Electroencephalographic characteristics of cognitive-specific alerting attention in verbal learning: III. Localized characteristics of EEG spatial synchronization

Electroencephalograms (EEGs) were recorded in 19 standard derivations in 88 healthy subjects (students) in the state of rest with eyes open and during memorization (learning) of verbal bilingual semantic pairs (the Latin and Russian languages) and retrieval of information from memory (control). The estimates of EEG coherence in these states were compared for the following frequency bands: θ (4–7 Hz), α₁ (7–10 Hz), α₂ (10–13 Hz), β₁ (13–18 Hz), β₂ (18–30 Hz), and γ (30–40 Hz). Compared to the state of rest, the decrease in coherence in the pairs of derivations from the frontal and central cortical areas in all EEG frequency bands was the most pronounced for memorization, and the increase in coherence in the interhemispheric derivation pairs of the parietal-occipital region in most of the frequency bands was the most pronounced for retrieval. In addition, in the pairs formed by derivations from the parietal-occipital region with derivations from the frontal and central regions, retrieval is also characterized by an increase in coherence in the β₂ and γ bands along with its decrease in the low-frequency ranges. The dynamics of EEG coherence, when comparing the states of memorization and retrieval, is more statistically significant in the interhemispheric and cross-hemispheric pairs of derivations than in the intrahemispheric pairs. The revealed topographic specificity of the dynamics of EEG coherence owing to the change of state is considered in terms of the notion on cognitive-specific forms of sustained goal-directed mental attention.     

Differential effects of aging on EEG after baclofen administration

Baclofen is a selective gamma-aminobutyric acid (GABA) type B agonist that may have important medicinal uses, such as in analgesics and drug addiction treatment. In addition, evidence is accumulating that suggests GABAergic-mediated neurotransmission is altered during aging. This study investigated whether baclofen administration (5 mg kg⁻¹) induces differential effects on cortical electrical activity with age. Electroencephalograms (EEGs) were recorded from young (3–4 months) and aged (15–17 months) rats, and both the absolute and relative powers in five frequency bands (delta: 2–4 Hz; theta: 4–8 Hz; alpha: 8–12 Hz; beta: 12–20 Hz; gamma: 20–100 Hz) were analyzed. Before administration of baclofen, we found that the EEG relative power in the beta band was higher in the aged than that in the young rats. After administration of baclofen, there was a slower increase in the relative power in the delta band in the aged than that in the young rats. Moreover, there was no significant difference between the two age groups in absolute power in any frequency band. These findings indicate that baclofen treatment appears to differentially modify cortical EEG activity as a function of age. Our data further elucidate the relationship between GABA_B receptor-mediated neurotransmission and aging.     

Activities of antioxidant enzymes in mitochondria of growing and dormant sugar beet roots

In mitochondria isolated from growing (70–85 days) and dormant (stored for 8–12 weeks) sugar beet (Beta vulgaris L.) roots, activities of superoxide dismutase (SOD) and enzymes of the ascorbate-glutathione cycle were determined. The activity of SOD, the enzyme involved in superoxide detoxification, was much higher in mitochondria of the growing root, whereas activities of ascorbate peroxidase (APO) and glutathione reductase (GR), key enzymes of the ascorbate-glutathione cycle involved in the hydrogen peroxide degradation, increased substantially in mitochondria of dormant storage roots. Catalase (CAT) activity was detected in the fraction of root mitochondria purified in the sucrose density gradient, which activity was inhibited by cyanide by 85–90% and much weaker, by aminotriazol (by 30–35%). Submitochondrial localization of APO and CAT was analyzed using proteinase K. It was established that a substrate-binding APO center is localized on the external side of the inner membrane, whereas CAT is localized in the mitochondrial matrix. A possible role of mitochondria as ROS (hydrogen peroxide) acceptors in the cells of storage parenchyma of the stored root is discussed.     

Fine structure of the low-frequency spectra of heart rate and blood pressure

Background  

The aim of this study was to explore the principal frequency components of the heart rate and blood pressure variability in the low frequency (LF) and very low frequency (VLF) band. The spectral composition of the R–R interval (RRI) and systolic arterial blood pressure (SAP) in the frequency range below 0.15 Hz were carefully analyzed using three different spectral methods: Fast Fourier transform (FFT), Wigner-Ville distribution (WVD), and autoregression (AR). All spectral methods were used to create time–frequency plots to uncover the principal spectral components that are least dependent on time. The accurate frequencies of these components were calculated from the pole decomposition of the AR spectral density after determining the optimal model order – the most crucial factor when using this method – with the help of FFT and WVD methods.     

An acoustical and physiological analysis of buzzing in cicada killer wasps (Sphecius speciosus )

Cicada killers (Sphecius speciosus) are large solitary wasps capable of producing a high-amplitude buzzing sound. The buzz was acoustically characterized and its thermal and energetic effects examined. The sound was amplitude modulated, variable in frequency, had many harmonics, and was sometimes interrupted by broad-band buzz pulses. Cicada killer body size was directly related to sound pressure level and inversely related to frequency. Buzzing in males was 70 ± 0.8(21) dB (re 20 μPa measured 3 cm from the dorsum of the thorax) in sound pressure amplitude, with a fundamental frequency of 209 ± 6(20) Hz, while in females buzzes were 72.6 ± 8.3(30) dB and 152.5 ± 5.2(29) Hz. Males, the smaller of the sexes, had buzzes of significantly lower amplitude and higher frequency. Metabolic rate was 0.293 ± 0.024(13) W g⁻¹, or 88% of maximal, during buzzing, and was 5–100 times more costly than file-and-scraper stridulation. Thorax temperature climbed rapidly during sound production and peaked at levels that were nearly optimal for flight. Buzzing may play a role in both interspecific and intraspecific defensive interations. Accepted: 16 July 1998     

Investigating the effects of opioid drugs on electrocortical activity using wavelet transform

 Fetal electrocortical activity (ECoG) is characterized by two distinct patterns: HVSA (high voltage, slow activity) and LVFA (low voltage, fast activity). Using the wavelet transform (WT), we recently reported that the frequency characteristics of these two ECoG patterns undergo significant maturational changes prior to birth (Akay et al. 1994a). We now report that fetal ECoG can also be significantly affected by pharmacological agents. In this paper, we compared the effects of two opioid drugs (morphine and [D-Pen², D-Pen⁵]enkephalin, DPDPE) on fetal ECoG, using the chronically instrumented fetal lamb model. Morphine was infused intravenously (i.v.) at 2.5 mg/h, while DPDPE was infused into the lateral cerebroventricle (i.c.v.) at 30 μg/h. The ECoG was analyzed using WT. We performed multiresolution decomposition for four sets of parameters D _{2 j} where −1<j<−4. The four series WTs represent the detail signal bandwidths: (1) 16–32 Hz, (2) 8–16 Hz, (3) 4–8 Hz, (4) 2–4 Hz. The data were subjected to statistical analysis using the Kolmogorov–Smirnov (KS) test. Both morphine and DPDPE resulted in a significant increase in power in the first wavelet band, while power was reduced in the second, third and fourth wavelet bands. In addition, both drugs resulted in a disruption of the normal cyclic pattern between the two ECoG patterns. There was a difference in the time course of action between morphine and DPDPE. This is the first occasion in which continuous ECoG has been subjected to rigorous statistical analysis. The results suggest that the WT-KS method is most suitable for quantitating changes in the ECoG induced by pharmacological agents. Received: 21 January 1994/Accepted in revised form: 15 September 1994     

Frequency-intensity characteristics of cricket cercal interneurons: low-frequency-sensitive units

Three identified interneurons of the cercal system were investigated electrophysiologically; these interneurons are sensitive only to stimulation of cercal filiform-hair sensilla by low-frequency sound. Measurement of the frequency ranges revealed cut-off frequencies between ca. 20 and 70 Hz. Analysis of the responses near threshold and at higher intensities in the frequency range 5–500 Hz shows that one of them (Interneuron 9-1b) exhibits a sensitivity maximum at the frequency-intensity combination necessary for the perception of an intraspecific signal at 30 Hz. This band-pass behavior disappears at higher stimulus intensities. In order to investigate the mechanism of the low-frequency selectivity of the interneurons, two-tone stimulation experiments were performed. When stimuli in the best-frequency range were superimposed by a 100-Hz tone, the spiking activity was suppressed in an intensity-dependent manner. Accepted: 22 July 1998     

Mechanisms of stepping rhythm formation in decerebrated and chronic spinal cats under epidural stimulation

A study was made of the stepping pattern formation in decerebrated and in chronic spinal cats during epidural stimulation (ES). The hindlimb stepping performance depended on the parameters of ES and afferent input. At non-optimal ES parameters, no stepping was induced, only muscle reflexes followed the stimulation rhythm. Optimized ES (3–5 Hz, 50–100 μA for decerebrated and 20–30 Hz, 150–250 μA for spinal cats) evoked coordinated stepping movements at a natural rate (0.8–1 Hz) accompanied by electromyographic burst activity of the corresponding muscles. In decerebrated cats, the bursts are formed owing to modulation of early responses and the late polysynaptic activity. In chronic spinal cats, this process is mainly due to amplitude modulation of the early responses. Formation of the stepping pattern in decerebrated cats involves spinal interneurons responsible for the polysynaptic activity, which allows its correction based on processing the afferent signals. Activation of this system in chronic spinal cats can be realized by afferent stimulation alone, without ES.     

Frequency-intensity characteristics of cricket cercal interneurons: broadband units

The bilateral pairs of cercal interneurons 10-2a and 10-3a in the cricket terminal ganglion are supposed to constitute a functional system for measuring the direction of air-borne signals, based on their phase-locked responses and selective directional sensitivity. The purpose of this study was to obtain information on the frequency and intensity characteristics and thus the potential working range of this system. By recording intracellularly from the axons of the interneurons we measured responses for stimuli of varying frequency, intensity, and direction. Typically, the stimulus frequency range examined extended from 5 to 600 Hz, at intensities of 0.03–30 mm s⁻¹ (peak-to-peak air-particle velocity). The results show that interneurons 10-2a and 10-3a preserved their level of activity, response type, and direction tuning in the whole frequency range tested. Stimulus-response cross-correlograms revealed that spike trains were synchronized with stimulus waves at even higher frequencies, at least up to 1000 Hz. At a given air-particle velocity in the range of about 2–2.5 logarithmic units, the spike number responses of the interneurons were nearly constant over a wide frequency range. Directional diagrams appeared to be independent of stimulus frequency, both in orientation and in amplitude. Accepted: 14 October 1998     

Response properties and biological function of the skate electrosensory system during ontogeny

This study examined the response properties of skate electrosensory primary afferent neurons of pre-hatch embryo (8–11 weeks), post-hatch juvenile (1–8 months), and adult (>2 year) clearnose skates (Raja eglanteria) to determine whether encoding of electrosensory information changes with age, and if the electro-sense is adapted to encode natural bioelectric stimuli across life history stages. During ontogeny, electrosensory primary afferents increase resting discharge rate, spike regularity, and sensitivity at best frequency. Best frequency was at 1–2 Hz for embryos, showed an upwards shift to 5 Hz in juveniles, and a downward shift to 2–3 Hz in adults. Encapsulated embryos exhibit ventilatory movements that are interrupted by a “freeze response”” when presented with weak uniform fields at 0.5 and 1 Hz. This phasic electric stimulus contains spectral information found in potentials produced by natural fish predators, and therefore indicates that the embryo electrosense can efficiently mediate predator detection and avoidance. In contrast, reproductively active adult clearnose skates discharge their electric organs at rates near the peak frequency sensitivity of the adult electrosensory system, which; facilitates electric communication during social behavior. We suggest that life-history-dependent functions such as these may shape the evolution of the low-frequency response properties for the elasmobranch electrosensory system. Accepted: 19 February 1998     

Nectar intake rate is modulated by changes in sucking pump activity according to colony starvation in carpenter ants

Dynamics of fluid feeding has been deeply studied in insects. However, the ability to vary the nectar-intake rate depending only on the carbohydrate deprivation has been clearly demonstrated only in Camponotus mus ants. When insect morphometry and fluid properties remain constant, changes in intake rate could only be attributed to variations in sucking pump activity. Previous records of the electrical activity generated during feeding in C. mus have revealed two different signal patterns: the regular (RP, frequencies: 2–5 Hz) and the irregular (IP, frequencies: 7–12 Hz). This work studies the mechanism underlying food intake-rate modulation in ants by analysing whether these patterns are involved. Behaviour and electrical activity generated by ants at different starvation levels were analysed during feeding on sucrose solutions. Ants were able to modulate the intake rate for a variety of sucrose concentrations (10, 40 and 60%w/w). The IP only occurred for 60% of solutions and its presence did not affect the intake rate. However, during the RP generated under the starved state, we found frequencies up to 7.5 Hz. RP frequencies positively correlated with the intake-rate for all sucrose concentrations. Hence, intake-rate modulation according to sugar deprivation is mainly achieved by the ant’s ability to vary the pumping frequency.     

Peculiarities of myocardial electrogenesis in laboratory rats under conditions of acute nitrite intoxication

In anesthetized male rats the arterial blood pressure in femoral artery and electrocardiogram in standard leads were recorded uninterruptedly for 1–1.5 h under conditions of acute nitrite intoxication produced by a subcutaneous injection of water solution of sodium nitrite (donor of nitric oxide) at concentrations of 10, 30, and 50 mg/kg body mass. Results of the study have shown dose-dependent changes of arterial pressure as well as of time and amplitude characteristics of electrocardiogram under effect of NaNO₂. At the threshold hypoxic dose, an increase of amplitude of R and S waves was observed by the 30–45th min, while at the maximal NaNO₂ dose, amplitude of all waves rose by the 15th min of intoxication. High nitrite doses often caused an elevation of the ST segment above the isoelectric line and a rise of the amplitude of the T wave, on which a notch appeared in some cases. The change of the ECG time parameters was expressed in the dose-dependent development of bradycardia for the first 4–7 min; its level correlated with the progressively decreasing arterial pressure in the beginning (the 2–4th min) of nitrite intoxication. Variation analysis of the heart rate spectral characteristics by Baevskii’s method has revealed a rise of the total spectral power of pulse oscillations. Under effect of nitrite, in the specter of cardiointervals, the slower oscillations have been revealed with frequency of 0.15–0.2 Hz in the LF diapason with subsequent recovery of the normal ECG specter at the end of the experimental period. The maximal nitrite dose produced more pronounced shifts of the heart rate specter towards the LF and VLF diapasons that were not restored for 1 h of experiment. Transitory processes of readjustment of the cardiac rhythm had discrete character. The nitrite dose of 100 mg/kg body mass increased the RR-interval after 4–7 min with amplitude steps of 3–5 imp/s and the time constant of 20–40 s. The revealed ECG changes had the reflex (enhancement of parasympathetic tonus) and metabolic (the hypoxic and histotoxic damage of myocardium) nature.     

Topographic analysis of dimension estimates of EEG and filtered rhythms in epileptic patients with complex partial seizures

Nonlinear dynamic properties were analyzed on the EEG and filtered rhythms recorded from healthy subjects and epileptic patients with complex partial seizures. Estimates of correlation dimensions of control EEG, interictal EEG and ictal EEG were calculated. The values were demonstrated on topograms. The delta (0.5–4 Hz), theta (4–8 Hz), alpha (8–13 Hz), beta (13–30 Hz) and gamma (30–40 Hz) components were obtained and considered as signals from the cortex. Corresponding surrogate data was produced. Firstly, the influence of sampling parameters on the calculation was tested. The dimension estimates of the signals from the frontal, temporal, parietal and occipital regions were computed and compared with the results of surrogate data. In the control subjects, the estimates between the EEG and surrogate data did not differ (P > 0.05). The interictal EEG from the frontal region and occipital region, as well as its theta component from the frontal region, and temporal region, showed obviously low dimensions (P < 0.01). The ictal EEG exhibited significantly low-dimension estimates across the scalp. All filtered rhythms from the temporal region yielded lower results than those of the surrogate data (P < 0.01). The dimension estimates of the EEG and filtered components markedly changed when the neurological state varied. For each neurological state, the dimension estimates were not uniform among the EEG and frequency components. The signal with a different frequency range and in a different neurological state showed a different dimension estimate. Furthermore, the theta and alpha components demonstrated the same estimates not only within each neurological state, but also among the different states. These results indicate that the theta and alpha components may be caused by similar dynamic processes. We conclude that the brain function underlying the ictal EEG has a simple mechanism. Several heterogeneous dynamic systems play important roles in the generation of EEG. Received: 10 December 1999 / Accepted in revised form: 8 May 2000     

Stability and activity of lipase in subcritical 1,1,1,2-tetrafluoroethane (R134a)

The stability and activity of commercial immobilized lipase from Candida antarctica (Novozym 435) in subcritical 1,1,1,2-tetrafluoroethane (R134a) was investigated. The esterification of oleic acid with glycerol was studied as a model reaction in subcritical R134a and in solvent-free conditions. The results indicated that subcritical R134a treatment led to significant increase of activity of Novozym 435, and a maximum residual activity of 300% was measured at 4 MPa, 30 °C after 7 h incubation. No deactivation of Novozym 435 treated with subcritical R134a under different operation factors (pressure 2–8 MPa, temperature 30–60 °C, incubation time 1–12 h, water content 1:1, 1:2, 1:5 enzyme/water, depressurization rate 4 MPa/1 min, 4 MPa/30 min, 4 MPa/90 min) was observed. While the initial reaction rate was high in subcritical R134a, higher conversion was obtained in solvent-free conditions. Though the apparent conversion of the reaction is lower in subcritical R134a, it is more practicable, especially at low enzyme concentrations desired at commercial scales.     

Natural environmental associations in a 50-day human electrocardiogram

Meteorotropic associations of heart rate (HR) and HR variability (HRV) were investigated in a clinically healthy 48-year-old man in Kiev. His electrocardiogram (ECG) was determined over 50 days by fitting him with an ambulatorily wearable device; various natural physical environmental variables were also monitored. The mean inter-beat interval, the standard deviation of these intervals, the spectral power in several frequency ranges, the power ratio of the approx. 10.5-s/approx. 3.6-s spectral components and other aspects of HRV were computed over consecutive 14.4-min intervals. Together with ordinary meteorological variables, geomagnetic disturbances (GMD) and fluctuations of atmospheric pressure (FAP) in the range 0.01–0.10 Hz (10–100 s) were measured. The assessable infradian spectra (with frequencies lower than 1 cycle/28 hours) of all HRV parameters showed two major components with periods of about 3.5 and 10 days. Two environmental variables, FAP and wind speed (with which FAP is closely related), revealed both of these rhythms and showed the greatest cross-spectral coherence (0.70–0.98) with corresponding oscillations of HRV. Less specific but statistically significant product-moment correlations with major HRV indices were also found; most of these were with FAP, but correlations with air temperature, humidity, wind speed and geomagnetic disturbances were also found. Long-term ECG recording, essential in the detection of infradian rhythms, proved to be sensitive to physical environmental variables, notably meteorological ones. FAP, usually neglected since its role has not been considered in previous biometeorological studies, or some factor closely related to FAP is probably involved in synchronizing or influencing the approximately 3.5-day HR and HRV rhythms in humans. Received: 27 July 2000 / Revised: 13 November 2000 / Accepted: 28 November 2000     

Evidence of dominant parasympathetic nervous activity of great cormorants (<Emphasis Type="Italic">Phalacrocorax carbo</Emphasis>)

The characteristics of autonomic nervous activity were examined on captive great cormorants Phalacrocorax carbo hanedae, using a power spectral analysis of heart rate variability. Heart rates were calculated from recordings of the electrocardiograms of the birds via embarked data loggers. We investigated the effects of blockades of the sympathetic or parasympathetic nervous systems using the indices of autonomic nervous activity such as high frequency (0.061–1.5 Hz) component, low frequency (0.02–0.060 Hz) component and the low frequency power component to high frequency power component ratio. Resting heart rate (85.5 ± 6.1 bpm) was lower than the intrinsic heart rate (259.2 ± 15.3 bpm). The heart rate drastically increased after the injection of the parasympathetic nervous blocker, on the other hand it slightly decreased after the injection of the sympathetic nervous blocker. The sympathetic, parasympathetic and net autonomic nervous tones calculated from heart rate with and without blockades were 40.9 ± 27.6, −44.5 ± 7.4 and −29.5 ± 9.0%, respectively. The effect of the parasympathetic nervous blockade on low frequency and high frequency power was greater than that of the sympathetic nervous blockade. Those data suggested that the parasympathetic nervous activity was dominant for great cormorants.     

Electroencephalograms of patients with initial signs of depression: Independent component analysis

Independent component analysis (ICA) of 19-channel background EEG was performed in 111 patients with the early signs of depressive disorders and in 526 healthy subjects. The power spectra of the independent components were compared in the depressive patients and in healthy subjects at the eyes closed and eyes opened states. Statistically significant differences between the groups were detected in three frequency bands: θ (4–7.5 Hz), α (7.5–14 Hz), and β (14–20 Hz). Increased θ and α activities in parietal and occipital derivations of depressive patients may have been caused by a reduced cortical activity in the projection of these derivation. Diffuse enhancement of the β activity may be correlated with anxiety symptoms that are pronounced in the clinical picture of depressive disorders at early stages of the disease. ICA used to compare quantitative EEG parameters in different groups of patients and in healthy persons makes it possible to localize the differences more accurately than the traditional analysis of EEG spectra.     

Baseline EEG gamma activity and induced responses to facial stimuli during the formation of a visual cognitive set

The power spectra of cortical potentials of baseline activity during interstimulus intervals (4 s; Fourier transform in the frequency band of 1–60 Hz) and short-term (0.8 s) induced responses to facial stimuli (wavelet transform in the 15–60 Hz band) were assessed during the study of the visual cognitive set to facial expression. Significant differences between groups of subjects with different set plasticities were observed only at the set-testing stage. Estimation of short-term (0.8 s) induced responses of wavelet spectra in the group with the plastic set revealed an increase in the power (compared to the power of background activity) of the γ₂ band (41–60 Hz) in the temporal, central and occipital areas of the left hemisphere, whereas in the group with the rigid set these power spectra decreased. At the same time, the power in the γ₁ band (21–40 Hz) was significantly lower (at the same level with the rigid form), indicating the discrete nature and functional selectivity in the γ frequency band.     

Time-frequency analysis of the electrocortical activity during maturation using wavelet transform

In this study, we introduce the wavelet transform (WT) as a method for characterizing the maturational changes in electrocortical activity in 24 fetal lambs ranging from 110–144 days gestation (term 145 days). The WT, based on multiresolution signal decomposition, is free of assumptions regarding the characteristics of the signal. The approximation of the electrocortical activity at resolutions varying from 2^j+1 to 2^j can be extracted by decomposing the signal on a wavelet orthonormal basis of L ²(R). We performed multiresolution decomposition for four sets of parameters D _2j, where −1<j<−4. The four series WT represent the detail signal bandwidths: (1) 16–32 Hz, (2) 8–16 Hz, (3) 4–8 Hz, (4) 2–4 Hz. The data were divided into three groups according to gestational age: 110–122 days (early), 123–135 days (middle), and 136–144 days (late). In the early group, the power was highest in the fourth signal bandwidth, with relatively low power in the other bands. Increase in gestational age was characterized by increased power in all four bandwidths. Comparison of the cumulative distribution function of the power in the four wavelet bands confirmed the presence of two statistically different patterns in all three age groups. These two patterns correspond to the visually identified patterns of HVSA (high-voltage slow activity) and LVFA (low-voltage fast activity). The earliest development change occurred in HVSA, with progressive increase in power in the 2–8 Hz band. Later changes occurred in LVFA, with a significant increase in power in the 16–32 Hz band. The same database was also analyzed by the short-term Fourier transform (STFT) method, the most common time-frequency analysis method. Comparison of the results clearly show that the WT provided much better time-frequency resolution than the STFT method and was superior in demonstrating maturational changes in electrocortical activity. Received: 7 July 1993/Accepted in revised form: 15 November 1993     

The effects of maturation on self-induced dynamic body sway frequencies of girls performing acrobatics or classical dance

We investigated the effects of maturation on the dynamic body sways of healthy girls. Prepubertal and postpubertal girls practising professional physical activities requiring a good ability to maintain equilibrium (acrobats and dancers) were asked to stand on a free seesaw platform and the results compared to those for untrained age-matched girls. This platform (stabilometer) allows self-induced body sways. Stabilograms were obtained by a double integration of the angular acceleration from the recordings of the platform sways made with an accelerometer. Fast Fourier transform processing of stabilograms allowed spectral frequency analysis. The total spectrum energy and the energies of three frequency bands (0–0.5 Hz, 0.5–2 Hz, 2–20 Hz) were determined. ANOVA showed that, for all groups of different equilibrium activity and independent of visual input, prepubertal girls had higher energy values than postpubertal girls in the 0- to 0.5-Hz band whereas the opposite was true for 0.5- to 2-Hz band. Ballet dancers were more dependent than acrobats on visual inputs for the regulation of their postural control but were less dependent than untrained girls at both ages. Maturation seemed to shift body sways towards higher frequencies and the utilization of the cues of postural control was different according to the type of equilibrium activity practised by the subjects. Accepted: 7 February 1997