Gradual changes in amplitude, frequency, or spatial distribution of rhythms is known as?

Gradual changes in amplitude, frequency, or spatial distribution of rhythms are encompassed by the term "evolution." In the context of neurophysiology, evolution refers to the progressive development of brain wave patterns over time. This may manifest as alterations in the characteristics of brain rhythms, indicating changes in neural activity associated with different cognitive or behavioral states.

For instance, during different phases of sleep or when transitioning between levels of alertness, brain activity may exhibit gradual changes reflective of evolutionary patterns. Recognizing these evolutions can provide insights into the functioning of the brain and the various states of alertness or sleep cycles.

The other options do not capture this concept effectively. Asymmetry typically refers to differences in waves or signals between two sides of the brain, which is not about gradual changes. Attenuation relates to a reduction in amplitude or power of a signal, rather than changes in its characteristics over time. Background activity describes the ongoing electrical activity of the brain that is unrelated to specific tasks, but it does not specifically address the systematic and gradual changes that evolution implies.