A model of intrinsic and driven spindling in thalamocortical neurons

Dynamical Mechanism of Hyperpolarization-Activated Non-specific Cation Current Induced Resonance and Spike-Timing Precision in a Neuronal Model

Hyperpolarization-activated cyclic nucleotide-gated cation current (I_h) plays important roles in the achievement of many physiological/pathological functions in the nervous system by modulating the electrophysiological activities, such as the rebound (spike) to hyperpolarization stimulations, subthreshold membrane resonance to sinusoidal currents, and spike-timing precision to stochastic factors. In the present paper, with increasing g_h (conductance of I_h), the rebound (spike) and subthreshold resonance appear and become stronger, and the variability of the interspike intervals (ISIs) becomes lower, i.e., the enhancement of spike-timing precision, which are simulated in a conductance-based theoretical model and well explained by the nonlinear concept of bifurcation. With increasing g_h, the stable node to stable focus, to coexistence behavior, and to firing via the codimension-1 bifurcations (Hopf bifurcation, saddle-node bifurcation, saddle-node bifurcations on an invariant circle, and saddle homoclinic orbit) and codimension-2 bifurcations such as Bogdanov-Takens (BT) point related to the transition between saddle-node and Hopf bifurcations, are acquired with 1- and 2-parameter bifurcation analysis. The decrease of variability of ISIs with increasing g_h is induced by the fast decrease of the standard deviation of ISIs, which is related to the increase of the capacity of resisting noisy disturbance due to the firing becomes far away from the bifurcation point. The enhancement of the rebound (spike) with increasing g_h builds up a relationship to the decrease of the capacity of resisting disturbance like the hyperpolarization stimulus as the resting state approaches the bifurcation point. The “typical”-resonance and non-resonance appear in the parameter region of the stable focus and node far away from the bifurcation points, respectively. The complex or “strange” dynamics, such as the “weak”-resonance for the stable node near the transition point between the stable node and focus and the non-resonance for the stable focus close to the codimension-1 and −2 bifurcation points, are discussed.

Adaptation through minimization of the phase lag in coupled nonidentical systems

We show that the internal control of adaptation can be obtained from the properties of the phase lag that results from phase synchronization of two nonidentical chaotic oscillators. The direction and magnitude of the phase lag depend upon the relative internal properties of the coupled units, and they can be used as indicators during the adjustment of dynamics, i.e., adaptation of the target unit to match that of the control. The properties of the phase lag are obtained using a method based on the estimation of properties of the distributions of relative event times of both (target and control) units. The phase lag dependent mechanism to control the adaptation process was applied to a system of nonidentical Rössler oscillators and a system of nonidentical Lorenz oscillators. We also elucidate its importance as a control mechanism of the changes of neuronal activity showing its application to neural adaptation.

Interactions between membrane conductances underlying thalamocortical slow-wave oscillations

Neurons of the central nervous system display a broad spectrum of intrinsic electrophysiological properties that are absent in the traditional "integrate-and-fire" model. A network of neurons with these properties interacting through synaptic receptors with many time scales can produce complex patterns of activity that cannot be intuitively predicted. Computational methods, tightly linked to experimental data, provide insights into the dynamics of neural networks. We review this approach for the case of bursting neurons of the thalamus, with a focus on thalamic and thalamocortical slow-wave oscillations. At the single-cell level, intrinsic bursting or oscillations can be explained by interactions between calcium- and voltage-dependent channels. At the network level, the genesis of oscillations, their initiation, propagation, termination, and large-scale synchrony can be explained by interactions between neurons with a variety of intrinsic cellular properties through different types of synaptic receptors. These interactions can be altered by neuromodulators, which can dramatically shift the large-scale behavior of the network, and can also be disrupted in many ways, resulting in pathological patterns of activity, such as seizures. We suggest a coherent framework that accounts for a large body of experimental data at the ion-channel, single-cell, and network levels. This framework suggests physiological roles for the highly synchronized oscillations of slow-wave sleep.

Origins of medial geniculate body projections to physiologically defined zones of rat primary auditory cortex

Medial geniculate body neurons projecting to physiologically identified subregions of rat primary auditory cortex (area 41, Te1) were labeled with horseradish peroxidase in adult rats. The goals were to determine the type(s) of projection neuron and the spatial arrangement of these cells with respect to thalamic subdivisions. Maps of best frequency were made with single neuron or unit cluster extracellular recording at depths of 500-800 microm, which correspond to layers III-IV in Nissl preparations. Tracer injections were made in different cortical isofrequency regions (2, 11, 22, or 38 kHz, respectively). Labeled neurons were plotted on representative sections upon which the architectonic subdivisions were drawn independently. Most of the cells of origin lay in the ventral division in every experiment. Injections at low frequencies labeled bands of neurons laterally in the ventral division; progressively more rostral deposits at higher frequencies labeled bands or clusters more medially in the ventral division, and through most of its caudo-rostral extent. Medial division labeling was variable. Labeled cells were always in the lateral half of the nucleus and were often scattered. There were few labeled cells in the dorsal division. Seven types of thalamocortical neuron were identified: ventral division cells had a tufted branching pattern, while medial division neurons have heterogeneous shapes and sizes and were larger. Dorsal division neurons had a radiate branching pattern. The size range of labeled neurons spanned that of Nissl stained neuronal somata. Area 41 may receive two types of thalamic projection: ventral division input is strongly convergent, highly topographic, spatially focal, and restricted to one type of neuron only, while the medial division projection is more divergent, coarsely topographical, involves multiple cortical areas, and has several varieties of projection neuron. Despite species differences in local circuitry, many facets of thalamocortical organization are conserved in phylogeny.