![[Radio National Main Page]](/web/20001109180400im_/http://abc.net.au/rn/graphics/rnleft.gif)
|
Radio National
|
|
with Norman Swan
Hypnagogic Images in Normals and Amnesics
Summary: Research from Harvard University found that the dreams we have just as we're about to fall asleep, rely on memory of the day's events. But people with amnesia, with no memory of what's just happened to them, have the same so-called hypnagogic dreams as others. Norman Swan: Today on the program, surgery on the beating heart; isn’t that what cardiac surgeons normally do? you may ask. Well no, they normally stop the heart but leaving it beating is a growing trend, although operating on a moving target isn’t that easy. Surgeon: We lifted the heart up and applied the clamp and occluded the blood supply to that area of the muscle, the muscle showed signs of ischemia. In other words, if we’d left it on there for any length of time, and we don’t really know how long, he could have had an infarct or a heart attack. And of course the operation’s designed to prevent that, not to cause it. Norman Swan: That special feature from Richard Aedy later, after we’ve explored our dreams. Because research from Harvard University has found that the dreams we have just as we’re about to fall asleep, rely on memory of the day’s events. Yet people with amnesia, with no memory of what’s just happened to them, have the same so-called hypnagogic dreams as you and me, especially after playing a video game. Dr Robert Stickgold is in the Department of Psychiatry at Harvard, and his findings are opening a window into dreaming, memory and the nature of consciousness itself. In fact he’s a hypnagogic dreamer himself. Robert Stickgold: Although not from video games, actually from mountain climbing. I was up in Vermont, and I went off one morning with my family and I climbed up a mountain, Camel’s Hump, and that night as I was going to bed I laid down and I closed my eyes and could suddenly feel the rocks under my hand from this one critical point; it’s mostly a walk-up, but there’s this one short stretch where you actually have to use hands and feet carefully to climb up a chute, and I could feel the rocks under my hands from that critical moment. And I sort of woke myself back up and said, ‘Well that’s rather fascinating’ and let myself drift off again, and there were the rocks again a second time. And then I was really fascinated. And I thought, ‘OK let’s think about something else’. I had this paper that was supposed to be submitted last week; that wasn’t done yet, and I could feel the rocks under my hands again. So I said, ‘There’s something really strong in the brain at this point that’s producing these intrusive images, I’m not trying to produce them. It’s as if the brain has decided that there’s something it has to deal with at this particular time. And that’s what triggered all the interest. This was five years ago, and I had this desire to do a study of it, and then I thought about trying to get permission to take people climbing up nasty rock walls, or downhill skiing who had never skiied before. Norman Swan: Somehow the grant-giving authorities didn’t feel that this was a good spend of their money. Robert Stickgold: I just had this image of the Human Studies Committee saying, ‘You’re going to do what?’ and I was complaining about it a couple of years later, and someone just said to me, ‘Well use Tetris then’. And I started playing Tetris, they said, ‘That’s all I could see when I was falling asleep.’ And someone else in the room said, ‘Oh that happened to me too.’ And at that point we were off and running. Norman Swan: Now you’d just better explain the Tetris game for people who escaped the video game revolution. Robert Stickgold: How could anybody not know Tetris? It is one of the most popular and widespread games at least in the States; in fact it took us a long time to come up with a dozen students at Harvard who had never played it before, to participate. The game has these shapes, which appear at the top of the screen and slowly float down, and as they float down you can move them side to side and rotate them, and the game is to get them to all fit together like keys into locks at the bottom of the screen, and if you fill up a whole segment, they disappear and you get more play time. Norman Swan: And people have reported to you that if they’ve played Tetris just before going to bed, that’s all they could see when they were just about to fall asleep? Robert Stickgold: Not even just before. It can be hours before they go to bed, but it’s when they first started playing it that they remember. And they would just describe seeing the Tetris pieces floating down in front of their eyes as they were going to sleep. Norman Swan: So what study did you do? Robert Stickgold: Well we decided to see just how prevalent and how real and how consistent this was, so we started out by getting a dozen students who had never played the game; we had them play for three hours on the first day and then a couple of hours on each of a couple of successive days, split between the morning and the afternoon, or the morning and evening in some cases. And then when they went to bed we had them wear this device we’ve developed called the nightcap, which they can take home with them and hook up to a laptop computer that monitors their wake/sleep cycle, and as they would fall asleep it would, in the first couple of minutes of sleep, wake them up and ask them to grab a micro cassette recorder and just report whatever was going through their minds. We did that with a dozen novices, we did it with 10 experts, we averaged for people who had played at least 50 hours of Tetris in their lives, and almost everybody came in between 200 and 500 hours of Tetris. And then we ran five amnesics as well. Norman Swan: Why? Robert Stickgold: Why? Well because we wanted to find out what types of memory systems in the brain were critical for producing these kinds of sleep onset images. Let me back up a bit and say that one of the fascinating findings was that everybody had the same images. These are sleep onset dreams and they’re very different from your classic REM or Rapid Eye Movement sleep dreams that come later in the night, in that they’re very simple, and what people report seeing without exception is seeing these Tetris pieces floating down in front of their eyes, and sometimes they would describe rotating them or moving them or fitting them in at the bottom, but mostly just seeing those pieces float down. And the question was, Where are these images coming from in the brain? Now it turns out that there are two fundamentally different memory systems up there in our brains, that we usually use so effectively with each other that we don’t really notice. But one of them, which is evolutionarily older and located deep in the centre of the brain, is based around the structure called the hippocampus, and that memory system holds memories of actual events from our life. So if I ask you What did you have for breakfast this morning? you go to your hippocampus to find the answer to that. The other brain system, memory system, is located in the neo-cortex, which is that big folded outer surface of the brain that we always think of when we think of the brain. It’s relatively newer evolutionarily and it’s storing what we call semantic memories, which have to do with memories of actual facts and pieces of information rather than events, usually highly integrated into associative networks. So if I would ask you, ‘What do you like for breakfast in general?’ that question you go to the neo-cortex for. Norman Swan: It’s everyday information in a sense. Robert Stickgold: Everyday information. And if you ask yourself in your mind those two questions, ‘What did I have for breakfast today’ or better yet, ‘What did I have for breakfast yesterday?’ and ‘What do I generally like for breakfast?’ it feels different, the way you go looking for them in your mind, and that’s because you’re using different sets of rules to access these two different memory systems.’ Norman Swan: And these people with amnesia you studied, they had amnesia to distant events; what sort of memory loss did they have? Robert Stickgold: These subjects all had brain damage, either from infection or from a period often involved with other unrelated surgery, where they lost oxygen supply to the brain. So they’ve lost the hippocampus and the structures around them. David Rodenbury, my student who actually ran the amnesic patients, would go to them the first morning and spend two hours with them while they played Tetris after he taught them how, and he’d come back in the afternoon or the early evening, and they wouldn’t remember having seen him before, and they wouldn’t know why there is a computer in their room, and they wouldn’t remember having played Tetris. So they can form no new memories at all. So we assumed rather simply, that they obviously would not be able to remember these when they go to sleep either. And the absolutely startling finding was that although in fact they do not remember having played the game, they still got the exact same images. So we have a report from one of these patients saying, ‘I’m seeing these shapes that turn on their side; I can’t remember what they’re from, I wish I could but they’re like blocks.’ And another one reports seeing these shapes floating down on a screen. But neither of them remembered having played Tetris. Neither of them knew where these images came from. So they’re dreaming about things that they can’t remember, and what that tells us is that they’re not using that hippocampal event-related memory system, but must instead be using that neo-cortical system which just sort of has general images and general knowledge and facts about life and the world, it’s not any longer connected to specific events. Norman Swan: So if you just turned up here, I mean many of us have experienced that sort of eerie, semi-detached state where funny things go through your brain just as you’re dropping off to sleep, have you just discovered a quirky, short-circuit in the brain which re-runs certain events, or have you turned up something that tells us more about consciousness and dreaming? Robert Stickgold: I think this is really telling us about functionality of the sleep process itself. It’s strange that we still argue over what the function of sleep is, and it’s starting to look again like the primary function of sleep is exactly to take memories either from the very recent past or even the more distant past and do processing of it during sleep, and there’s a couple of different types of processing that are going on I think, as we sleep. So one of them is to simply take events from the day that appear by some calculation of the brain to have been important, and extract from them the critical information that’s in that. So when my subjects and my patients – Norman Swan: So there’s a videotape rerun during the first couple of minutes of sleep, of the day? Robert Stickgold: No, but it’s not, because nobody reports seeing the computer, nobody reports seeing the table or the room, or reports seeing the keyboard or using the keyboard, they just see the shapes floating down in front of their eyes, as if the brain has already extracted from the event, from the actual behaviour and experiences of the day, the most critical pieces of that experience, and it’s focusing just on those. We’ve started now another set of studies using an arcade game called Alpine Racer, where the subjects stand on a pair of pretend skis and have to push them to the left and right to control our video image, skiing down a slope. And what they report is again at sleep onset, they see the images but they’re always seeing the images of where they crash. Just like when I did my mountain climb. Norman Swan: So this fits with the research done at the University of California, Irvine, and others, which shows that memories attached to emotional experiences are ones which get laid down preferentially. Robert Stickgold: Absolutely, and I suspect that this is exactly part of that process. Norman Swan: What if any relationship is there then between these semi-somnolent dreams and the ones you have when you’re in really deep sleep, when you’re in REM sleep? Robert Stickgold: Well one of the fascinating things is that the animal studies all suggest that during REM sleep the information flow out of this hippocampal memory system is shut off, so it looks like even during REM sleep we’re going to be in a state where we don’t have access to actual memories of things that have happened to us, but rather just of that sort of extracted and abstracted information that we obtain from it, and when you think about it that way, all of a sudden a lot of the features of dreams start to make sense. So I drive home one day and almost get broadsided by some guy who runs a stop sign, and I go home and I swear that we’re going to move to Iowa where people drive sanely, but that night I have a dream that I’m at an amusement park with my son Eli and we’re in bumper cars and everybody’s crashing into us from either side, and he’s roaring and having a great time, and I’m saying ‘This isn’t fun, this is really upsetting’, but I don’t dream about the accident I was almost in, I dream about this strange, almost bizarre association to it. And I think that what’s happening in REM that’s different from sleep onset is that the brain is trying to find in its memory storage, which must have tens of thousands of bits of information in it, trying to find what do I have already in this collection? Norman Swan: It’s simply a filing exercise and getting at the right spot. Robert Stickgold: It’s exactly that, and you have a really good filing secretary, they’ll tell you it’s not easy because it’s not filing it in one spot, it’s more like a computer linking it to a dozen different spots all over the place. Norman Swan: And the link between that people talk about here, between mind and brain? In other words you’re talking here about consciousness which most of us think of as our mind, and the brain function itself, this is really what you’re getting to? Robert Stickgold: That’s in large part one of the most exciting pieces. We’re looking at the brain when it’s in a state that we know is physiologically very different in sleep than in waking. We have different areas of the brain that are activated, we have different chemicals circulating through the brain, and what we’re seeing is how that alters our very consciousness, it’s almost like the poor man’s version of consciousness expanding drugs, that the brain automatically in sleep is changing that environment of the brain, and we’re starting to see how these very consistent changes that all of us go through every night, produce these equally consistent changes in how our mind and our consciousness actually work. Norman Swan: So there you are, as most fuddy duddies have long suspected, video games can mess with your brain. Dr Robert Stickgold is a cognitive neuroscientist at Harvard Medical School in Boston. Reference: Stickgold R. et al. Replaying the game: hypnagogic images in normal and amnesics. Science 2000;290:350-352 Guests:
Main Index Recent Stories Search by Subject All Stories 
|