Life expectancy has dramatically increased over the last 100 years. At the beginning of last century, the average life expectancy was 30-40 years, while the current world average life expectancy is almost 70 years. Unfortunately there are still great variations in life expectancy, between countries (guess what? people living in more developed countries live longer...) and within countries. (Guess what? Wealthier people live longer...). Today, people in the wealthier strata of developing countries can expect to live more than 80 years old. While the disparity in life expectancy is a policy issue (not discussed here), the overall dramatic increase in life expectancy brings out some interesting science issues. How can we fight the cognitive decline associated with aging (a side effect of the nice fact that we live longer)? How can we fix mood disorders often associated with a general cognitive decline? The real game changer will be the immortal cognition (well, not really, but close enough) and boundless happiness (ok, again, not really, but close enough) provided by painless brain stimulation.
Today, we have two main ways of stimulating the brain painlessly and non invasively: Transcranial Magnetic Stimulation (TMS) and Transcranial Direct Current Stimulation (TDCS). TMS stimulates the brain by inducing local magnetic fields over the scalp (which in turn induce electric currents in the brain), whereas TDCS uses weak direct currents. There are many different ways of stimulating the brain, and obviously many brain areas can be stimulated. We will be able to delay significantly cognitive decline and improve mood by stimulating brain areas that are collectively called 'association cortices.' Association cortices connect many other brain areas (their name comes from the fact that they associate many brain areas in neural networks). There are two main types of association cortices, in the front of the brain (called 'anterior' association cortices) and in the back of the brain (called 'posterior' association cortices). TMS has already been experimentally used for some years to treat depression by stimulating the anterior association cortices. The results are so encouraging that TMS is now an approved treatment for depression in many countries (FDA has approved it for the United States in October 2008). I believe we will see in the next two decades a great improvement in our ability to stimulate the brain to treat mood disorders. We will improve the hardware and the 'stimulation protocols' (how frequently we stimulate and for how long). We will also improve our ability to target specific parts of the anterior association cortices using brain imaging. Each brain is slightly different, in both anatomy and physiological responses. Brain stimulation coupled with brain imaging will allow to design specific treatments tailored to specific individuals, resulting in highly effective treatments.
The posterior association cortices (the ones in the back of the brain) are the first ones affected by Alzheimer's disease, a degenerative brain disorder affecting higher cognitive functions, for instance memory. The posterior association cortices also have reduced activity in the less dramatic cognitive decline that is often associated with aging. Brain stimulation will facilitate the activity of the posterior association cortices in the elderly by inducing synchronized firing of many neurons at specific frequencies. Synchronous neuronal firing at certain frequencies is thought to be critical for perceptual and cognitive processes. Our aging brain will get its synchronized neuronal firing going thanks to brain stimulation.
A final touch (a critical one, I would say) will be given by our ability to induce specific brain states during brain stimulation. The brain never rests, obviously. Brain stimulation always stimulates the brain in a given state. The effect of brain stimulation can be thought of the interaction between the stimulation itself and the state of the brain while it is stimulated. Stimulating the brain while inducing specific brain states in the stimulated subject (for instance, playing word association games that require the subject to associate words together, or showing the subject stimuli that are more easily associated with happiness) will result in much more effective treatments of cognitive decline and mood disorder.
This will be a real game changer. If my prediction is correct, we will also see dramatic changes in policy. People won't tolerate to be excluded from the beneficial effects of brain stimulation. Right now, people don't easily grasp insidious environmental factors or subtle differences in health care that result in dramatic individual differences in the long term (approximately ten years of life between the wealthy and the poor living in the same country), but they will immediately grasp the beneficial effects of brain stimulation, and will demand not to be excluded anymore. That's also a game changer.