Ljiljana Martac

Fractal analysis of rat brain activity after injury

With application of the Higuchi algorithm, fractal dimension (FD) values of the electrocortical activity of the rat parietal cerebral and paravermal cerebellar cortex were calculated, before and after unilateral discrete injury of the left parietal cortex. Immediately following the first acute injury, in a group of six rats, a reversible increase in mean FD was found at the left (ipsilateral side to the injury) cerebral cortex, from 1.38 to 1.59, and at the left cerebellar cortex from 1.51 to 1.73. In addition, an indication of plastic changes after repeated (third) injury was found as an irreversible increase in mean FD: 1.54 on the left and 1.48 on the right side of parietal cortex.

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.

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)}

Use of the Hurst Exponent for Analysis of Electrocortical Epileptiform Activity Induced in Rats by Administration of Camphor Essential Oil or 1,8-Cineole

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

Early physical and motor development of mouse offspring exposed to valproic acid throughout intrauterine development

m_y^{(n)}

Fractal Dimension in Animal Model of Alzheimer’s Dementia

, 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.

Wavelet and fractal analysis of rat brain activity in seizures evoked by camphor essential oil and 1,8-cineole

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.

Fractal dimension values of cerebral and cerebellar activity in rats loaded with aluminium

In this study, we investigated the presence of long-range correlation effects in the electrocortical activity of rats using the Hurst exponent (H) calculated by dispersion analysis (DA) and an aggregated variance method (AGV). A slow decline of the autocorrelation function during time expansion and the existence of a correlation between distant time points of electrocorticograms (ECoGs) were shown to be typical of various pathophysiological states. In these cases, the H values were within a 0.5 < H < 1 range. A particularly slow decay of the autocorrelation function is typical of a long-range dependence (LRD). We found that ECoGs after i.p. administrations of camphor essential oil or its main constituent, 1,8-cineole, included attacks of uncontrolled electrical discharges and showed the presence of long-range correlation effects. Such findings are in agreement with recent data obtained by other authors and suggest that initiation of seizures can be predicted by certain ECoG indices. We estimated the critical period where the H values for ECoGs containing uncontrolled electrical discharges continuously increased within a few minutes before the attack. We believe that the AGV demonstrates certain advantages over DA in calculations of the H.

Spectral and fractal measures of cerebellar and cerebral activity in various types of anesthesia

Clinical research has identified developmental delay and physical malformations in children prenatally exposed to the antiepileptic drug (AED) valproic acid (VPA). However, the early signs of neurodevelopmental deficits, their evolution during postnatal development and growth, and the dose effects of VPA are not well understood. The present study aimed to examine the influence of maternal exposure to a wide dose range (50, 100, 200 and 400mg/kg/day) of VPA during breeding and gestation on early physical and neuromotor development in mice offspring. Body weight gain, eye opening, the surface righting reflex (SRR) and tail suspension test (TST) were examined in the offspring at postnatal days 5, 10 and 15. We observed that: (1) all tested doses of VPA reduced the body weight of the offspring and the timing of eye opening; (2) offspring exposed to VPA displayed immature forms of righting and required more time to complete the SRR; (3) latency for the first immobilization in the TST is shorter in offspring exposed to higher doses of VPA; however, mice in all groups exposed to VPA exhibited atypical changes in this parameter during the examined period of maturation; (4) irregularities in swinging and curling activities were observed in animals exposed to higher doses of VPA. This study points to delayed somatic development and postponed maturation of the motor system in all of the offspring prenatally exposed to VPA, with stronger effects observed at higher doses. The results implicate that the strategy of continuous monitoring of general health and achievements in motor milestones during the early postnatal development in prenatally VPA-exposed offspring, irrespectively of the dose applied, could help to recognize early developmental irregularities.