[Rolland Swank]

I enjoyed the book very much and hope it can stimulate at lot of new research. In the same week that I read On Intelligence I found another new book which may be of interest to readers of this forum:

"A Brief Tour of Human Consciousness", by V.S. Ramachandran.

In many ways, the two books complement each other.

In working through Chapter 6 of On Intelligence, I ran into a possible typo.

On page 144, 2nd paragraph from the top, Hawkins is discussing the interconnections between regions. In the last sentence of the paragraph, he seems to be saying that when axons leave a layer 6 region, the
signals leave the higher region at layer 6, travel through the myelin insulated "wire", then enter a new column (I assume in
the lower region) at layer 6.

Yet, on page 142 he discusses how feedback starts in a layer 6 in a higher region then spreads across layer 1 in a lower region.

So shouldn't the last sentence in the 2nd paragraph, page 144 read:

"When axons leave the white matter, they enter a new cortical column at layer 1." (not layer "6" as it states).

Am I right about this, or am I missing something?

Rolland

[Jeff Hawkins]

I agree this may be a bit confusing, but it is correct as written. Let me try to explain. Layer 1 of the cortical sheet for the most part is up agains the skull. All axons leave and enter the cortex via layer 6, the "bottom" side of the cortex. If the cortex was a napkin, all the axons coming and going hang off of one side.

However, even though they enter and leave through layer 6 they can originate in different layers or terminate and form synapses in different layers.

So cells in layer 6 send axons down into the white matter. These axons reenter the cortex in another region through layer 6 but the axons rise up to layer 1 where they spread.

I hope that makes it clearer.

[Rolland Swank]

Yes, thanks, that does clear things up.

It is also unfortunate that the brain "numbering systems" conflict. For example, in discussion the visual regions, V1 is lower than V2 which is below V4, etc. while in the cortex layers, L6 is below L5 which is below L4 etc. It just seems to make things more complicated than they have to be.


Rolland

[bhartsb]

Yes just putting in "All axons leave and enter the cortex via layer 6, the "bottom" side of the cortex" would help a lot.

[Don]

To keep things straight, I find it helpful to recall that the layers of cortex were numbered from the anatomist's perspective, as he dissected the brain, going from the outside in. Regions like V1, V2, and A1, A2, and simklar "fields" discussed in neuropsychology and neural models reflect "pathway order", typically running from sensory receptors, through the thalamus and on to successive cortical fields.
_________________
Don Loritz

[danshawen]

The engineering discussion of the neocortex was interesting, but I had a few minor problems with it.

"Feedback" of various kinds are used for many different functions in electronic engineering:

1) NEGATIVE feedback superimposes a portion of the output that is OUT OF PHASE or INVERTED with the input, in order to eliminate distortion that might otherwise occur as a result of....

2) POSITIVE feedback, because it superimposes a portion of the output that is IN PHASE with the input, eventually causes distortion in the form of clipping. In the case of human neurons which operate between the ionization energy levels of sodium and potassium ions, this must be a particularly sensitive balance, because the diffence is so small.

Negative feedback may also be used to attenuate (gains less than unity), OR ELSE TO SCALE INPUTS FROM VARIOUS SENSOR INPUTS, so that they can be effectively stored in a form that will be useful.

[danshawen]

The engineering discussion of the neocortex was interesting, but I had a few minor problems with it.

"Feedback" of various kinds are used for many different functions in electronic engineering:

1) NEGATIVE feedback superimposes a portion of the output that is OUT OF PHASE or INVERTED with the input, in order to eliminate distortion that might otherwise occur as a result of....

2) POSITIVE feedback, because it superimposes a portion of the output that is IN PHASE with the input, eventually causes distortion in the form of clipping. In the case of human neurons which operate between the ionization energy levels of sodium and potassium ions, this must be a particularly sensitive balance, because the diffence is so small.

Negative feedback may also be used to attenuate (gains less than unity), OR ELSE TO SCALE INPUTS FROM VARIOUS SENSOR INPUTS, so that they can be effectively stored in a form that will be useful.