The Ravenous Brain: How the New Science of Consciousness Explains Our Insatiable Search for Meaning (17 page)
Authors: Daniel Bor
BOOK: The Ravenous Brain: How the New Science of Consciousness Explains Our Insatiable Search for Meaning
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As most of the basic functions of our reptilian brains carry on unabated when we lose consciousness, we can safely say that whatever awareness is for, it isn’t concerned with those basic internal processes, like breathing, that are vital to our survival. Likewise, consciousness probably has little to do with the brain stem.
However, our two remaining brain layers, our limbic brain and our cortices, enter a special noncommunicative state during anesthesia, making consciousness impossible.
UNCONSCIOUS NEURONS MARCHING IN STEPOur best guess as to the mechanism of most anesthetic agents is that they increase the production of a neurotransmitter, called gamma-amino butyric acid (GABA), that acts to dampen neuronal activity throughout the cortex. In this subdued state, the firing of our neurons becomes more harmonized, and less differentiated, than usual: Strong global brain spikes pulse through the cortex a few times a second in a slow, strong rhythm (known as a delta rhythm). At first blush, it might seem puzzling, even paradoxical, that as our consciousness dissolves, our brain activity becomes in some sense stronger and more rhythmic. But this mystery disappears if we bear in mind the prime, ongoing context of our brains—that they are first and foremost an information-processing device. To explain how information processing relates to brain rhythms, I need to make a small digression to explain just what is being detected when we talk of brain rhythms.
Brain rhythms are regularly mentioned in the press—beta waves for attention, theta for meditation, and so forth. But what does it actually mean to have such a brain pattern? In order to detect these hidden brain waves, you need to use electroencephalography (EEG). This technique involves attaching an array of electrodes across the scalp. Each of these electrodes detects the combined local electrical activity emitted by millions of neurons.
Imagine neuronal activity as a haphazard mix of vacation-goers. These tourists (or neurons) are on a large, boisterous cruise, where, although initially strangers, many are now friendly. On a day trip from the cruise, they are now scrambling in every direction across the rolling hills of a national park near the coast, each chatting briefly with anyone who passes by—for instance, about an accident they witnessed on the road below, or some interesting ancient stone circle on the horizon.
Now, imagine a similar number of people a week later, but this time they are in an army, being ordered by a sergeant-major to march up and down the hills in unison. A distant witness in a passing plane (EEG electrodes) would feel that the soldiers were a more impressive, potent group, and might even imagine there were more soldiers here than tourists in the neighboring hills a week earlier (which there weren’t). It looks from the air as if a great swath of khaki green rises up and drops down the countryside in a slow but steady and powerful rhythm. In contrast, the tourists were so spread out as to make it difficult to count them, with far fewer at any one point on the hill summits than now.
But even though the soldiers are more orderly than the tourists, they are less interesting, and also less curious. Unlike the tourists, they don’t notice the road, or the stone circle, or really anything besides the gait of the soldier directly in front of them. They are effectively a single group. What’s more, anyone caught chatting to his neighbors, trying to liven up the dull walk with a bit of gossip, will be severely admonished by the sergeant-major, and the chatter will die down fast. This all severely limits the power of the soldiers (or neurons) to grab and pass on any useful details about the surroundings.
So, being heavily unconscious, such as under general anesthesia, is associated with a more orderly, slow, thumping march of neuronal activity, which is capable of carrying only minimal information around the brain. These neurons may really struggle to broadcast anything further afield than their immediate neuronal friends; they aren’t receiving anything very original to pass on anyway, as so many neurons are singing the same tune.
And here is an important initial clue as to why we can be conscious, while bacteria and plants cannot: Consciousness occurs when there is an active transfer and intermingling of information across much of the neural landscape. In contrast, any information processing in bacteria and plants is distinctly local to some small pocket of the entire protein-DNA machinery.
LEARNING ON THE OPERATING TABLEMy linking of consciousness with complex information processing is in accord with this unconscious general-anesthesia scenario, in which mechanisms that would usually support such processing are no longer available: Brain waves have become slow and lumbering, and the latest, smartest parts of the brain have been turned off. So, does it follow that all sophisticated learning is unavailable when anesthesia strips us of consciousness?
Problematically, responses to anesthesia can differ markedly from one patient to another. On top of this, thankfully very rarely, some patients have remained awake during their operations and have been traumatized by their very conscious, very intense pain. So before testing for any learning, you first need to ensure that the anesthesia is sufficiently deep that the patient is truly unconscious.
The main method to establish that the patient is fully unconscious is by using EEG to ensure that the brain waves are sufficiently slow and deep, with little or no neural communication across regions. What can be learned after such checks have been confirmed? From the consensus of studies on learning in anesthesia, where testing only occurred after appropriately deep levels of anesthesia were carefully detected and monitored, there is no evidence at all of subjects, on waking, recalling anything from their operation. If word lists to be memorized are read out during the operation, patients have no memory of any of the words. If instructions were repeatedly given in the midst of the procedure, say, to lift a finger when the patient hears the name “Rumpelstiltskin,” then nothing happens later in recovery when the experimenter gives the cue—patients do not lift a finger or recall having been given any instructions.
But, despite this, there are still some more subtle forms of learning that are possible. We actually learn all the time, in a weak sense of the word, without knowing that we’ve learned anything. For instance, as I mentioned in Chapter 1, if I say “artichoke artichoke artichoke artichoke artichoke” to you a hundred times in the next minute, you’ll spend the rest of the day predisposed to react more to this word than usual. You’ll read “artichoke” a little faster when you come across it, you’ll notice it quicker in the supermarket, you’ll think of artichoke a little earlier if I tell you to come up with as many vegetables as you can, and you might even be a little more inclined to buy an artichoke at the market. You won’t be aware of any of this, and you’ll have little control over it, but it happens nevertheless.
What occurs, from the neurons’ point of view, when you’ve been exposed to such a word? The neurons that collectively represent “artichoke” in your brain were reactivated, and in the process, their thresholds for firing again were tweaked. They therefore will be a little quicker to draw their neuronal firing gun the next time you hear about or see artichokes. In one sense, this is akin to a micro-muscle getting a little exercise and becoming stronger from the use. But, actually, far more is going on. This little collection of neurons firing together a little more readily in response to “artichoke” is in fact an important predictive computation. The neurons are effectively saying: “Aha—artichoke is around again, perhaps it’s now a bit more important and frequent, and we should reflect that fact by getting faster and louder to respond to it, or even anticipate it more keenly.” Every time we are exposed to virtually anything whatsoever, this neuronal fine-tuning occurs.
There’s no doubt that our unconscious minds are bubbling, spitting cauldrons of computations, based on this constant stream of neuronal tweaks that are dedicated to predicting the world around us. Our sensory perception is not a direct mirror to the world outside, but a series of computational steps designed to give our conscious minds the most pertinent information available. We move our bodies based partly on rich feedback from our senses as to where our limbs are and where the objects we’re reaching for are placed in relation to our limbs. All this occurs seamlessly, unconsciously. Many of these low-level lessons are hardwired. We are primed to predict that the sun is above us, that objects have edges, and so on. This hardwiring is the product of many millions of years of evolution and designed with ruthless efficiency, so that we humans, and our mentally simpler ancestors, can swiftly extract the dangers and delights of the environment—and react before the predator or a competitor does. Many other unconscious lessons may once have been born as conscious explorations of the world when we were infants, but now they are so embedded into our world picture, and so buried under a mountain of more meaningful ideas, that we never consciously acknowledge their existence.
In one sense, this unconscious machinery for predictive learning is indeed complex, but only because of the sheer number of simple statistical calculations occurring, not because of the grand truths that are being unpeeled before our eyes. These neuronal tweaks that occur under the surface can only ever be the servants of our understanding, because only when their largest lessons are combined in consciousness can we really learn the interesting, deep patterns of life.
Just how limited is our unconscious mind, when applying these simple neuronal calculations? If you tell a patient recovering from an operation to complete the partial word “ash,” she may be equally likely to say “ashcan” or “ashtray.” But if you repeated the word “ashtray” when she was deeply unconscious, she will in fact be more likely to say “ashtray” in recovery. She will have absolutely no knowledge that she has just heard the word “ashtray” an hour or so ago; nevertheless, some part of her brain will remember. Some family of neurons has been tweaked to reflect this recognition, and she will respond accordingly. In other words, she has been “primed” to repeat a word to which she has already been exposed. Examples like this show that at some very superficial, unconscious level at least, words can be noticed.
But there are multiple features of a word—for instance, there’s the sound, the grammatical features, the linguistic relationship a word has to others in various ways, and there’s also the meaning of the word. Meaning is the first main level at which our minds structure information, since meaning requires relationships between items in a dense web, hierarchies of categories, and so on. In this way, meaning is an especially pertinent test for the argument that consciousness is equated not only with information processing, but especially with structured information.
Can patients be primed for the meaning of the word as well as the sound? For instance, if asked after the operation to complete the same partial word “ash,” are patients more likely to say “ashtray” instead of “ashcan” if they were exposed during the operation to the word “cigarette”? If so, this would mean there had been a deeper triggering of activity, so that the neuronal population had spread from the sound of the word to activating any neurons coding for a related meaning. This is precisely what some researchers tested, and it turns out that, when under a sufficiently deep anesthesia, this form of learning is beyond us.
So, when profoundly unconscious, as happens under deep levels of general anesthesia, we can faintly learn under the radar of our consciousness that a certain word has just been presented to us, but that’s about the limit of it. Anything remotely more complex, such as a word’s meaning, is beyond our unconscious selves and requires at least some level of awareness. And, of course, for anything that we are actually conscious of learning—creating a strategy, memorizing a list, learning from instructions, or any of the myriad forms of information we manipulate every day—consciousness is certainly required.
UNCONSCIOUS BETTER THAN CONSCIOUS?General anesthesia is the gold-standard method for studying just what our unconscious minds are capable of, because it puts us in a situation where we are fully unconscious, even though our brains are otherwise quite healthy and capable. Therefore, the limitations on unconscious processing described above should be taken as definitive. But science is always improved when it adopts multiple approaches to examine the same question. Indeed, various other techniques have been used to explore unconscious learning.
For instance, what about when we’re already awake? Could it be that the deep ocean of our unconscious minds, when fed material from our conscious gaze, can churn over vast swaths of information and quickly allow conclusions to surface that are far more advanced than the insights that our deliberate, slow, conscious cogitations could ever produce? A Dutch researcher, Ap Dijksterhuis, carried out a series of experiments to argue just this point. He claimed that there were many situations where we should follow our gut instinct, where the slow, integrative processing of our unconscious minds was vastly superior to our clunky, far more limited conscious thoughts.
In one of Dijksterhuis’s experiments (there are now quite a few, all of a similar mold), volunteers were asked to rank four imaginary cars in order of preference, based on a set of attributes they were given, one at a time. One car had 75 percent of its features set as desirable (for instance, “The Dasuka has cupholders”); another two cars were neutral, with 50 percent of facts good and the other half bad; and one car was the worst of the bunch, with only 25 percent of the attributes set as positive. Once participants were shown all the features for all the cars in turn, they were split into two groups. One group, the “conscious” group, spent 4 minutes thinking about all the attributes they’d just read about and tried to work out the most accurate ranking of the cars. A second group, the “unconscious” group, spent 4 minutes being distracted by anagram puzzles instead. This, according to Dijksterhuis, allowed their unconscious minds sufficient time to process and integrate the facts unfettered by their consciousness, which was adequately engaged in an irrelevant task. In fact, so Dijksterhuis’s theory goes, the more the conscious mind is distracted by some other task, the better it is for the unconscious understanding of complex information. In the final, crucial stage, after the 4 minutes were up, both groups had to pick their favorite car.
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