Q: Why do cellphones turn people into such crummy drivers?

A: Activities such as driving and being aware of your surroundings (a.k.a. â€not being a jerkâ€) have a few things in common: Both are complicated tasks that require the brain´s full attention, and both are often sidelined as we overwhelm our frontal lobes´ processing power with the ultra-distracting cellphone.

â€Multitasking†is a term that originally referred to a computer´s ability to execute several commands concurrently. Naturally, we assume our brains can do the same thing. But many researchers agree that our alleged modern ability for gaming, downloading, texting, and talking simultaneously is just a myth. Technically, our big human brains can´t even do two things at the same time without paying a price.

The multitasking myth, says cognitive researcher Jordan Grafman of the National Institute of Neurological Disorders and Stroke, stems from the ability of part of the frontal lobe to toggle back and forth among simple tasks in as little as a few hundred milliseconds and among complex tasks in only a few seconds. It may seem like doing two things at once, but even these tiny lapses create delayed response times that can lead to car accidents. What´s more, Grafman says, the frontal lobe is also responsible for your ability to observe and reflect on your surroundings. Cellphones degrade this ability because of their extra demand on your brain (which probably explains why people on the street bray into their phones, despite your giving them the evil eye). Finally, according to a recent University of Utah study, phoning while driving doubles the likelihood of rear-ending the car in front of you, even if you´re using a hands-free headset - the lack of visual cues, compared with just speaking to a passenger, is too taxing.

Q: Do you use more energy when you´re thinking really hard?

A: Need to lose some flab? Sit your big butt down with a math book-and feel the burn. The human brain is a 24-hour workhorse. While you´re thinking, millions of neurons fire messages back and forth to each other and to the various tissues in the body. These neurons need fuel, consuming a full 75 percent of the blood sugar from the liver and 20 percent of the body´s total used oxygen. Here´s how your neurons feed: Astrocytes-the cells near the capillary walls in your brain-suck energy-rich glucose from the bloodstream and convert it into a form that the neurons can soak up. The neurons then use it to fuel the production of neurotransmitters and, eventually, conscious thought. â€The more energy an area of the brain wants, the more glucose that part of the brain will break down,†explains neurologist Harry Chugani of the Children´s Hospital of Michigan. â€So yes, if you´re thinking really hard and really struggling with your thoughts, the neurons in the frontal lobes of your brain will be burning a lot more glucose.â€

Simply to survive, your brain requires a tenth of a calorie per minute. Compare this with a walk to the doughnut shop, when your body burns approximately four calories a minute. Kickboxing zaps 10 calories a minute. And when you´re hunched over a crossword puzzle? Your brain is blasting through a respectable 1.5 calories a minute. Pass the Cheetos.