Two models of the brain

Until five years ago, the dominant model of the brain was hierarchical, focused on individual neurons and patterned on the way digital computers work. In brief, the hypothesis held that single neurons operated by detecting features in the environment. At the base level, individual neurons in the optic region of the brain, for example, would detect simple features, such as lines and edges. At the next level, higher order neurons integrated data from the hundreds of lower order neurons to which each was linked to detect more sophisticated features — a red ball, for example, or green squares. At the highest level, cardinal neurons would integrate sensations of higher order neutrons to recognize concepts such as "grandmother's face."

Problems confronted the hypothesis from the start. First, there was the "binding" problem — how could information obtained by different means be bound together into a single perception? How could the neuron that recognized grandmother's face, the neuron that recognized her voice, and the one that recognized the word "grandmother" all work together to create a single perception of grandmother? Closely linked with this was how billions of individual neurons could produce a single consciousness.

A competing model, now becoming dominant, contends that the brain stores and processes information only when millions of neurons work together, with their electric potentials correlated or synchronized in patterns at various frequencies. Large-scale electrical fields produced by the brain and recorded as electroencephalograms can only be produced by the cooperative actions of many neurons, the theory holds. These cell assemblies, as they are called, are not anatomical entities. Rather, they are temporary functional collections of neurons scattered across wide areas, or even throughout the brain, whose firings are correlated or synchronized at a given frequency.

The newer model makes it much easier to understand the data from brain mapping which show that close coordination of several relatively large regions of the brain are essential for almost any activity. In turn, since the model hypothesizes that it is the patterns of brain activity in space and time that are important, not the states of individual neurons, it makes brain mapping essential to understanding how the brain works.

Also:

Two models of the brain

Brain maps old and new