Neuron count: about 86 billion neurons. Energy use: roughly 20 watts—about the power of a dim light bulb. Glial cells: supportive stars of brain signaling. Plasticity: brains rewire with learning and experience. Adult neurogenesis: new neurons can form in the hippocampus. Memory is fallible: recall can be distorted. Sleep: essential for memory and toxin clearance. Smell → memory: scents strongly cue emotions and memories. Neurotransmitters: dopamine, serotonin, acetylcholine shape mood and learning. Brain networks: default mode, salience, and control networks coordinate thinking.