High-frequency oscillations in a pulse wave signal and their relation to differential blood count leucocytes

High-frequency oscillations in a pulse wave signal in the range of 1–50 Hz and their relation to differential blood count leucocytes have been investigated. It is shown that the correlation coefficients grow in the frequency range of 1–12.5 Hz between high-frequency oscillations in a pulse wave signal and stab neutrophils, monocytes and segmented granulocytes. The procedure of smoothing the coefficients of harmonic variation has been proposed.     

High-frequency oscillations in a pulse wave signal and their relation to adaptation responses

High-frequency oscillations in a pulse wave signal in the range of 1-50 Hz and their relation to heart rhythms have been investigated. Informative parameters to estimate the adaptation reactions have been determined using the Kohonen maps, the results of simulating the pulse wave signal (single rheocycles), and the experimental data. The coefficient of harmonic variation was used as an informative parameter. It was shown that the space of signs in the frequency range of 1-12.5 Hz, formed on the basis of the coefficient of harmonic variation, possesses a significant degree of structuring relative to the distribution of data for different types of adaptation reactions.     

Effect of pulse electromagnetic radiation on erythrocyte ghosts

The pulse microwave radiation has been shown to increase the fluorescence intensity of 2-toluidinonaphthanene-6-sulfonate (2,6-TNS) and 1-anilinonaphthalene-8-sulfonate (1,8-ANS) built-in membranes of erythrocyte ghosts. In experiments with 2,6-TNS a frequency dependence of the effect of microwave radiation with maximum within the frequency range of 55-65 Hz has been found. It is suggested that the changes registered with fluorescent probes are induced by mechanical oscillations generated by the pulse microwave radiation.     

Human gamma oscillations during slow wave sleep

Neocortical local field potentials have shown that gamma oscillations occur spontaneously during slow-wave sleep (SWS). At the macroscopic EEG level in the human brain, no evidences were reported so far. In this study, by using simultaneous scalp and intracranial EEG recordings in 20 epileptic subjects, we examined gamma oscillations in cerebral cortex during SWS. We report that gamma oscillations in low (30-50 Hz) and high (60-120 Hz) frequency bands recurrently emerged in all investigated regions and their amplitudes coincided with specific phases of the cortical slow wave. In most of the cases, multiple oscillatory bursts in different frequency bands from 30 to 120 Hz were correlated with positive peaks of scalp slow waves ("IN-phase" pattern), confirming previous animal findings. In addition, we report another gamma pattern that appears preferentially during the negative phase of the slow wave ("ANTI-phase" pattern). This new pattern presented dominant peaks in the high gamma range and was preferentially expressed in the temporal cortex. Finally, we found that the spatial coherence between cortical sites exhibiting gamma activities was local and fell off quickly when computed between distant sites. Overall, these results provide the first human evidences that gamma oscillations can be observed in macroscopic EEG recordings during sleep. They support the concept that these high-frequency activities might be associated with phasic increases of neural activity during slow oscillations. Such patterned activity in the sleeping brain could play a role in off-line processing of cortical networks.     

Somatic evoked high-frequency magnetic oscillations reflect activity of inhibitory interneurons in the human somatosensory cortex

High-frequency potential oscillations in the range of 300–900 Hz have recently been shown to concur with the primary response (N20) of the somatosensory cortex in awake humans. However, the physiological mechanisms of the high-frequency oscillations remained undetermined. We addressed the issue by analyzing magnetic fields during wakefulness and sleep over the left hemisphere to right median nerve stimulation with a wide bandpass (0.1–2000 Hz) recording with subsequent high-pass (> 300 Hz) and low-pass (< 300 Hz) filtering. With wide bandpass recordings, high-frequency magnetic oscillations with the main signal energy at 580–780 Hz were superimposed on the N20m during wakefulness. Isofield mapping at each peak of the high-pass filtered and isolated high-frequency oscillations showed a dipolar pattern and the estimated source for these peaks was the primary somatosensory cortex (area 3b) very close to that for the N20m peak. During sleep, the high-frequency oscillations showed dramatic diminution in amplitude while the N20m amplitude exhibited a moderate increment. This reciprocal relation between the high-frequency oscillations and the N20m during a wake-sleep cycle suggests that they represent different generator substrates. We speculate that the high-frequency oscillations represent a localized activity of the GABAergic inhibitory interneurons of layer 4, which have been shown in animal experiments to respond monosynaptically to thalamo-cortical input with a high-frequency (600–900 Hz) burst of short duration spikes. On the other hand, the underlying N20m represents activity of pyramidal neurons which receive monosynaptic excitatory input from the thalamus as well as a feed-forward inhibition from the interneurons.     

Oscillatory depth as a function of temporal frequency

The percept of oscillatory motion in depth was generated by a luminance modulation of a sinusoidal nature induced within each dot pair of a stationary random assembly of paired dots. The dots were miniature sources of polarized light viewed through a rotating ocular polarizer, which facilitated both the percept of oscillations and the modulation of luminance at any desired frequency. Depth responses were studied as a function of frequency within the 0-2 Hz range. A strong amplitude decrease was noticed at a mean frequency of f(1)=0.81 Hz; oscillations were perceived as 'rectified' for f > f(1) with an additional minimum of crossed-disparity depth at f(2)=1.60 Hz. It is suggested that the intensity modulation of the light beams mapping the stationary stimuli onto the retinae was a likely factor responsible for the observed depth minima and the rectification of faster oscillations. Results are compared to those obtained in a traditional setting, where the percept of oscillations in depth had been generated by disparity variations due to lateral motion of the stimuli.     

The variability of respiratory pattern and gas exchange

It is known, that spectral analysis of heart rate and respiratory variability allows to find out the very low frequency (VLF) rhythm. However it is not known, it is necessary to carry this rhythm to what type of wave processes. The purpose of the present researches was to study the respiratory variability and the variability of gas exchange parameters. 10 healthy subjects have been surveyed. The pneumogramms within 30 minutes spent record, and then a method "breath-by-breath" within 30 minutes registered gas exchange parameters (Ve--lung ventilation, V(O2) -O2 consumption and other parameters). Fast Fourier transform method has found out two groups of the basic peaks. The first--in a range 0.2-0.3 Hz (a time cycle--3-5 s), that corresponds respiratory frequency which size at subjects varied from 12 to 20 per minute. The second--in a range 0.002-0.0075 Hz, that corresponds VLF diapason (a time cycle--1-3.5 minutes). At the analysis pneumogramms rhythms in the same ranges have been established. The carried out researches allow to draw a conclusion on steady character of wave process in a VLF-range. It can be carried to quasi-periodic oscillations type. First oscillator or respiratory frequency it is formed by means of mechanisms of chemoreception. Considering, that V(O2) and V(CO2) are function energy exchange, it is possible to believe, what exactly energy demand define the second oscillator.     

Characterization of electro-olfactogram oscillations and their computational reconstruction

Electro-olfactogram (EOG) oscillations induced by odorant stimulation have been often reported in various vertebrates from fishes to mammals. However, the mechanism of generation of EOG oscillations remains unclear. In the present study, we first characterized the properties of EOG oscillations induced by amino acid odorants in the rainbow trout and then performed a computer simulation based on the main assumption that olfactory receptor neurons (ORNs) have intrinsic oscillatory properties due to two types of voltage-gated ion channels, which have not yet been reported in vertebrate ORNs. EOG oscillations appeared mostly on the peak and decay phases of negative EOG responses, when odorant stimuli at high intensity flowed regularly anterior to posterior olfactory lamellae in the olfactory organ. The appearance of EOG oscillations was dependent on the odorant intensity but not on the flow rate. The maximum amplitude and the maximum power frequency of EOG oscillations were 3.51 +/- 3.35 mV (mean +/- SD, n = 232, range 0.12-16.79 mV) and 10.59 +/- 5.05 Hz (mean +/- SD, n = 232, range 3.51-40.03 Hz), respectively. The simulation represented sufficiently well the characteristics of EOG oscillations; occurrence at high odorant concentration, odorant concentration-dependent amplitude and the maximum power frequency range actually observed. Our results suggest that EOG oscillations are due to the intrinsic oscillatory properties of individual ORNs, which have two novel types of voltage-gated ion channels (resonant and amplifying channels). The simulation program for Macintosh ('oscillation 3.2.4' for MacOS 8.6 or later) is available on the world wide web (http://bio2.sci.hokudai.ac.jp/bio/chinou1/noriyo_home.html).     

The significance of the high-frequency components in the cortical potentials of dogs in a study of learning mechanisms

Electrical activity was studied of five different regions of dogs neocortex in inter-stimuli periods in the process of learning of motor habit of pressing the feeder pedal. Epidural electrodes were used. The processing was performed by means of correlation-spectral analysis in a wide band of 1-256 Hz. Values of cross-correlation coefficients, spectra of power, coherence and phase shifts were obtained. In the process of the habit consolidation the high frequencies power increased significantly (within the limits from 60 to 150-170 osc/sec), as well as the part of high coherence (over 0.75), falling on these limits, with low phase shifts. Relatively slow-wave oscillations (1-20 osc/sec) underwent changes of considerably lesser degree. A greater locality of high frequencies (in comparison with the traditional range of 1-20 Hz) was shown. The question of the nature of high frequency EEG components is discussed.     

Oscillation-Induced Signal Transmission and Gating in Neural Circuits

Reliable signal transmission constitutes a key requirement for neural circuit function. The propagation of synchronous pulse packets through recurrent circuits is hypothesized to be one robust form of signal transmission and has been extensively studied in computational and theoretical works. Yet, although external or internally generated oscillations are ubiquitous across neural systems, their influence on such signal propagation is unclear. Here we systematically investigate the impact of oscillations on propagating synchrony. We find that for standard, additive couplings and a net excitatory effect of oscillations, robust propagation of synchrony is enabled in less prominent feed-forward structures than in systems without oscillations. In the presence of non-additive coupling (as mediated by fast dendritic spikes), even balanced oscillatory inputs may enable robust propagation. Here, emerging resonances create complex locking patterns between oscillations and spike synchrony. Interestingly, these resonances make the circuits capable of selecting specific pathways for signal transmission. Oscillations may thus promote reliable transmission and, in co-action with dendritic nonlinearities, provide a mechanism for information processing by selectively gating and routing of signals. Our results are of particular interest for the interpretation of sharp wave/ripple complexes in the hippocampus, where previously learned spike patterns are replayed in conjunction with global high-frequency oscillations. We suggest that the oscillations may serve to stabilize the replay.     

Spontaneous fluctuations in cerebral blood flow: insights from extended-duration recordings in humans

To determine the dependence of cerebral blood flow (CBF) on arterial pressure over prolonged time periods, we measured beat-to-beat changes in mean CBF velocity in the middle cerebral artery (transcranial Doppler) and mean arterial pressure (Finapres) continuously for 2 h in six healthy subjects (5 men and 1 woman, 18-40 yr old) during supine rest. Fluctuations in velocity and pressure were quantified by the range [(peak - trough)/mean] and coefficients of variation (SD/mean) in the time domain and by spectral analysis in the frequency domain. Mean velocity and pressure over the 2-h recordings were 60 +/- 7 cm/s and 83 +/- 8 mmHg, associated with ranges of 77 +/- 8 and 89 +/- 10% and coefficients of variation of 9.3 +/- 2.2 and 7.9 +/- 2.3%, respectively. Spectral power of the velocity and pressure was predominantly distributed in the frequency range of 0.00014-0.1 Hz and increased inversely with frequency, indicating characteristics of an inverse power law (1/f(alpha)). However, linear regression on a log-log scale revealed that the slope of spectral power of pressure and velocity was steeper in the high-frequency (0.02-0.5 Hz) than in the low-frequency range (0.002-0.02 Hz), suggesting different regulatory mechanisms in these two frequency ranges. Furthermore, the spectral slope of pressure was significantly steeper than that of velocity in the low-frequency range, consistent with the low transfer function gain and low coherence estimated at these frequencies. We conclude that 1) long-term fluctuations in CBF velocity are prominent and similar to those observed in arterial pressure, 2) spectral power of CBF velocity reveals characteristics of 1/f(alpha), and 3) cerebral attenuation of oscillations in CBF velocity in response to changes in pressure may be more effective at low than that at high frequencies, emphasizing the frequency dependence of cerebral autoregulation.     

In situ measurements of external pH and optical density oscillations in Dictyostelium discoideum aggregates

In situ measurements of extracellular pH by means of microelectrodes and in situ measurements of optical density were performed on aggregating cells of Dictyostelium discoideum. Early aggregation stage AX2 cells showed sinusoidal pH oscillations, which could be inhibited by the specific relay inhibitor caffeine, indicating that they were coupled to cAMP oscillations. Sometimes biphasic pH oscillations were found, which can be explained by the superposition of two harmonic pH oscillations. These harmonic oscillations might arise by gating of the cAMP signal; a part of the cells respond to every cAMP signal and another subpopulation to every second cAMP pulse. Late aggregation-stage cells showed complex changes of the extracellular pH, which could be inhibited by caffeine. Optical density measurements of wave propagation in aggregation streams of HG220 also revealed gating behavior. In addition to sinusoidal optical density oscillations, biphasic and still more complex oscillations were observed.     

Different origins of gamma rhythm and high-gamma activity in macaque visual cortex

During cognitive tasks electrical activity in the brain shows changes in power in specific frequency ranges, such as the alpha (8-12 Hz) or gamma (30-80 Hz) bands, as well as in a broad range above ～80 Hz, called the high-gamma band. The role or significance of this broadband high-gamma activity is unclear. One hypothesis states that high-gamma oscillations serve just like gamma oscillations, operating at a higher frequency and consequently at a faster timescale. Another hypothesis states that high-gamma power is related to spiking activity. Because gamma power and spiking activity tend to co-vary during most stimulus manipulations (such as contrast modulations) or cognitive tasks (such as attentional modulation), it is difficult to dissociate these two hypotheses. We studied the relationship between high-gamma power, gamma rhythm, and spiking activity in the primary visual cortex (V1) of awake monkeys while varying the stimulus size, which increased the gamma power but decreased the firing rate, permitting a dissociation. We found that gamma power became anti-correlated with the high-gamma power, suggesting that the two phenomena are distinct and have different origins. On the other hand, high-gamma power remained tightly correlated with spiking activity under a wide range of stimulus manipulations. We studied this relationship using a signal processing technique called Matching Pursuit and found that action potentials are associated with sharp transients in the LFP with broadband power, which is visible at frequencies as low as ～50 Hz. These results distinguish broadband high-gamma activity from gamma rhythms as an easily obtained and reliable electrophysiological index of neuronal firing near the microelectrode. Further, they highlight the importance of making a careful dissociation between gamma rhythms and spike-related transients that could be incorrectly decomposed as rhythms using traditional signal processing methods.     

Role of membrane potential in vasomotion of isolated pressurized rat arteries

Vasomotion, the phenomenon of vessel diameter oscillation, regulates blood flow and resistance. The main parameters implicated in vasomotion are particularly the membrane potential and the cytosolic free calcium in smooth muscle cells. In this study, these parameters were measured in rat perfused-pressurized mesenteric artery segments. The application of norepinephrine (NE) caused rhythmic diameter contractions and membrane potential oscillations (amplitude; 5.3 +/- 0.3 mV, frequency; 0.09 +/- 0.01 Hz). Verapamil (1 microM) abolished this vasomotion. During vasomotion, 10(-5) M ouabain (Na(+)-K(+) ATPase inhibitor) decreased the amplitude of the electrical oscillations but not their frequency (amplitude; 3.7 +/- 0.3 mV, frequency; 0.08 +/- 0.002 Hz). Although a high concentration of ouabain (10(-3) M) (which exhibits non-specific effects) abolished both electrical membrane potential oscillations and vasomotion, we conclude that the Na+-K+ ATPase could not be implicated in the generation of the membrane potential oscillations. We conclude that in rat perfused-pressurized mesenteric artery, the slow wave membrane type of potential oscillation by rhythmically gating voltage-dependent calcium channels, is responsible for the oscillation of intracellular calcium and thus vasomotion.     

High-frequency oscillations and sequence generation in two-population models of hippocampal region CA1

Hippocampal sharp wave/ripple oscillations are a prominent pattern of collective activity, which consists of a strong overall increase of activity with superimposed (140 − 200 Hz) ripple oscillations. Despite its prominence and its experimentally demonstrated importance for memory consolidation, the mechanisms underlying its generation are to date not understood. Several models assume that recurrent networks of inhibitory cells alone can explain the generation and main characteristics of the ripple oscillations. Recent experiments, however, indicate that in addition to inhibitory basket cells, the pattern requires in vivo the activity of the local population of excitatory pyramidal cells. Here, we study a model for networks in the hippocampal region CA1 incorporating such a local excitatory population of pyramidal neurons. We start by investigating its ability to generate ripple oscillations using extensive simulations. Using biologically plausible parameters, we find that short pulses of external excitation triggering excitatory cell spiking are required for sharp/wave ripple generation with oscillation patterns similar to in vivo observations. Our model has plausible values for single neuron, synapse and connectivity parameters, random connectivity and no strong feedforward drive to the inhibitory population. Specifically, whereas temporally broad excitation can lead to high-frequency oscillations in the ripple range, sparse pyramidal cell activity is only obtained with pulse-like external CA3 excitation. Further simulations indicate that such short pulses could originate from dendritic spikes in the apical or basal dendrites of CA1 pyramidal cells, which are triggered by coincident spike arrivals from hippocampal region CA3. Finally we show that replay of sequences by pyramidal neurons and ripple oscillations can arise intrinsically in CA1 due to structured connectivity that gives rise to alternating excitatory pulse and inhibitory gap coding; the latter denotes phases of silence in specific basket cell groups, which induce selective disinhibition of groups of pyramidal neurons. This general mechanism for sequence generation leads to sparse pyramidal cell and dense basket cell spiking, does not rely on synfire chain-like feedforward excitation and may be relevant for other brain regions as well.     

Quantitative estimation of connection of the heart rate rhythm with motor activity in rat fetuses

In rat fetuses over E17-20 with preserved placental circulation with use of mathematical analysis there were revealed value and character of connections of slow wave oscillations of the heart rhythm with motor activity for 30 min of observation. In the software PowerGraph 3.3.8, normalization and filtration of the studied signals were performed in three frequency diapasons: D1-0.02–0.2 Hz (5–50 s), D2-0.0083-0.02 Hz (50 s-2 min), and D3-0.0017–0.0083 Hz (2–10 min). The EMG curves filtrated by diapasons or piezograms were compared with periodograms in the corresponding diapasons of the heart rhythm variations. In the software “Origin 8.0”, quantitative estimation of the degree of intersystemic interrelations for each frequency diapason was performed by Pearson correlation of coefficient, by the correlation connection value, and by the time shift of maximum of cross-correlation function. It has been established that in the frequency D1, regardless of age, the connection of heart rhythm oscillations with motor activity is expressed weakly. In the frequency diapason D2, the connection in most cases is located in the zone of weak and moderate correlations. In the multiminute diapason (D3), the connection is more pronounced. The number of animals that have a significant value of the correlation connection rises. The fetal motor activity fires in the decasecond diapason in all age groups are accompanied by short-time decelerations of the heart rhythms. In the minute diapason, there is observed a transition from positive connections in E17 and E18 to the negative ones in E19-20. Results of the study are considered in association with age-related changes of ratios of positive and negative oscillations of the heart rhythm change depending on the character of motor activity.     

Involvement of sympathetic nerve activity in skin blood flow oscillations in humans

We have used the wavelet transform to evaluate the time-frequency content of laser-Doppler flowmetry (LDF) signals measured simultaneously on the surfaces of free microvascular flaps deprived of sympathetic nerve activity (SNA), and on adjacent intact skin, in humans. It was thereby possible to determine the frequency interval within which SNA manifests itself in peripheral blood flow oscillations. The frequency interval from 0.0095 to 2 Hz was examined and was divided into five subintervals: I, approximately 0.01 Hz; II, approximately 0.04 Hz; III, approximately 0.1 Hz; IV, approximately 0.3 Hz; and V, approximately 1 Hz. The average value of the LDF signal in the time domain as well as the mean amplitude and total power in the interval from 0.0095 to 2 Hz and amplitude and power within each of the five subintervals were significantly lower for signals measured on the free flap (P < 0.002). The normalized spectral amplitude and power in the free flap were significantly lower in only two intervals: I, from 0.0095 to 0.021 Hz; and II, from 0.021 to 0.052 Hz (P < 0.05); thus indicating that SNA is manifested in at least one of these frequency intervals. Because interval I has recently been shown to be the result of vascular endothelial activity, we conclude that we have identified SNA as influencing blood flow oscillations in normal tissues with repetition times of 20-50 s or frequencies of 0.02-0.05 Hz.     

Transcranial electrical currents to probe EEG brain rhythms and memory consolidation during sleep in humans

Previously the application of a weak electric anodal current oscillating with a frequency of the sleep slow oscillation (～0.75 Hz) during non-rapid eye movement sleep (NonREM) sleep boosted endogenous slow oscillation activity and enhanced sleep-associated memory consolidation. The slow oscillations occurring during NonREM sleep and theta oscillations present during REM sleep have been considered of critical relevance for memory formation. Here transcranial direct current stimulation (tDCS) oscillating at 5 Hz, i.e., within the theta frequency range (theta-tDCS) is applied during NonREM and REM sleep. Theta-tDCS during NonREM sleep produced a global decrease in slow oscillatory activity conjoint with a local reduction of frontal slow EEG spindle power (8-12 Hz) and a decrement in consolidation of declarative memory, underlining the relevance of these cortical oscillations for sleep-dependent memory consolidation. In contrast, during REM sleep theta-tDCS appears to increase global gamma (25-45 Hz) activity, indicating a clear brain state-dependency of theta-tDCS. More generally, results demonstrate the suitability of oscillating-tDCS as a tool to analyze functions of endogenous EEG rhythms and underlying endogenous electric fields as well as the interactions between EEG rhythms of different frequencies.     

Diaphragm‐based optical fiber sensor for pulse wave monitoring and cardiovascular diseases diagnosis

Arterial pulse wave has been considered as a vital sign in assessment of cardiovascular diseases. Noninvasive pulse sensor with compact structure, immunity to electro‐magnetic interference and high sensitivity is the research focus in recent years. While, optical fiber biosensor is a competitive option to meet these needs. Here, a diaphragm‐based optical fiber pulse sensor was proposed to achieve high‐precision radial pulse wave monitoring. A wearable device was developed, composed of a sports wristband and an aluminum diaphragm‐based optical fiber sensor tip of only 1 cm in diameter, which was highly sensitive to the weak acoustic signal. In particular, coherent phase detection was adopted to improve detection signal‐to‐noise ratio, so as to recover the high‐fidelity pulse waveforms. A clinical experiment was carried out to detect and morphological analyze the pulse waveforms of four subjects, the results of which preliminarily demonstrated the feasibility of pulse diagnosis method. The proposed pulse fiber sensor provides a comfortable way for pulse diagnosis, which is promising in early cardiovascular diseases indicating.     

Causes and consequences of oscillations in the cerebellar cortex

Cerebellar high-frequency oscillations have been observed for many decades, but their underlying mechanisms have remained enigmatic. In this issue of Neuron, two papers indicate that specific intrinsic mechanisms in the cerebellar cortex contribute to the generation of these oscillations. Middleton et al. show that GABA(A) receptor activation and nonchemical transmission are required for nicotine-dependent oscillations at 30-80 Hz and 80-160 Hz, respectively, while de Solages et al. provide evidence that recurrent inhibition by Purkinje cells is essential for oscillations around 200 Hz.