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machine brains

ray scanlon rscanlon at wsg.net
Tue Sep 16 19:48:51 EST 1997


                                 Learning

Learning has two phases: one before genesis, the other epigenet-
ic. The part that comes before encompasses the entire history of
the living cell; survival has written it in the genome. The
genome constructs a brain-driven organism that can survive to
reproduce. The excitation of a particular pattern of neurons in
this brain is a drive. The part that comes after involves the
location of food and water sources, of sex partners, of secure
resting places, and the characteristics of the predator. The
neural plasticity that the genome installed is sufficient to
explain epigenetic learning. All epigenetic learning follows from
the satisfaction or frustration of a drive or from pain. 

The brain is plastic. Synapses are strengthened and weakened,
axons grow and new synapses are formed, weakened ones are
sloughed. Some specific cases are highly time dependent, others
continue throughout a lifetime. The Hebbian hypothesis is popu-
lar, that synapses are strengthened by coincident activation of
presynaptic and postsynaptic neurons. I suggest another
procedure. If either the approach or the averse network is
activated, recently active synapses in particular regions of the
brain are strengthened. This could be a hormonal effect.

The DNA wires a subset of the neurons in the NN to cause the
animal to approach things that in the past lead to survival of
the DNA. If the sensory neurons at the head end of a simple
creature sense food the DNA has wired the circuit to swing the
head toward the food. Some of these neurons evolved to form a
reinforcement circuit. They alter the brain to seek the good at a
greater distance. When the good has been acquired these neurons
will cause synapses to be strengthened that will cause the animal
to approach this good more forcibly in the future. An important
part of this network is the medial forebrain bundle. I call this
network the approach circuit.

The universe excites a sensory neuron. It excites one or more
interneurons that, in turn, excite a motor neuron. As humans, we
possess many interneurons (100 to 1000 billion, say). We speak of
this action as drive and motor response. Self excitation compli-
cates this process in the brain stem.

Third hypothesis: When a drive is satisfied the approach network
is activated, it strengthens recently energized synapses in the
reticular formation and the cerebellum.

Conjecture: When signal energy (internal or external) excites a
constellation of neurons in the brain stem or they self-excite,
we experience it subjectively as a drive; it causes motor activi-
ty. If the motor activity quiets the drive, it also excites
neurons of the approach network. The DNA has hardwired this group
of neurons to respond to the satisfaction of a drive.

Observation

When my approach network is active, I experience it with various
nuances; I know it as satisfaction, pleasure, success, euphoria.
When signal energy turns on the approach network, it strengthens
recently active synapses in that portion of the reticular forma-
tion that we denote the arousal system. If this complex of signal
energy occurs in the future, the arousal system will inhibit the
reticular nucleus of the thalamus and the associated motor
program will proceed through the thalamus to the motor and pre-
motor areas.

Conjecture: The DNA hardwired the approach network but neural
plasticity allows the environment to fine tune it.

Fourth hypothesis: When signal energy arouses the averse network,
it strengthens recently energized synapses in the reticular
nucleus of the thalamus.

Conjecture: The DNA has hardwired a group of neurons, the central
grey, to respond to failure to satisfy a drive or to body damage.
This is the averse network. When signal energy turns on the
averse network, it strengthens recently active synapses in the
reticular nucleus of the thalamus. If this complex of signal
energy occurs in the future, the reticular nucleus of the thala-
mus will halt motor programs flowing through the thalamus.

Conjecture: The DNA hardwired the averse network but neural plas-
ticity allows the environment to fine tune it.

Observation

I experience the activity of these neurons as frustration,
failure, depression, or pain. That which my genome wired my body
to approach, I am aware of as good; that which it wired my body
to avoid, I am aware of as bad. The approach and averse networks
exist because previous generations of the organism survived; I
may not ask for further explanation.

ray

-- 

email: rscanlon at wsg.net

If you are interested in how the brain works, visit
http://www.wsg.net/~rscanlon/brain.html 





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