a thinking brain

ray scanlon rscanlon at nycap.rr.com
Sun Jul 4 22:05:33 EST 2004


David Longley writes:

> When I read what you write I'm usually annoyed by it. Why I ask?

It is received wisdom that if you say anything that challenges a
person’s basic beliefs, say in metaphysics, politics, family values,
religion, whatever, he will react with anger. Anyone who insists on
talking politics in a waterfront bar shall end up with his teeth
kicked in.

> You make assertions which are false.

I am entitled to examples. Please do give a few..


>  You make
> assertions which purportedly are at odds with what radical behaviourists
> have said and which probably are not.

This was what I was referring to in my first answer. I fail to see how
we can even talk about the brain without being in violation. So I must
accept your anger. (I could say that I tie this anger to excitation of
the thalamic reticular nucleus, and that this anger circuitry is
directly constructed by the DNA. Thus releasing a flood of
vituperation. Please consider it unsaid.)

> Let's start with what you refer to
> as "Central Pattern Generators" for example (in what follows, I'm not
> endorsing, just referencing).
> 
> <http://crab-lab.zool.ohiou.edu/hooper/cpg.pdf>

I had this paper in my files, so I dragged it out. Now what? I might
note at the outset that the “Central” conveys absolutely no
information. If there were lateral or peripheral pattern generators,
that would be a different story. But the literature is full of
“Central”. I suggest we speak of plain “pattern generators”.

> What's the origin of the notion "fictive motor programs" and how do you
> use the term?

Someone in the dim past, I think Nauta, at a conference on the basal
ganglia, said, “What is thinking but a (something, possibly motor act
or program) that is not connected to a motoneuron.” I thought this
idle remark as  having fundamental truth and started thinking of this
sequence of neural activity as “motor programs”. For a long time, I
thought of them as “potential motor programs”, but nowadays I think
“fictive” the better descriptive.

I use this phase to name the sequence of axonal impulses as it arrives
at the ventral anterior-ventral lateral complex. Coming into the
complex it is fictive, going out it is actual. Coming in it is fictive
because it may never get by the VA-VL complex. It may be halted and
disappear into the general neural excitement of the brain. Going out
it is actual because it is headed for the pre-motor and motor cortex
and thence to motoneurons and the muscles. Nothing can stop it once it
gets by the VA-VL complex.
 
> When you read the literature on this, do you think of operant behaviour?
> Does that lead you to think of operant *conditioning*? Seemingly not. Is
> that just because new terms have been coined and this distracts you
> (think intensional opacity) or is it that you are hoping to ground your
> folk psychological ideas in something which sounds like it's respectable
> biological/physical science (do you recall the Quine extract from "Mind
> and Verbal Dispositions" on this?).
 
No. I do not read that type of literature. As for Quine, he studied
under my hero, Whitehead, but it didn’t seem to take. Quine thought
there was fundamental truth in the predicate calculus, but Whitehead,
as a mathematician, knew better. Whitehead realized the predicate
calculus was flawed when he, together with Russell, tried to extend
the Principia Mathematica to include geometry. We still have a
plethora of analytic philosophers running around peddling gibberish.

Don’t ever get me started on Wittgenstein.

> There's another abstract from the web below. When you think about the
> thalamic reticular nucleus incidentally, do you think back to Hebb and
> his non specific thalamic projection system, and the EEG work in the 50s
> on the ARAS? Or do you think about what's been done on 5-HT, NA and DA
> ie the monoamine systems (which comprise a good part of the reticular
> formation?). These are "modulators". What modulates the modulators? As
> long as you don't go into the details, sure, you can sound like you're
> talking sense. The problem is that as soon as you do look into it, I bet
> you'll not only get cold feet, but you'll start to appreciate how *all
> of this talk is premised on an analysis of *b e h a v i o u r* in the
> first place*. People forget that when they read and write what they do.
> It's almost as if that ceases to be important!

Why should I get “cold feet”? I instantiated these things in computer
programs years and years ago. There is absolutely nothing like
computer programming to focus you attention on the details.

Hebbian association is interesting but trivial. It is the
strengthening (and weakening) of synapses in the presence of
neurohormones that I see as fundamental to learning. Just once,
touching a hot stove, creates fundamental changes in the brain. We do
not need hundreds of Hebbian “hot stove touchings” to learn that it
doesn’t pay to touch hot stoves.

(snip) then a quotation-- 
 
> "The thalamic reticular nucleus: more than a sensory nucleus?
> 
> McAlonan K, Brown VJ.
> 
> School of Psychology, University of St. Andrews, St. Andrews, United
> Kingdom.
> 
> "Sensory information is routed to the cortex via the thalamus, but
> despite this sensory bombardment, animals must attend selectively to
> stimuli that signal danger or opportunity. Sensory input must be
> filtered, allowing only behaviorally relevant information to capture
> limited attentional resources. Located between the thalamus and cortex
> is a thin lamina of neurons called the thalamic reticular nucleus (Rt).
> The thalamic reticular nucleus projects exclusively to thalamus, thus
> forming an essential component of the circuitry mediating sensory
> transmission. This article presents evidence supporting a role for Rt
> beyond the mere relay of sensory information. Rather than operating as a
> component of the sensory relay, the authors suggest that Rt represents
> an inhibitory interface or "attentional gate," which regulates the flow
> of information between the thalamus and cortex. Recent findings have
> also implicated Rt in higher cognitive functions, including learning,
> memory, and spatial cognition. Drawing from recent insights into the
> dynamic nature of the thalamic relay in awake, behaving animals, the
> authors present a speculative account of how Rt might regulate
> thalamocortical transmission and ultimately the contents of
> consciousness."

This is the old “Searchlight of Attention”. Forget it.

The halting of sensory input at the lateral and medial geniculate
bodies, and the basal complex is of the greatest interest and basic to
“thinking”, but it is fictive motor programs (not sensory information)
that is our present interest.

ray



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