Sladjana Spasić

Estimation of parameter kmax in fractal analysis of rat brain activity.

Abstract: We recorded electrocortical activity in anesthetized rats and constructed kmax new self‐similar time series, applying Higuchis algorithm. The aim of this study was to estimate value of the parameter kmax in order to obtain fractal dimension values as an optimum measure of biosignal change. After our analysis, electrocortical activity recordings resulted in a family of curves f(kmax). Three regions could be distinguished 2 ≤ kmax < 8, with a U‐shape; 8 ≤ kmax≤ 30, with a steeper quasilinear increase; and kmax≥ 30, with a smaller slope quasilinear increase. We suggest the optimum region for kmax: 8 < kmax < 18, specifically kmax= 8.

Distribution and accumulation of elements (As, Cu, Fe, Hg, Mn, and Zn) in tissues of fish species from different trophic levels in the Danube River at the confluence with the Sava River (Serbia)

Pikeperch (Sander lucioperca), European catfish (Silurus glanis), common carp (Cyprinus carpio), and gobies (Neogobius gymnotrachelus, Neogobius melanostomus) were collected from the Danube River (Belgrade section), and samples of liver, muscle, or whole-body composites (in the case of gobies) were analyzed for As, Cu, Fe, Hg, Mn, and Zn with inductively coupled plasma optical spectrometry to find out if there was a correlation between accumulation of these elements in predatory and prey species, as well as in pairs of species with overlapping diets. Concentrations of all analyzed elements were either higher (Cu, Fe, Mn, Zn) in liver than in muscle, or equal (As, Hg), except for Hg in carp, which was higher in muscle. Mercury concentration in liver and muscle of predators (catfish, pikeperch) was significantly (<10−4) higher than in prey fishes (carp and gobies). The results indicate that Hg concentration was biomagnified through the food chain. Concentrations of As, Fe, and Hg in carp liver and gobies whole-body composite were similar, but carp had significantly (<10−4) higher values of Zn and Cu in liver. The regression analysis and trendline equations indicate that the concentrations of all tested elements, except for As in liver, and Mn and Fe in muscle, were similar in predatory fish (pikeperch and catfish), on one hand, and in prey fish (carp and gobies), on the other hand. Distinctly high Zn concentration in carp is very common in this species due to its physiology. Concentrations of Hg and Zn were higher than the maximum acceptable concentration due to the high pollution level in this section of the Danube River, accordingly posing a risk for the human consumption of these fish species.

DIFFERENT ANESTHESIA IN RAT INDUCES DISTINCT INTER-STRUCTURE BRAIN DYNAMIC DETECTED BY HIGUCHI FRACTAL DIMENSION

The complexity, entropy and other non-linear measures of the electroencephalogram (EEG), such as Higuchi fractal dimension (FD), have been recently proposed as the measures of anesthesia depth and sedation. We hypothesized that during unconciousness in rats induced by the general anesthetics with opposite mechanism of action, behaviorally and poligraphically controlled as appropriately achieved stable anesthesia, we can detect distinct inter-structure brain dynamic using mean FDs. We used the surrogate data test for nonlinearity in order to establish the existence of nonlinear dynamics, and to justify the use of FD as a nonlinear measure in the

CONSECUTIVE DIFFERENCES AS A METHOD OF SIGNAL FRACTAL ANALYSIS

We propose a new method for calculating fractal dimension (DF) of a signal y(t), based on coefficients

Spectral and Fractal Analysis of Cerebellar Activity After Single and Repeated Brain Injury

m_y^{(n)}

Common barbel (Barbus barbus) as a bioindicator of surface river sediment pollution with Cu and Zn in three rivers of the Danube River Basin in Serbia.

, mean absolute values of its nth order derivatives (consecutive finite differences for sampled signals). We found that logarithms of

Independent complexity patterns in single neuron activity induced by static magnetic field

m_y^{(n)}

Surrogate data modeling the relationship between high frequency amplitudes and Higuchi fractal dimension of EEG signals in anesthetized rats

, n = 2,3,…,nmax, exhibited linear dependence on n: \[ \log\left(m_y^{(n)}\right)=({\rm slope})n+Y_{\rm int} \] with stable slopes and Y-intercepts proportional to signal DF values. Using a family of Weierstrass functions, we established a link between Y-intercepts and signal fractal dimension: \[ {\rm DF}=A(n_{\max}) Y_{\rm int}+B(n_{\max}), \] and calculated parameters A(nmax) and B(nmax) for nmax = 3,…,7. Compared to Higuchis algorithm, advantages of this method include greater speed and eliminating the need to choose value for kmax, since the smallest error was obtained with nmax = 3.

Effects of the static and ELF magnetic fields on the neuronal population activity in Morimus funereus (Coleoptera, Cerambycidae) antennal lobe revealed by wavelet analysis

The cerebellum, even when not directly damaged, is potentially interesting for understanding the adaptive responses to brain injury. Cerebellar electrocortical activity (ECoG) in rats was studied using spectral and fractal analysis after single and repeated unilateral injury of the parietal cortex. Local field potentials of cerebellar paravermal cortex were recorded before brain injury, in the acute phase (up to 2.5 hours) after a first injury of anesthetized rats, and then before and after second, third, and, in some cases, fourth injury. Relative gamma power (32.1–128.0 Hz) and fractal dimension of ECoGs were temporarily increased after the first injury. However, there was a permanent mild increase in gamma activity and a mild increase in the fractal dimension of cerebellar activity as a chronic change after repeated remote brain injury. There was a negative linear correlation between the normalized difference in fractal dimensions and normalized difference in gamma powers of cerebellar activity only in the case of repeated brain injury. This is the first study showing that correlation between the parameters of spectral and fractal analyses of cerebellar activity can discriminate between single and repeated brain injuries, and is, therefore, a promising approach for identifying specific pathophysiological states.

Ouabain modulation of snail Br neuron bursting activity after the exposure to 10 mT static magnetic field revealed by Higuchi fractal dimension.

River sediments are a major source of metal contamination in aquatic food webs. Due to the ability of metals to move up the food chain, fishes, occupying higher trophic levels, are considered to be good environmental indicators of metal pollution. The aim of this study was to analyze the metal content in tissues of the common barbel (Barbus barbus), a rheophilous cyprinid fish widely distributed in the Danube Basin, in order to find out if it can be used as a bioindicator of the metal content in the river sediment. We analyzed bioavailable concentrations of 15 elements (Al, As, B, Ba, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Se, Sr, and Zn) in sediments of the Danube (D), the Zapadna Morava (ZM), and the Južna Morava (JM) using the inductively coupled plasma spectroscopy (ICP-OES). The barbel specimens were collected in the proximity of sediment sampling sites for the analysis of metals in four tissues, gills, muscle, intestine, and liver. The sediment analysis indicated that the ZM is the most polluted with Cu, Ni, and Zn compared to other two rivers. The JM had the lowest concentrations of almost all observed elements, while the Danube sediments were mainly characterized by higher concentrations of Pb. The fish from the ZM had the highest concentration of Cu and Ni in the liver and intestine, and of Zn in the muscle tissue, which was in accordance with the concentrations of these metals in the sediment. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS) was used for further analyses of metal interactions with fish tissues. The results suggest that the barbel can potentially be used as a bioindicator of sediment quality with respect to metal contamination.