PURPOSE: The study analyzes the occurrence of high frequency oscillations in 
different types of focal cortical dysplasia in 22 patients with refractory 
epilepsy. High frequency oscillations are biomarkers for epileptic tissue, but 
it is unknown whether they can reflect increasingly dysplastic tissue changes as 
well as epileptic disease activity.
METHODS: High frequency oscillations (80-450 Hz) were visually marked by two 
independent reviewers in all channels of intracranial implanted grid, strips, 
and depth electrodes in patients with focal cortical dysplasia and refractory 
epilepsy. Rates of high frequency oscillations in patients with pathologically 
confirmed focal cortical dysplasia of Palmini type 1a and b were compared with 
those in type 2a and b.
KEY FINDINGS: Patients with focal cortical dysplasia type 2 had significantly 
more seizures than those with type 1 (p < 0.001). Rates of high frequency 
oscillations were significantly higher in patients with focal cortical dysplasia 
type 2 versus type 1 (p < 0.001). In addition, it could be confirmed that rates 
of high frequency oscillations were significantly higher in presumed 
epileptogenic areas than outside (p < 0.001).
SIGNIFICANCE: Activity of high frequency oscillations mirrors the higher 
epileptogenicity of focal cortical dysplasia type 2 lesions compared to type 1 
lesions. Therefore, rates of high frequency oscillations can reflect disease 
activity of a lesion. This has implications for the use of high frequency 
oscillations as biomarkers for epileptogenic areas, because a detailed analysis 
of their rates may be necessary to use high frequency oscillations as a 
predictive tool in epilepsy surgery.