Sondagem ativa de redes neurais epileptogênicas, em humanos, utilizando Respostas Auditivas Evocadas em Regime Permanente (ASSR)

Abstract

CANCADO, Sérgio Augusto Vieira. Active Probing of Epileptogenic Neural Networks, in Humans, Using Auditory Steady-State Evoked Responses (ASSR). 116 pages. Doctoral Thesis in Physiology– Universidade Federal de Minas Gerais, 2021.

Epilepsy is a group of diseases that predispose to recurrent epileptic seizures and their consequences. The estimated prevalence in the Brazilian population is around 2%. 70 to 80% of patients with epilepsy have satisfactory seizure control with medication, the remainder being candidates for surgical treatment. Despite advances in the discovery of new medications and the development of new surgical therapies, the prognosis of patients with drug-resistant epilepsy remains virtually unchanged. Only 20-40% of patients with extratemporal epilepsy evolving with seizure control. To evaluate a biomarker for active probing of epileptogenic networks, we carried out a study with drug-resistant patients who underwent for investigation stereo-electroencephalography. Steady Evoked Auditory Responses (ASSR), initially described to assess the auditory threshold in uncooperative patients, have already been shown to be useful in the assessment of psychiatric disorders. Through the presence or not of ASSR, it is possible to define whether the individual with schizophrenia is in a psychotic state, for example. As it is a response that depends on the synchronism between neural circuits and the interictal and auditory processing is impaired in several individuals with epilepsy, the ASSR was chosen to carry out the active probing of the epileptogenic circuits. The evaluations were performed in the interictal period. The energy and the Phase Locking Value (PLV) of the auditory steady-state responses evoked by a white noise modulated in amplitude in the 40Hz range were measured. To investigate the effects of partial epileptogenic zone damage on ASSR at 40Hz, pre- and post-thermocoagulation radiofrequency responses were compared. Partial damage to the epileptogenic zone caused an increase in energy normalized by baseline in the ASSR range. There was also a significant increase in phase synchronism between the ASSR generator circuits and the auditory stimulus. The results suggest that epileptic circuits hijack part of the oscillators involved in ASSR genesis. Based on the characteristics of ASSR and its behavior in relation to epileptogenesis, it is possible to affirm that ASSR has a high potential as an active probing method for patients with epilepsy.