Changes In Firing Patterns Research Articles

Operant control of precentral neurons: Bilateral single unit conditioning

Two Macaca mulatta monkeys were reinforced to operantly control a precentral neuron's firing pattern while a contralateral unit was monitored simultaneously. The results from 38 complete experiments indicate the following: (a) upon altering to the operant task, both the contingent and the non-contingent neurons changed firing patterns from preconditioning levels. However, as the monkey brought the contingent unit under operant control, there were no significant changes in the firing pattern of the non-contingent neuron; (b) when the contingencies were reversed so that the monkeys were reinforced to control the originally non-contingent neuron, the firing pattern off the originally contingent neuron returned to near baseline levels. These data indicate that although many precentral units may change firing patterns when the monkey attends to the operant task, the reinforced changes in firing pattern are not the result of a generalized phenomenon at the spinal level.

Synaptic organization of tuberal hypothalamus in tissue culture: Effects of electrical stimulation and blockers of synaptic transmission

Poststimulus histograms were used to quantitate effects of focal electrical stimulation on spontaneously active neurons in tuberal hypothalamic tissue cultures. After electrical stimulation, changes in firing patterns were observed in 94 of 108 spontaneously active units. Three possible components were observed: an early excitation, a subsequent inhibition, or a prolonged facilitation. The early, presumably antidromic, activation was resistant to perfusion by Ca 2+-free/high-Mg 2+ salt solution; later, synaptic effects were abolished. Perfusion of 10 −5 m picrotoxin reduced or abolished these longer-latency inhibitions in a majority of cells. These results suggest first, that there is a high degree of functional synaptic connection in tuberal hypothalamic tissue cultures, and second, that there exist intrinsic inhibitory interneurons in this region, which utilize γ-aminobutyric acid as their transmitter and are involved in the generation of the normally encountered firing patterns.

The role of forewing muscles in the control of direction in flying locusts

1. Locust forewing muscles were recorded whilst the animal was free to manoeuvre. 2. First and second mesothoracic basalars (depressors) and first and second tergosternal muscles (elevators) show changes in firing patterns associated with turning. 3. The phase between left and right first basalars was subject to large and rapid changes. The phase between left and right first tergosternals changed less markedly. 4. Ipsilateral first and second basalars were not tightly linked in either burst length or phase. 5. Ipsilateral first and second tergosternals were very tightly linked in burst and phase changes. 6. The mesothoracic subalar changed its firing pattern less than any other of the muscles studied. 7. The results are discussed in relation to known pathways in the flight motor system.

Effect of dopamine on firing patterns of striatal units in adult and 21-day-old rats

The experiments in the present work were designed to characterize firing patterns of striatal units in adult rats and to exmine the effects of iontophoretically applied dopamine on those patterns. A parallel study was carried out using 21-day-old rats as a comparable system with a less effective dopaminergic influence. The results showed characteristic phasic activity in the striatum which could be modulated by iontophoretic application of dopamine. In the young animals a smaller proportion of the units initially exhibited phasic activity and the responses to dopamine did not show such a profound effect of dopamine on the pattern of firing. The changes in firing pattern in these experiments are interpreted as being a possible mechanism for the influence of the nigrostriatal pathway on motor control via the pallidum and thalamus.

Discharge patterns of the nucleus parabrachialis lateralis neurons of the cat during sleep and waking

Discharge patterns of the nucleus parabrachialis lateralis (PbL) neurons located in the dorsolateral pontine tegmentum were investigated in 7 unrestrained, freely behaving cats with a multiwire electrode bundle method. Among 84 PbL units recorded so far, 31% of the units exhibited a marked reduction or complete cessation of firing during paradoxical sleep (PS) (PS-off cells), while 55% of the units exhibited an increase of firing during PS (PS-on cells) as compared with quiet wakefulness (QW) and slow wave sleep (SWS). The remaining 14% of the PbL units exhibited no remarkable change of firing rate and pattern during the sleep-walking cycle. The PbL PS-off cells were further characterized by a slow and regular firing pattern during QW and SWS, and they were similar in several respects to the PS-off cells reported in the nucleus raphe dorsalis and locus coeruleus complex. Six of the PbL PS-on cells were tightly phase-locked with PGO waves, and the spikes preceded by 5-25 msec the onset of the PGO waves recorded in the lateral geniculate nucleus. Seven other PbL PS-on cells were related to the locomotor activity observed in active wakefulness. In light of the present results, the functional significance of the PbL units has been discussed.

Response patterns to noxious and non-noxious stimuli in rostral trigeminal relay nuclei: Brain Res., 97 (1975) 47–60

Postimulus time histogram analysis of second-order neuron responses in rostral trigeminal relay nuclei of cat demonstrated characteristic firing patterns after noxious (tooth pulp) and non-noxious (tooth tap) stimuli. The response to noxious stimulation was prolonged and frequently bimodal while the response to non-noxious stimulation was brief. The same neurons were fired by electrical stimuli applied directly to nucleus caudalis but with longer latencies suggesting a contributory role of nucleus caudalis to the characteristic prolonged bimodal response pattern to noxious stimuli. Interacting noxious and non-noxious stimuli using condition-test sequences demonstrated further stimulus mode-related changes in firing patterns. Electrical conditioning stimuli in nucleus caudalis reduced some responses while strychnine sulfate applied into nucleus caudalis augmented the responses evoked in rostral nuclei by both noxious and non-noxious peripheral stimuli. Nucleus caudalis appeared to contain elements which may modulate activity in rostral trigeminal nuclei by either augmenting or reducing specific firing patterns of second-order neurons in rostral relay nuclei.

Synchronization of respiratory frequency by somatic afferent stimulation.

In cats anesthetized with chloralose-urethan, vagotomized, paralyzed, and artifically ventilated, superficial radial (cutaneous) and hamstring (muscle) nerve afferents were stimulated while phrenic nerve electrical activity was recorded. The results obtained with both types of nerves were similar. Stimulation in mid and late expiration advanced the onset of the next inspiration, shortening its duration. Stimulation in early inspiration advanced, while that in late inspiration delayed, the onset of the next expiration. These effects were often accompanied by changes in phrenic motoneuron firing patterns (earlier recruitment, increased discharge frequency, increased slope of integrated phrenic neurogram). Repetitive somatic afferent stimulation produced sustained increases in respiratory frequency in all cats and in half of them entrainment of respiratory frequency to the frequency of stimulation occurred at ratios such as 4:3, 4:5, 1:2, 1:3, 1:4, and 1:7. The lowest stimulus intensity required for evoking these phase shifts was between 5 and 10T (threshold of most excitable fibers) for muscle afferents and between 1 and 2T for cutaneous afferents. These results demonstrate the existence of a reflex mechanism capable of locking respiratory frequency to that of a periodic somatic afferent input. They also provide an experimental basis for the hypothesis that reflexes are resposible for the observed locking between step or pedal frequency and respiratory rate during exercise in man.

A network model for control of inspiratory cutoff by the pneumotaxic center with supportive experimental data in cats.

A network model for the control of inspiratory cutoff by the pneumotaxic center (PC) in cats, based on a previously described anatomical model, is proposed. It is postulated that in vagotomized cats early expiratory cells in the PC produce the inspiratory cutoff. The firing patterns of neurons derived from the model were similar to those observed in the PC. Systematic changes in any one of several parameters in the model resulted in a marked change in inspiratory amplitude with no significant change in inspiratory duration; this response is similar to that already observed in vagotomized cats during changes in ventilatory drive. The basic conformation of the model was tested experimentally in the isolated respiratory center preparation of the cat. Discharges of 48 cells in the PC were recorded and the firing patterns analyzed to determine the change in frequency and temporal pattern of activity associated with spontaneous changes in the amplitude and/or duration of inspiration. 47 of the 48 cells exhibited changes in firing pattern that were consistent with the model.

Labyrinthine and extralabyrinthine effects on spontaneous spinal interneuronal activity of cats during rocking

Responses of 170 single, spontaneously active interneurons in the lumbar and sacral segments (L5-S1) of the spinal cord of normal and labyrinthectomized cats were investigated extracellularly during rocking. The neurons were selected from the regions of Rexed's laminae VII–IX. The results were analyzed by computer. During rocking, the firing pattern of neurons in intact animals is substantially changed. The firing rate could be raised or lowered and a rhythmbound with the rocking appeared. No change in firing pattern occurred in 10.4% of cells. Labyrinthectomy did not completely abolish these responses but reduced them quantitatively. The results are discussed from the standpoint of convergence of vestibular and extravestibular receptive flows on spinal interneurons.

Response patterns to noxious and non-noxious stimuli in rostral trigeminal relay nuclei

Postimulus time histogram analysis of second-order neuron responses in rostral trigeminal relay nuclei of cat demonstrated characteristic firing patterns after noxious (tooth pulp) and non-noxious (tooth tap) stimuli. The response to noxious stimulation was prolonged and frequently bimodal while the response to non-noxious stimulation was brief. The same neurons were fired by electrical stimuli applied directly to nucleus caudalis but with longer latencies suggesting a contributory role of nucleus caudalis to the characteristic prolonged bimodal response pattern to noxious stimuli. Interacting noxious and non-noxious stimuli using condition-test sequences demonstrated further stimulus mode-related changes in firing patterns. Electrical conditioning stimuli in nucleus caudalis reduced some responses while strychnine sulfate applied into nucleus caudalis augmented the responses evoked in rostral nuclei by both noxious and non-noxious peripheral stimuli. Nucleus caudalis appeared to contain elements which may modulate activity in rostral trigeminal nuclei by either augmenting or reducing specific firing patterns of second-order neurons in rostral relay nuclei.

Reexamination of the force relationship of cortical cell discharge patterns with conditioned wrist movements

Single unit recordings were obtained from 103 precentral cortical cells whose activity was related to an alternate wrist flexion-extension task in monkeys. Although the task was carried out under different loads only a weak relationship between cortical cell firing rates and static force levels was observed for force in one direction. A large change in firing rate occurred, however, when direction of force shifted as a result of a change in the predominant activity between extensor and flexor muscles. The firing patterns of the observed cortical cells suggest that the motor cortex is involved in specifying the muscles to be activated for a given movement and not the level of force to be produced by these muscles. During the dynamic phase of the movement little change in cortical cell firing pattern was observed for large changes in the rate of change of force. Motor cortex cell firing patterns appear to be unrelated to the large values of rate of change of force seen in this experiment.

Single cell activity in the ventral lateral thalamus of the unanesthetized monkey

Spontaneous single cell activity was studied in the ventrolateral region of the thalamus in the unanesthetized monkey. The method used allowed recording in stereotaxic conditions as well as behavioral observations. Recorded cells were localized on histological sections. Patterns of discharge were analyzed and their relationship to the state of vigilance, posture, and movements were examined. Phasic changes in neuron firing patterns were shown to have a clear-cut behavioral counterpart. During alertness, with or without movements, the thalamic cells displayed a sustained but irregular firing associated with a desynchronized EEG. During states of relaxation and immobility, the cells tended to fire in high frequency bursts associated with high amplitude slow waves on the EEG. This burst activity was present only in the absence of movement. In the ventral part of the ventrolateral nucleus most of the cells could be activated by various natural stimuli, particularly those which provoked a quick muscle stretch. In general, the firing frequency of the cells was much greater if the animal made a spontaneous movement than if the same movement was made passively. On the basis of the reported findings it is suggested that ventrolateral neurons play an important role in the general adjustment of posture preliminary to voluntary movement.

Effects of Diffuse Transcerebral Electrical Currents on Cortical Unit Potential Activity

A study of the effects of electroanesthesia (EA) currents on unit potential activity in the sensorimotor cortex was conducted to obtain further knowledge regarding the mechanisms of transcerebral currents. The study showed that the applied electroanesthesia currents obliterate or drive the ongoing cortical activity, or cause cortical units driven at the nucleus posterior ventralis lateralis (VPL) to fire randomly during application of EA. Reversible changes in neuronal firing rates and patterns were observed. This study suggested that EA may interfere with the transmission of neural information at the cortical level studied and may contribute to the unresponsive state observed during application of EA.

Discharge patterns of reticular neurons subjected to direct electrical polarization.

The relationship between firing rate and pattern was analyzed in neurons of the mesencephalic reticular formation of curarized rats using direct polarization through the recording extracellular micropipette to simulate wide range of firing rates. 40% of initially slow irregular cells change firing pattern when accelerated and 60% remains stable. 18% of initially fast regular cells change firing pattern when retarded and 82% remains stable. Since it is generally assumed that change in firing pattern can result only from change in overall synaptic drive it is suggested that in cases firing pattern is stable the polarizing current presumably influences the value of the transmembrane potential whereas clearcut changes in firing pattern accompanying shift in mean firing rate imply the change in synaptic inflow presumably due to enhanced or decreased excitability of some part of postsynaptic membrane.

Deafferentation effects in lateral cuneate nucleus of the cat: Correlation of structural alterations with firing pattern changes

A correlated anatomical and physiological investigation of the effects of unilateral cervicothoracic dorsal rhizotomies upon lateral cuneate nucleus of the cat (LCN) is reported. Pairs of adult cats with identical survival times were selected to correlate structural and functional changes. Two phases are described in the development of alterations of neuronal firing patterns. In the first phase, a relative silence within LCN was associated with depletion of round synaptic vesicles in the presynaptic profiles (LR boutons) of primary dorsal root afferents. The second phase was characterized by a development of spontaneous electrical hyperactivity which corresponded anatomically to the presence of denuded postsynaptic specializations, transient increase of adjacent extracellular space and an apparent decrease in the number of dendritic spines. There was a persistence of an unaltered population of small presynaptic boutons with flattened vesicles (SF boutons). The LCN neuronal membrane is viewed as having an intrinsic tendency for repetitive firing which is enhanced by the functional effects of denuded postsynaptic specialization. A marked similarity was found between some of the spontaneous firing patterns of normal animals (doublets) and the high frequency bursting firing pattern in deafferented preparation. Three models for repetitive spike production are considered in our analysis: oscillator-produced spikes; EPSP-produced spikes; and spike-evoked spikes. The spike-evoked spikes model is considered to be the origin of normal doublet activity and a candidate for the deafferented burst activity. Abnormal hyperactivity after deafferentation may be a function of changes in the membrane characteristics occurring at or near the denuded postsynaptic specializations.

Unit activity of bulbar raphe nuclei and reticular formation in cats.

Spontaneous activity and single unit responses of the bulbar raphe nuclei (NR) and mesencephalic reticular formation (MRF) were studied in unanesthetized cats. In addition to the general features, a number of special features of the unit activity of these two structures were discovered: a) in most cases NR neurons respond predominantly or entirely to cutaneous stimulation of 3 to 4 limbs; b) spontaneous activity (SA) of NR neurons is more regular and less variable in time than that of MRF neurons. Under the influence of various peripheral stimulations the spontaneous activity of NR neurons briefly increases in frequency without any change in firing pattern, whereas the increase in frequency of MRF neurons occurs for much longer and is accompanied by marked changes in spontaneous activity c) NR neurons respond to all peripheral stimuli used by an absolutely uniform, short and compact volley of spikes, whereas MRF neurons respond differently to each stimulus, with various numbers of spikes and different firing patterns. These peculiarities of NR unit activity are evidently attributable to its simpler synaptic organization than that of MRF.

Patterned discharge of six different neurons in a single enteric ganglion.

Impulses from six different neurons within a single ganglion of the myenteric plexus of an isolated segment of feline small intestine, which previously had been stored at 5°C for a period of 48 h, were recorded and each of the neurons is characterized by data collected over a continuous recording period of at least 40 min duration. Discharge of individual members of a group of four cells was detected concurrently by a single microelectrode at one position within the ganglion and spikes of two additional cells were detected later at a different electrode position within the same ganglion. Each of the neurons was spontaneosly active and periodically discharged bursts of action potentials with stereotyped patterns. Within the first group of four cells, variation of the discharge pattern of two of the cells was related to changes in firing pattern of a third cell. The two neurons of the second group displayed close temporal coupling indicative of driver-follower neurons.

Effect of interruption of descending cortical connections on unit responses to extracellular polarization in the lateral geniculate body

Acute experiments on cats showed that unilateral division of projection connections from the cerebral cortex gives rise to definite changes in the effects of extracellular polarization of lateral geniculate neurons: in 40% of cells the regular firing pattern is disturbed in the initial period of action of anodal polarization, the number of cells with after-responses and prolonged changes in spontaneous firing pattern is significantly reduced, and the number of neurons capable of modifying their type of activity under the influence of an incoming polarizing current is also reduced. After interruption of the descending cortical connections the functional characteristics of the lateral geniculate neurons are altered, with a resulting narrowing of the range of their physiological responses to the polarizing current. These facts suggest that the most complex processes of tonic regulation of unit activity in the lateral geniculate bodies require the active participation of the cerebral cortex.

Electrophysiological concomitants of spreading depression in caudate and thalamic nuclei of the cat

Spreading depression (SD) was induced by injection of KCl into striatal and thalamic sites. Unit activity, EEG and direct coupled (DC) recordings were made simultaneously from a number of different brain sites before and after KCl injection. Recording sites included the nucleus into which the injection was made, contiguous nuclei (i.e. not separated by white matter), known projection areas of the injected nucleus and areas which were anatomically unrelated to the site of injection. The large slow potential changes characteristic of SD were generally confined to the injected nucleus and to contiguous nuclei. Unit activity in these areas infrequently ceased, but firing rate and pattern were often dramatically changed. Smaller DC changes were recorded in projection areas. Changes in unit firing patterns were also induced in these areas. The EEG changes little at any subcortical recording site. The experimental results suggest (1) that the method may have some utility as a neuronographic tool and (2) that subcortically-induced SD might be considered as a ‘disorganization’ rather than as a functional ablation.

Influence of thyroxine and steroid hormones on spontaneous and evoked unitary activity in the olfactory bulb of goldfish

Three different types of discharge patterns of single cells were observed in the glomerular and subglomerular layers of the olfactory bulbs of normal goldfish, and these patterns were studied also in hormone-treated fish. The Type I pattern is a series of small spikes of relatively higher discharge rate seen in control and thyroxine-treated fishes with the recording electrode in the subglomerular layers of the bulb. Thyroxine treatment elicited a remarkable increase in the “spontaneous” Type I firing rate. Type B, also recorded from the subglomerular zone, a discharge pattern characterized by bursts of spikes, was obtained mostly after sex steroid treatment. Type G is a pattern of somewhat large action potentials, regularly firing, recorded from cells in the glomerular layer of all animals studied. Observations were made of the changes in rate and pattern of firing during infusion of 0.06 M NaCl into the olfactory sac. Estradiol pretreatment produced a strong facilitatory effect on the NaCl response of cells exhibiting the Type G pattern, but it did not alter the responses of cells of the Type B pattern. In contrast, testosterone did not affect the responsiveness of cells of the Type G pattern, but it facilitated NaCl-evoked changes in the firing rate of cells initially presenting the type B pattern. Progesterone and thyroxine were similar in their tendency to inhibit NaCl-evoked changes in rates of these single unit discharges. However, there was a pattern difference in the altered Type I and B firing, after NaCl infusion, between the progesterone and the thyroxine-treated fishes.