Intracranial electrodes are sometimes implanted in the brains of patients with epilepsy as a part of pre-surgical evaluation. This operation is performed by a skilled neurosurgeon, and the patient is monitored for several days to examine the EEG and seek out a seizure focus. Traditionally, these studies are done at a relatively low sampling rate of 200 HZ. This restricts intracranial EEG (or SEEG) to an examination of EEG events within a range of 0 Hz to 60 or 70 Hz.
Recent studies of rodents who had artificially inducted seizures and recordings of epileptic patients with depth electrode implantation during the pre-surgical evaluation showed that high frequency activity in the 80 to 500 Hz range may be present interictally (ripples and fast ripples) and related to the seizures. It has been hypothesized that they could have an epileptigenic role. The EEG department at the MNI has recently acquired some amplifiers which are capable of recording EEG at a 2000 Hz sampling rate. This is allowing us to examine the effects of brief, high frequency oscillations (HFOs) of 80 Hz to 500 Hz. Our group has begun such an examination of high frequency components in patients who have been implanted with intracranial electrodes for pre-surgical evaluation. Data collection and processing is ongoing, but still in a relatively early stage. The first studies are centered in the changes during the different stages of seizures and in the pre and post spike periods.
This study can use several methods to examine the SEEG, such as Fourier transforms and wavelet transforms. However, in our lab we worked a lot with visual marking of HFOs and spikes by clinicians. An example of how this is done is given here: 
hfos_marking_for_webpage.pps