Neurobiology of Sleep-Wakefulness Cycle 2(3-4): 64-74, 2002
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© 2002 NSWC
Accepted in revised form 20 November 2002; recieved 31 July 2002.
The dynamics of neuronal activity of the so-called association zones (AZ) of the parietal regions (AZPR) of the cerebral cortex in the sleep-wakefulness cycle (SWC) has been studied in chronic cats. Analysis of the obtained experimental data leads to the following conclusions: 1. Activity of the majority of neurons in the AZPR throughout the SWC undergoes qualitative changes, that manifest themselves in the transformation of their discharge pattern from regular, i.e. evenly distributed in time, type, characteristic of the state of wakefulness, to the cluster-pause type, characteristic of the slow-wave sleep (SWS). And the neuronal activity, typical of wakefulness, is restored in the paradoxical sleep (PS) phase. 2. Against the background of deep SWS (DSWS), the mean frequency of neuronal cluster discharges, in the AZPR of the cortex, is appreciably higher than that in active wakefulness. This fact provides evidence for the postsynaptic inhibition of neurons during pauses, which upon termination, are immediately followed by the rebound of activity and the respective rise in the frequency of neuronal discharges. 3. At DSWS, the mean duration of a pause between the discharge clusters is considerably longer than that of a cluster. 4. A smaller portion of neurons in AZPR of the cortex, exhibits only quantitative changes in SWC, without transforming their activity to the cluster-pause type. In one group of neurons these changes are evidenced by a decrease in the discharge in SWS, as compared with waking and PS, while the other group may reveal an opposite picture, by enhancing their activity just in the phase of SWS. 5. In the AZPR of the cortex there can also be detected such neurons that are activated selectively in one or another SWC phase. 6. Most neurons in the cortex AZ enhance their activity at the change from SWS to PS with the occurrence of single ponto-geniculo-occipital spikes, prior to the appearance of any signs of changes in the electrocorticogram. 7. Most neurons in the cortical AZPR abruptly sometimes down to a full stoppage, reduce their activity immediately after termination of PS, as well as with the occurrence of short episodes of EEG desynchronization without sings of behavioral arousal against the background of DSWS. 8. It is conjectured that the changes in neuronal activity of the AZPR of the cerebral cortex over SWC display the dynamics of cognitive processes, which on their part, are determined just by the transformation (both quantitative and qualitative) of the neuronal activity of the cerebral cortex, in general, and of its AZ, in particular.
Key Words: Neuronal activity, sleep-wakefulness cycle, association zones of the parietal regions of the cerebral cortex.
Correspondence: Oniani Tengiz, Prof.,
Department of Neurobiology of Sleep-Wakefulness Cycle,
I.S. Beritashvili Institute of Physiology, Georgian Academy of Sciences,
14, L. Gotua str., Tbilisi, 380060, Georgia.
E-mail: nswc@neurobiology.ge