It's not even known how many kinds of cells there are in the brain. If you were looking for a periodic table of the brain, there is no such thing. I really like to think of the brain as a computer.
Edward BoydenFor the last century of neuroscience, lots of people have tried to control neurons using all sorts of different technologies - pharmacology (drugs), electrical pulses, and so on. But none of these technologies are precise. With optogenetics, we can aim light at a single cell, or a set of cells, and turn just that set of cells on or off.
Edward BoydenYou can imagine over very long timescales, perhaps far beyond the multi-decade time scale, we might be able to ask very deep questions about why we feel the way we feel about things, or why we think of ourselves in certain ways - questions that have been in the realm of psychology and philosophy but have been very difficult to get a firm mechanistic laws-of-physics grasp on.
Edward Boyden