Complex sentence: NAA gives off the largest signal in magnetic resonance spectroscopy of the human brain, and the levels measured there are decreased in numerous neuropathological conditions ranging from brain injury to stroke to Alzheimer's disease.
Split into simpler sentences: NAA gives off the largest signal in magnetic resonance spectroscopy of the human brain. The levels measured there are decreased in numerous neuropathological conditions ranging from brain injury to stroke to Alzheimer's disease.