MEG, RFFTs, and the Hunt for High Frequency Oscillations

We describe early results of our effort to induce high frequency brain activity in normal subjects. By studying the magnetic field spectrum within a specially shielded room we have discovered strong signals which we had assumed would not be present. We have developed a really fast Fourier transform for computing the short-time spectrum in linear time in the window size and in the signal length, the fastest possible. We present results from some simple experiments using our RFFT algorithm to calculate short-time spectra of the magnetic field.