Measuring fundamental frequencies in local field potentials.

Neural processes display rhythmic oscillations in local field potentials; identification of their characteristic frequencies is complicated due to their highly non-stationary nature. A simple technique, combining Fourier transforms and correlation coefficients yields unambiguous determinations of the frequencies without a priori filtering. This procedure also provides quantitative information concerning interactions between frequencies. Fundamental frequencies in local field potential data acquired from the hippocampus, cortex, and striatum from awake, behaving rats were calculated using this technique. Characteristic frequencies identified using this technique from hippocampus and cortex agreed with known oscillations. Application to dorsal striatal local field potentials identified a low-frequency theta component as well as a narrow gamma band oscillation at 50-55 Hz.