The brain is a massively parallel computer implemented on special
purpose biological hardware. The computing element in the brain is a
neuron. The neocortex (most recently evolved part of the brain) has 28
billion neurons, in comparison to the 42 million transistors in the early
Pentium IV processor. There are perhaps twice as many neurons in the
cerebellum. Some neurons in the cerebellum receive inputs from as many as
200,000 neurons. In the neocortex, fan in is approximately equal to fan out
with a branching factor of about 10,000.
The above describes the low-level parallelism in the brain. The neocortex
is also exhibits hierarchical parallelism. Neurons form minicolumns.
Minicolumns form macrocolumns. Macrocolumns form cortical sheets. Cortical
sheets interact to perform computations that we call thinking.
This presentation describes this concurrency and hierarchical organization
with an eye toward developing large scale brain simulations on the new LITE
facility.