Final answer:
In REM sleep, the response to CO2 may show REM rebound in non-depressed individuals as a way to cope with stress, with brain activity resembling that of wakefulness, and muscle paralysis except for essential functions. REM sleep's regulation of CO2 response is neither identical to wakefulness nor depressed but can vary.
Step-by-step explanation:
The response to CO2 (carbon dioxide) during REM (Rapid Eye Movement) sleep can be complex. In a non-depressed individual, the processing and regulation of CO2 may demonstrate REM rebound as an adaptive response to stress, which aims to suppress the remembrance of aversive events experienced during wakefulness. REM sleep is characterized by rapid eye movements, brain waves similar to those during wakefulness, and a paralysis of voluntary muscles except those necessary for circulation and respiration. REM sleep is involved in various aspects of learning, memory and emotional regulation. A deficiency in REM sleep can lead to REM rebound when normal sleep patterns resume, suggesting that REM sleep is homeostatically regulated. Therefore, in a normal individual, the response to CO2 during REM sleep is neither the same as when awake (wakefulness) nor necessarily depressed; it can be complex and may vary depending on individual conditions like stress or insomnia.