Mu rhythm and alpha rhythm differ in all of the following respects EXCEPT:

Mu rhythm and alpha rhythm are both types of brain waves measured by EEG and share similarities, particularly in terms of frequency. The frequency of both mu and alpha rhythms falls within a comparable range, typically around 8-12 Hz. Therefore, when considering the differences between these two rhythms, frequency is not a distinguishing factor, making it the correct choice for this question.

In contrast, incidence refers to how often these rhythms occur and their typical presence in different states of consciousness or during specific activities, which diverges between mu and alpha rhythms. Topography involves the spatial distribution of the rhythms across the scalp, which also varies significantly. Additionally, the form of the wave, including its shape and characteristics, differs between the two rhythms, reflecting variations in their underlying neural sources and functional roles in brain activity. Thus, frequency remains the only aspect where mu rhythm and alpha rhythm do not differ significantly.