Final answer:
b) Low oxygen levels in the bloodstream can cause symptoms affecting the entire brain, such as anxiety, restlessness, and confusion, due to oxygen's critical role in brain function.
Step-by-step explanation:
The symptom that affects the entire brain, often causing anxiety, restlessness, and confusion, is most likely due to low oxygen levels in the bloodstream. Oxygen is essential for the brain's extensive electrical activity, and without a steady supply, the nervous tissue cannot function properly. Low oxygen levels in the bloodstream can lead to symptoms involving the entire brain because brain cells die quickly if their oxygen supply is cut off. Conditions such as a stroke, which involve a blockage of blood supply to the brain, can also lead to a loss of neurological function and similar symptoms.