Ans. is 'a' i.e., Eye closed with active mindEEG rhythms and sleep wake cycleo Following EEG rhythms (Berger's rhythm) are important in relation to sleep wake cycle : -Alpha rhythm : - In adult humans who are awake but at rest with mind wandering and the eye closed, a- rhythm is prominent. It is a regular rhythm with a frequency of 8-13 Hz and amplitude of 50-100 V. It is most marked in parietal and occipital lobe. It is associated with decreased level of attention, i.e., person is awake but has decreased attention (relaxed) - Person is thinking but with decreased attention (subconscious thinking).Beta rhythm : - When attention is focused on something, the alpha rhythm is replaced by Beta rhythm. It is an irregular 13-30 Hz low voltage activity. It is most evident on frontal lobe and occurs when patient is fully awake and alert. Therefore this replacement of beta rhythm for alpha rhythm is called arousal or alerting response or alpha block. This phenomenon can be produced by any form of sensory stimulation or mental concentration such as solving arithmetic problems. Person is thinking with a maximum concentration - Conscious thinking.Theta rhythm (4-7 Hz) : - When person with alpha rhythm becomes slightly more relaxed (as occurs when there is transition from wakefullness to sleep, i.e., stage 1 of REM), alpha rhythm is replaced by theta rhythm. Thinking is present but with even less attentiveness than which was present in alpha rhythm stage (Deep subcsoncious thinking). Two types of theta rhythm have been described : -Hippocampal (occurs in mammals other than men, i.e., cat dogs, etc).Cortical (occurs in men)Delta rhythm (3-5 Hz) : - It is present when the person is in deep sleep (NREM stage 3 & 4) and there is no thinking.