Abstract
In recent decades, a significant body of evidence based on invasive clinical research has showed that high-frequency oscillations (HFOs) are a promising biomarker for localization of the seizure onset zone (SOZ), and therefore, have the potential to improve postsurgical outcomes in patients with epilepsy. Emerging clinical literature has demonstrated that HFOs can be recorded noninvasively using methods such as scalp electroencephalography (EEG) and magnetoencephalography (MEG). Not only are HFOs considered to be a useful biomarker of the SOZ, they also have the potential to gauge disease severity, monitor treatment, and evaluate prognostic outcomes. In this article, we review recent clinical research on noninvasively detected HFOs in the human brain, with a focus on epilepsy. Noninvasively detected scalp HFOs have been investigated in various types of epilepsy. HFOs have also been studied noninvasively in other pathologic brain disorders, such as migraine and autism. Herein, we discuss the challenges reported in noninvasive HFO studies, including the scarcity of MEG and high-density EEG equipment in clinical settings, low signal-to-noise ratio, lack of clinically approved automated detection methods, and the difficulty in differentiating between physiologic and pathologic HFOs. Additional studies on noninvasive recording methods for HFOs are needed, especially prospective multicenter studies. Further research is fundamental, and extensive work is needed before HFOs can routinely be assessed in clinical settings; however, the future appears promising.
Highlights
High-frequency oscillations (HFOs) were first discovered and investigated using microelectrode arrays in the 1990s (Bragin et al 1999b,c; Fisher et al 1992; Huang and White 1989)
Ictal highfrequency oscillations (HFOs) and interictal HFOs were compared in a study by Zijlmans et al, and the findings showed that ictal HFOs may have more specificity for seizure onset zones (SOZs) than interictal HFOs, despite their similar locations (Zijlmans et al 2011)
It has been reported that scalp interictal HFOs could reflect epileptogenesis, predict seizure activity, sensitively monitor the response to pharmacological treatment with methylprednisolone in CSWS and with adrenocorticotropic hormones in West syndrome, and could be associated with pathological brain networks; they could be used to assess epileptogenic seizure risk post-brain injury (Thomschewski et al 2019).Here, we describe the literature published on this topic since 2019
Summary
High-frequency oscillations (HFOs) were first discovered and investigated using microelectrode arrays in the 1990s (Bragin et al 1999b,c; Fisher et al 1992; Huang and White 1989). In 2004, ictal high frequency activities (up to 100 Hz) were first recorded using noninvasive scalp EEG in children with West syndrome experiencing epileptic spasms (Kobayashi et al 2004).
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