θ oscillation in the anterior cingulate and β-1 oscillation in the medial temporal cortices: A human case report

In previous studies we observed γ (30-150Hz) and β-1 (10-20 Hz) oscillations in the medial temporal lobe (MTL) using subdural electrodes. The β-1 was present during wake and REM sleep while γ was present in all states. Recently we studied a patient (35 years M) with electrodes attached to the anterior cingulate cortex (ACC). This structure showed regular θ (5-6 Hz) oscillations. In the first recording, electrodes were attached to the MTL, that demonstrated the β-1 and γ oscillations. Two months later, electrodes were placed on orbitofrontal and ACC and an all night sleep recording was carried out. The ACC exhibited a highly regular and continuous θ oscillation during wakefulness and REM sleep, but not during NREM sleep. Since this same subject showed β-1 oscillations in the MTL, it is probable that the θ in the ACC is independent of β-1 in the MTL. This single case suggests the existence of two different frequency oscillators in the human limbic system. Elucidating their functional roles will be an interesting challenge for future studies.