What is mainly measured by electroencephalography (EEG)?

Electroencephalography (EEG) is primarily used to measure the electrical activity in the brain. This technique involves placing electrodes on the scalp to detect electrical impulses produced by the activity of neurons. Because neurons communicate with one another through electrical signals, EEG provides valuable insights into brain function, including identifying neurological disorders, monitoring brain activity during surgeries, and understanding various states of consciousness such as sleep.

The other options pertain to different physiological measurements. For instance, measuring blood flow in the brain is more commonly associated with techniques like functional magnetic resonance imaging (fMRI) or positron emission tomography (PET). Hormonal levels would typically be measured through blood tests or other biochemical assays, while temperature regulation is monitored by thermometers or physiological measures related to homeostasis. Thus, the focus of EEG on electrical activity distinguishes it from these other monitoring techniques.