Brain Day

Medical Meanderings 18 October 2006

It’s All In Your Head

“… art thou but a dagger of the mind, a false creation, proceeding from the heat-oppressed brain?”
William Shakespeare, “Macbeth”

When your alarm clock rings in the morning, the sound enters your auditory cortex of your brain, located just under your ears on the sides of your head. The auditory cortex sends the information to your reticular formation, a very primitive area at the top of your brainstem, stimulating multiple areas of the brain. You become conscious, dreams disappear, and another day starts.

You, in every way that we can understand, are contained in a three-pound lump of grayish-brown tissue in your skull. This wrinkled lump consumes 20% of your body’s energy and is an unimaginably complex network of some million billion connections, containing and creating your every memory, emotion, decision, sight and sensation.

As you shower, shave and brush your teeth, your frontal lobe, the newest part of your brain (in evolutionary terms) thinks about your day. Simultaneously, your motor cortex and sensory cortex--both inch-wide strips, running side to side, across the top of your head—coordinate and execute the complex behaviors of getting ready for your day. These activities occur with almost no input from your conscious, active frontal lobe.

You head out to the garage to go to work and, without looking, grab your keys out of your pocket or purse. Your sensory cortex, located just above your ears, effortlessly identifies the right key by its shape. You back out of the garage and your cerebellum, sitting just behind the brainstem, coordinates all the complex movements of your feet on the pedals, hands on the wheel and eyes on the rearview mirror. Suddenly, your visual cortex notes a dark shape move behind the car in the rearview mirror. Within milliseconds, the information is interpreted and sent to the motor cortex, and your feet hit the brakes. A second or two pass before your higher brain areas catch up, and you interpret the shape as the neighbor kid recklessly riding by on his new bike.

All day at work, as you concentrate on your job, a small area of the brain located a few inches behind your eyes regulates your heart beat, your rate of breathing, your body temperature and your appetite. Every new fact that enters your mind is processed by the hippocampus, a little seahorse-shaped area deep in the brain at the level of your temples. The hippocampus decides, like a master filing clerk, what facts are worth saving in long-term memory and what’s worth forgetting.

Procedural memory--the kind used to brush your teeth or ride a bike—is stored mainly in the cerebellum and motor areas of the frontal lobe. This kind of memory allows you to cook supper after work while using your attention to talk to a friend on the phone. Nothing gets dropped or burned. Your reticular formation, in concert with the tiny, melatonin-making pineal gland near the center of the brain, starts making you feel tired. Time for bed. You climb in, turn out the light and, as portion after portion of your brain enters sleep…another busy day ends.