I am going to write a few post on basic concepts in brain science. This first one is about oscillations.
A group of neurons that are close together is referred to as a population or cluster. A population will have a specific role, e.g. responding to a particular stimulus such as for example a cat.
When the neurons in a population fire at roughly the same time, then go quiet, and then fire again and repeat this process this is called an oscillation. The time when they fire is called a burst of firing. The number of bursts in a second is the frequency of the oscillation. A frequency of 1 Hertz or for short ‘Hz’ is 1 oscillation a second, which means that there will be one burst of firings and one period of silence. 10 Hz is 10 oscillations a second, 50 Hz is 50 oscillations a second etc.
Different names are given to different ranges of the frequency (Hz) of the oscillation (also called rhythms). The delta band rhythm ranges from 0.1−3.5 Hz. Theta rhythm ranges from 4−7.5 Hz. Alpha band is 8−13 Hz. Beta is 14−30 Hz, and gamma is 30-80 Hz.
The amplitude or power of the oscillation/rhythm is dictated by the number of neurons in a population that fire during a burst. If there is a population of 200 neurons and 10 fire in the burst that will have a lower power than if 150 neurons fire. 200 neurons firing during the burst in a population of 200 neurons will have the maximum possible amplitude/power.
The various rhythms have diverse associations. Thalamocortical networks display increased delta band power during deep sleep. Theta activity is increased during memory encoding and retrieval. Alpha band changes are associated with attentional demands. Beta oscillations have been related to the sensorimotor system. Of all the frequency bands the role of gamma is thought to be most extensive and is hypothesized to provide a mechanism that underlies many cognitive functions such as: attention, associative learning, working memory, the formation of episodic memory, visual perception, and sensory selection.
So for example, a population that responds to a cat with a gamma oscillation of very high power may indicate that you attending to a very strong visual perception of a cat.
I love that you’re providing a basic intro to oscillations! If I may correct you though — oscillations are a separate, but intertwined, phenomenon from spiking. Oscillations occur from rhythmic changes in membrane voltage potentials, which can be driven by upstream spiking and can lead to spiking, but they are not necessarily the product of rhythmic on/off spiking by the oscillating neurons. In other words, groups of neurons can produce oscillations without spiking.