M. Ćulić

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)}

Effect of neurotoxin DSP4 on EEG power spectra in the rat acute model of epilepsy

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

Amphetamine and haloperidol modulatory effects on Purkinje cell activity and on EEG power spectra in the acute rat model of epilepsy

m_y^{(n)}

The effect of cortical lesion on systemic penicillin epilepsy in 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.

The functional neuroimaging evidence of cerebellar involvement in the simple cognitive task.

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.

SLOW OSCILLATIONS OF THE PURKINJE CELL FIRING RATE INDUCED BY ELECTRICAL STIMULATION OF THE LOCUS COERULEUS IN RATS

The effect of the adrenergic neurotoxin N-(chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) on electroencephalographic (EEG) activity was studied in the model of epilepsy induced by systemic application of penicillin (1,000,000 IU/kg, i.p). DSP4 (50 mg/kg, i.p.) was administrated to male Wistar rats, while the control animals were rats from the same litters. EEG activity was recorded in acute and chronic experiments 3 or 4 weeks after DSP4 treatment, before and after penicillin administration. Occasional locus coeruleus (LC) stimulation served as an electrophysiological test of DSP4 toxic effect. EEG power spectra in DSP4 treated animals showed a tendency to be greater in lower frequency bands than in controls before penicillin administration; there was almost no effect of electrical LC stimulation, regardless on penicillin treatment. In the model of epilepsy, the mean total EEG power spectra were greater in the period of 135-330 min after penicillin administration, as well as during 345-540 min, in DSP4 treated animals as compared to the controls. It seems that neurotoxin DSP4 is an optimal tool for studying the removal of LC influence in the acute model of epilepsy. It is also suggested that norepinephrine (NE) may have a modulatory role in the systemic penicillin epilepsy.

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

The modulation of cerebellar Purkinje cell activity and EEG from parietal cortex was studied in the rat model of epilepsy induced by penicillin under acute haloperidol and amphetamine treatment. The discharge pattern of Purkinje cells showed tendency towards inhibition and EEG power spectra increased after parenteral administration of penicillin (1000000 IU/kg, i.p.). Acute haloperidol treatment (1 mg/kg, i.p.), performed after the development of penicillin induced epileptic episodes, elicited a prominent excitation of Purkinje cell discharges associated with parallel increase in mean EEG power spectra. However, acute DL-amphetamine treatment induced marked suppression of Purkinje cell discharges as well as outstanding decrease of the mean EEG power spectra. These results indicate that cerebellar Purkinje cells may be important in the control of seizure activity and that noradrenergic influences are relevant.