The third age of computing - The Computing Universe: A Journey through a Revolution - page 328

Hawkins ( B.16.4 ) has built on these ideas of neurons and memory and proposed
an alternative model of the brain to the computationalist view discussed in the
preceding text. We briefly outline some of the key ideas of his memory-prediction
theory of intelligence.
Hawkins believes that any model of the brain and intelligence needs to
incorporate neurons with feedback and be able to respond to rapidly chang-
ing streams of information. He focuses his attention on the architecture of the
human cortex, the part of the brain responsible for higher functions, such as
voluntary movement, learning, and memory. As we described in Chapter 15 , the
cortex is about 2.5 millimeters deep and is made up of six layers, each about as
thick as a playing card. The cortex is estimated to contain around thirty billion
neurons, each with thousands of connections making a total of more than thirty
trillion synapses, the junctions at which nerve impulses pass from one neuron
to another. Neurologists have found that the cortex consists of many different
functional regions, each semiindependent and specialized for certain aspects of
thought and perception. Each region is arranged in a hierarchy, with “lower”
areas feeding information up the hierarchy and “higher” areas sending feed-
back back down toward the lower layers, although the terms higher and lower are
not necessarily related to their physical arrangement in the brain. The lowest
areas are the primary sensory areas, where sensory information arrives. The cor-
tex has regions to process sensations from the eyes, the ears, and the skin and
internal organs, and each region has its own hierarchies of regions. The cortex
also has “association” areas where inputs from more than one sense can be com-
bined. There is also a motor system in the frontal lobes of the brain that sends
signals to the spinal cord and thus moves muscles. The hierarchies of all these
sensory areas look very similar. This similarity led Vernon Mountcastle ( B.16.5 ), a
neuroscientist from Johns Hopkins University in Baltimore, to propose a model
for the basic structure of the cortex in a paper titled “An Organizing Principle
for Cerebral Function.”
In 1950, Mountcastle had discovered that the cortex was organized into
vertical columns of neurons, with each column having a particular function.
In 1978, he proposed that all parts of the cortex operate on a common prin-
ciple, with the cortical column being the fundamental computational unit
( Fig. 16.10 ). All the inputs from our primary sensory areas arrive at the cortex as
patterns of partly chemical and partly electrical signals. We rely on our brains
to make sense of this stream of data and to produce a consistent and stable
view of the world. For example, several times a second, our eyes make sudden
movements called saccades . With these saccades, the focus of our eyes moves
around, locating interesting parts of the scene so that our brain can build up
a three-dimensional model of what we are seeing ( Fig. 16.11 ). Our impression
of a stable world with objects and people moving in a continuous way is only
possible because our brain has the processing capability to make sense of this
continuous stream of changing retinal patterns ( Fig. 16.12 ). Mountcastle spec-
ulated that all neurons in the cortex use the same basic algorithm to process
the different input patterns arriving at the different sensory input regions -
those for vision, hearing, language, motor control, touch, and so on. In other
words, the brain processes patterns and constructs a model of the world that
it then holds in memory made up of neurons and their synapses.

B.16.4. Jeff Hawkins is a computer
entrepreneur most known for
his work on handheld computing
devices such as the Palm Pilot and
the Treo. He invented the handwrit-
ing character recognition system
known as Graffiti for use with such
devices. In addition to his success-
ful career in the computer industry
Hawkins has a deep interest in the
function of the brain and wrote the
topic On Intelligence describing his
memory-prediction framework of how
the brain works.

B.16.5. Vernon Mountcastle is
Professor Emeritus at Johns Hopkins
University. He is best known for his
discovery of the columnar organ-
ization of the cerebral cortex in the
1950s. In 1978 he proposed that
all parts of the cortex operate on a
common principle based on these
cortical columns.