Response of rabbit visual cortex neurons to direct stimulation by current of different intensities

Response was investigated in 47 rabbit visual cortex neurons to direct intracortical electrical stimulation consisting of single biphasic pulses of increasing intensities within the 150–2,700 µA range. Minimum level for generating all components of response to electrical stimulation remained similar from one neuron to the next, ranging between 150 and 600 µA. Three different patterns of dependence between numbers of spikes at different stages of response and current amplitude were identified: stable, gradual and selective patterns. Percentages of stable dependences were lower for after-discharges in comparison with initial firing (at 11 and 26% respectively) and the proportion of selective dependences were somewhat higher (at 32 and 21%). The selective dependence observed could imply the existence of optimum current levels at which peak neuronal response occurs. At the same time, duration of inhibitory pauses lengthened uniformly in the response of all test neurons during increasing intensity of the electrical stimuli. Findings obtained during this study may have a practical application in matters connected with visual prosthetics in the blind.M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 239–247, March–April, 1989.     

Correlations of the Peculiarities of the Motivational Sphere and Characteristics of Event-Related EEG Potentials in Humans

We studied the relations between generalized characteristics of the state of the motivational sphere, the levels of need for achievements (N-Ach) and achievement motivation (AchM) typical of an individual, and the parameters of cerebral event-related potentials (ERPs). The examined group included 70 adults of both sexes. The ERPs were recorded in the course of realization of two behavioral test acts with motor components. In task А, the subject should press a button with the minimum delay with respect to an imperative signal preceded by a warning signal (with the measurement of the time of sensorimotor reaction); in this case, the contingent negative variation (CNV) and Р300 potential were recorded. Under conditions of task B, the subject should measure a definite time interval limiting the latter by two pushings of the button; in this case, the readiness potential (RP) was recorded in addition to CNV and Р300. The ERPs were recorded in the С3 and С4 leads (according to the 10-20 system). The peculiarities of the motivational sphere were diagnosed using Orlov’s and Mechrabian’s questionnaires. We found that a relatively high amplitude of the early CNV component (СNV-O) and low amplitudes of the integral CNV and Р300 in task A and a low amplitude of the RP can serve as task B-related EEG markers of a high NA level. In task A, high levels of the AchM correlated with higher amplitudes of the CNV and Р300, and amplitudes of these potentials were higher in the left hemisphere. The observed interrelations were probably determined by a considerable dependence of the N-Ach and AchM characteristics, on the one hand, and CNV amplitude parameters, on the other hand, on the hereditary factors, in particular neurochemical ones. It is obvious that such peculiarities of the neurodynamic constitution of an individual are, to a considerable extent, determined by the specificity of organization and functioning of a few neurotransmitter (in particular aminergic) and neurohumoral systems.     

Auditory memory for temporal characteristics of sound

This study evaluates auditory memory for variations in the rate of sinusoidal amplitude modulation (SAM) of noise bursts in the European starling (Sturnus vulgaris). To estimate the extent of the starling’s auditory short-term memory store, a delayed non-matching-to-sample paradigm was applied. The birds were trained to discriminate between a series of identical “sample stimuli” and a single “test stimulus”. The birds classified SAM rates of sample and test stimuli as being either the same or different. Memory performance of the birds was measured as the percentage of correct classifications. Auditory memory persistence time was estimated as a function of the delay between sample and test stimuli. Memory performance was significantly affected by the delay between sample and test and by the number of sample stimuli presented before the test stimulus, but was not affected by the difference in SAM rate between sample and test stimuli. The individuals’ auditory memory persistence times varied between 2 and 13 s. The starlings’ auditory memory persistence in the present study for signals varying in the temporal domain was significantly shorter compared to that of a previous study (Zokoll et al. in J Acoust Soc Am 121:2842, 2007) applying tonal stimuli varying in the spectral domain.     

Temporal resolution of the Florida manatee (<Emphasis Type="Italic">Trichechus manatus latirostris</Emphasis>) auditory system

Auditory evoked potential (AEP) measurements of two Florida manatees (Trichechus manatus latirostris) were measured in response to amplitude modulated tones. The AEP measurements showed weak responses to test stimuli from 4 kHz to 40 kHz. The manatee modulation rate transfer function (MRTF) is maximally sensitive to 150 and 600 Hz amplitude modulation (AM) rates. The 600 Hz AM rate is midway between the AM sensitivities of terrestrial mammals (chinchillas, gerbils, and humans) (80–150 Hz) and dolphins (1,000–1,200 Hz). Audiograms estimated from the input–output functions of the EPs greatly underestimate behavioral hearing thresholds measured in two other manatees. This underestimation is probably due to the electrodes being located several centimeters from the brain.     

Contribution of homosynaptic depression to stabilization of spinal cord potentials

The following were measured during experiments on spinal anesthetized cats: firstly, variations in the amplitude of dorsal root potentials produced by applying single or regular stimuli in 120–150 trails to hindlimb cutaneous nerves and dorsal surface of the spinal cord and secondly, numbers of extracellular discharges in neurons involved in generating these potentials. A reduction in the variation between these parameters was found when applying stimulation at the rate of 0.1–5.0 Hz. The authors attribute the effect observed to the influence of homosynaptic depression.Institute of Biology, State University Commemorating 300th Anniversary of Russian-Ukrainian Reunion, Dnepropetrovsk. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 180–185, March–April, 1988.     

Differences between Spontaneous and Evoked Monoquantum Signals in the Frog Neuromuscular Junction

In experiments on the frog cutaneous-pectoris muscle, the amplitude-temporal parameters of monoquantum end-plate currents (EPC) and miniature EPC (mEPC) were investigated using extracellular recording. A significant dependence of the risetime of the signals on their amplitude was found after analyzing mEPC; at the same time, such dependence was absent for EPC. Approaches leading to disorganization of the active zones (AZ) of the nerve ending (NE), prolonged action of a Ca-free solution, and denervation resulted in an increased dependence of the risetime of the monoquantum signals on their amplitude; moreover, these dependences were similar for both mEPC and monoquantum EPC. Mathematical simulation showed that the obtained data could be explained by the spatial heterogeneity of the sites of spontaneous and evoked transmitter release within the regions of the AZ. A new hypothesis interpreting spontaneous and evoked transmitter release is proposed.     

Role of cortical inhibition in heterosensory interaction of neurons of the cat sensorimotor cortex

Background and evoked neuronal activity in the cat sensorimotor cortex was recorded under a-chloralose anesthesia. Pairs of heterogeneous stimuli were applied, spaced at intervals of 0, 100, 200, 300, and 400 msec. A clicking sound, flashing light, and electroshock to the contralateral forepaw were used as stimuli. Partial or complete blockade of response to test stimuli presentations spaced 100–200 msec apart were observed when using stimulation of varying modality. The greatest test response was recorded at interstimulus intervals of 200–300 msec. Intracellular mechanisms of heterosensory interaction were investigated by applying the inhibitory transmitter antagonist picrotoxin microiontophoretically to the test cell to produce local attenuation of inhibitory effects. This substance also reduced the duration of blockage following the conditioning stimulus and the occurrence of peak level test response at a lower interstimulus interval than in the controls. Either a consistent increase in the number of spikes per response at one of the interstimulus intervals or a uniform reinforcement in unit response to several different interstimulus intervals were observed in a proportion of the cells. The contribution of intracortical inhibitory influences to the mechanisms of heterosensory interaction on neurons of the cat sensorimotor cortex is discussed in the light of our findings.A. A. Ukhtomskii Institute of Physiology, A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 147–156, March–April, 1987.     

The relationship between a conditioned slow negative potential and focused attention]

A conditioned slow negative vertex potential (CSNP) was studied in the interval between two stimuli: anticipatory and trigger, under different experimental conditions, namely; in response to a trigger stimulus the subject was to press an operating key; or to memorize the number of trigger stimuli; or to respond to the trigger stimulus by pressing the key and memorizing the number of anticipatory stimuli. A sound, geomatrical figures and separate words flashing up on a screen were used as stimuli. All of them were presented both as anticipatory and trigger signals. If a sound was used as an anticipatory stimulus, and a word as trigger one, the recorded CSNP was at its maximum in the case of a simple motor reaction, and at its lowest during retention. When the stimuli interchanged, was drawn to the anticipatory verbal stimulus, the CSNP amplitude diminished and the latency became shorter. The dependence of SCNP parameters on the subject's attention drawn to the anticipatory resp. trigger stimuli is discussed.     

Dependence of the evoked potentials of the auditory cortex on the parameters of acoustic stimulus]

Experiments were conducted on 40 rabbits; a study was made of the dependence of the amplitude and the latent period of the auditory evoked potentials on the intensity, duration, accretion front, frequency and the rhythm of the acoustic stimuli (the intervals between them). The intensity of the stimuli, the accretion front and the interstimulus intervals proved to influence the induced potential parameters.     

Characteristics of evoked potentials and single neuron responses in the cat sensorimotor cortex to sound stimuli with different frequencies.

The characteristics of the averaged evoked potentials (AEP) (experiments with awake non-paralysed animals), of the evoked potentials (EP) and of the responses of single sensorimotor cortical neurons (acute experiments) of cats to tone-bursts with frequencies within 0.1-6.0 kHz were studied. Response selectivity to the tone-burst frequencies which are energetically pronounced in some biologically significant sounds for the cat was observed. The averaged curve of the dependence of the amplitude of AEP in the somatosensory cortical region (S1) on the tone-burst frequency has reliable maximum values at the frequencies of 0.8, 1.6 and 2.0-3.0 kHz. Most pronounced changes in the heart rhythm were observed within the tone-burst frequency ranges in which the AEP of the highest amplitudes were recorded. The amplitude of the AEP was found to increase during the conditioned reflex elaboration. The curve of the dependence of the probability of the EP occurrence on the frequency at equal sound pressure levels had maximum values at the frequencies of 1.6 and 3.2 kHz. The highest amplitude values of EP were found at frequencies of 0.8, 1.6 and 3.2 kHz. More than half of the recorded neurons revealed the lowest values of the response thresholds and the maximum values of the occurrence probability under suprathreshold stimulation at frequencies close to 0.8, 1.6, and 3.2 kHz. It is supposed that the above mentioned feature of the input frequency organization in sensorimotor cortex is connected with the selectivity as to the biological significance of acoustic stimuli.     

Development of the brain’s organization of working memory in young schoolchildren

In 7–8 and 9–10-years old children, we studied event-related potentials (ERPs) during paired comparison of non-verbalizable visuospatial stimuli presented at an interval of 1.5–1.8 s. Age-related differences were found in the involvement of various cortical areas in the formation and retention of a short-term memory trace of the reference stimulus and during comparison of the short-term trace with the test stimulus presented. In both age groups, working memory was associated with an elevation of the amplitude of the sensory-specific N1 component in the visual cortical areas. Age-related differences in the processing of sensory-specific characteristics of a stimulus were the greatest in the ERPs to the test stimulus: at the age of 9–10, the N1 component amplitude was significantly increased in all caudal leads and, in the occipital and inferior temporal leads, this component was preceded by P1 component. At this age, we observed the early involvement of the inferior frontal cortex, which was not observed at the age of seven. The increase in positivity over that area was observed in the interval of 100–200 ms. Substantial differences between age groups were found in the late ERP component corresponding to cognitive processes. At the age of 7–8, the presentation of both the reference and test stimuli causes the increase in the amplitude of the slow positive complex (SPC) in the caudal liads with the maximum enhancement found in the interval of 300–800 ms in the parietal leads. At the age of 9–10, the SPC increase, much like in adults, was observed in ERP to the test stimulus only. At this age, adult-like specific changes in the late phases of ERPs were observed in the fronto-central regions at the different stages of working memory. They are the increases in the negative N400 wave in the ERP to the reference stimulus and the SPC to the test stimulus. These data show that, at the age of 9–10, the functional organization of working memory of the adult type is formed; however, the extent to which the frontal cortex, and its dorsal regions in particular, is involved into working memory processes does not meet yet a definitive level.     

Reflection of the Emotional Significance of Visual Stimuli in the Characteristics of Evoked EEG Potentials

Healthy subjects (n = 88) were asked to passively visualize positive and passive emotiogenic visual stimuli and also stimuli with a neutral emotional content. Images of the International Affective Picture System (IAPS) were used. Amplitude/time characteristics of the components of evoked EEG potentials (EPs), P1, N1, P2, N2, and P3 and topographic distribution of the latter components were analyzed. The latencies, amplitudes, and topography of the EP waves induced by presentation of positive and negative stimuli were found to be different from the respective values for the EPs induced by neutral stimuli. The level and pattern of these differences typical of different EP components were dissimilar and depended on the sign of the emotions. Specificities related to the valency of an identified stimulus were observed within nearly all stages of processing of visual signals, for the negative stimuli, beginning from an early stage of sensory analysis corresponding to the development of wave Р1. The latencies of components Р1 in the case of presentation of emotiogenic negative stimuli and those of components N1, N2, and Р3 in the case of presentation of the stimuli of both valencies were shorter than the latencies observed at neutral stimuli. The amplitude of component N2 at perception of positive stimuli was, on average, lower, while the Р3 amplitude at perception of all emotiogenic stimuli was higher than in the case of presentation of neutral stimuli. The time dynamics of topographic peculiarities of processing of emotiogenic information were complicated. Activation of the left hemisphere was observed during the earliest stages of perception, while the right hemisphere was activated within the intermediate stages. Generalized activation of the cortex after the action of negative signals and dominance of the left hemisphere under conditions of presentation of positive stimuli were observed only within the final stages. As is supposed, emotiogenic stimuli possess a greater biological significance than neutral ones, and this is why the former attract visual attention first; they more intensely activate the respective cortical zones, and the corresponding visual information is processed more rapidly. The observed effects were more clearly expressed in the case of action of negative stimuli; these effects involved more extensive cortical zones. These facts are indicative of the higher intensity of activating influences of negative emotiogenic stimuli on neutral systems of the higher CNS structures.     

Formation of a micropinch and generation of multiply charged ions at the front of a current-carrying plasma jet

The formation of a neck in the cathode plasma jet in the initial stage of a low-voltage vacuum spark is investigated experimentally and theoretically. X-ray bursts corresponding to an electron temperature of 150–300 eV are detected. With the use of a pinhole camera, it is found that an emitting region less than 1 mm in size is located near the cathode. The free expansion of a current-carrying cathode plasma jet with a current growing in accordance with the experimentally observed time dependence is simulated using a hydrodynamic model. It is shown that the neck forms at the front of the plasma jet due to the plasma compression by the magnetic self-field. In the constriction region, the plasma is rapidly heated and multiply charged ions are generated. The calculated spatial and temporal variations in the electron temperature and average ion charge are close to the measured dependences over a wide range of the discharge parameters.     

The dependence of the neuronal reactions of the sensorimotor cortex to a simultaneous complex stimulus on the level of the differentiation of its components]

On alert animals the change was studied of the neuronal activity of the sensorimotor cortical area of cats brain in dependence on the level of differentiation of the components of simultaneous heteromodal complex stimulus. According to the character of this dependence and a number of other parameters two groups of neurones were singled out in the sensorimotor cortex. It was shown that parameters of reactions of all recorded neurones of the sensorimotor cortex to the positive conditioned signal were the first established after consolidation of the animal conditioned motor activity. In the course of elaboration following parameters changed: expressiveness, intensity, duration and value of latency. Reactions of neurones of both groups to the inhibitory stimuli were stabilized only after consolidation of the habit of differentiation. Responses of the first group neurones changed only by the pattern of discharge, while the responses of the second group neurones could change by expressiveness of response, its sign, duration and value of latency. Oscillations of the differentiation level after finishing of the elaboration of inhibitory conditioned reactions affected only the responses of the second group neurones to complex components.     

Evoked cortical activity to sounds of differing signal meaning in young and elderly subjects

In elderly people, in comparison with the young ones, the latency of wave P300 is increased in response to all applied acoustic signals, the amplitude of P300 is lower only in response to significant stimuli. No age changes of the wave N150 parameters are noticed. P300 (or N150) wave amplitude depends on signal significance of the sound; it is the lowest in response to significant stimuli and the highest to the ignored ones. Possible reasons of this paradoxical phenomenon are discussed. Preferential participation of different stages of cortical information processing is determined by the difficulty of perceptive task solution. Cortical electrical reaction to separate stimuli is significantly determined by the context of the information perceived in the given period, creating psychological state of the personality.     

Immediate effect of individual bars of insoles and their combination on gait parameters in asymptomatic healthy adults

Abstract

Objective: The way how individual bars of sensorimotor insoles influence the gait kinematics is not fully understood yet. Therefore, this study aimed to explore the effect of three sensorimotor orthotic conditions (the medial calcaneal and retrocapital lateral bars and their combination) on the gait parameters in healthy adults during the stance phase of gait cycle.

Materials and methods: Twenty-six young adults performed 20 gait cycles in each condition using their self-selected cadence and provided standardised shoes with the base-sole and the three types of orthotics. A three-dimensional motion analysis system (8 cameras; 200?Hz) was used and a six-degrees of freedom model was applied. The cadence, the stride length, the first peaks of foot external rotation, eversion and dorsal flexion as well as the first peak of hip adduction were analysed.

Results: Significant differences (p?<?0.05) were found for all parameters between the orthotic conditions, except the cadence. Significant difference in the first peak of hip adduction (p?=?0.008) was found between the dominant and non-dominant leg. There were no significant interactions between the factors of condition and leg dominance (p?>?0.05).

Conclusions: There seems to be overall tendencies in immediate changes in ankle joint kinematics caused by all three sensorimotor orthotic conditions and besides the mechanical principles, also ‘proprioceptive mechanism’ seems to play a role. However, maximum observed average angular change was 2° and some variability in reactions to each orthotic condition exists among the individuals. Therefore, clinical relevance of such changes remains unclear and careful analysis of expected outcomes should be the common part of every orthotic intervention.     

Thermodynamic description of oligonucleotide self-association in DNA concatamer structures

A scheme of equilibrium formation of concatamers by two different oligonucleotides has been considered. It is shown that in the general case, the dependence of the concentration of oligonucleotide components on temperature cannot be found in analytical form. Therefore, it is impossible to find the thermodynamic parameters of concatamer formation (ΔH ⁰, ΔS ⁰) and melting temperatures by analyzing the profiles of thermal denaturation of oligonucleotide complexes. An algorithm for numerical solution of implicit dependences has been developed. A number of approaches are considered that simplify the analysis of heat denaturation curves for concatamer complexes. It is shown that the dependence of the efficiency of concatamerization on temperature can be described analytically when duplex fragments have close stability and there is no cooperativity at the oligonucleotide junction. In this case, the dependence of melting temperature on thermodynamic parameters and oligonucleotide concentration has the same form as in the case of the duplex structure formed by a pair of non-self-complementary oligonucleotides. The ability of various model approaches to describe the experimental curves of concatamer heat denaturation is evaluated. For concatamer structures used as signal amplifiers in DNA hybridization analysis, a function is introduced that shows the relative contribution of a concatamer of given length to the magnitude of signal amplification. The dependence of the maximum of this function on the concentration of oligonucleotides, the thermodynamic characteristics of their complexes, and temperature has been determined. It is shown by the gel retardation assay that the function of the length distribution of concatamers qualitatively correlates with the experimental dependences.     

Functional Organization of the Brain during the Operation of Working Memory

Event-related potentials (ERPs) recorded from various cortical areas during matching of two consecutive pictures were analyzed. Reflecting the process of trace fixation, the ERP to the reference stimulus was characterized by an increase in components P150 and P300 in the occipital and temporo-parieto-occipital areas and components N300 and N400 in the precentral areas as compared with the ERP elicited by the warning stimulus. The ERP to the test stimulus, which reflected trace retrieval and matching with current information, was characterized by a generalized increase in the late positive complex in the interval 300–600 ms. Similarity and/or dissimilarity of the test and reference stimuli was reflected in the parameters of the ERP to the test stimulus. The results testify to the difference in functional and topographic organization of the brain cortex at the initial and late stages of operation of the working memory.     

The effect of summation of contraction on acceleration signals in human skeletal muscle

The purpose of this study was to determine the effects of summation of contraction on acceleration signals in human skeletal muscle. The torque parameters of dorsiflexion and acceleration signals in the tibialis anterior muscle were measured during evoked isometric contractions. In an examination of two-pulse trains with different inter-pulse intervals, the torque and accelerometer responses to inter-pulse intervals of 10–100 ms were recorded. In an investigation of the effects of different numbers of stimuli, the torque and accelerometer responses to 1–8 pulses with a constant inter-pulse interval of 10 ms were recorded. The present study found that there was a difference in acceleration amplitude between the single-pulse and two-pulse trains with an inter-pulse interval of 10 ms but not two-pulse trains with an inter-pulse interval of 20 ms or more. In the investigation of different numbers of stimuli, we found a similar MMG amplitude across 2–8 pulses. Moreover, we observed that the maximal time to the peak acceleration signal was ～27 ms. In a comparison of torque parameters with acceleration signals, the present study clearly shows that acceleration amplitude is poorly correlated to changes in force parameters when the inter-pulse interval or the number of stimuli are increased. These results suggest that the absence of associated changes in acceleration peak is due to the long interval for the subsequent pulses relative to the time at which acceleration peak is achieved (～27 ms). These findings will provide useful information concerning the method for assessing summation of contraction with an accelerometer.     

Evoked potentials of the cerebral cortex during the comparison of visual stimuli

Visual evoked potentials (EP) were recorded when the test subjects accomplished the tasks of a comparison of a current stimulus with the previous one, the stimuli being presented in a continuous sequence. In the first task, rare repetition of two stimuli (Russian letters) in the continuously changing flow of stimuli was relevant, and the test subject had to press the button when it happened; in the second task, the relevant stimulus was a rare change in the flow of stimuli. The influence of the stimulus repetition/change factor on EP was analyzed. The processes related to the comparison of the current and previous stimuli were most manifest in four time intervals: 120–140, 180–210, 260–280, and 350–370 ms. The occipito-temporal component of EP revealed in the interval of 180–210 ms, which we denoted as the negative component of visual mismatch (NCVM), proved a special component, differing in its functional and temporal characteristics from theN _2b component. WhereasN _2b is modulated by the factor of stimulus probability, the NCVM by that of stimulus repetition/change.