How much energy does the human brain consume?

The answer

The human brain accounts for only about 2% of total body weight but consumes approximately 20% of the body's total energy output, running on roughly 20 watts of power, comparable to a dim light bulb. This disproportionate energy demand stems from the metabolic cost of maintaining electrochemical gradients across the membranes of roughly 86 billion neurons, each forming up to 10,000 synaptic connections. The brain consumes about 5.6 milligrams of glucose per 100 grams of brain tissue per minute and is so sensitive to energy deprivation that just 10 seconds without blood flow causes unconsciousness.