Effect of Morphine on γ-band of EEG Activity in the Orbital Frontal Cortex of Rhesus Monkey

Previous studies have shown that the ventral part of prefrontal cortex (vPFC) plays an important role in drug addiction. The increased interest in γ oscillations, now widely regarded as functionally relevant signals of the brain, underlines the importance of the concept of event-related oscillations for bridging the gap between single neurons and neural assemblies. In the present study, we examined the dynamics of γ oscillation activity (or γ-band power) associated with the development of morphine dependence in the vPFC by using electrophysiological techniques after injecting morphine (0, 0.5, 1.6, 5.0 and 8.0 mg/kg) in rhesus monkeys. The results show that the γ-band power had a long-term decrease associated with the development of morphine dependence, and the decrease in γ power had a negative relationship with the concentration of morphine. Those results suggest strongly that γ oscillation activities in the vPFC reflect morphine addiction, and indicate that the EEG γ oscillation may reflect the processes underlying morphine addiction.