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Conversation with Jeff Hawkins – on the Thalamus Episode 10: Conversation with Jeff Hawkins – On the Thalamus Jeff: 00:00 One of the things we knew is that sequences in the brain have to be able to do is you have to be able to speed them up, slow them down. Matt: 00:04 Right. Yeah. Jeff: 00:05 Like I can play a melody back faster. I can recognize it faster. I can speak faster and slower. So there's all these - Matt: 00:09 And it's not different patterns. It's the same pattern. Jeff: 00:11 Yeah. It's the same pattern. But you can speed up and slow it down and so, there had to be a mechanism for that in the brain and if you think about it, that mechanism has to apply not to one column in the cortex, it would apply to like all the columns that are doing, that are doing speech, something like that. Music playing Christy: 00:35 You’re listening to Numenta On Intelligence, our podcast series on how intelligence works in the brain and how to implement it in non-biological systems. In this episode, we’re going to take you back to where the podcast started – a conversation with our co-founder Jeff Hawkins. In fact, for the next few episodes, we’re going to try something a little different than the previous few episodes, which featured Interviews with Neuroscientists. Matt Taylor, our Open Source Community manager, will be bringing you conversations with Jeff Hawkins, or Subutai Ahmad, our VP of Research, on a variety of topics. These could include anything from Jeff’s latest research developments that haven’t yet been documented, to Subutai’s updates on applying our theories to today’s machine learning systems. These will be casual conversations, the kind that happen every day here at Numenta, and we want to share them with you, our listeners. Some of them may get pretty technical, but we’ll provide links to resources for further reading. I hope you enjoy these conversation from Numenta On Intelligence. Matt: 01:34 So I'm here with Jeff Hawkins in his office. It's early in the morning here at Numenta. There's just me and you and we're going to talk about some speculative thoughts and thinking you have about the thalamus, right? Jeff: 01:45 Yeah. Yeah. So, uh, we chosen, I've chosen, uh, to talk about the Thalamus now. I'll tell you what it is and why we think it's important. And then some new ideas we have about what it might be doing. Matt: 01:57 I think people will be interested cause we, we voted, we usually just talk about neocortex. So it's a little refreshing to go to somewhere else in the brain. Jeff: 02:04 Yeah. So let's just paint a picture in your mind. You know, the neocortex is, is like a big sheet, like a big napkin wrinkled up on top of your brain. And it's only a couple of millimeters thick. The thalamus, it's right in the center of the brain and it's two parts, like everything in the brain. And there's like maybe like the shape of two eggs, two small eggs. Matt: 02:22 Right. One on either end, either hemisphere. Right? Jeff: 02:24 So we, you know, that's everything in the brain has got two parts. We don't usually focus on that, but they're doing the same thing, just divided in half. So the thalamus is right in the middle and um, it has a very, uh, unique relationship to the neocortex. In fact, myself and some other people studying the thalamus really don't think you could separate them. Um, and the reason is, is that when information goes to the neocortex, from your eyes, your skin or your, or your ears, it always goes through the thalamus, always. Matt: 02:53 Sensory information... Jeff: 02:53 All sensory information, pretty much, pretty much almost any sensory information. And so the object nerve, it doesn't go from the back of the retina, it doesn't go straight to the cortex. It goes to the thalamus and the thalamus then goes to the cortex. Matt: 03:05 Right. Jeff: 03:06 And when two regions in the neocortex project to each other, you know, region A and region B or v1, v2, there's they primarily do that through the thalamus again. So v1 projects to the thalamus and then the thalamus predicts to v2 that there are direct connections between these cortical regions, but there's always one that goes through the thalamus. And since all information goes through the thalamus, it used to be thought that the thalamus is like the gateway to the cortex. Like when you get through this gateway, you're in. But now it's believed that everything that goes between cortical region, the cortical region goes through the Thalamus. And that way you could think of it as a part of the neocortex. I kind of think of it like an extra layer of cells or extra set of tissue that has been, that's been consolidated down the center of the brain. But it's almost, it's so intimately connected with the neocortex. You can't really separate them out. Matt: 03:58 But it is an older part of the brain, right? Jeff: 04:01 Ah, I don't know that's true actually, Matt. I, you know, it's in the sense that it's not neocortex. We often tend to think about everything that's not the neocortex is the older part of the brain. I don't know if the thalamus existed prior to the neocortex. I don't know that. Yeah. So, um, it probably did in some form, but really I think we, if you really want to understand how the neocortex works, ultimately you have to understand how the, what the thalamus is doing. Matt: 04:25 There are no mammals that we can find that just have a thalamus and no neocortex. Jeff: 04:29 No mammals, all mammals have a neocortex of the question is, or the non mammals that have a thalamus that don't have an neocortex. I don't know the answer that one, but we can, we can pretty much say right now the neocortex is intimate and required, and the thalamus, is required to have a neocortex. So you can't really separate the two out. Matt: 04:48 Well definitely the projections show that Jeff: 04:50 That's right. The projections show that, physically it's separated. But the projections are very intimate and um, and so we've always known that any theory of neocortex is going to have to explain what the thalamus is doing. Um, and the thalamus itself is not super complicated, but it's not super simple either. And I'm going to break it into two broad categories. There's one broad category we've just been talking about, which are called relay cells Matt: 05:16 Relay cells. Jeff: 05:17 Yeah, so like an axon comes from your eyeball and Matt: 05:20 Oh it's synapses in the thalamus... Jeff: 05:22 It makes a connection to one of these relay cells in the thalamus and the relay cells in the thalamus goes to the neocortex and it literally looks like one to one. Matt: 05:30 Wow. So just one, one stop and then Jeff: 05:32 That's right and not only one stop. It's, there's very little con-, there's no convergence in the thalamus. It's like it's literally like you took a long wire and you cut it and cut it in half and then connect it back together. Matt: 05:44 So why do it? Jeff: 05:44 That's right. Right. That's a good question. So the call of the relay is a little bit misleading because we know it must be, there's no reason you're not going to have this to do nothing. Right. But that's kind of what it looks like. They can say, this will show in many situations, it's one to one correspondence. A spike comes in and spike comes out and there's a, the topology of the arrangement of the cells in the retina are preserved in the Thalamus and they project to the cortex and they're preserved in the cortex. So, one thing is why are there relay cells? The second thing, there's a whole bunch of other cells and by the way it was a relay cells, a group of relay cells that go between the retina and V1 - that's called LGN lateral geniculate nucleus. That's just a bunch of cells in the thalamus and the separate ones that go between all the other regions. So these are dedicated cells for these units. Matt: 06:26 Right. They're localized to Jeff: 06:29 to whatever that projection is. There's another set of cells in the thalamus which are much more diffuse. They project to the cortex and they project very diffusely. So these cells, uh, they go by different names. I prefer the one that sometimes they're called matrix cells. I'm not referring to the movie, but referring to the, uh, the fact that they're sort of interstitial to these other, they're sort of in the matrix of the thalamus.
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