Dynamic processes in the human EEG

The possible mechanisms which determine the temporal dynamics of discrete narrow-band spectral components of human EEG recorded by a single electrode in the state of rest were analyzed. The dynamics of short-segment spectra was observed by application of Fast Fourier Transform (FFT) to 5-s EEG epochs successively shifted by 0.32 s. For each subject the matrices were formed and presented in a graphic mode. Matrix rows represented the number of points in each short-segment spectrum, and the columns represented the number of short-segment spectra. The columns reflect the amplitude dynamics of a given frequency, and power transition between the columns reflects the frequency dynamics. The most common type of the amplitude dynamics consisted in short (2-8 s) periods of stable activity of the discrete spectral components replaced by symmetrical bifurcation or confluence of spectral peaks. The obtained results suggest by the presence of both additive and multiplicative mechanisms of oscillatory interactions in the EEG. More detailed analysis of the amplitude-modulated EEG processes is provided by application of some additive features of the FFT to both EEG and computer-simulated signals.     

Baroreflex stabilization of the double (pressure-rate) product at 0.05 Hz in conscious rabbits

The product of heart rate (HR) and systolic blood pressure (SBP), the double product (DP), is an indirect index of cardiac oxygen consumption. We used spectral analysis to test the hypothesis that baroreflex adjustments of HR stabilize the DP during spontaneous variations in SBP. SBP and HR were recorded by telemetry in five male conscious rabbits. HR and SBP power spectra each exhibited a low frequency peak at approximately 0.05 Hz that was associated with high (>0.5) spectral coherence and a positive phase relationship between SBP and HR (SBP leading). A prominent peak was absent in the spectra of their product, suggesting that SBP and HR interacted to reduce DP variability in this frequency region. In contrast, a prominent 0.05-Hz peak was present in the power spectrum of calculated surrogates of the DP in which reflex interactions between HR and SBP had been removed. Our results suggest that baroreflex adjustments of HR stabilize the DP during spontaneous low-frequency variations in SBP in conscious rabbits.     

Measurement and theory of wheezing breath sounds

We measured the time and frequency domain characteristics of breath sounds in seven asthmatic and three nonasthmatic wheezing patients. The power spectra of the wheezes were evaluated for frequency, amplitude, and timing of peaks of power and for the presence of an exponential decay of power with increasing frequency. Such decay is typical of normal vesicular breath sounds. Two patients who had the most severe asthma had no exponential decay pattern in their spectra. Other asthmatic patients had exponential patterns in some of their analyzed sound segments, with a range of slopes of the log power vs. log frequency curves from 5.7 to 17.3 dB/oct (normal range, 9.8-15.7 dB/oct). The nonasthmatic wheezing patients had normal exponential patterns in most of their analyzed sound segments. All patients had sharp peaks of power in many of the spectra of their expiratory and inspiratory lung sounds. The frequency range of the spectral peaks was 80-1,600 Hz, with some presenting constant frequency peaks throughout numerous inspiratory or expiratory sound segments recorded from one or more pickup locations. We compared the spectral shape, mode of appearance, and frequency range of wheezes with specific predictions of five theories of wheeze production: 1) turbulence-induced wall resonator, 2) turbulence-induced Helmholtz resonator, 3) acoustically stimulated vortex sound (whistle), 4) vortex-induced wall resonator, and 5) fluid dynamic flutter. We conclude that the predictions by 4 and 5 match the experimental observations better than the previously suggested mechanisms. Alterations in the exponential pattern are discussed in view of the mechanisms proposed as underlying the generation and transmission of normal lung sounds. The observed changes may reflect modified sound production in the airways or alterations in their attenuation when transmitted to the chest wall through the hyperinflated lung.     

Regional features of electrical reactions (in the frequency band of 1-225 Hz) in the cerebral cortex to conditioned stimuli in the course of instrumental conditioning

Power spectra of short-term (less than 1 s) EEG-reactions (in the frequency band of 1-225 Hz) were studied in dogs in the course of instrumental food conditioning. These reactions were observed in different areas of the cortex in response to positive and differentiated conditioned stimuli. Regional features between the spectra were found both in the power level and frequency structure. The power of the reactions in the visual and parietal areas of the left hemisphere was higher than in the motor areas. Power spectra of reactions to differentiated stimuli were significantly lower than the spectra of reactions to positive stimuli mainly owing to the high-frequency components (80-225 Hz). In these both cases, prestimulus power spectra did not differ. The frequency structure of corresponding EEG-reactions consisted of individual spectral peaks, mainly both gamma (30-80 Hz) and higher-frequency (80-225 Hz) bands.     

Evoked frequency stabilization in the electrical activity of the cat brain

In this study, our previous results on the important relation between EEG and EPs were extended by experiments with chronically implanted and freely moving cats, which had electrodes at the acoustical cortex, inferior colliculus and reticular formation. During the experiments the frequency stabilization upon sound stimulation was shown in the frequency domain by comparison of the pre-stimulus power spectra and post-stimulus amplitude frequency characteristics. Comparative frequency domain analysis of about 75 EEG-EPograms (sample of spontaneous activities just prior to stimulation and single evoked potentials following the stimulation), which were recorded from all the brain nuclei mentioned above and from each of the 11 cats, was performed as follows: 1) Power spectra of the EEG-records prior to stimulus were evaluated. 2) Instantaneous frequency characteristics of single EPs were obtained by the Fourier transform. 3) Distribution of the amplitude maxima of the EP-frequency characteristics and the distribution of the EEG-spectral peaks were compared by plotting two types of histograms containing relevant spectral peaks before and after the stimulation. In a frequency range between 1–1000 Hz, the frequency distribution of the EP records from RF and IC were accumulated in narrow discrete frequency channels, whereas, the distribution of the spectral peaks of the EEG depicted frequency spread in broad channels. The frequency stabilization of the EP records from GEA, in the alpha frequency range, was also observed. This effect was described by a factor which we called as the Frequency Stabilization Factor. The results presented in this study showed that the frequency stabilization of the brain's electrical activity induced by sensory stimulation displayed a fluctuation leading to frequency stabilization factors between 0.95 and 5.00. The frequency stabilization and relevant power enhancement upon stimulation strongly support our contention that evoked potential results from the frequency stabilization of the spontaneous activity, triggered by stimulation.Supported by Grant No. TAG-345 of the Scientific and Technical Research Council of Turkey     

Lateral line nerve fibers do not code bulk water flow direction in turbulent flow

The discharges of anterior and posterior lateral line nerve afferents were recorded while stimulating goldfish, Carassius auratus, with bulk water flow. With increasing flow velocity lateral line afferents increased their discharge rates. However, an increased response to flow rates occurred even if flow direction was reversed. Thus, individual lateral line afferents did not encode the direction of running water. Frequency spectra of the water motions quantified with particle image velocimetry revealed flow fluctuations that increased with increasing flow velocity. Maximal spectral amplitudes of the flow fluctuations were below 5 Hz (bulk flow velocity 4–15 cm s⁻¹). The frequency spectra of the firing rates of lateral line afferents also showed an increase in amplitude when fish were exposed to running water. The maximal spectral amplitudes of the recorded data were in the frequency range 3–8 Hz. This suggests that the lateral line afferents mainly responded to the higher frequency fluctuations that developed under flow conditions, but not to the direct current flow or the lower frequency fluctuations. Although individual lateral line afferents encoded neither flow velocity nor flow direction we suggest that higher order lateral line neurons can do so by monitoring flow fluctuations as they move across the surface of the fish.     

Spectral characteristics of vowel-like sounds in children of the first year of life and speech development

To study the continuity in speech development, an investigation of vowel-like sounds recorded in the course of longitudinal research of speech formation was carried out in 12 infants beginning with the first month up to 12 months of their life. It was revealed that features ensuring separation of vowel-like sounds are specific by their amplitude relation and frequency location of the most expressed spectral maxima, including the maxima corresponding to the fundamental frequency. As fundamental frequency increased, the vowel-like sounds [a], [u], [i] began to exhibit specific changes of the amplitude ratios of the spectral maxima. It was established that peculiarities of frequency positions of spectral maxima and relations of their amplitudes may be the very features on the bases of which children compare their own vowel-like sounds to the vowels of the adults in sound imitation. These findings and literature data corroborated the opinion of continuity in speech development, beginning with the early preverbal vocalizations.     

Surface EMG alterations induced by underwater recording.

BACKGROUND AND PURPOSE: This study aims to verify if amplitude and spectral characteristics of surface EMG signal are modified due to recording in a wet environment. METHODS: Isometric contractions of the biceps brachii muscle of ten subjects were performed in several different set-up combinations, both in dry (D) and in water from hydrotherapy pools (PW), with (PWM) or without moving the pool water and with (T) or without water-resistant adhesive taping. RESULTS: In PW condition the amplitude of the recorded signal is reduced to 5-10% of the corresponding signal recorded in D condition. In PWM the power spectrum is drastically reduced and altered by the water movement that introduces an increase of spectral power in the frequency range 0-20 Hz. The use of T modality allows to record signals with both amplitude and spectral frequencies comparable with those obtained in the D conditions. DISCUSSION AND CONCLUSION: This work demonstrates the need for water resistant taping when EMG signals are recorded in water. Signals recorded without such a protective film are strongly affected in their amplitude and frequency characteristics by the conductivity and the movement of water.     

Topography of alpha and theta oscillatory responses upon auditory and visual stimuli in humans

Brain resonance phenomena and induced rhythms in the brain recently gained importance in electroencephalographic, magnetoencephalographic and cellular studies (Ba\c sar and Bullock 1992). It was hypothesized that evoked potentials are superpositions of induced rhythms caused by resonance phenomena in neural populations (Ba\c sar et al. 1992). According to Ba\c sar (1972), such resonance phenomena are reflected in the main peaks of the amplitude frequency characteristics computed from EEG responses. The present study is based on a frequency domain approach for the evaluation of topography- and modality-dependent properties of oscillatory brain responses. EEG and evoked potentials were recorded from vertex, parietal and occipital scalp locations in 24 volunteers. Two combined methods were applied: (1) amplitude frequency characteristics were computed from the transient evoked responses, and (2) frequency components of the transient responses were obtained by adaptive digital filtering. Our main goal was to investigate theta (4--7 Hz) and alpha (8--15 Hz) response components. (1) Amplitude frequency characteristics. Auditory stimuli elicited theta-alpha compound responses in the 4--11 Hz frequency band (e.g. typical peaking frequency around 7 Hz for vertex recordings). Visual stimuli elicited alpha responses (e.g. typical peaking frequency for vertex recordings around 9--12 Hz). Frequency maxima for visual stimuli thus had main peaks at higher frequency values than frequency maxima for auditory stimuli. (2) Digital filtering confirmed these results: for vertex recordings, theta vs. alpha response amplitudes were 9 vs 6 for auditory stimuli and 5 vs 5 for visual stimuli, thus confirming a shift towards higher frequencies, i.e. a more prominent contribution of the alpha range, in the case of visual stimulation. We hypothesize that these properties might reflect site- and modality-specific features of stimulus encoding in the brain in which resonance properties of neuron populations are involved. Furthermore we emphasize the utility of the systems theory approach for a better understanding of brain function by means of EPs. Received: 25 February 1994 / Accepted in revised form: 5 August 1994     

Intramuscular and surface electromyogram changes during muscle fatigue

Twelve male subjects were tested to determine the effects of motor unit (MU) recruitment and firing frequency on the surface electromyogram (EMG) frequency power spectra during sustained maximal voluntary contraction (MVC) and 50% MVC of the biceps brachii muscle. Both the intramuscular MU spikes and surface EMG were recorded simultaneously and analyzed by means of a computer-aided intramuscular spike amplitude-frequency histogram and frequency power spectral analysis, respectively. Results indicated that both mean power frequency (MPF) and amplitude (rmsEMG) of the surface EMG fell significantly (P less than 0.001) together with a progressive reduction in MU spike amplitude and firing frequency during sustained MVC. During 50% MVC there was a significant decline in MPF (P less than 0.001), but this decline was accompanied by a significant increase in rmsEMG (P less than 0.001) and a progressive MU recruitment as evidenced by an increased number of MUs with relatively large spike amplitude. Our data suggest that the surface EMG amplitude could better represent the underlying MU activity during muscle fatigue and the frequency powers spectral shift may or may not reflect changes in MU recruitment and rate-coding patterns.     

Motor unit activity and surface electromyogram power spectrum during increasing force of contraction

Twelve male subjects were tested to determine the relationship between motor unit (MU) activities and surface electromyogram (EMG) power spectral parameters with contractions increasing linearly from zero to 80% of maximal voluntary contraction (MVC). Intramuscular spike and surface EMG signals recorded simultaneously from biceps brachii were analyzed by means of a computer-aided intramuscular MU spike amplitude-frequency (ISAF) histogram and an EMG frequency power spectral analysis. All measurements were made in triplicate and averaged. Results indicate that there were highly significant increases in surface EMG amplitude (71 +/- 31.3 to 505 +/- 188 microV, p less than 0.01) and mean power frequency (89 +/- 13.3 to 123 +/- 23.5 Hz, p less than 0.01) with increasing force. These changes were accompanied by progressive increases in the firing frequency of MU's initially recruited, and of newly recruited MU's with relatively larger spike amplitudes. The group data in the ISAF histograms revealed significant increases in mean spike amplitude (412 +/- 79 to 972 +/- 117 microV, p less than 0.01) and mean firing frequency (17.8 +/- 5.4 to 24.7 +/- 4.1 Hz, p less than 0.01). These data suggest that surface EMG spectral analysis can provide a sensitive measure of the relative changes in MU activity during increasing force output.     

Brainstem auditory evoked potentials in the rabbit.

Eight white New Zealand rabbits were submitted to auditory stimulation in order to obtain normative BAEP parameters. A monaural alternating 0.1 ms click stimulation at 20 Hz, 90 dB was used. Two series of 1000 responses were averaged (10 ms time-base, 160-3000 Hz band-pass) and highly reproducible peaks were obtained. Peaks P1, P2, P3, P4 were obtained in all ipsilateral recordings, whereas peak P5 was detectable in only 6 animals. In contralateral recordings P1 was absent and the following peaks were similar to those of ipsilateral recordings. Normative values of absolute and interpeak latencies, peak amplitudes and amplitude ratios were obtained. The procedure was repeated 24 hours after basal recordings and measures of test-retest variability were obtained.     

Optimization of resolution and sensitivity of 4D NOESY using Multi-dimensional Decomposition

Highly resolved multi-dimensional NOE data are essential for rapid and accurate determination of spatial protein structures such as in structural genomics projects. Four-dimensional spectra contain almost no spectral overlap inherently present in lower dimensionality spectra and are highly amenable to application of automated routines for spectral resonance location and assignment. However, a high resolution 4D data set using conventional uniform sampling usually requires unacceptably long measurement time. Recently we have reported that the use of non-uniform sampling and multi-dimensional decomposition (MDD) can remedy this problem. Here we validate accuracy and robustness of the method, and demonstrate its usefulness for fully protonated protein samples. The method was applied to 11 kDa protein PA1123 from structural genomics pipeline. A systematic evaluation of spectral reconstructions obtained using 15–100% subsets of the complete reference 4D ¹H–¹³C–¹³C–¹H NOESY spectrum has been performed. With the experimental time saving of up to six times, the resolution and the sensitivity per unit time is shown to be similar to that of the fully recorded spectrum. For the 30% data subset we demonstrate that the intensities in the reconstructed and reference 4D spectra correspond with a correlation coefficient of 0.997 in the full range of spectral amplitudes. Intensities of the strong, middle and weak cross-peaks correlate with coefficients 0.9997, 0.9965, and 0.83. The method does not produce false peaks. 2% of weak peaks lost in the 30% reconstruction is in line with theoretically expected noise increase for the shorter measurement time. Together with good accuracy in the relative line-widths these translate to reliable distance constrains derived from sparsely sampled, high resolution 4D NOESY data.     

Power spectral analysis of heart rate variability for assessment of diurnal variation of autonomic nervous activity in miniature swine.

BACKGROUND AND PURPOSES: The purpose of the study was to document diurnal variation of autonomic nervous functions by use of power spectral analysis of heart rate (HR) variability. METHODS: To clarify characteristics of power spectral analysis of HR variability, electrocardiogram (ECG), blood pressure (BP), and respiratory (Resp) waveform simultaneously were recorded. RESULTS: Two major spectral components were examined at low (LF)- and high (HF)-frequency bands for HR variability. Coherence between HR and Resp variabilities and HR and BP variabilities was maximal at approximately 0.14 and 0.03 Hz, respectively. On the basis of these data, two frequency bands of interest--LF (0.01 to 0.07 Hz) and HF (0.07 to 1.0 Hz)--were defined. Autonomic blockade studies indicated that the parasympathetic system mediated the HF and LF components, whereas the sympathetic system mediated only the LF component; HR had a diurnal pattern. The LF and HF bands in the dark phase tended to be higher than those in the light phase. The LF-to-HF ratio had a diurnal pattern similar to that of the HR. CONCLUSION: Parasympathetic nervous activity in miniature swine may be predominant in the dark phase. The characteristics of power spectra and diurnal variations of autonomic nervous functions are almost the same as those of humans. Therefore, miniature swine may be a useful animal model for future biobehavioral and pharmacotoxicologic studies.     

Effect of recording electrode position along a muscle fibre on surface potential power spectrum

Extracellular action potentials produced by a muscle fibre of finite length were calculated for recordings at the skin surface. The sensitivity of power spectra to variations in propagation velocity (ν) and intracellular action potential (IAP) duration (T_in) was studied theoretically. The magnitude and distribution of the spectral power of muscle fibre potentials depend on the electrode longitudinal position. The relative shifts of the spectra in dB induced by variation in ν or T_in hardly depend on the longitudinal position of the electrode. A variation in ν affects only the power spectrum positive slope and the initial part of the high-frequency roll-off and a variation in T_in affects only the remaining part of the high-frequency roll-off. The total spectral amplitude is practically non-sensitive to variations in the wavelength, b = ν.T_in. The total power is sensitive to variations in ν, T_in as well as in b, and its relative changes depend on the electrode longitudinal position. The whole power spectrum is shifted along the frequency axis and mode (F_max), median (F_med) and mean (F_mean) frequencies have practically equal percentage changes only when ν and T_in vary jointly in such a way that the product ν.T_in keeps unchanged.     

Urinary proteome profiling using microfluidic technology on a chip

Clinical diagnostics and biomarker discovery are the major focuses of current clinical proteomics. In the present study, we applied microfluidic technology on a chip for proteome profiling of human urine from 31 normal healthy individuals (15 males and 16 females), 6 patients with diabetic nephropathy (DN), and 4 patients with IgA nephropathy (IgAN). Using only 4 microL of untreated urine, automated separation of proteins/peptides was achieved, and 1-7 (3.8 +/- 0.3) spectra/bands of urinary proteins/peptides were observed in the normal urine, whereas 8-16 (11.3 +/- 1.2) and 9-14 (10.8 +/- 1.2) spectra were observed in urine samples of DN and IgAN, respectively. Coefficient of variations of amplitudes of lower marker (1.2 kDa), system spectra (6-8 kDa), and upper marker (260.0 kDa) were 22.84, 24.92, and 32.65%, respectively. ANOVA with Tukey post-hoc multiple comparisons revealed 9 spectra of which amplitudes significantly differed between normal and DN urine (DN/normal amplitude ratios ranged from 2.9 to 3102.7). Moreover, the results also showed that 3 spectra (with molecular masses of 12-15, 27-28, and 34-35 kDa) were significantly different between DN and IgAN urine (DN/IgAN amplitude ratios ranged from 3.9 to 7.4). In addition to the spectral amplitudes, frequencies of some spectra could differentiate the normal from the diseased urine but could not distinguish between DN and IgAN. There was no significant difference, regarding the spectral amplitude or frequency, observed between males and females. These data indicate that the microfluidic chip technology is applicable for urinary proteome profiling with potential uses in clinical diagnostics and biomarker discovery.     

Functional restitution of cardiac control in heart transplant patients

Cardiovascular control is fundamentally altered after heart transplantation (HT) because of surgical denervation of the heart. The main goal of this work was the noninvasive characterization of cardiac rate control mechanisms after HT and the understanding of their nature. We obtained 25 recordings from 13 male HT patients [age = 28-68 yr, time after transplant (TAT) = 0.5-62.5 mo]. The control group included 14 healthy men (age = 28-59 yr). Electrocardiogram, continuous blood pressure (BP), and respiration were recorded for 45 min in the supine position and then during active change of posture (CP) to standing. The signals were analyzed in the time domain [mean and variance of heart rate (HR) and rise time of HR in response to CP] and the frequency domain [low and high frequency (LF and HF)]. Our principal finding was the consistent pattern of evolution of the HR response to standing: from no response, via a slow response (>40 s, TAT > 6 wk), to a fast increase (<20 s, TAT > 24 mo). HR response correlated with TAT (P < 0.001). LF correlated with HR response to CP (P < 0.0001); HF and HR did not. An important finding was the presence of very-high-frequency peaks in the power spectrum of HR and BP fluctuations. Extensive arrhythmias tended to appear at the TAT that corresponds to the transition from slow to fast HR response to CP. Our results indicate a biphasic evolution in cardiac control mechanisms from lack of control to a first-order control loop followed by partial sympathetic reinnervation and, finally, the direct effect of the old sinoatrial node on the pacemaker cell of the new sinoatrial node. There was no indication of vagal reinnervation.     

Features of parkinsonian and essential tremor of the human hand

Using spectral, wavelet, multifractal, and recurrence analyses we examined the features of involuntary shaking (tremor) that occur during the performance of a given motor task. The task was to maintain the efforts of fingers under isometric conditions by a healthy subject, a patient with primary bilateral parkinsonism, and a patient with essential tremor syndrome. The physiological tremor was characterized by the lowest amplitude, a broad power spectrum, the lowest energy of the wavelet spectrum, the highest degree of multifractality, the lowest degree of determinism, and the highest entropy of the recurrence time density. In the case of the essential tremor we observed a significant enhancement of the wavelet spectrum energy and a decrease of the oscillation complexity. This was evident via the occurrence of clear peaks in the power spectra, a decrease in the degree of multifractality, the emergence of a quasi-periodic structure in the recurrence diagrams, an increase in determinism and a decrease of the entropy of recurrence time density. All these trends were increased for the parkinsonian tremor data. These characteristics enable us to quantitatively estimate the degree of deviation of motor function from the healthy case.     

Analysis of the robustness of spectral indices during ventricular fibrillation

The spatiotemporal characteristics of cardiac fibrillation are often investigated by using indices extracted from the spectrum of cardiac signals. However different signal acquisition systems may produce signals of different spectra and affect the estimation of some spectral indices. In this study, we investigate the robustness of four spectral indices previously proposed for describing fibrillation, namely the dominant frequency (DF), the peak frequency (PF), the median frequency (MF) and the organization index (OI). The effects of different lead configurations on the values of the spectral indices are statistically quantified and further analyzed in a database consisting of unipolar and bipolar intracardiac electrograms (EGM), recorded by implantable cardioverter-defibrillators during ventricular fibrillation. Our analysis shows that the lead configuration significantly affects the PF, the MF and the OI, whereas the DF remains unaffected. We further explore the nature of cardiac spectrum and show that unipolar EGM concentrate power at lower frequencies than bipolar EGM. We conclude that indices that depend on the envelope of the spectrum of cardiac signals are in general sensitive to the lead configuration.     

兔血压功率谱低频峰与交感神经活动的关系

观察了阿托品化家兔血压功率谱低频峰与交感神经活动的关系。结果表明,血压功率谱低频峰与交感神经活动有关,当交感张力增加,则低频峰密度增加,反之则降低;肾神经放电与低频峰密度呈正线性相关(r=0.89,P<0.0001)。因此,在阻断副交感神经的条件下,血压功率谱低频峰可以客观、定量地反映阻力血管的交感神经活动水平。