High-frequency oscillations in human and monkey neocortex during the wake-sleep cycle

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Beta (β)- and gamma (γ)-oscillations are observed in cortical areas and are theorized to be inhibition-driven.
• The specific role of inhibitory neurons in human γ-oscillations and the large-scale organization of these oscillations remain unclear.

Purpose of the Study:

• To investigate the involvement of inhibitory neurons in β- and γ-oscillations in humans and monkeys.
• To examine the propagation and coherence of these oscillations across cortical areas during wakefulness and sleep.
• To determine the functional significance of oscillation coherence during different sleep stages, particularly slow-wave sleep (SWS).

Main Methods:

• Analysis of high-density microelectrode array recordings from human and monkey brains during the wake-sleep cycle.
• Classification of neuronal units into excitatory and inhibitory cell types.
• Examination of firing rates and phase-locking of neurons relative to β- and γ-oscillations.
• Assessment of oscillation propagation velocity and large-scale coherence across the cortical array.

Main Results:

• γ-oscillations in humans and β-oscillations in monkeys show significant involvement of inhibitory neurons in their firing rate and phase-locking.
• β- and γ-oscillations propagate consistently across the recording array during both wake and sleep.
• High coherence and functional interactions of β- and γ-oscillations across millimeters of neocortex are observed specifically during SWS, with pronounced interaction among inhibitory cells.

Conclusions:

• Inhibitory neurons play a dominant role in the generation and large-scale organization of β- and γ-oscillations in the awake and sleeping brain.
• The heightened oscillation coherence during SWS suggests a mechanism for coherent reactivation of wake-related neural patterns.
• This reactivation during SWS may be crucial for memory consolidation processes.