PGO waves

Ponto-geniculo-occipital waves or PGO waves are phasic field potentials. These waves can be recorded from the pons, the lateral geniculate nucleus (LGN), and the occipital cortex regions of the brain, where these waveforms originate. The waves begin as electrical pulses from the pons, then move to the lateral geniculate nucleus residing in the thalamus, and then finally end up in the primary visual cortex of the occipital lobe. The appearances of these waves are most prominent in the period right before rapid eye movement sleep (or REM sleep), and are theorized to be intricately involved with eye movement of both wake and sleep cycles in many different animals.

The discovery of PGO waves goes back to 1959, when three French scientists released their scientific article of their study of these waves in animal test subjects. Although at this time, they did not have a specific name for this neurological phenomenon.

It was not until the published work of two American scientists that these waves became known as PGO waves. Their research focused on the propagation of these waves in cats, noticing that these field potentials started in the pons, propagating down to the lateral geniculate nucleus and the occipital lobe.

Other studies with these waves have been done on rats as well. Scientists tried to discern whether the rats had PGO waves, but learned that they are present only in the pons, and wave propagation does not excite any neurons in the lateral geniculate nucleus. As a result of this study, PGO waves are known as P waves in rodents.

PGO waves have been studied mostly through cat and rodent animal models. Despite the focus of the research, PGO waves have been found to exist in other mammalian species including humans and nonhuman primates, such as the macaque and baboon.

In the original experiments, PGO waves (or P waves in rodent models) are found by placing electrodes inside the brain, next to either the pons, lateral geniculate nuclei, or occipital lobe. Along with electroencephalography (EEG) recording techniques, scientists are also able to show the correlation between other brain waves associated with REM sleep and PGO waves.

Although scientists know they exist, PGO waves have not been detected in healthy humans due to the ethical concerns about accessing these areas where the readings need to be taken from. However, advances in deep brain stimulation has made it possible to put electrodes inside the brains of humans with different pathologies and make EEG recordings of different nuclei. Due to the similarities with the animal models, we can infer that PGO waves are happening at the same frequency in human EEGs. Thus, scientists can infer that PGO waves exist in humans.

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Wikipedia