Sunday, April 01, 2007

Transient global amnesia as an experiment in consciousness

Mostly here I refer to the consciousness that neuroscience studies, sometimes called phenomenal consciousness. Toward the end I get to implications about consciousness in the sense of something beyond our biology. As I was writing this my mind was mostly on memories I have. A different sort of image popped up in my mind several times. I dismissed it each time until I realized what name I would put to it. This was not a fleeting image as a memory is, but a dream-like image, one that is startlingly clear and detailed, more so than any actual memory, even one from earlier today. It was a book cover with a drawing on it where a few people were in a medieval scene, something worthy of either The Arabian Nights or Grimm’s Fairy Tales. It was a new creation from somewhere within me or outside of me, a mimicry of book covers I have seen, but not a memory. It was exactly the same each time until I gave it words, “This is a fairy tale?” It didn’t come back after that. What I am saying here isn’t a fairy tale. It relates my professional experience. Is the concept of consciousness a fairy tale? Which part? Who says so? I have more on that later.

On my last day as a first-year neurology resident in 1982 I had to get up early to see a woman of around 60 years old in the ER. Even earlier that morning she had awoken her husband, saying she had chest pain and needed an ambulance. Shortly after he made the necessary call, she asked him what he was talking about. She didn’t have chest pain. She didn’t need an ambulance. I’m sure this latter conversation repeated many times before I made my way to see her.

When I saw her she had as dense an anterograde amnesia as one will ever see. Amnesia is nothing like it’s portrayed in the movies. Some psychiatric patients may deny knowing who they are as a dissociative symptom, but that’s never a neurological condition. With the brain, our vulnerable memories are the ones we’re making now and next most vulnerable the ones from the recent past, ones lost in the retrograde part of an amnesia. Many things can interfere with making new memories, what’s called anterograde amnesia. It’s unusual though to have a profound dysfunction of memory without any other impairment neurologically, which is what transient global amnesia is.

Everyone with this condition acts the same way, the way this woman did. When the impairment in making new memories is total, the patient will engage in conversation that recycles about every 5 minutes. The patient might say he or she just woke up, as this woman did repeatedly. Then they’ll ask what’s going on, where they are. The conversation follows a rational course. Then 5 minutes later it starts all over again as the patient has forgotten everything and believes again he or she has just awoken, because that’s what it seems like to them. Their motivations and strategies in asking questions are about the same as they were the time before, so there is a striking similarity to how the patient proceeds on each “awakening”. Fortunately this rarely lasts more than an hour or two until the patient is starting to make some memories again. Usually people have complete recovery within 24 hours. Early on though, it’s like the movie Groundhog Day, only it’s every 5 minutes instead of 24 hours that things start again, and I’m the one who remembers, not the patient.

Traditionally such a patient is said to have normal consciousness, but this only means that someone looks awake and normal. One difficulty with studying consciousness is that we do take an all or nothing approach to the meaning of that word. We are either conscious or unconscious ordinarily. We do allow a state of drowsiness when this is about the difference between being conscious and asleep, but then we speak of drowsiness as a special state of consciousness where one has not quite become fully conscious. If instead one is looking for states that are between conscious and unconscious, transient global amnesia is one, an altered state of consciousness.

It’s curious that we don’t take such patients at their word that they continuously must have just awoken because everything before just now is dark to them. Of course I saw that this person wasn’t asleep 5 minutes ago, so officially we go with that. But imagine what it’s like for the person who has no memory of the last few hours, none at all. No wonder they all talk alike, searching for a handle on how they suddenly wound up with me. Any other handle is completely different from their long-term memories of how such a present can happen. Many have seen someone suddenly materialize somewhere on Star Trek, but no one thinks of that. People go to what they know personally. We remember waking up from sleep many times, but not being transported ourselves, so we go with what we know for an explanation.

When people have permanent anterograde amnesia of this magnitude, which rarely happens from trauma or some radical epilepsy surgery once done in the past, they aren’t quite so obvious. We do have a second unconscious memory that helps us feel more comfortable without the conscious images to tell us what we’ve been doing recently. The well-studied amnesiac H.M. whose memory stopped in 1956 due to surgery was able to locate things around his house that were new since the surgery, such as where the knives and forks were in his kitchen, without remembering anything explicit about why he could do that. That is unconscious memory, similarly to motor memory of how we walk, talk, or use a tool with no thought of how, once we’ve practiced enough to know how.

Still such patients will write in journals about how it feels they just woke up or became conscious for the first time, as Susan Blackmore describes in her book Consciousness: A Very Short Introduction. Blackmore comments on a number of neurological syndromes that profoundly affect perception, mentioning each time that no spiritual or supernatural consciousness manages to rescue the brain from the affects of injury. So isn’t the brain all there is when it comes to what a mind is?

Most of those syndromes are about the consciousness that’s left when a brain injury takes away half the world from consciousness or one of our senses in one way, but not another. What’s left is consciousness, albeit on a different stage. What maintains it?

Mainstream neuroscience says that what maintains consciousness is something trivial. We have all these modules, perhaps 30 places where a visual map of the outside world exists in a portion of our brain, some for seeing color, some for seeing movement, some for detecting objects. Then there are modules for other senses, both senses that map the world around us and senses that map our bodies. Then there are cognitive areas, some that contain everything we know in terms of verbal symbols, in the speech areas of the left hemisphere, some that are non-verbal associations, including who I am and who and what is close to me, even essential to me. There are memories involving all these things to give us a context for the present. Cobble all those things together and boom (to mimic John Madden), we’re conscious. That’s the mainline theory of consciousness as an emergent property, a trivial expression of everything else we know to be real.

Memory may be the last piece in that puzzle. Most people have the experience that their conscious memories don’t begin until around age 3. We learn before that age, but it’s not through the event-based memory that we can replay in our minds, not what we think of as memory ordinarily. It’s through unconscious memory that we first learn anything. Then we change, unfortunately at a time when no child is able to appreciate the change, much less describe going through it. Is it a coincidence that this is the age when we see children as going from those who say, “No,” to those who say, “Why”?

Age 3 corresponds to when the hippocampus becomes fully myelinated, when it is fully mature. All neuroscientists think these two things go together. The hippocampus is the oldest mammalian structure in our cerebral cortex. It is vital to making new memories. This patient I describe turned out to be one bit of evidence for that as a research PET scanner was available that morning, so while we waited for her to recover, we did the first PET scan ever done during an episode of transient global amnesia. It showed decreased metabolism in the medial temporal lobes bilaterally, where the hippocampus is. Others would point to other evidence, but this evidence I can remember directly, through these fleeting images we have of the past called conscious memory, through which I can remember a few pieces of one day in 1982 as if they were happening now, even if most days in 1982 have left me no such memories. It may be the closest to time travel we ever get.

Our limbic system built up from these, as emotions attached to memories, as relationships between people and things in the world and me, something vital to mammals for mother-child relationships, often more than that. Toward the end of all this evolution came our symbolic abilities, so that we could not only express ourselves in words, but abstract words, even words that make no sense.

What is all this? Is the hippocampus the seat of consciousness? Mainstream neuroscience doesn’t talk that way, having been burned when Descartes said the pineal gland was the seat of the soul. The mainstream view is that memory is just one more module to consciousness, so patients with transient global amnesia are seen as fully conscious, but lacking the memory making module. The patients just don’t remember their consciousness from one moment to the next, while an observer does. At least the observer remembers from moment to moment that the patients looked conscious and rational.

Furthermore, children before age 3 seem conscious, and the maturity of the hippocampus at age 3 isn’t the final development in our consciousness. Our ability for abstract thought isn’t complete until our teens. So isn’t the hippocampus just another actor in the play?

Children before the age of 3 may not have the ability to replay entire scenes in their head or maybe what scenes they do have all fade until the hippocampus is mature. Somehow they look like they maintain a stream of consciousness without that, though not as well as an adult does with an adult’s will, desires, language, all these things that fill our mind.

For things like will and desire we have no clear anatomy as we do for conscious memory. Experiments have been done during brain surgery with awake patients where electrical signals in the brain related to a patient’s intent to push a button to change a slide projector, as instructed, are used to change the slide projector electronically before the patient can do that manually. The patients reported that what happened was that they were going to push the button, but the slide projector changed itself first. It was their will that this happened, but unless that will goes through what we’re used to as our voluntary muscles, we don’t recognize it. Scientists aren’t much better at recognizing what we do by will.

Our memories give us our models of what we think and do. Patients with transient global amnesia have a concept of self. At any moment they see a scene that makes sense to them except for how they got there. They know what objects are outside of them and what objects are them, like their hands. Memory in the sense of that sort of knowledge is intact. They have some remote memory because they used to have a functioning hippocampus, but they are making no new memories, none. So the last few hours are a blank. They must have just awoken. Only observers know they haven’t. They weren’t asleep. 5 minutes ago they were just as they are now. It’s just that some writer has been failing to move the plot along, and the patient doesn’t realize that.

Normally many things move our consciousness along. The outside world moves along at its normal pace. We keep up in terms of perception, memory, and planning what we’re going to do about what goes on around us. We may even develop our own plans out of something within us, our will and desires. Somewhere they enter our consciousness as well and turn into wordy thoughts or images of what we desire or why we are so determined.

Neuroscience soon may do better at following all that through neuroimaging than it has before now. But what there is now is the link between the hippocampus and memory, something that happened in mammals before any other expansion of cerebral cortex. It is a strange plan to the brain. There are sensory areas in the midbrain and the thalamus. In birds these are the most important areas for vision and hearing, not so in us. In us everything in cerebral cortex recreates sensory and motor areas that already exist in the brainstem, apart from new abilities like language. Why? Is it so these areas can be conscious in being linked up to the hippocampus? Is it so our consciousness can be seamless, apart from things such as how the world looks behind my head? Many of us in neuroscience equate cerebral cortex with conscious brain. That’s not quite true as many things happen in cortex that are not conscious, but nothing to my knowledge outside of cortex can be conscious. An entire section of the brain had to be built for us to be conscious, and that started with the hippocampus, with an ability to replay scenes from the past, the present being the most detailed scene we can have played. We see it as it happens, but only through our consciousness built for memories.

Consciousness could be what our brain had to create to make memories as well as it does, to create a virtual reality where we pick out useful or emotionally significant pieces to be stored as memory. Without that our minds in their current state just spin their wheels, confabulating as best they can to explain why we don’t have explicit memories of how we got here – we just woke up, yeah that makes sense. It doesn’t if the condition goes on. If the condition goes on, people learn just to accept the absence of new memories, except when they’re freely writing in a journal. When the absence is fresh, people do what we do easily with the memories we already have. They ask where their mind went. I must have been asleep.

We know so little about the details of making memories. Something is known about the electricity and chemicals involved in a normally functioning hippocampus, how there are long-term changes in the hippocampus which seem to relate to a new memory starting. Then this new memory is transferred to be stored diffusely in the cerebral cortex. At some point a memory is so mature in the rest of the brain that it will persist despite the hippocampus losing function. How long does this take? One can investigate how far back a retrograde amnesia goes in a patient with a brain injury or stroke that isn’t quite as restricted as transient global amnesia, but is close. One can test such subjects on historical events. Compared to controls, subjects perform poorly on events weeks or months before they developed amnesia. Yet for events 25 years in the past, the groups perform equally. How far back does the deficit preceding the amnesia go? According to studies by Larry Squire of UCSD, the two groups differ as far back as 15 years into the past. 15 years?!

That means the hippocampus is helping to support our memories for up to 15 years. After that they are finally permanent, some of them becoming more permanent all that time. Imagine that. My mental processes that I think of as being in the present are reaching back 15 years to provide an immediate context for me, in addition to the context that I call the distant past. Without that immediate context, I can only imagine that I just awoke. That is my only experience like this. I awake each morning, and I remember the things around me. I remember who I am. Even if I awoke in strange surroundings, things would be behaving in familiar way. Gravity would be obvious. If there were no gravity, that would be a big clue – I’ve awoken on a spaceship! I’d know that from video of astronauts I remember that video along with however that association is stored cognitively. My joining them would be something to remember, if I could.

Such elements would fill whatever this consciousness is I have, and if my hippocampus isn’t working, I’ll think exactly the same thing 5 minutes later, instead of being able to build on my recent memories as I usually do. All other memories and associations were formed when my hippocampus was working, long enough ago that they have become permanent, capable of filling my waking mind even when my hippocampus has shut down.

How does that happen? Good question. 36 years ago Karl Pribram likened such recall of memories to a hologram. If a stimulus matched a little of the memory, the brain is wired to reproduce the rest of it, having been rewired because of what the hippocampus does when the memory is formed. That continues to be how neuroscientists think a memory becomes permanent.

None of this would happen without a hippocampus. There would be unconscious memory and learning, as happens in all species, but it may be that only mammals are conscious because only mammals have this system that keeps stimuli reverberating within our brain to become this seamless ongoing virtual reality that our brain makes, and we live in. In that consciousness we have will instead of merely reacting to everything. In that consciousness we have desires that we can choose to embrace or deny depending on how we feel about the consequences of either one. It is a different world to be conscious, a world we try to re-enter if our hippocampus shuts down, just as we re-enter it from sleep, but without a functioning hippocampus this doesn’t work. We just keep waking up, waking up, and waking up, using our permanent memories to orient us and tell us what to say and do. It’s not enough for us to be ourselves.

I don’t know that there is a formal theory in neuroscience that consciousness exists so we can make better memories. Susan Blackmore argues in her books that the concept of consciousness is a delusion, which seems silly to me, a denial of the unknown more than anything. More mainstream would be to say that consciousness is just the sum of its parts. I don’t know that this will change until scientists can fully explore all those parts and say, “You know, there is something else.”

Will they have to do that in this century, in the next century, sometime? Will those who see consciousness as primary and the brain as trivial have to admit that the brain is not trivial? I myself have wondered if our mind might control the brain the way our brain control the spinal cord. An injury to the spinal cord prevents the brain from expressing itself through the corresponding limbs. Does an injury to the brain prevent the mind from expressing itself through the half of the world that no longer exists for the brain or through language that no longer exists? Is that so strange a perspective?

Of course the big dividing line is whether my consciousness extends beyond my brain or receives input from beyond my brain. I am forced to conclude that it might because of my spiritual experiences, though I’ll never have proof that these experiences are beyond my brain’s capacity to teach me or entertain me. It just seems too much to be entirely natural to me.

Consider the image I described at the beginning, a symbol for “fairy tale”. Who said that? It wasn’t a verbal part of me, or it wouldn’t have been an image. It could have been some dissenting part of me I keep locked up in some dungeon of my consciousness, but I don’t have any sense this was a dissent. I wasn’t starting to tell a fairy tale. Yet there are certainly fairly tales told about consciousness. I think Susan Blackmore is telling a fairy tale in calling the concept of consciousness delusional. I think those who say the brain is irrelevant are telling a fairy tale. From wherever that image came from I feel satisfaction at saying that, both of those, just as the image no longer needed to repeat once I realized what it was saying. I’m used to this, some Other sharing my mind. She says She is not just a different part of me. I’ve gotten used to trusting Her.

I know that I pray to God. I know that I get direction, strength, hope, and comfort from doing that, but I don’t know exactly where that comes from. Is it from inside me or outside? Some say they know. Their words don’t read to me as though they know. How far out does consciousness reach? However far it is, I am constantly surprised at how things come to me beyond mechanisms I know. People confabulate to fill in what they don’t know, as those with transient global amnesia do their best to explain the state they find themselves in. In fact one would have to be a neurologist to have transient global amnesia and guess that is the case from the inside. And then what? I would still make that guess again five minutes later if it were me. Knowledge isn’t everything. There is something more. I’ve lived as if that something is helpful. I believe it is, and I don’t find any way to cram all of that helpfulness into me.

So call it God, Spirit, whatever you want, there is something more than me in this.

2 comments:

Tim said...

Hi David - nice post - in fact I wanted to ask you if you'd like to submit this essay to the upcoming Four Stone Hearth blog carnival I'm hosting this coming Wednesday, the 11th. If so, just drop me a line, or else you can submit via FSH, but no prob if you're not keen on the idea. Hope all is well with you, cheers for now.

Melatinini said...

This was a very interesting read, and I really admire your articulacy, knowledge, and the way you think. I'm a high school student who is becoming increasingly interested in neuroscience; don't be surprised if I lurk here in the future and comment occasionally.

Personally (and with support from having read Ramachandran's thoughts on the illusion/perception of "self"), I'd go for the sum-of-the-parts definition of consciousness. Neuroscience fascinates me mainly BECAUSE it is a purely physical way of explaining things that we could not otherwise fathom. So, needless to say, I differ from you in my belief that there is not "something more." The way I see it, one can have 100% assurance that there IS something external coming into play... but as is becoming increasingly obvious to me as I research confabulation and other phenomena of false perception, human certainty means little. I'm not accusing you of assuming, though: you have the hesitance that seems to be inherent in anyone knowledgeable (and I, too, am at least wise enough never to dare to say that I know anything for sure, as much as the evidence indicates to me that the physical realm is all there is.)

The fact that you know so much about evolutionary biology and other neurological theories striving to explain, physically, our conception of the metaphysical makes your faith all the more amazing and (if I have a right to judge) credible.

When you ponder whether or not your spirituality is "beyond [your] brain’s capacity to teach [you] or entertain [you]," it seems that you're considering two possibilities: that there IS something external that affects your consciousness or that everything you perceive is a function of what is going on in your brain. To me, it seems that there are more possibilities: maybe there is something external to which your conscious mind is sensitive (what you seem to be describing) OR maybe there is "something more" that is created by your mind, not sensed by it. I.e., maybe your "something more" is a part of you ("internal" by your definition) but goes beyond our current knowledge of the physical structure of the brain. I suppose the line between the possibilities is blurred -- maybe I'll be able to come up with more clear definitions when I think about it more. All I've really sorted out in my head is that there are more explanations for the spiritual than "it is objectively there" or "it is objectively not there." (Actually, I haven't read enough of your stuff to know if you believe in an objective reality or not, although one sentence in a post of yours strongly suggests the former [and I agree, although I guess much of "reality" is a gray area.])

My definition of the metaphysical (I do not believe in God or other spirits) is almost equivalent to "what is not known." This is not the "God of gaps" (the often-exploited theory that anything that science cannot explain is a result of "something more"; the gap is closing as we discover more and more) but rather a naive notion that anything that can't be explained according to what we know right now is beyond human perception. I haven't decided, though, if there are things that are decisively beyond our capacity to understand EVER... or if everything that is objectively real will eventually be fathomed by our species.

I guess I've digressed a lot, but I hope that out of my mess of words, I've expressed something understandable of my vague perception of consciousness. At this point in my life, I have far more questions than answers: far more decisions that "it's either this, that, or something in between" than actual stances.

Thank you for the interesting reads; I'll be on here a lot.