304 0090-2977/08/4004-0304 © 2008 Springer Science+Business Media, Inc. Neurophysiology, Vol. 40, No. 4, 2008 Correlation between the Activity of Dopaminergic Neurons of the Ventral Tegmentum and Spectral Power of the EEG Rhythms in Awake Cats Yu. O. Fokina, 1 А. М. Kulichenko, 1 and V. B. Pavlenko 1 Neirofiziologiya/Neurophysiology, Vol. 40, No. 4, pp. 359-367, July-August, 2008. Received July 15, 2008. We studied correlations between the frequency of background impulse activity (BIA) of dopaminergic (DA- ergic) neurons of the ventral tegmentum (VT) and spectral power (SP) of the frequency components of EEG samples recorded in awake cats. The EEG was recorded monopolarly (electrodes were fixed in the cranial bones) from the frontal, occipital, and right and left temporal regions of the cortex. In a great majority of the cases, the BIA frequency of VT DA-ergic neurons demonstrated significant positive correlations with changes in the SPs of the alpha and beta EEG rhythms. The closest correlations of the spiking frequency of DA-ergic cells with the SP of the alpha rhythm was observed in the occipital region, while those with the beta SP were found in the frontal area. Correlations of the activity of DA-ergic neurons with the SPs of the alpha and beta rhythms in the left temporal cortical zone were closer, as compared with those in the symmetrical right zone. Correlations of the SPs of the delta, theta, and gamma EEG components with the discharge frequency of VT DA neurons were of opposite directions, and in most cases such correlations did not reach the level of significance. The results of this study show that, in some cases, specific EEG patterns can be considered indicators of the state of the cerebral VT DA-ergic system. Keywords: dopaminergic neurons, ventral tegmentum, impulse activity, EEG, spectral composition. 1 Vernadskii Tavricheskii National University, Autonomic Republic of Crimea, Simferopol’, Ukraine. Correspondence should be addressed to Yu. O. Fokina (e-mail: fokina1985@mail.ru), A. M. Kulichenko (e-mail: kulichenkoa@mail.ru), or V. B. Pavlenko (e-mail: pavlenkovb@crimea.edu). INTRODUCTION Recording and analysis of EEG are effective means for estimation of the functional state of the CNS; the corresponding techniques are extensively used in research and clinical practice. At the same time, it should be recognized that the mechanisms underlying the formation and modifications of the EEG frequency components (rhythms) remain unclear in many respects [1, 2]. The relations between the activity of neuromodulatory cerebral systems and EEG characteristics attract significant interest from researchers. In 1997, Lubar supposed that the activity of neurons belonging to the aminergic cerebral systems crucially influences the process of formation of EEG rhythms [3]. Our earlier studies showed that rather clear correlations between the parameters of spike activity of brainstem serotonergic neurons of the nuclei raphe and noradrenergic cells of the locus coeruleus, on the one hand, and changes in the spectral power (SP) of a few main EEG rhythms, on the other hand, do exist [4]. The dopamine (DA)-ergic system is another main aminergic brainstem system. The activity of this system demonstrates clear relations to the organization of motor acts [5, 6], formation of memory engrams [7], changes in the state of systems providing attention [8], and the development of positive emotions [8, 9]. The DA-ergic system is also a component of the mechanisms of motivation [10] and exerts a significant modulatory influence on the psychophysiological state of animals and humans. It can be expected that this system, similarly to other aminergic systems, will definitely contribute to the formation of EEG rhythms and influence their parameters. This is why we examined, in the experiments on unanesthetized cats described below, correlations between the characteristics of impulse activity of DA-ergic neurons (supposedly identified according to their localization and parameters of their spikes) of the ventral tegmentum (VT) of the cat midbrain and changes in the SPs of the main EEG rhythms.