Ionic mechanisms for intrinsic slow oscillations in thalamic relay neurons.

The oscillatory properties of single thalamocortical neurons were investigated by using a Hodgkin-Huxley-like model that included Ca2+ diffusion, the low-threshold Ca2+ current (lT) and the hyperpolarization-activated inward current (lh). lh was modeled by double activation kinetics regulated by intracellular Ca2+. The model exhibited waxing and waning oscillations consisting of 1-25-s bursts of slow oscillations (3.5-4 Hz) separated by long silent periods (4-20 s). During the oscillatory phase, the entry of Ca2+ progressively shifted the activation function of lh, terminating the oscillations. A similar type of waxing and waning oscillation was also observed, in the absence of Ca2+ regulation of lh, from the combination of lT, lh, and a slow K+ current. Singular approximation showed that for both models, the activation variables of lh controlled the dynamics of thalamocortical cells. Dynamical analysis of the system in a phase plane diagram showed that waxing and waning oscillations arose when lh entrained the system alternately between stationary and oscillating branches.     

A model of the electrophysiological properties of nucleus reticularis thalami neurons.

A model of the electrophysiological properties of rodent nucleus reticularis thalami (NRT) neurons of the dorsal lateral thalamus was developed using Hodgkin-Huxley style equations. The model incorporated voltage-dependent rate constants and kinetics obtained from recent voltage-clamp experiments in vitro. The intrinsic electroresponsivity of the model cell was found to be similar to several empirical observations. Three distinct modes of oscillatory activity were identified: 1) a pattern of slow rhythmic burst firing (0.5-7 Hz) usually associated with membrane potentials negative to approximately -70 mV which resulted from the interplay of ITs and IK(Ca); 2) at membrane potentials from approximately -69 to -62 mV, rhythmic burst firing in the spindle frequency range (7-12 Hz) developed and was immediately followed by a tonic tail of single spike firing after several bursts. The initial bursting rhythm resulted from the interaction of ITs and IK(Ca), with a slow after-depolarization due to ICAN which mediated the later tonic firing; 3) with further depolarization of the membrane potential positive to approximately -61 mV, sustained tonic firing appeared in the 10-200-Hz frequency range depending on the amplitude of the injected current. The frequency of this firing was also dependent on the maximum conductance of the leak current, IK(leak), and an interaction between the fast currents involved in generating action potentials, INa(fast) and IK(DR), and the persistent Na+ current, INa(P). Transitions between different firing modes were identified and studied parametrically.     

RF-cell: A model for populations of randomly interconnected neurons

This paper is concerned with a population of neurons with dense random interconnections, in which the stimulations between neurons are independent of their distance apart. This study is conducted from the viewpoint of the General System Theory. Proposed and used for the first time in studies on the above subject is a new concept referred to as the ‘historical report’ of the mentioned population. It will be shown that the population exhibits cyclic modes of behaviour which are dependent on its structure and historical report and which in the phase space correspond to cycles of hysteresis. A simple model in discrete time is developed and demonstrates, by the help of a computer study, the existence of the cycles of hysteresis.     

Resonances and noise in a stochastic Hindmarsh-Rose model of thalamic neurons

Thalamic neurons exhibit subthreshold resonance when stimulated with small sine wave signals of varying frequency and stochastic resonance when noise is added to these signals. We study a stochastic Hindmarsh-Rose model using Monte-Carlo simulations to investigate how noise, in conjunction with subthreshold resonance, leads to a preferred frequency in the firing pattern. The resulting stochastic resonance (SR) exhibits a preferred firing frequency that is approximately exponential in its dependence on the noise amplitude. In similar experiments, frequency dependent SR is found in the reliability of detection of alpha-function inputs under noise, which are more realistic inputs for neurons. A mathematical analysis of the equations reveals that the frequency preference arises from the dynamics of the slow variable. Noise can then transfer the resonance over the firing threshold because of the proximity of the fast subsystem to a Hopf bifurcation point. Our results may have implications for the behavior of thalamic neurons in a network, with noise switching the membrane potential between different resonance modes.     

Methods for parameter identification in oscillatory networks and application to cortical and thalamic 600 Hz activity.

Directed information transfer in the human brain occurs presumably by oscillations. As of yet, most approaches for the analysis of these oscillations are based on time-frequency or coherence analysis. The present work concerns the modeling of cortical 600 Hz oscillations, localized within the Brodmann Areas 3b and 1 after stimulation of the nervus medianus, by means of coupled differential equations. This approach leads to the so-called parameter identification problem, where based on a given data set, a set of unknown parameters of a system of ordinary differential equations is determined by special optimization procedures. Some suitable algorithms for this task are presented in this paper. Finally an oscillatory network model is optimally fitted to the data taken from ten volunteers.     

Unit responses of the thalamic and ventral anterior thalamic nuclei to electrical stimulation of thalamic relay nuclei in cats

Responses of 92 neurons of the reticular (R) and 105 neurons of the ventral anterior (VA) thalamic nuclei to stimulation of the ventrobasal complex (VB) and the lateral (GL) and medial (GM) geniculate bodies were investigated in cats immobilized with D-tobocurarine. Altogether 72.2% of R neurons and 76.2% of VA neurons responded to stimulation of VB whereas only 15.0% of R neurons and 27.1% of VA neurons responded to stimulation of GM and 10.2% of R neurons and 19.6% of VA neurons responded to stimulation of GL. The response of the R and VA neurons to stimulation of the relay nuclei as a rule was expressed as excitation. A primary inhibitory response was observed for only two R and three VA neurons. Two types of excitable neurons were distinguished: The first respond to afferent stimulation by a discharge consisting of 5–15 spikes with a frequency of 250–300/sec; the second respond by single action potentials. Neurons of the first type closely resemble inhibitory interneurons in the character of the response. Antidromic responses were recorded from 2.2% of R neurons and 7.8% of VA neurons during stimulation of the relay nuclei. Among the R and VA neurons there are some which respond to stimulation not only of one, but of two or even three relay nuclei. If stimulation of one relay nucleus is accompanied by a response of a R or VA neuron, preceding stimulation of another nucleus leads to inhibition of the response to the testing stimulus if the interval between conditioning and testing stimuli is less than 30–50 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 597–605, November–December, 1976.     

A model for repetitive firing in neurons

This paper describes a model for the generation of repetitive firing patterns in single neurons to be used as a module in large-scale network simulation studies. The model is based on the combination of extended versions of Hill's model for accomodation and of Kernell's model for adaptation. Both digital computer and electronic circuit realizations of the model are presented. The model is shown to produce strength-duration curves for accomodation which are compatible with available data from real neurons. Both “high ceiling” and “low ceiling” cell types can be matched by adjusting parameters in the model. An equation relating steady-state firing rate to amplitude of applied steady current is presented which includes the accumulation of potassium conductance changes with repetitive firing. The occurence of phasic and tonic responses to step stimulation is mapped in the parameter space of the model. Several representative response patterns to irregular inputs are presented.     

The initiation of bursts in thalamic neurons and the cortical control of thalamic sensitivity

Thalamic neurons generate high-frequency bursts of action potentials when a low-threshold (T-type) calcium current, located in soma and dendrites, becomes activated. Computational models were used to investigate the bursting properties of thalamic relay and reticular neurons. These two types of thalamic cells differ fundamentally in their ability to generate bursts following either excitatory or inhibitory events. Bursts generated with excitatory inputs in relay cells required a high degree of convergence from excitatory inputs, whereas moderate excitation drove burst discharges in reticular neurons from hyperpolarized levels. The opposite holds for inhibitory rebound bursts, which are more difficult to evoke in reticular neurons than in relay cells. The differences between the reticular neurons and thalamocortical neurons were due to different kinetics of the T-current, different electrotonic properties and different distribution patterns of the T-current in the two cell types. These properties enable the cortex to control the sensitivity of the thalamus to inputs and are also important for understanding states such as absence seizures.     

Neuronal response produced in the human thalamic nucleus reticularis by significant and non-significant verbal and sensory stimuli

Response recorded by microelectrode techniques during the course of 46 stereotaxic operations on dyskinesia patients was investigated in 340 units of the nucleus reticularis (rt) of the human thalamus. Differences were found between the multistage response of three types of rt neurons (A, B, and C) to verbal (or acousticcum-sensory) functionally significant stimuli (FSS) at both the stage of stimulus presentation and during the performance of goal-directed motion. Phasic activation produced by FSS presentation (as well as onset and execution of movement) in 102 out of 183 type A cells (or 55.7%) was characteristic of these cells, combined with inhibition of B type neurons in 82 out of a 139 sample (or 59.0%) produced by FSS and at the preparatory as well as the execution stage of movement. Activity of type C neurons remained unchanged. A correlation was revealed between response in A and B cells and "excitatory" trigger stimuli, but no specificity with respect to physical or semantic parameters of verbal signals. A correlation occurred during the course of movement performance with somatosensory afferents without any specific relationship to type and somatotopic aspects of movement. The time-related dynamics of A and B cell response is thought to illustrate the interaction of two neuronal subsystems within the rt participating in the performance of goal-directed motor performance triggered by speech.Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Institute of Neurosurgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 441–451, June–July, 1990.     

Dynamics of neuronal interaction in the human thalamic nucleus reticularis produced by significant and non-significant verbal stimuli

Dynamics of neuronal interaction recorded by microelectrodes were examined in 90 arrays of cells of the human thalamic reticular nucleus (Rt) during stereotaxic surgical procedures. Cooperative interaction between adjacent neurons was found to occur in neuronal arrays after presentation of verbal (or sensory-cum-acoustic) functionally significant stimulus (FSS) as well as at stages of initiation and performance of goal-directed movement. Specialized dynamics were noted in the pattern of interaction between neuronal arrays of two types (A and B) with irregular background activity and 2–5 Hz bursting rhythm (types A and B respectively). This dynamic local neuronal interaction correlates with the stage of significant verbal stimulus presentation and that of performing goal-directed movements. The matching transient correlation between activity of A and B cell arrays reflects matching operation of two sequences of regulatory and control processes involved in processing of functionally significant verbal (or sensory) information and performance of goal-directed movement.Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow Institute of Neurosurgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 451–459, June–July, 1990.     

Activation of thalamic ventroposteriolateral neurons by phrenic nerve afferents in cats and rats.

It has been demonstrated that phrenic nerve afferents project to somatosensory cortex, yet the sensory pathways are still poorly understood. This study investigated the neural responses in the thalamic ventroposteriolateral (VPL) nucleus after phrenic afferent stimulation in cats and rats. Activation of VPL neurons was observed after electrical stimulation of the contralateral phrenic nerve. Direct mechanical stimulation of the diaphragm also elicited increased activity in the same VPL neurons that were activated by electrical stimulation of the phrenic nerve. Some VPL neurons responded to both phrenic afferent stimulation and shoulder probing. In rats, VPL neurons activated by inspiratory occlusion also responded to stimulation on phrenic afferents. These results demonstrate that phrenic afferents can reach the VPL thalamus under physiological conditions and support the hypothesis that the thalamic VPL nucleus functions as a relay for the conduction of proprioceptive information from the diaphragm to the contralateral somatosensory cortex.     

Cholinergic and catecholaminergic neurons relay striatal information to the optic tectum in amphibians.

In the amphibians Rana perezi and Xenopus laevis, the involvement of cholinergic and catecholaminergic neurons in the relay of basal ganglia inputs to the tectum was investigated. Tract-tracing experiments, in which anterograde tracers were applied to the basal ganglia and retrograde tracers to the optic tectum, were combined with immunohistochemistry for choline acetyltransferase and tyrosine hydroxylase. The results of these experiments suggest that dopaminergic neurons of the suprachiasmatic nucleus and pretectal region, noradrenergic cells of the locus coeruleus and the cholinergic neurons of the pedunculopontine and laterodorsal tegmental nuclei mediate at least part of the basal ganglia input to the tectum in anurans.     

A system model for investigating passive electrical properties of neurons.

Passive membrane properties of neurons, characterized by a linear voltage response to constant current stimulation, were investigated by busing a system model approach. This approach utilizes the derived expression for the input impedance of a network, which simulates the passive properties of neurons, to correlate measured intracellular recordings with the response of network models. In this study, the input impedances of different network configurations and of dentate granule neurons, were derived as a function of the network elements and were validated with computer simulations. The parameters of the system model, which are the values of the network elements, were estimated using an optimization strategy. The system model provides for better estimation of the network elements than the previously described signal model, due to its explicit nature. In contrast, the signal model is an implicit function of the network elements which requires intermediate steps to estimate some of the passive properties.     

A basic biophysical model for bursting neurons

Presented here is a basic biophysical cell model for bursting, an extension of our previous model (Av-Ron et al. 1991) for excitability and oscillations. By changing a limited set of model parameters, one can describe different patterns of bursting behavior in terms of the burst cycle, the durations of oscillation and quiescence, and firing frequency.     

Neuronal response in nucleus reticularis thalami and neighboring thalamic structures to natural stimulation during chronic experiments on cats

Spike response was investigated in 104 neurons of the nucleus reticularis thalami (R) and adjoining thalamic nuclei to acoustic, tactile, and visual stimuli during chronic experiments on cats. Of the test neurons, 29% responded to acoustic stimulation and 11% showed no preference in relation to different acoustic stimuli. Minimum latencies of response to sounds measured 12–37 msec in excitatory and 18–27 msec in inhibitory cells. Duration of excitation produced by acoustic stimuli reached 50–250 msec; inhibition lasted 27–190 msec. Most cells belonging to this nucleus were excited by different stimuli; the proportion of inhibitory neurons did not exceed 4–10%.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 451–461, July–August, 1989.     

A model for generalization and specification by single neurons

A rule for environmentally dependent modification of the neuronal state is examined. Under the rule, the neuron selects a trigger feature that matches either a particular pattern in the stimulus set, or the most common pattern component, depending on a certain parameter. Thus a neuron may evolve to respond to its stimulus environment in one of two capacities, namely specification or generalization. Neurons of the former variety are labelled S-cells; and those of the latter, G-cells. In the model, synaptic modification is modulated by two postsynaptic mechanisms which act antagonistically to strengthen or weaken the synaptic connectivities. The functional dependence of these mechanisms on the postsynaptic activity is shown to determine whether the neuron acts as an S-cell or a G-cell. A circuit is proposed for a module that consists of a G-cell and several S-cells sharing a common set of inputs. By inhibiting the G-cells, the S-cell acts as a contrast-enhancing element, increasing their specificities for individual patterns in the stimulus set. The output from the module is a recoded representation of the environment with respect to its general and distinctive features.This work was supported in part by United States Office of Naval Research Contract N00014-81-K-0136     

Event-related coherence and event-related desynchronization/synchronization in the 10 Hz and 20 Hz EEG during self-paced movements

To investigate the activity of cortical regions in the control of movement, we studied event-related desynchronization/synchronization (ERD/ERS), event-related coherence (ERC), and phase coherence in 29-channel EEGs from 9 subjects performing self-paced movements of the right index finger. Movement preparation and execution produced ERD over the sensorimotor areas at 10 Hz and 20 Hz, followed by ERS. ERD corresponded spatiotemporally to an increase in coherence over the frontocentral areas. For both frequency bands, ERD began over the left sensorimotor areas and became bilateral at the time of movement onset. The coherence increase with frontal areas began in the left central areas and became symmetrical after EMG onset. The ERD and coherence increase was longer at 10 Hz than at 20 Hz. Phase coherence at 10 Hz showed a lead of anterior regions to posterior regions throughout the time period, and at 20 Hz showed a tendency toward zero phase delay corresponding with the movement. EEG desynchronization parallels functional coupling over sensorimotor and frontal areas. Event-related coherence and phase coherence findings implicate the frontal lobes in control of movement planning and execution. The involvement of different frequency bands with different timings may represent parallel changes in the cortical network.