Quantifying Learning at the Synapse: Has the “Gold Standard” Been Set for Understanding Consciousness?
Scientists reported this month in the journal Neuron what happens in the brain—literally, in real time, on the intercellular level—when an animal learns.
Given some context, which every claim requires, I believe my title is accurate. Scientists at Cold Spring Harbor Laboratory on Long Island reported this month in the journal Neuron what happens in the brain—literally, in real time, on the intercellular level—when an animal learns. Their experimental animal was the fruit fly, a creature that lives its whole life—birth, reproduction, death—in just 24 hours and so is ideal for breeding generations modified to suit the designs of scientists. The observation and measurement—this is crucial—were of how a synapse is modified, by how much, and how this changes behavior, when learning occurs.
Why is this of the essence? A synapse is the where two neurons, brain cells, communicate; it is the miniscule gap between neurons across which an electrical/chemical signal passes. No mental activity, as far as we know, occurs in the brain without synaptic signaling.
The report in Neuron will not be hailed as “a breakthrough,” not some giant stride in biology. You won’t see it reported even in the science section of your news media. Nevertheless, it is a “first” and makes a telling point about brain science. It makes an even more telling point, actually several of them, about knowledge.
I am relying, here, on two sources. One is the brilliant and astonishingly, free online publication by the veteran observer of biomedical science, Ray Kurzweil, author of Fantastic Voyage: How to Live Long Enough to Live Forever. He is an inventor, futurist, and impassioned and disciplined follower of science. The publication I am using is Kurzweil Accelerating Intelligence, delivered free to your email if you subscribe. The other is the abstract of the article in the December issue of Neuron entitled “Heterosynaptic Plasticity Underlies Aversive Olfactory Learning in Drosophila.”
Drosophila, literally “dew loving,” is the fruit fly. The experiment was to train the fruit fly to react aversely to the odor of cherries, to which fruit flies are usually attracted especially if the fruit is rotted. The intervention was to use a laser beam to zap the dopamine that ordinarily makes the fly hot for cherries. To quote the article: “Presenting the smell of cherries, for example, which is normally an attractive odor to flies, while at the same time stimulating a particular dopamine neuron, trains the fly to avoid cherry odor.”
To the poet reading this, the pathos is evident. The poor fruit fly lives a single day and one of its few pleasures in this brief span is the odor of cherries, but science demands its sacrifice. Where is PETA when the fruit fly needs them?
The pivotal point in this remarkable report is a new technology of measurement, so often the real key to advancement in science.
The pivotal point in this remarkable report is a new technology of measurement, so often the real key to advancement in science. Until this experiment, scientists seeking to observe and measure the activity at the synaptic gap when this simplest of all organisms learned its lesson—“cherry smell is not pleasurable”—was a technique called “calcium imaging.”
I will quote here, since we are at the crux: “This approach enabled researchers to observe changes in neural activity that accompany learning. However, this technique doesn’t reveal precisely how the electrical activity of the neurons is modified [emphasis added], since calcium is not the only ion [charged atom or molecule] involved in neuronal signaling.”
In the research now reported, scientists “were able to make electrophysiological recordings to directly examine changes in synaptic strength at this site before and after learning for the first time.”
In other words, scientists could record how the strength of the synaptic connection changed from before to after the fly learned for the first time to avoid cherry odor. At this level, learning was a measurement of the change in strength of the synaptic connection—and this measurement, the amount of physical change that equated with learning, had never before been made.
Additional context, here, must be elaborated.
There are many levels at which learning, or any mental activity, can be observed. Prehistoric man observed learning when a child poked his hand into the fire and learned that fire singes small fingers. And since then, libraries have been filled with books, articles, microfilms, and whatever else about learning. Observation of learning on all these levels is in principle valid, useful, and, if the observations are accurate, can be integrated in the end with observations on all other levels—including the synaptic. No level at which learning is observed is inherently more legitimate than any other level.
And yet, demonstration of how any process, including any mental process, proceeds at the basic physical level has a distinctive role in science. In a sense, it is the final confirmation of our understanding of a process—as when scientists explain differing human characteristics on the level of DNA.
Neuroscientists aspire to make exact physical measurements of what happens in the brain when we think. Arguably, the first such truly basic physical measurement was reported this month in the simplest of all experimental animals in one of the simplest known acts of learning. In the experiment, writes Kurzweil in his précis of the Neuron article, the scientists utilized “the relative simplicity of…neural anatomy—there are just two synapses separating odor-detecting antenna from an olfactory-memory brain center…”
One of science’s root premises is that any and every process, however “advanced,” can be analyzed and demonstrated at this irreducible physical level. They are convinced this will hold throughout the realm of consciousness.
Jump, for a moment, from learning in the fruit fly to the most complex mental process known: “free will.” There is a theory in psychology that our volition is genuinely undetermined and that introspection—a valid level of observation of learning—suggests that this free will is to be found in the human choice to “turn on,” or “focus,” or elevate the level of conscious activity in response to challenge. Obviously, there is no evidence that this capability exists in species other than man because either they cannot introspect or cannot report their introspection—still the chief evidence for free will.
I once asked a psychologist who espoused this theory, based on introspective evidence plus certain contradictions in the claim that man’s thinking is determined, how in principle volition might occur in the human brain at the basic physical level. It was a naïve question and it received the only possible answer. We do not at this time even entirely understand at the basic physical level how the brain manages the simplest act of sensory awareness—much less evolution’s most advanced expression of neural complexity, the emergence, at a certain level of brain development, of volition.
Science’s root conviction, today, is that ultimately—even if “ultimately” means a century or more—free will, too, will be demonstrated at the basic physical level of the brain.
And yet, science’s root conviction, today, is that ultimately—even if “ultimately” means a century or more—free will, too, will be demonstrated at the basic physical level of the brain. Until that distant day, scientists won’t have fully and completely demonstrated that somehow, which today we cannot even imagine, the human brain enables acts of consciousness undetermined by anything but our choice. That demonstration is the final destination of the discovery reported this month in Neuron.
Another crucial context must be mentioned. Although neuroscience may analyze and explain learning and other conscious experience in terms of the brain’s physical processes and altered states, those processes and states cannot be equated with consciousness. That is “reductionism,” which, admittedly, is the creed of many—but far from all—brain scientists, who believe that talking of “consciousness” is merely a different way of discussing what happens in the brain—exactly the same thing at two different levels of discourse. Philosophically, the identification of brain processes with states of consciousness—the view that acts of consciousness are nothing but brain processes seen from another perspective—runs into irresolvable problems.
To mention the most obvious objection to this equation: I introspectively experience that apples are sweeter than limes, but that I love limes more because my wife makes me wonderful lime drinks on Friday evenings after a week of work. And this conscious experience of mine is nothing like any combination of neurons, however complex, and their firing across synapses and thereby altering their states. The neurons and their firing are not even in the same realm of discourse.
Consciousness is actual. It has its own nature. It cannot be equated with, reduced to, any movements of neurons, however complex—even if my consciousness, which I readily admit, may depend for its existence on these brain processes. To take an imperfect analogy—and there are no perfect analogies to consciousness—my SUV depends for its existence on the molecular structures of the metals, plastics, and other materials of which it is composed. But my SUV obviously cannot be identified with those molecular states. It has emerged from those states because their complexity has given rise to entirely new characteristics, properties, and qualities—and those are as real as the molecules and different.
Explanation at the physical level has a distinctive importance—and not only in scientific demonstration. This is the level at which we often gain the ability to change things.
And yet, explanation at the physical level has a distinctive importance—and not only in scientific demonstration. This is the level at which we often gain the ability to change things. The miracle drugs, as they rightly are called, that can ameliorate, improve, or even cure diseases from cholera to cancer to schizophrenia are acting on the level probed by the scientists reporting this month. Typhus, cholera, smallpox, polio, bipolar disorder, and depression were well observed and characterized on a certain level for centuries. But until scientists found ways to deal with them specifically on the level of the cell, little progress was made.
The dry first sentence of the abstract in Neuron, if you understand, now, what it reports, tolls forth the mind’s triumphant progress—the achievements of reason—that still endure and even prevail in our time.
Don’t let it go.
About the Author: Walter Donway
« A Free Market in Interest Rates Janet Yellen Fights the Tide of Falling Interest »
