Alan Lightman in The New Yorker:
Every moment, our brains are bombarded with information, from without and within. The eyes alone convey more than a hundred billion signals to the brain every second. The ears receive another avalanche of sounds. Then there are the fragments of thoughts, conscious and unconscious, that race from one neuron to the next. Much of this data seems random and meaningless. Indeed, for us to function, much of it must be ignored. But clearly not all. How do our brains select the relevant data? How do we decide to pay attention to the turn of a doorknob and ignore the drip of a leaky faucet? How do we become conscious of a certain stimulus, or indeed “conscious” at all?
For decades, philosophers and scientists have debated the process by which we pay attention to things, based on cognitive models of the mind. But, in the view of many modern psychologists and neurobiologists, the “mind” is not some nonmaterial and exotic essence separate from the body. All questions about the mind must ultimately be answered by studies of physical cells, explained in terms of the detailed workings of the more than eighty billion neurons in the brain. At this level, the question is: How do neurons signal to one another and to a cognitive command center that they have something important to say?