Instantaneous Firing Rate Research Articles

Jaw muscle afferent firing during an isotonic jaw-positioning task in the monkey.

The activity of jaw muscle receptors was studied by recording neurons in the mesencephalic nucleus of the trigeminal nerve in monkeys trained to control the position and movement of their mandible. Jaw position was measured by a weighted lever resting on the mandibular incisors. The force required to maintain the position of the lever was varied; in most cases it was either 25 or 360 g. Firing rates of neurons were related to stationary mandibular positions and to the velocity of movements during intervals when the movement velocity was constant. Of 49 neurons studied in detail, 21 fired at rates that were consistently and linearly related to static incisal openings. This static position sensitivity was typically about 5 spikes/mm of incisal opening. Most position-sensitive neurons fired at higher rates during opening movements and at lower rates during closing movements than would be accounted for by their position sensitivity. This sensitivity to the velocity of movement was not linear, however; slow closing movements sometimes did not produce a decrease in firing rate, and an actual increase during muscle shortening was seen in a few instances. The position sensitivity of eight neurons was evaluated during different loading conditions; in no case did it change substantially. Of the remaining 28 neurons, 26 fired at high rates during all opening movements and either stopped firing or fired at low, sporadic rates during closing movements. The static position sensitivity of these neurons was weak and variable both within and between neurons. The velocity sensitivity of these stretch-sensitive neurons was very nonlinear. Except for a range of slow movements (+/- 5 mm/s), the firing rate was maximal (200 spikes/s or higher) for most opening movements and zero for most closing movements. Maximal firing rates were higher when the loads being moved were increased from 25 to 360 g. The majority of position-sensitive neurons exhibited a large interspike-interval variability at wide incisal opening. In most of these neurons, this interspike-interval variability was periodic, usually at a rate of about 10 periods/s, and took the form of "saw-tooth" modulation on a record of instantaneous firing rate. Neurons that exhibited this modulation in a very prominent form also exhibited, in many instances, a substantial increase in firing rate during closing jaw movements.

A new electronic device for quantitation of EMG activity

A description is given of a new electronic device capable of analysing and converting the EMG response in a small volume of muscle in such a way that two output signals are obtained: one as an analogue voltage proportional to the instantaneous firing rate, the other as a number of impulses counted in a preselectable measurement-time window. The method thus allows quantitative measurements of reflex responses and has proved its value, especially in the investigation of reflex reactions in the pelvic sphincters.

Stochastic constancy, variability and adaptation of spike generation: Performance of a giant neuron in the visual system of the fly

The stochastic structure of the spike activity generated by a movement processing wide-field element in the visual system of the fly has been studied over the whole performance area of the neuron. The structure of this discharge is described in terms of an Adaptive Integrate-to-Threshold model for a wide variety of spatio-temporal stimuli as well as steady-state stimuli. In order to reproduce the experimental results it is shown that the source of randomness in the model (e.g. the threshold) behaves like a random variable which is distributed according to a two-state Markov renewal process. In the case of stationary discharges generated by moving sinewave patterns the shape of the interspike interval distribution (which, in the Integrate-to-Threshold model, reflects the shape of the threshold distribution) changes continuously from a two-state distribution at low firing rates to a one-state distribution at high firing rates. In dynamic conditions of the discharge, generated by temporal dynamic stimuli, the experimental results show that the shape of the (demodulated) interval distribution of the discharge is determined by the highest instantaneous firing rate with an adaptation time constant of a few seconds. The physioligical origin of this intriguing behaviour remains -- up till now -- out of the picture.

An auditory-nerve model for interaural time discrimination of high-frequency complex stimuli

Recent data on interaural time discrimination of high-frequency complex stimuli are described by a model based on auditory-nerve activity. This model is a simple extension of a model that was developed for detection and discrimination of low-frequency stimuli and that includes an explicit description of the activity in the auditory-nerve fibers. In the extension to high frequencies it is assumed, consistent with available physiological data, that the high-frequency neurons have instantaneous firing rates that follow the envelope of the tuning-curve filtered signal. Beyond the auditory nerve description, the model assumes a structure for processing timing information on high-frequency fibers that is the same as the structure for low frequencies. [Work supported by NIH.]

Doublet and burst firing patterns within the dorsal column nuclei of cat and man

We have examined extracellularly the firing pattern of neurons in the cat external cuneate nucleus and in the human main cuneate nucleus, focusing upon both the spontaneous firing patterns and its modification by natural stimulation. Many of these neurons exhibit stereotyped doublet or burst firing patterns, e.g., the interval between the spikes might be 1.0 ± 0.1 msec in a given cell. For most cells, this characteristic doublet interval was between 0.8 and 2.0 msec, with a few extending to 5 msec. While doublets were most common, the number of spikes per burst ranged to six or more. When the external cuneate neurons were synaptically driven by forelimb position changes, the firing rate increased but the proportion of spikes occurring within bursts (the “burst index”) often fell. The doublets that occurred became broader during synaptic drive. This paradoxical behavior (the peak instantaneous firing rate falling as the average firing rate rises) is analogous to the doublet firing patterns occasionally observed in spinal motoneurons; there, the doublet is caused by a large depolarizing afterpotential (postspike hump) which rises through the falling threshold at the end of the relative refractory period to elicit an “extra spike.”

Response of type B atrial vagal receptors to changes in wall tension during atrial filling.

In anesthetized curarized cats with their chests open, we recorded the activity of type B right atrial vagal stretch receptors, right atrial pressure, and instantaneous dimensional changes of the right atrium. The nervous activity was analyzed during alterations in atrial dynamics produced by acute volume loading of the right atrium under control conditions and during sympathetic and vagal stimulations. Our results demonstrated that the mean frequency of discharge in the burst was dependent on the absolute tension and the rate of change in tension developed in atrial muscles during filling. The responses of different receptors to changes in atrial dynamics were qualitatively similar but characteristic for each receptor studied. In some experiments nervous activity was recorded after the cats had been killed: static and dynamic changes in atrial tension were then produced by injecting blood into the right atrium. Under these conditions dynamic stimuli always activated the receptors at tensions below the threshold for static stimuli. During dynamic stimuli the instantaneous firing rate was always higher than it was during static stimuli applied at the same level of tension. This study indicates that the nervous activity of type B atrial vagal receptors is closely dependent on static and dynamic changes in atrial wall tension.

Diversity of coding profiles of mechanoreceptors in glabrous skin of kittens

We examined stimulul-response (S-R) profiles of 35 single mechanoreceptive afferent units having small receptive fields in glabrous forepaw skin of 24 anesthetized domestic kittens. Single unit activity was recorded with tungsten microelectrodes from cervical dorsal root ganglia. The study was designed to be as quantitatively descriptive as possible. We indented each unit's receptive field with a broad battery of simple, carefully controlled stimuli whose major parameters, including amplitude, velocity, acceleration, duration, and interstimulus interval were systematically varied. Stimuli were delivered by a small probe driven by a feedback-controlled axial displacement generator. Single unit discharge data were analyzed by a variety of direct and derived measures including dot patterns, peristimulus histograms, instantaneous and mean instantaneous firing rates, tuning curves, thresholds for amplitude and velocity, adaptation rates, dynamic and static sensitivities, and others. We found that with respect to any of the S-R transactions examined, the properties of our sample of units were continuously and broadly distributed. Any one unit might exhibit either a slow or rapid rate of adaptation, or might superficially appear to preferentially code a single stimulus parameter such as amplitude or velocity. But when the entire range of responsiveness of units to the entire stimulus battery was surveyed by a variety of analytic techniques, we were unable to find any justifiable basis for designation of discrete categories of S-R profiles. Intermediate response types were always found, and in general, all units were both broadly tuned and capable of responding to integrals of several stimulus parameters, our data argue against the usefulness of evaluating a unit's S-R coding capabilities by means of a limited ste of stimulation of response analysis procedures.

A statistical model for interpreting neuroelectric responses

Neuroelectric activity recorded after presentation of a controlled stimulus is called an “evoked response.” Evoked responses are random, in that repeated presentations of a stimulus do not produce identical responses despite all effort to maintain identical conditions for all stimulus presentations. Responses may then be described statistically. The present model attempts to relate statistical characteristics of evoked responses, recorded by gross electrodes, to the statistical activity of the neural elements that contribute to the responses. The model postulates one or more populations of elements which, when they fire, contribute elemental waveforms to a gross response in which these waveforms are linearly summed. The statistical behavior of the elements in a population is described by their instantaneous firing rate, which is a function of time. In terms of the model, the statistical properties of the gross response (such as the mean and variance, both of which are functions of time) are shown to be related in a simple way to the instantaneous firing rates and elemental waveforms of the populations that contribute to the response. The model is an extension of the shot-noise model to time-variant phenomena; but some of the assumptions of the shot-noise model (specifically, statistical independence of firings) are relaxed.