Six to seven Hz theta activity in a normal adult is typically seen during which condition?

Six to seven Hz theta activity is indeed typically observed in normal adults during the onset of drowsiness. This frequency range is associated with the transition from wakefulness to sleep, where the individual may experience a relaxed state and an increasing propensity to drift into sleep.

During this phase, the brain begins to shift its electrical activity from the faster beta waves that characterize alertness, to slower theta waves, indicative of a decrease in sensory processing and an increase in internal thought processes. Theta activity is significant in the drowsy state as it reflects a moment of reduced engagement with the external environment and an approach towards sleep initiation.

In contrast, deep sleep predominantly features delta waves (below 4 Hz) rather than theta waves. Intense concentration typically results in beta activity (above 12 Hz), reflecting heightened cognitive engagement and focus. Being awake and alert is associated with a predominance of beta waves, representing active processing and wakeful states. Thus, the distinction of theta activity as seen during drowsiness makes it a clear marker for that specific transitional phase.