Grant 4-T11E-108-22 of the committee for scientific research, Republic of Poland.

Significance of existence of high frequency oscillations (HFO) identified in EEG records became  very interesting  during evaluation of the cerebral functional states, especially during evaluation of  epileptic  reorganization  of brain functions. The information presented In this communication is the result of continuation of analysis of the data presented in already published  paper*,  illustrating the results of investigation concerning the organization of the  patterns of intracortical EEG (IcEEG), including  intracortical  cellular activity using permanently implanted multicontact electrode in experimental, animal models of epilepsy. This study was performed in attempt to receive explanation  of  the  background of normal and abnormal  EEG patterns, including high frequency EEG oscillations (gamma waves and high frequency oscillations).    

The received data from the neocortical association area illustrate complexity of the functional patterns of the cortical structure:

- probability of appearance of the transient periods of existence of the  cellular discharges  scattered in cortical layers (excluding possibility of existing  movement, EMG and 50 Hz artefacts), with existence of  the  groups of discharges appearing within the frequencies  of  EEG gamma rhythm, especially 40-55 Hz. This type of activity was observed  during control EEG recordings after full recovery of the animals after  implantation of the electrodes, as well as during  study of epileptogenic reorganization of the cortical activity – in definite conditions,  

- relative independence of this type of activity with respect to the EEG patterns  of cortical activity: absence or presence during slow wave sleep  as well as REM sleep, especially evident on transition of SWS to REM sleep ,

- cellular discharges are especially frequent  in deep  cortical layers – probably especially in the layer fourth,

- in the same localizations the discharges disappear during appearance of the localized high degree bioelectrical positivity in the bioelectrical pattern of intracortical structure. This phenomenon  is associated with the appearance of superficial cortical negativity  recorded in epicortical derivation as slow EEG waves  (within  delta EEG frequency waves)  during SWS sleep, as well as the element of slow wave-spike complex during epileptogenic reorganization of cortical activity,

- groups of low amplitude  cellular discharges within the gamma wave frequency range were observed at the border with the deep positive slow waves (negative in  superficial derivations)   in conditions of potassium model of epilepsy. 

- the cellular discharges were absent during appearance of the rhythms of waves creating EEG pattern typical as EEG seizures appearing in penicillin and potassium models of epilepsy,

- short lasting groups of ripples preceding appearance of the EEG seizure type activity were observed in potassium model of epilepsy.

Conclusions:  it appears  that “ripples” reflect functional state of the definite cellular network  reflecting and/or participating in creating normal as well as abnormal  EEG patterns of brain activity. Interdisciplinary approach is necessary in order to receive more accurate evaluation of this phenomenon.  

* A. Sobieszek Cellular and EEG Patterns of the Reorganization of Cortical Activity in Animal Experimental Models of Epilepsy (in cats). In: Epilepsy During the Lifespan - Beyond the Diagnosis and New Perspectives. Marco Carotenuto (Editor). IntechOpen, 2024, chapter 1, pp. 3-15