The book is about Hawkins' theory of how the mammalian cortex, especially the human cortex, works. Hawkins thinks it is only by understanding the cortex that we will be able to build truly intelligent machines. Blakeslee has aided him in presenting this theory so that it is accessible by the general public. I am very impressed by the theory of the cortex, but I do not agree that the cortex is the only way to achieve intelligence.
Hawkins defines intelligence as the ability to make predictions. I think this is an excellent definition of intelligence.
He says the cortex makes predictions via memory. The rat in the maze has a memory which includes both the motor activity of turning right and the experience of food. This activates turning right again, which is equivalent to the prediction that if he turns right, food will occur.
The primate visual system, which is the sense best understood, has four cortical areas that are in a hierarchy. In the lowest area, at the back of the head, cells respond to edges in particular locations, sometimes to edges moving in specific directions. In the highest area you can find cells that respond to faces, sometimes particular faces, such as the face of Bill Clinton.
But the microscopic appearance of the cortex is basically the same everywhere. There is not even much difference between motor cortex and sensory cortex. The book makes sense of the connections found in all areas of the cortex.
The cortex is a sheet covering the brain composed of small adjacent columns of cells, each with six layers. Information from a lower cortical area excites the layer 4 of a column. Layer 4 cells excite cells in layers 2 and 3 of the same column, which in turn excite cells in layers 5 and 6. Layers 2 and 3 have connections to the higher cortical area. Layer 5 has motor connections (the visual area affects eye movements) and layer 6 connects to the lower cortical area. Layer 6 goes to the long fibers in layer 1 of the area below, which can excite layers 2 and or 3 in many columns.
So there are two ways of exciting a column. Either by the area below stimulating layer 4, or by the area above stimulating layers 2 and 3. The synapses from the area above are far from the cell bodies of the neurons, but Hawkins suggests that synapses far from the cell body may fire a cell if several synapses are activated simultaneously.
The lowest area, at the back of the head, is not actually the beginning of processing. It receives input from the thalamus, in the middle of the brain (which receives input from the eyes). Cells in the thalamus respond to small circle of light, and the first stage of processing is to convert this response to spots to response to moving edges.
And the highest visual area is not the end of the story. It connects to multisensory areas of the cortex, where vision is combined with hearing and touch, etc.
The very highest area is not cortex at all, but the hippocampus.
Perception always involves prediction. When we look at a face, our fixation point is constantly shifting, and we predict what the result of the next fixation will be.
According to Hawkins, when an area of the cortex knows what it is perceiving, it sends to the area below information on the name of the sequence, and where we are in the sequence. If the next item in the sequence agrees with what the higher area thought it should be, the lower area sends no information back up. But if something unexpected occurs, it transmits information up. If the higher area can interpret the event, it revises its output to the lower area, and sends nothing to the area above it.
But truly unexpected events will percolate all the way up to the hippocampus. It is the hippocampus that processes the truly novel, eventually storing the once novel sequence in the cortex. If the hippocampus on both sides is destroyed, the person may still be intelligent, but can learn nothing new (at least, no new declarative memory).
When building an artificial auto-associative memory, which can learn sequences, it is necessary to build in a delay so that the next item will be predicted when it will occur. Hawkins suggests that the necessary delay is embodied in the feedback loop between layer 5 and the nonspecific areas of the thalamus. A cell in a nonspecific thalamic area may stimulate many cortical cells.
I think this theory of how the cortex works makes a lot of sense, and I am grateful to Hawkins and Blakeslee for writing it in a book that is accessible to people with limited AI and neuroscience.
But I am not convinced that the mammalian cortex is the only way to achieve intelligence. Hawkins suggests that the rat walks and sniffs with its "reptilian brain", but needs the cortex to learn the correct turn in the maze. But alligators can learn mazes using only their reptilian brains. I would have been quite surprised if they could not.
Even bees can predict, using a brain of one cubic millimeter. Not only can they learn to locate a bowl of sugar water, if you move the bowl a little further away each day, the bee will go to the correct predicted location rather than to the last experienced location.
And large-brained birds achieve primate levels of intelligence without a cortex. The part of the forebrain that is enlarged in highly intelligent birds has a nuclear rather than a laminar (layered) structure. The parrot Alex had language and intelligence equivalent to a two year old human, and Aesop's fable of the crow that figured out to get what he wanted from the surface of the water by dropping stones in the water and raising the water level, has been replicated in crows presented with the problem.
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- Reviewed in the United States on April 26, 2010
- Reviewed in the United States on September 11, 2009
Top reviews from other countries
- Mike AdamsReviewed in Australia on September 30, 2018
The breakthrough book on brain science that the neuroscience community missed! Still relevant.
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- M A MohamedReviewed in the United Kingdom on September 8, 2014
Is this the M-Theory of the Intelligent Machines?
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