a thinking brain
Glen M. Sizemore
gmsizemore2 at yahoo.com
Tue Jun 29 05:42:13 EST 2004
Ray's view that CPG's are a big part of the key to understanding behavior
has much merit. And, perhaps, so does his view of the role played by the
thalamic structures. But anyone who thinks that the processes of
habituation, classical conditioning, and operant conditioning (especially
operant conditioning!) are irrelevant to this endeavor has clearly missed
the boat. The basic principles investigated in the laboratory are exactly
what must be explained. The acquisition of operant behavior and its control
by certain stimulus configurations is a matter of the alteration of
spontaneous behavior by its consequences. This process is central to
behavior; the only process that is more fundamental is that which
necessarily preceded it - i.e., the very occurrence of behavior that is
spontaneous at the level of behavior (that is, not elicited), and this is a
very old, and fundamental, phenomenon indeed.
"ray scanlon" <rscanlon at nycap.rr.com> wrote in message
news:363d693e.0406280918.31f79c1 at posting.google.com...
> Learning is not fundamentally part of the process of thinking,
> although thinking presupposes learning. If the thalamic reticular
> nucleus were active in the brain as constructed by the DNA, it is
> difficult to image anything of interest happening. When we talk about
> thinking, we subconsciously posit a brain that has been up against the
> environment and has learned a few things.
> Before we consider what in learning is germane to the design of a
> thinking brain, we should point out what is not. The research on
> learning by psychologists is almost wholly irrelevant. What is
> behavior except the expression of a motor program through the
> motoneurons? Our interest is in the motor program as it passes through
> the thalamus. At this level, all motor programs are the same. They are
> just motor programs. They all have their origin in a pattern
> generator. We think of pattern generators in groups. For instance,
> reaching, grasping, and punching form a group that we distinguish from
> kicking. However, future research may locate all of these pattern
> generators in one small region, in which case we might want to group
> them together on anatomical grounds. Who can say? It is not important.
> It is widely held that there are two basic types of memory, long term
> and short term. It is also held (but not so widely) that long term
> memory involves structural change in the neuron and that short term
> does not. Both are involved in thinking
> Many candidates for structural change are advanced. The most popular
> ones involve the synapse. The area of the synapse can be increased or
> new synapses formed. The post-synaptic density can be increased. The
> pre-synaptic potential or propensity for releasing neurotransmitter
> can be increased. There seems no end to possibilities.
> To those interested in thinking, these many choices have little
> meaning. The brain can learn and that is enough.
> With learning comes forgetting. And forgetting may be just as
> important. New synapses can be formed, but old ones can be sloughed.
> The brain is alive and interacting with the environment. At the same
> time, we must always remember that the basic architecture of the
> brain, as laid down by the DNA, is unalterable. The nuclei remain
> unaltered, but smaller regions may be reorganized.
> There are endless schemes, of course, for explaining how one learns to
> avoid fire and other dangerous things, but we will choose one that
> appeals on grounds of simplicity.
> Learning to avoid the bad and approach the good are two sides of the
> same coin. We will assume that upon disaster a neurohormone is
> released-call it the A neurohormone. Upon a success, a different
> neurohormone is released-call it the B neurohormone.
> The A neurohormone strengthens recently exercised excitatory synapses
> in the thalamic reticular nucleus and also (possibly) inhibitory
> synapses in the central pattern generator that initiated the action.
> Note that excitatory synapses in the thalamic reticular nucleus
> include not only the motor program but also sensory input from the
> If the same bad situation arises again, the motor program will tend
> not to be activated, and if it is activated it will tend to be stopped
> at the ventral anterior-ventral lateral complex. Bad things are
> Exactly the reverse happens with the B neurohormone. Recently
> exercised inhibitory synapses in the thalamic reticular nucleus and
> also (possibly) excitatory neurhormones in the central pattern
> generator that initiated the action.
> If the same good situation arises again, the motor program will tend
> to be activated and will be passed through the ventral
> anterior-ventral lateral complex. Good things are approached.
> This fandango with the A and B neurohormones is enough to get us
> through life.
> A neurohormone is a hormone produced by or acting on the nervous
> system, compared to hormones produced by the endocrine system.
> The brain could have been organized as a mass of equipotential
> neurons. It wasn't. One wonders why. A possible explanation is to
> restrict the activity of neurohormones. Releasing a neurohormone in
> the thalamic reticular nucleus, as an instance, would tend to
> concentrate the hormonal activity where it would do the most good. If,
> of course, the goal of the neurohormone is to reach neurons in the
> thalamic reticular nucleus.
> In the last analysis, we are always reduced to the principle of
> survival. That which survived, survived. A brain composed of nuclei
> did survive.
> When one reaches for a cup of coffee, a hierarchy of neurons is
> activated. A reaching pattern controller is activated. It fires a
> reaching pattern initiator. The reaching pattern initiator releases a
> reaching pattern generator that, in turn, sets off the motoneurons. We
> We speak of these as units, but in the mammalian brain they are
> populations of neurons, not individual neurons. To return to the cup
> of coffee, does the reaching pattern controller consist of fifty or
> five hundred neurons? It is certainly a relatively small number, but
> not too small. It is important to remember that the reaching pattern
> controller, initiator, generator, is set up by the DNA, not by
> experience. Experience modifies the pattern generator and the thalamic
> reticular nucleus, as we have set out above.
> In one sense, of course, all the neurons are working all the time, but
> some are more equal than others. On the one hand, we see the original
> neural net as it exists in the most primitive animals. Excitation
> flows back and forth through the neural net. At one glance, all are
> equal. But there are cusps. The excitation does become concentrated at
> points. Evolution has caused these cusps to reside in nuclei-that's
> about all there is to it.
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