Tool Module: Similarities and Differences Between the Brain and a Computer
Beyond the obvious analogies and differences between computer hardware and the human brain (for instance, between the computer’s RAM and the brain’s working memory, or the computer’s hard drive and the brain’s long-term memory), the two are often said to resemble each other. But do they really? Just how close are the similarities?
Digital versus analog
The vast majority of computers are digital, which means that they perform their operations using a binary system that has only two possible, discrete states: “on“ and “off “, or if you prefer, “0” and “1”. In the analog form of encoding used on old vinyl records, for example, the musical information was recorded in the continuous variations in the contours of the grooves, and minor errors were inevitably audible when the recordings were played back. In contrast, digital encoding provides higher fidelity, because its automatically eliminates all of these errors unless they are large enough to replace a 0 with a 1.
So does the human brain operate as an analog system, or a digital one? The answer is “both”. On the one hand, a neuron either does or does not transmit an action potential. This is an “all-or-nothing” process, and in this sense, the brain operates digitally. But the frequency at which a neuron transmits action potentials can vary continuously, thus giving it this property of an analog system as well.
Neurons operate analogically in another sense as well. Every neuron is constantly receiving numerous nerve impulses (action potentials) from other neurons across their synapses with its dendrites. Depending on the receptors at which these potentials are received on the complex surface of the dendrite membrane, they will have either an excitatory or an inhibitory effect. The neuron constantly sums these two types of potentials, so that the overall state of polarization of its membrane varies continuously, in analog fashion, under the effect of its numerous synapses. And it is only at the neuron’s axon cone that this analog signal is converted into a digital action potential.
Serial verus parallel
Most computers process information very rapidly, but they do so in serial fashion: all of the information is processed by a single central processing unit (CPU) that performs one operation after another. But the CPU can also simulate parallel processing by subdividing its various tasks into subtasks and alternating rapidly among them.
The brain’s neurons are much slower than a computer’s integrated circuits. But the brain’s power comes from its being a machine that performs massively parallel processing. The brain does not have a CPU. Instead, it has millions of neurons that combine signals simultaneously. At any given time, many large, specialized areas of the brain are operating in parallel to perform a variety of tasks, such as processing visual or auditory information or planning an action. And even within each of these areas, information flows through neural networks that have no significant serial structures.
However, just as computers are serial systems that can simulate parallel processing, the brain is a parallel system that can simulate serial operations (in handling spoken and written language, for example).
Deterministic versus non-deterministic
Computers are deterministic machines in the sense that with a given input, they will always produce the same output. This does not mean that this output is always predictable. For example, computers can simulate non-deterministic systems by introducing pseudo-random variables. Computers can also apply equations from chaos physics , in which the results of deterministic processes can be greatly influenced by tiny variations in the initial conditions.
The brain as a whole is considered a non-deterministic system, for the very simple reason that it is never completely the same from one moment to the next. It is constantly forming new synapses and strengthening or weakening existing ones according to how they are being used. Consequently, a given input will never produce exactly the same output twice. However, the physiochemical processes underlying brain activity are considered to be deterministic.
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