[Peculiar and random activity in Macaca: delta rhythm at the vertex]

Area of Science:

• Neuroscience
• Primate Electrophysiology
• Sleep Research

Background:

• Waking and sleeping electroencephalogram (EEG) activities are established in Cercopithecinae primates.
• A previously undocumented EEG phenomenon was observed in several macaque species.

Purpose of the Study:

• To describe a novel, random EEG activity observed in macaque species.
• To characterize the features and prevalence of this unique brainwave pattern.

Main Methods:

• EEG recordings were conducted on three macaque species: M. mulatta, M. fascicularis, and M. nemestrina.
• Analysis focused on identifying and quantifying bursts of monophasic slow waves during waking and REM sleep.

Main Results:

• A distinct 'delta vertex rhythm' was identified, characterized by slow waves (250-400 msec) at approximately 3 Hz.
• This rhythm occurred in bursts (2-24 sec duration) with waxing and waning amplitude (50-480 microV), predominantly in midline, precentral, and supplementary motor areas.
• Occurrence varied between individuals and recording sessions; its total duration was minimal (0.45% and 0.065% in M. mulatta and M. fascicularis, respectively, over 12h).

Conclusions:

• The delta vertex rhythm represents a novel EEG finding in macaques, distinct from typical waking and sleeping patterns.
• Its occurrence is not correlated with age, sex, eye movements, or sawtooth waves, suggesting a unique physiological basis.