Is the analogy of brain to computer circuitry reasonable?
Brain circuit vs. electrical circuit
Electrical current and electrical circuits have different meaning to electrical engineers and neuroscientists.
To electrical engineers, current is the movement of charged particles through an immobile system called a circuit. Computers use this kind of current.
Electrical circuits defined by electrical engineers are paths consisting of a closed loop through which current flows. In an electric circuit the charged particles always end up back at their source when they complete their path.
In the brain, current flow refers to a serial shift in the voltage difference across a neuron’s cell membrane rather than a flow of charged particles in a particular direction. The fluctuating membrane voltage called an action potential occurs because of charged ions that flow out of and into the neuron. Action potentials are electrical in nature. And, action potentials do progress along a path through the brain. But, the particular charged particles responsible for the current are not themselves moving along the path.
Brain circuits consist of linked neurons. Connections between neurons are mobile and the circuit configuration is subject to modification. Connections between neurons experience constant readjustment based upon the quantity and quality of incoming signals. Brain circuits are not closed loops where charged particles end up back at their source when they complete their circuit.
The dry systems used by computers are trillions of times faster than the wet ware system used by brain. Yet, brains are very fast. They almost instantly carry out extraordinary feats of problem solving and environmental analysis with little to no error.
Synaptic breaks in brain’s electrical circuits
Information is processed in computers by simple ‘on’ and ‘off’ signals flowing through uninterrupted circuits. Information processing schemes used by the brain are far more complex because there are physical breaks between the wiring components (neurons) called synapses.
Transfer of brain electrical activity across synapses occurs by a chemical process. The chemical process is graded and variable. There are many components to brain synapses that add to this variability. Individual synaptic structures may enhance or impede transfer of an electrical signal to the next neuron in a circuit.
For example, astrocytes surround many brain synapses and it is their job to quickly remove the chemical called a neurotransmitter from a synaptic cleft. Additional incoming signals are not recognized when the synaptic cleft remains saturated with neurotransmitter.
In addition to physical breaks in brain circuits there are also functional restraints on brain circuits. Functional control of electrical flow in brain is created by little neurons called interneurons. Interneurons are so small that it is hard to tell the difference between their dendrites and axons. Most interneurons increase polarization of the charge across pre- and post-synaptic membranes. Such hyperpolarization of pre- and postsynaptic membranes blocks the spread of action potentials from neuron to neuron.
Neuron coding in brain
Early studies based upon the signaling patterns of sensory neurons of the retina and other sensory organs led investigators to theorize that brain neurons also coded information by strings of ‘on’ and ‘off’ signals. It was believed that information was coded either by the rate of action potentials or by the time between action potentials. Acquiring hard data to distinguish between these two theories was difficult because individual neurons display a background action potential rate that is equivalent to noise.
Newer data suggest that brain neurons never code alone. Rather brain action potential coding is carried out by groups of neurons responding to similar input. This is called ensemble coding. The model assumes that ensemble coding works better because noise of individual neurons is cancelled out.
There is also evidence for recruitment of neurons from reserve pools to core ensemble circuits. The reserve pool neurons share input and output circuits with the core ensemble but release a different neurotransmitter than the core group. Such flexible composition of neuron ensembles allows graded output in response to incoming signals.
The future may bring computers that work much like the human brain. But, technology will first have to advance far enough to discover how the brain’s neuron circuits actually create awareness, memory and responses to a shifting environment. Neuroscience is still a long way from knowing all of what goes on inside the closed world of the brain.
If you struggle to understand the words describing neural physiology, it may help for your to check out the first chapter of my new book “Inside the Closed World of the Brain.” Here is a FREE link to its first chapter,“Tips & Tricks for Learning Scientific Language.”
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Margaret Thompson Reece PhD, physiologist, former Senior Scientist and Laboratory Director at academic medical centers in California, New York and Massachusetts and CSO at Serometrix LLC is now CEO at Reece Biomedical Consulting LLC.
Dr. Reece is passionate about helping students, online and in person, pursue careers in life sciences. Her books “Physiology: Custom-Designed Chemistry” (2012), “Inside the Closed World of the Brain” (2015) and upcoming “Step-by-step Guide for Study of Physiology” (2016) are written for those new to life science.
Dr. Reece offers a free 30 minute “how-to-get-started” phone conference to students struggling with human anatomy and physiology. Schedule an appointment by email at DrReece@MedicalScienceNavigator.com.by