Introduction

The two greatest unsolved mysteries in science are the origin of life and how a collection of cells in the brain can give rise to consciousness, emotion and the myriad of other sensations that collectively give us the feeling of being a human being. The origin of life is a possibly unique historical event, which is not now and may never be subject to experimental analysis. Consequently, understanding of this problem may be forever out of our reach. In contrast, brain function is amenable to experimental study at every level. The current impediment to understanding appears to be the massive complexity of neural systems, a more extreme example of a general problem in understanding biological systems. There is complexity at the molecular, cellular and anatomical/circuitry levels as well as complexity at the organizational/algorithmic levels. It is currently believed that this complexity is not necessarily out of reach of human understanding. Even partial success in solving these issues will have an impact on a broad range of human endeavors, from the understanding of mental diseases to questions about free will and the relationship between the individual and society.

This text focuses primarily on the ‘nuts and bolts’ of the nervous system, the electrical and biochemical functions of neurons. Unlike a computer program, where there is an overarching algorithmic design that can potentially be instantiated in multiple, very different hardware implementations, nervous system function is a tightly integrated product of evolution. The higher level functions of the nervous system are strongly constrained by the long evolutionary history of the underlying molecular and cellular biology. Brain function is intimately tied to the particulari-ties and peculiarities of this biology. For the brain, the computer engineering dichotomy between hardware and software does not exist. There is an intermingling of functions at every level of organization. Cognitive function, in all its forms, has a material basis that is directly knowable, subject to description and experimentation. Theories of brain function must ultimately be tied into our understanding of the material basis of neural function.