Which scenario typically does NOT cause an attenuation of the posterior dominant alpha rhythm in a normal adult?

In the context of EEG patterns, the posterior dominant alpha rhythm is typically observed in a relaxed, alert state, particularly when the eyes are closed. When the eyes are closed and the individual is relaxed, this rhythm is pronounced and can be seen prominently on the EEG. This state is characterized by the eyes being shut, leading to a reduction in visual sensory input, which allows for the full expression of the alpha rhythm in the brainwaves.

In contrast, opening the eyes or engaging in complex cognitive tasks like solving math problems can lead to an attenuation of the alpha rhythm. This is because visual stimuli and cognitive processing activate other brain areas, which can disrupt and diminish the alpha frequency activity. Light sleep, while it may initially show alpha activity, typically transitions into different sleep stages where alpha rhythms are suppressed or altered.

Thus, relaxed wakefulness with the eyes closed is the scenario that does not attenuate the alpha rhythm in a normal adult, as this is the condition under which the alpha rhythm is most robustly observed.