent nature of the
neural beta band synchrony in Parkinson's disease is achieved in the model due
to the interplay of the timing of STN input to pallidum and pallidal neuronal
dynamics, resulting in sensitivity of pallidal output to the phase of the
arriving STN input. Thus the mechanism considered here (the change in firing
pattern of subthalamic neurons through the dopamine-induced change of membrane
properties) may be one of the potential mechanisms responsible for the
generation of the intermittent synchronization observed in Parkinson's disease.Comment: 27 pages, 9 figure
A Fast-Slow Analysis of the Dynamics of REM Sleep
Waking and sleep states are regulated by the coordinated activity of a number of neuronal population in the brainstem and hypothalamus whose synaptic interactions compose a sleep-wake regulatory network. Physiologically based mathematical models of the sleep-wake regulatory network contain mechanisms operating on multiple time scales including relatively fast synaptic-based interations between neuronal populations, and much slower homeostatic and circadian processes that modulate sleep-wake temporal patterning. In this study, we exploit the naturally arising slow time scale of the homeostatic sleep drive in a reduced sleep-wake regulatory network model to utilize fast-slow analysis to investigate the dynamics of rapid eye movement (REM) sleep regulation. The network model consists of a reduced number of wake-, non-REM (NREM) sleep-, and REM sleep-promoting neuronal populations with the synaptic interactions reflecting the mutually inhibitory flip-flop conceptual model for sleep-wake regulation and the reciprocal interaction model for REM sleep regulation. Network dynamics regularly alternate between wake and sleep states as goverend by the slow homeostatic sleep drive. By varying a parameter associated with the activation of the REM-promoting population, we cause REM dynamics during sleep episodes to vary from supression to single activations to regular REM-NREM cycling, corresponding to changes in REM patterning induced by circadian modulation and observed in different mammalian species. We also utilize fast-slow analysis to explain complex effects on sleep-wake patterning of simulated experiments in which agonists and antagonists of different neurotransmitters are microinjected into specific neuronal populations participating in the sleep-wake regulatory network
A note on Keen's model: The limits of Schumpeter's "Creative Destruction"
This paper presents a general solution for a recent model by Keen for
endogenous money creation. The solution provides an analytic framework that
explains all significant dynamical features of Keen's model and their
parametric dependence, including an exact result for both the period and
subsidence rate of the Great Moderation. It emerges that Keen's model has just
two possible long term solutions: stable growth or terminal collapse. While
collapse can come about immediately from economies that are nonviable by virtue
of unsuitable parameters or initial conditions, in general the collapse is
preceded by an interval of exponential growth. In first approximation, the
duration of that exponential growth is half a period of a sinusoidal
oscillation. The period is determined by reciprocal of the imaginary part of
one root of a certain quintic polynomial. The real part of the same root
determines the rate of growth of the economy. The coefficients of that
polynomial depend in a complicated way upon the numerous parameters in the
problem and so, therefore, the pattern of roots. For a favorable choice of
parameters, the salient root is purely real. This is the circumstance that
admits the second possible long term solution, that of indefinite stable
growth, i.e. an infinite period.Comment: 25 pages, 12 figures, JEL classification: B50, C62, C63, E12, E4
Complex and unexpected dynamics in simple genetic regulatory networks
Peer reviewedPublisher PD
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