Why do I get a slump in mental energy after eating a meal?                                                       —Pranati Kapadia, via e-mail

Paul Li, lecturer of cognitive science at the University of California, Berkeley, offers an explanation:
FALLING ASLEEP at your desk after that heaping bowl of pasta? You may be experiencing what people commonly refer to as a “food coma.” Medically known as postprandial somnolence, a food coma isn’t an actual coma but rather a lack of mental energy that people often experience after eating a large meal. Symptoms include drowsiness, lethargy and a lack of motivation. But not to worry—this postmeal phenomenon is harmless and can strike anyone who pigs out on foods loaded with carbohydrates, fats or sugars.
What is the link between eating a big meal and feeling sleepy? The process begins as food hits the stomach and small intestine. Eating stimulates activity in the parasympathetic nervous system, which tells your body to slow down and digest. The more food you consume, the more the parasympathetic nervous system revs up, causing your body to focus the bulk of its energy on digestion.
Although large quantities of any food can cause a food coma, common table sugar, or sucrose, found in desserts tends to be the main culprit. As food breaks down into glucose—the simplest form of sugar, which the body uses for fuel—you will experience a surge in
blood sugar. To counter this spike, your body releases the hormone insulin. Insulin helps to mop up the excess glucose in the blood and returns levels to normal. The increase in insulin also causes your brain to produce more serotonin and melatonin—two neurochemicals that can leave you feeling drowsy. Luckily, this sleepy sensation does not last long

How long does it take for your brain to realize you have started to wear a hearing aid?
—Eugene Rice, via e-mail

Kelly Tremblay, associate professor of speech and hearing sciences at the University of Washington, responds:

THE ANSWER is “instantly.” The brain is able to detect amplified sounds immediately after the insertion of a hearing aid, as long as the damage is not too significant.

Normally when sound enters the ear, acoustic information is relayed from the ear to the brain via nerve cells, called neurons. As the sound gets louder, more neurons fire simultaneously, which in turn allows the brain to detect the change in volume.

A hearing aid acts as a microphone, magnifying sounds that enter the ear. Hearing aids are mostly used in people who suffer from hearing loss because of damage to hair cells, the small sensory cells in the inner ear. Healthy hair cells can detect the magnified sounds from a hearing aid and convert them into neural signals. But the greater the damage to a person’s hair cells, the more severe the hearing loss and the more the hearing aid will need to make up the difference.

Hearing aids are able to help millions of people decipher sounds they could not access before, but these devices do not help everyone to the same degree. That is because although hearing aids make sounds louder, they do not repair or compensate for the damage that has taken place in the ear and the brain. As a result, hearing aids help the signals reach the brain, but the brain may not be able to process the signals, making the hearing aid less effective.