116. Brain Complexity

5 Jul

In my Blog-114, I provide some information on brain micro-structure:
“Our nervous system is composed of billions of nerves with around 150 trillion interconnections called synapses, and other connection variations. Further, each synapse (which functions like a transistor) has a complicated and variable structure. The nerve cells, their branching structures, and connections, provide all of our simple and complex behaviors.”

In my study of neuron science, I often see proposals and conjectures
regarding total brain simulations, and even the transfer of stored brain info
to a gigantic computer as a way of prolonging life. One speculator proposes that a person’s intellect could continue after death.

My study of all these conjectures suggests that the writers do not
appreciate the size and levels of brain complexity. My assessment is that
our current and future knowledge will not be capable of producing any
such copying or sizable transfer. Perhaps in 400 or 500 years different viewpoints will be more acceptable.

What follows is a further description and clarification of brain complexity.

A computer has transistors, diodes, resistors, conducting wires and other electronic components that function in concert to provide logic, control,
computation, sensory systems, memory, and information transfer over a
distance.

Analogous systems in the brain are various types of connections between
nerve cells, and elongated cell structures (axons) that are like transmission
wires. The electrical pulse that is mostly used for communication over a distance
is the “action potential.”

I could include, here, a few relevant pictures, but to really see most of
the known variations just use your browser to search “nerve cells” and also
“gap junctions.” (click “images” at top of page). Many of the pictures are
very current and show an amazing variety of structures.

There are two types of connection: chemical (synapses) and electrical (gap-junctions). The terminology can be a little inconsistent but the principles are clear. Neurons have (separate) sending and receiving points. For cells A and B to communicate, a sending point (terminal) of cell A must be in very close proximity to a receiving point (receptor site) for cell B. If the connection is a chemical synapse then the sending point of cell A sends transmitter chemicals across the gap to neuron B receptor. Sending is triggered by an electrical signal (action potential) that causes the release of a chemical (transmitter). The receiving point (or receptor) generates a transmittable signal when enough transmitter is received. Transmission can be excitatory (producing action potentials) or inhibitory (preventing action potentials). Some examples of common neuro-transmitters are acetylcholine, epinephrine, GABA, ATP, and Serotonin. There are about 25 different known transmitters.

Electrical connections between nerve cells operate similarly, except that the
excitation is more direct and transmitter chemicals are not used. Gap junctions
mediate electrical excitation by opening gates that allow the passage of ions.
Ions are tiny charged particles (atoms or molecules) that function in transmission. There can also be transferred electrical excitation without specific gap-junction structures, if parts of cells are making actual contact.

Further functioning (and more complexity) is related to the number of sending points that simultaneously contact a single receptor. A single nerve cell (neuron) could have hundreds of sending and receiving contacts and direct ommunication with many other cells.

Another layer of complexity is that there are many transmitter chemicals and countless substances that can affect the transmitters and the transmission process. Some of these excitatory or inhibitory substances in the brain are there naturally, and can depend on what you eat and your activities. There are also a multitude of drugs that can affect transmission in a multitude of ways.

All animal brains have specific structures and a very sophisticated organization.
Synaptic receptor sites (the receiving points) can have a variety of properties
depending on DNA coding and also actual usage. The extent of excitation by
sending points (pre-synaptic terminals) can be relatively fixed or variable.
In some situations, receiving points (postsynaptic sites) can produce a stream
of action potentials, or just one or two. If a synapse is used repeatedly,
transmission could be enhanced or inhibited, depending on a number of
temporal and chemical factors. Depending on usage, a receptor site could
store information that alters its performance — a “memory” function.

From the discussion above, you can see that there are numerous devices in
the brain that function as “logic.” The brain has common “and-gates”,
“or-gates”, “nor-gates” and many other types of gating to use in programming all of the fantastic abilities we enjoy. Much of the logic used by our brains is similar to that used in our computers. But brain logic has a far greater variation and is
really a combination of digital and analog systems. Information in a computer
is generally a universal pulse of a fixed voltage. In brains, information takes many forms including pulses, graded potentials, ion movements, and the presence or absence of a great number of chemicals. In computers, memory is achieved by manipulating magnetic and electrical properties of tiny bits of matter. In brains, some methods of storage are known and others are the subject of reasearch. It is likely that much of memory has to do with long-term facilitation (or inhibition) in synaptic transfer. There is much research on molecular structures that are altered to provide long-term information storage.

Imagine trying to construct something like a biological synapse with all
the properties described above. Your constructed synapse could have a hundred excitatory and inhibitory inputs, with several different transmitter chemicals. The receptor site should be able to produce a variety of action potential rates and be capable of changes related to memory. Even the construction of one
complete synapse would be very difficult. Imagine trying to create a human
brain with 150 trillion synapses with a variety of properties, AND with an
extremely complicated and as yet unknown organization.

Scientific brain research is valuable and should be continued. But productive
lines of inquiry should be promoted while most unrealistic speculation should be
ignored or presented as science fiction.

How did this extremely complicated biological computer system called a brain
develop? In a future blog I will deal with this question.

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