Researchers Discover Idling Brain Activity in Severely Brain Injured Patients Who “Wake Up” After Using a Sleep Drug

George Melendez has been called a medical miracle. After a near drowning deprived his brain of oxygen, Melendez remained in a fitful, minimally conscious state until his mother, in 2002, decided to give him the sleep aid drug Ambien to quiet his moaning and writhing. The next thing she knew, her son was quietly looking at her and trying to talk. He has been using the drug ever since to maintain awareness, but no one could understand why Ambien led to such an awakening.

Now, a team of scientists led by Weill Cornell Medical College has discovered a signature of brain activity in Melendez and two other similarly “awakened” patients they say explain why he and others regain some consciousness after using Ambien or other drugs or treatments. The pattern of activity, reported Nov. 19 in the journal eLife, was identified by analyzing the common electroencephalography (EEG) test, which tracks brain waves.

"We found a surprisingly consistent picture of electrical activity in all three patients before they receive the drug. Most interesting is that their specific pattern of activity suggests a particular process occurring in the brain cells of the cerebral cortex and also supports the role of a crucial brain circuit," says the study’s senior investigator, Dr. Nicholas Schiff, the Jerold B. Katz Professor of Neurology and Neuroscience and professor of public health at Weill Cornell. "These findings may help predict other patients who might similarly harbor reserve capacity, whether they are able to respond to Ambien or other approaches." Dr. Schiff is also on the faculty of the Feil Family Brain and Mind Research Institute at Weill Cornell and is a neurologist at NewYork-Presbyterian Hospital/Weill Cornell Medical Center.

"We are focused on finding ways to identify patients who have a functional reserve of cognitive capacities that can be rescued and how to achieve this result," Dr. Schiff adds. "These findings give us a very important lead to follow, and we will now rigorously test their implications in other patients."

Although it is not precisely known how many Americans are diagnosed as severely brain injured with disorders of consciousness, by one estimate there are nearly 300,000 patients trapped in a minimally conscious state who may retain some awareness, according to Dr. Schiff.

Riding a Wave of Excitation

The three patients in the study suffered brain damage in different ways. One fell and the other had a brain aneurysm that led to multiple strokes. Melendez was in a car accident that led to his nearly drowning. All three patients — two men and a woman — become aware when Ambien was used, a rare response that has been documented in fewer than 15 brain-injured patients.

The research team, which included scientists from Memorial Sloan-Kettering Cancer Center, Boston University School of Medicine, and the University Hospital of Liège in Belgium, used EEG to measure electrical activity in the patients’ brains before and after they were given the drug.

Although each patient’s brain was damaged in different ways, all showed the same unique features of low frequency waves in their EEG readings. These low frequency oscillations are most prominent over the frontal cortex, a region strongly dependent for its activity on other brain structures, particularly the central thalamus and the striatum, which together support short-term memory, reward, motivation, attention, alertness and sleep, among other functions.

In this setting of an idling brain, the investigators propose that Ambien works like any anesthesia drug, in that it briefly triggers a fast wave of excitation in brain cells before producing sleep — a phenomenon known as paradoxical excitation. Instead of going on to produce sedation and sleep, as it does in healthy people who use the drug, zolpidem further activates the brain after it’s affected the idling cells, allowing the patients to become more awake than at baseline. “What we think is happening in these patients is that the initial excitation produced by Ambien turns on a specific circuit. The drug creates the opportunity for the brain to effectively catch a ride on this initial wave of excitation, and turn itself back on,” Dr. Schiff says.

This proposed “mesocircuit” links the cortical regions of the brain to the central thalamus and striatum. Neurons in the central thalamus are highly connected to other parts of the brain, “so damage in one part of the brain or another will affect the thalamus, which is key to consciousness,” Dr. Schiff says. Neurons in the striatum “will only fire if there is a lot of electrical input coming to them quickly,” he says.

"We believe the switch that Ambien turns on is at the level of the joint connections between these three brain structures," Dr. Schiff says.

The pattern of brain activity seen in the EEG on Ambien was also the same in all the patients in the study. But the circuit turns off again when the effects of the drug diminish. Using the drug regularly at mealtimes, Melendez can speak fluently, and read and write simple phrases. His tremors and spasticity are significantly reduced on Ambien and he can use objects, such as a spoon, and is alert and can communicate. The first patient in the study can reliably move from minimally conscious to “the mid-range of what is called a confusional state — a more alert status, but not full consciousness,” Dr. Schiff says. “Use of Ambien offers a step in the right direction, but certainly not a cure.”

Different Ways to Kick-Start the Brain

The resting EEG pattern the researchers saw in the patients indicates they have a “recruitable reserve” of function in these critical brain areas that Ambien can harness to turn the brain on, even if only temporarily. “The idea is that hopefully we can screen other patients with EEG to find out if they also have such a reserve,” Dr. Schiff says.

And while some of these patients may not respond to Ambien — as the drug works at a very specific brain receptor and individuals can vary considerably in having enough of it in the key components of the proposed circuit — other drugs may target the same structures and potentially produce similar effects, he says. For example, two drugs (amantadine and L-Dopa) that provide extra dopamine, a brain chemical that fuels the part of the brain damaged in the study’s patients, have been shown to have similar effects on restoring function in patients with severe brain injuries, as has electrical brain stimulation of the central thalamus.

"Now that we have uncovered important insight into fundamental mechanisms underlying the dramatic and rare response of some severely brain-injured patients to Ambien, we hope to systematically explore ways to achieve such kick-starts in other patients — that is our goal," Dr. Schiff says.

(Image credit)

Patient in ‘vegetative state’ not just aware, but paying attention

Research raises possibility of devices in the future to help some patients in a vegetative state interact with the outside world.

A patient in a seemingly vegetative state, unable to move or speak, showed signs of attentive awareness that had not been detected before, a new study reveals. This patient was able to focus on words signalled by the experimenters as auditory targets as successfully as healthy individuals. If this ability can be developed consistently in certain patients who are vegetative, it could open the door to specialised devices in the future and enable them to interact with the outside world.

The research, by scientists at the Medical Research Council Cognition and Brain Sciences Unit (MRC CBSU) and the University of Cambridge, is published today, 31 October, in the journal Neuroimage: Clinical.

For the study, the researchers used electroencephalography (EEG), which non-invasively measures the electrical activity over the scalp, to test 21 patients diagnosed as vegetative or minimally conscious, and eight healthy volunteers. Participants heard a series of different words  - one word a second over 90 seconds at a time - while asked to alternatingly attend to either the word ‘yes’ or the word ‘no’, each of which appeared 15% of the time. (Some examples of the words used include moss, moth, worm and toad.) This was repeated several times over a period of 30 minutes to detect whether the patients were able to attend to the correct target word.

They found that one of the vegetative patients was able to filter out unimportant information and home in on relevant words they were being asked to pay attention to. Using brain imaging (fMRI), the scientists also discovered that this patient could follow simple commands to imagine playing tennis. They also found that three other minimally conscious patients reacted to novel but irrelevant words, but were unable to selectively pay attention to the target word.

These findings suggest that some patients in a vegetative or minimally conscious state might in fact be able to direct attention to the sounds in the world around them.

Dr Srivas Chennu at the University of Cambridge, said: ”Not only did we find the patient had the ability to pay attention, we also found independent evidence of their ability to follow commands – information which could enable the development of future technology to help patients in a vegetative state communicate with the outside world.

“In order to try and assess the true level of brain function and awareness that survives in the vegetative and minimally conscious states, we are progressively building up a fuller picture of the sensory, perceptual and cognitive abilities in patients. This study has added a key piece to that puzzle, and provided a tremendous amount of insight into the ability of these patients to pay attention.”

Dr Tristan Bekinschtein at the MRC Cognition and Brain Sciences Unit said: “Our attention can be drawn to something by its strangeness or novelty, or we can consciously decide to pay attention to it. A lot of cognitive neuroscience research tells us that we have distinct patterns in the brain for both forms of attention, which we can measure even when the individual is unable to speak. These findings mean that, in certain cases of individuals who are vegetative, we might be able to enhance this ability and improve their level of communication with the outside world.”

This study builds on a joint programme of research at the University of Cambridge and MRC CBSU where a team of researchers have been developing a series of diagnostic and prognostic tools based on brain imaging techniques since 1998. Famously, in 2006 the group was able to use fMRI imaging techniques to establish that a patient in a vegetative state could respond to yes or no questions by indicating different, distinct patterns of brain activity.

Psychologists report new insights on human brain, consciousness

UCLA psychologists have used brain-imaging techniques to study what happens to the human brain when it slips into unconsciousness. Their research, published Oct. 17 in the online journal PLOS Computational Biology, is an initial step toward developing a scientific definition of consciousness.

"In terms of brain function, the difference between being conscious and unconscious is a bit like the difference between driving from Los Angeles to New York in a straight line versus having to cover the same route hopping on and off several buses that force you to take a ‘zig-zag’ route and stop in several places," said lead study author Martin Monti, an assistant professor of psychology and neurosurgery at UCLA.

Monti and his colleagues used functional magnetic resonance imaging (fMRI) to study how the flow of information in the brains of 12 healthy volunteers changed as they lost consciousness under anesthesia with propofol. The participants ranged in age from 18 to 31 and were evenly divided between men and women.

The psychologists analyzed the “network properties” of the subjects’ brains using a branch of mathematics known as graph theory, which is often used to study air-traffic patterns, information on the Internet and social groups, among other topics.

"It turns out that when we lose consciousness, the communication among areas of the brain becomes extremely inefficient, as if suddenly each area of the brain became very distant from every other, making it difficult for information to travel from one place to another," Monti said.

The finding shows that consciousness does not “live” in a particular place in our brain but rather “arises from the mode in which billions of neurons communicate with one another,” he said.

When patients suffer severe brain damage and enter a coma or a vegetative state, Monti said, it is very possible that the sustained damage impairs their normal brain function and the emergence of consciousness in the same manner as was seen by the life scientists in the healthy volunteers under anesthesia.

"If this were indeed the case, we could imagine in the future using our technique to monitor whether interventions are helping patients recover consciousness," he said.

"It could, however, also be the case that losing consciousness because of brain injury affects brain function through different mechanisms," said Monti, whose research team is currently addressing this question in another study.

"As profoundly defining of our mind as consciousness is, without having a scientific definition of this phenomenon, it is extremely difficult to study," Monti noted. This study, he said, marks an initial step toward conducting neuroscience research on consciousness.

The research was conducted at Belgium’s University Hospital of Liege.

Monti’s expertise includes cognitive neuroscience, the relationship between language and thought, and how consciousness is lost and recovered after severe brain injury. He was part of a team of American and Israeli brain scientists who used fMRI on former Israeli Prime Minister Ariel Sharon in January 2013 to assess his brain responses.

Surprisingly, Sharon, who was presumed to be in a vegetative state since suffering a brain hemorrhage in 2006, showed significant brain activity, Monti and his colleagues reported.

The former prime minister was scanned to assess the extent and quality of his brain processing, using methods recently developed by Monti and his colleagues. The scientists found subtle but encouraging signs of consciousness.

Hawking: ‘in the future brains could be separated from the body’

Professor Stephen Hawking has predicted that it could be possible to preserve a mind as powerful as his on a computer - but not with technology existing today.

A hypnotic suggestion can generate true and automatic hallucinations

A multidisciplinary group of researchers from Finland (University of Turku and University of Helsinki) and Sweden (University of Skövde) has now found evidence that hypnotic suggestion can modify processing of a targeted stimulus before it reaches consciousness. The experiments show that it is possible to hypnotically modulate even highly automatic features of perception, such as color experience.  The results are presented in two articles published in PLoS ONE and International Journal of Clinical and Experimental Hypnosis. The Finnish part of the research is funded by the Academy of Finland.

The nature of hypnotically suggested changes in perception has been one of the main topics of controversy during the history of hypnosis. The major current theories of hypnosis hold that we always actively use our own imagination to bring about the effects of a suggestion. For example the occurrence of visual hallucinations always requires active use of goal directed imagery and can be experienced both with and without hypnosis.

The study published in PLoS ONE was done with two very highly hypnotizable participants who can be hypnotized and dehypnotized by just using a one-word cue.
The researchers measured brains oscillatory activity from the EEG in response to briefly displayed series of red or blue shapes (squares, triangles or circles). The participants were hypnotized and given a suggestion that certain shapes always have a certain color (e.g. all squares are always red). Participant TS-H reported constantly experiencing a change in color immediately when a suggested shape appeared on the screen (e.g. seeing a red square when the real color was blue). The researchers found that this experience was accompanied with enhanced high-frequency brain activity already 1/10 second after the stimulus appeared and it was only seen in response to the shapes mentioned in the suggestion. The second participant did not experience the color change or the enhanced activity. However, she reported a peculiar feeling when a suggestion-relevant shape was presented: “sometimes I saw a shape that was red but my brain told me it had a different color”.

This enhanced oscillatory brain activity is proposed to reflect automatic comparison of input to memory representations. In this case the hypnotic suggestion “all squares are red” led to a memory trace that was automatically activated when a square was presented. Furthermore, for the participant TS-H the effect was strong enough to override the real color of the square. The matching must have occurred preconsciously because of the early timing of the effect and the immediacy of the color change. Also, both participants reported having performed under posthypnotic amnesia without conscious memory of the suggestions.

In the article published in International Journal of Clinical and Experimental Hypnosis TS-H was tested in a similar type of setting, however, only behavioral data, including accuracy and response times in color recognition, were collected. These results further support that a hypnotic suggestion affects her color perception of targeted objects before she becomes conscious of them. Furthermore, TS-H was not capable of changing her experience of visually presented stable images without the use of hypnotic suggestions i.e. by using mere mental imagery.

Importantly, both of these experiments were done by using a posthypnotic suggestion. The effect was suggested during hypnosis but the experience was suggested to occur after hypnosis. Thus all the experiments were carried out while participants were in their normal state of consciousness.

This result indicates that all hypnotic responding can no longer be regarded merely as goal directed mental imagery.  It shows that in hypnosis it is possible to create a memory trace that influences early and preconscious stages of visual processing already about 1/10 second after the appearance of a visual target. This result has important implications in psychology and cognitive neuroscience especially when studying visual perception, memory and consciousness.

Electrical signatures of consciousness in the dying brain

A University of Michigan animal study shows high electrical activity in the brain after clinical death

The “near-death experience” reported by cardiac arrest survivors worldwide may be grounded in science, according to research at the University of Michigan Health System.

Whether and how the dying brain is capable of generating conscious activity has been vigorously debated.

But in this week’s PNAS Early Edition, a U-M study shows shortly after clinical death, in which the heart stops beating and blood stops flowing to the brain, rats display brain activity patterns characteristic of conscious perception.  

“This study, performed in animals, is the first dealing with what happens to the neurophysiological state of the dying brain,” says lead study author Jimo Borjigin, Ph.D., associate professor of molecular and integrative physiology and associate professor of neurology at the University of Michigan Medical School.  

“It will form the foundation for future human studies investigating mental experiences occurring in the dying brain, including seeing light during cardiac arrest,” she says.

Approximately 20 percent of cardiac arrest survivors report having had a near-death experience. These visions and perceptions have been called “realer than real,” according to previous research, but it remains unclear whether the brain is capable of such activity after cardiac arrest.

“We reasoned that if near-death experience stems from brain activity, neural correlates of consciousness should be identifiable in humans or animals even after the cessation of cerebral blood flow,” she says.

Researchers analyzed the recordings of brain activity called electroencephalograms (EEGs) from nine anesthetized rats undergoing experimentally induced cardiac arrest.

Within the first 30 seconds after cardiac arrest, all of the rats displayed a widespread, transient surge of highly synchronized brain activity that had features associated with a highly aroused brain.

Furthermore, the authors observed nearly identical patterns in the dying brains of rats undergoing asphyxiation.

“The prediction that we would find some signs of conscious activity in the brain during cardiac arrest was confirmed with the data,” says Borjigin, who conceived the idea for the project in 2007 with study co-author neurologist Michael M. Wang, M.D., Ph.D., associate professor of neurology and associate professor of molecular and integrative physiology at the U-M.

“But, we were surprised by the high levels of activity,” adds study senior author anesthesiologist George Mashour, M.D., Ph.D., assistant professor of anesthesiology and neurosurgery at the U-M. “ In fact, at near-death, many known electrical signatures of consciousness exceeded levels found in the waking state, suggesting that the brain is capable of well-organized electrical activity during the early stage of clinical death.­­­”

The brain is assumed to be inactive during cardiac arrest. However the neurophysiological state of the brain immediately following cardiac arrest had not been systemically investigated until now. 

The current study resulted from collaboration between the labs of Borjigin and Mashour, with U-M physicist UnCheol Lee, Ph.D., playing a critical role in analysis.

“This study tells us that reduction of oxygen or both oxygen and glucose during cardiac arrest can stimulate brain activity that is characteristic of conscious processing,” says Borjigin. “It also provides the first scientific framework for the near-death experiences reported by many cardiac arrest survivors.”

Do fish feel pain?

Fish do not feel pain the way humans do. That is the conclusion drawn by an international team of researchers consisting of neurobiologists, behavioural ecologists and fishery scientists. One contributor to the landmark study was Prof. Dr. Robert Arlinghaus of the Leibniz Institute of Freshwater Ecology and Inland Fisheries and of the Humboldt University in Berlin.

On July 13th a revised animal protection act has come into effect in Germany. But anyone who expects it to contain concrete statements regarding the handling of fish will be disappointed. The legislator seemingly had already found its answer to the fish issue. Accordingly, fish are sentient vertebrates who must be protected against cruel acts performed by humans against animals. Anyone in Germany who, without due cause, kills vertebrates or inflicts severe pain or suffering on them has to face penal consequences as well as severe fines or even prison sentences. Now, the question of whether or not fish are really able to feel pain or suffer in human terms is once again on the agenda. A final decision would have far-reaching consequences for millions of anglers, fishers, aquarists, fish farmers and fish scientists. To this end, a research team consisting of seven people has examined all significant studies on the subject of fish pain. During their research the scientists from Europe, Canada, Australia and the USA have discovered many deficiencies. These are the authors’ main points of criticism: Fish do not have the neuro-physiological capacity for a conscious awareness of pain. In addition, behavioural reactions by fish to seemingly painful impulses were evaluated according to human criteria and were thus misinterpreted. There is still no final proof that fish can feel pain.

This is how it works for humans

To be able to understand the researchers’ criticism you first have to comprehend how pain perception works for humans. Injuries stimulate what is known as nociceptors. These receptors send electrical signals through nerve-lines and the spinal cord to the cerebral cortex (neocortex). With full awareness, this is where they are processed into a sensation of pain. However, even severe injuries do not necessarily have to result in an experience of pain. As an emotional state, pain can for example be intensified through engendering fear and it can also be mentally constructed without any tissue damage. Conversely, any stimulation of the nociceptors can be unconsciously processed without the organism having an experience of pain. This principle is used in cases such as anaesthesia. It is for this reason that pain research distinguishes between a conscious awareness of pain and an unconscious processing of impulses through nociception, the latter of which can also lead to complex hormonal reactions, behavioural responses as well as to learning avoidance reactions. Therefore, nociceptive reactions can never be equated with pain, and are thus, strictly speaking, no prerequisite for pain.

Fish are not comparable to humans in terms of anatomy and physiology

Unlike humans fish do not possess a neocortex, which is the first indicator of doubt regarding the pain awareness of fish. Furthermore, certain nerve fibres in mammals (known as c-nociceptors) have been shown to be involved in the sensation of intense experiences of pain. All primitive cartilaginous fish subject to the study, such as sharks and rays, show a complete lack of these fibres and all bony fish – which includes all common types of fish such as carp and trout – very rarely have them. In this respect, the physiological prerequisites for a conscious experience of pain are hardly developed in fish. However, bony fish certainly possess simple nociceptors and they do of course show reactions to injuries and other interventions. But it is not known whether this is perceived as pain.

There is often a lack of distinction between conscious pain and unconscious nociception

The current overview-study raises the complaint that a great majority of all published studies evaluate a fish’s reaction to a seemingly painful impulse - such as rubbing the injured body part against an object or the discontinuation of the feed intake - as an indication of pain. However, this methodology does not prove verifiably whether the reaction was due to a conscious sensation of pain or an unconscious impulse perception by means of nociception, or a combination of the two. Basically, it is very difficult to deduct underlying emotional states based on behavioural responses. Moreover, fish often show only minor or no reactions at all to interventions which would be extremely painful to us and to other mammals. Pain killers such as morphine that are effective for humans were either ineffective in fish or were only effective in astronomically high doses that, for small mammals, would have meant immediate death from shock. These findings suggest that fish either have absolutely no awareness of pain in human terms or they react completely different to pain. By and large, it is absolutely not advisable to interpret the behaviour of fish from a human perspective.

What does all this mean for those who use fish?

In legal terms it is forbidden to inflict pain, suffering or harm on animals without due cause according to §1 of the German Animal Protection Act. However, the criteria for when such acts are punishable is exclusive tied to the animal’s ability to feel pain and suffering in accordance with §17 of the very same Act. The new study severely doubts that fish are aware of pain as defined by human terms. Therefore, it should actually no longer constitute a criminal offence if, for example, an angler releases a harvestable fish at his own discretion instead of eating it. However, at a legal and moral level, the recently published doubts regarding the awareness of pain in fish do not release anybody from their responsibility of having to justify all uses of fishes in a socially acceptable way and to minimise any form of stress and damage to the fish when interacting with it.

Source
Rose, J.D., Arlinghaus, R., Cooke, S.J., Diggles, B.K., Sawynok, W., Stevens, E.D. & Wynne, C.D.L (in print) Can fish really feel pain? Fish and Fisheries

Is the Brain No Different From a Light Switch? The Uncomfortable Ideas of the Philosopher Daniel Dennett

To a philosopher, is the human brain no different from a nonliving gizmo like a computer or a light switch? Is consciousness largely an illusion? Jonathan Weiner on the uncomfortable ideas of the thinker Daniel Dennett.

For Daniel Dennett, philosophers are like blacksmiths: they make their own tools as they go along. Unlike carpenters, who have to buy their drills and saws at Sears, blacksmiths can use their own hammers, tongs, and anvils to pound out more hammers, tongs, and anvils. Dennett, whose famous white beard gives him the look of both a blacksmith and a philosopher, has been particularly industrious at the anvil. He has been working as a philosopher for 50 years, and in his new book, Intuition Pumps and Other Tools for Thinking, he shares a few tricks to make the hard work easier. He is a master at inventing tools for thought—metaphysical jokes, fables, parables, puzzles, and zany Monty-Python-like sketches that can help thinkers feel their way forward. Dennett calls them hand tools and power tools for the mind, and he’s built dozens and dozens of them over the years.

“Thinking is hard,” he writes. “Thinking about some problems is so hard that it can make your head ache just thinking about thinking about them.” Thinking tools help philosophers work on the really deep, hard questions about life, the universe, and everything. They facilitate what another philosopher has called Jootsing, which stands for Jumping Out Of the System—the goal is to pop out of the goldfish bowl of commonplace ideas without drowning in thin air. Think of Plato’s Cave, for instance. That little story has helped philosophers puzzle about the nature of reality for more than 23 centuries and counting.

Dennett’s own inventions include “Swampman Meets a Cow-Shark,” “Zombies and Zimboes,” and many other thought experiments that illuminate great questions in philosophy. He focuses on problems of free will, evolution, and consciousness. His ideas about consciousness are rather shocking; he can make you feel that the human brain itself is just a collection of tongs, hammers, and intuition pumps. (More about that in a moment.) Dennett has written more than a dozen books about those deep topics. His best known are Darwin’s Dangerous Idea, and Consciousness Explained. He writes very well, in a colorful, lively, clear style, and he is a popular professor at Tufts University, to which he dedicates his new book. And every book and lecture is packed with intuition pumps for juicy, jootsy epiphanies.

In a way, we all use thinking tools, all the time, without thinking twice about them. Everyday speech is full of what Dennett calls “small hand tools,” familiar words and phrases like “wild goose chase” or “feedback” or “slam dunk.” The English language is a tool chest with a million metaphors that serve as a kind of verbal mathematics. They’re informal formulas for describing the way things go. Newton’s equations describe the behavior of a cannonball; “loose cannon” describes the behavior of a certain kind of cannoneer we’ve all had the misfortune to know.

Then there are simple, familiar intuition pumps like Aesop’s “The Boy Who Cried Wolf,” “The Ant and the Grasshopper,” and “The Fox and the Grapes.” We’ve all used those thinking tools too. “Look how much you can say about what somebody has just said by asking, simply, ‘Sour grapes?’” writes Dennett. You can get someone to rethink her position, to consider her situation from a completely different perspective. You can also insult her. (As Dennett observes, “Tools can be used as weapons too.”)

The intuition pumps that he’s created are really philosophical arguments in disguise. Dennett has designed them to push us to see the world his way, and that’s what he’s trying to do by recapitulating them here. “I will not just describe them,” he writes; “I intend to use them to move your mind gently through uncomfortable territory all the way to a quite radical vision of meaning, mind, and free will.”

And his ideas are uncomfortable. His essential claim is that there is no great gulf between nonliving, unconscious gizmos like computers and light switches, on the one hand, and the human brain, on the other. Our strong feeling that there’s something special and inexplicable about consciousness is largely an illusion. It will fade as science advances, like the illusion that the Earth is the center of the universe and everything revolves around us. Biologists used to believe that living things are made of some special material, some elan vital that sets us apart from the stuff of rocks and minerals. Now that we know about DNA, we no longer need an elan vital. Someday we won’t need consciousness either. There’s no metaphysical difference between your body and your mind, or between your laptop and your necktop, so to speak.

That’s a controversial position, obviously. It still feels counterintuitive to most of us, and to most philosophers too, in spite of all of Dennett’s intuition pumps. Does Consciousness Explained explain consciousness, or just explain it away? Check out Dennett’s story “The Sad Case of Mr. Clapgras” and see what you intuit. Mr. Clapgras wakes up one morning and finds that everything he sees is suddenly disgusting. His vision is still normal, but his associations with every color have somehow gone awry overnight. He now hates his old favorite color, red, and prefers his former least favorite, blue. Everything looks the same but nothing feels right. His food looks revolting—he has to eat in the dark. Dennett exploits the tale of poor Mr. Clapgras to raise difficult questions about the nature of perception, and thought, and to disrupt our faith in consciousness itself.

Even if you don’t love logic puzzles, brainteasers, and code-writing, all of which delight Dennett, you may still find this book an entertaining introduction to Dennett’s tenets. As you stretch your mind on his mind-twisters, you begin to feel your way to glimpses of his view of life. At the same time, it’s also something like torture to twist your thoughts into the pretzel-shaped path that Dennett wants you to follow—to walk the Mobius-shaped ribbon of highway on which, no matter how you hurry and scurry ahead, you can never arrive at a place where there is something special about the human mind.

Read this book carefully and you’ll find yourself Jumping Out of the System in all directions. Dennett will lift off the top of your head, and tie your forehead into knots. Is this really where the philosophy of mind is headed? There’s no question that as neuroscience hurtles ahead, our current system of thought is beginning to feel creaky and rusty in the extreme. Some bright new ideas probably are going to have to take its place. It may be that Dennett and his friends are the philosophers who are building them—Dennett most cheerfully of all, in his Santa’s workshop of intuition pumps.