December 5, 2022
Mind
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A Thousand Brains by Jeff Hawkins - Summary & Quotes

Table of Contents

Table of Contents

Note: The following are excerpts from A Thousand Brains: A New Theory of Intelligence by Jeff Hawkins.

Three Takeaways

1. Reference Frames

I. Intelligence is intimately tied to the brain’s model of the world; therefore, to understand how the brain creates intelligence, we have to figure out how the brain, made of simple cells, learns a model of the world and everything in it. Our 2016 discovery explains how the brain learns this model. We deduced that the neocortex stores everything we know, all our knowledge, using something called reference frames. I will explain this more fully later, but for now, consider a paper map as an analogy. A map is a type of model: a map of a town is a model of the town, and the grid lines, such as lines of latitude and longitude, are a type of reference frame. A map’s grid lines, its reference frame, provide the structure of the map. A reference frame tells you where things are located relative to each other, and it can tell you how to achieve goals, such as how to get from one location to another. We realized that the brain’s model of the world is built using maplike reference frames. Not one reference frame, but hundreds of thousands of them. Indeed, we now understand that most of the cells in your neocortex are dedicated to creating and manipulating reference frames, which the brain uses to plan and think.

II. In more abstract terms, we can think of reference frames as a way to organize any kind of knowledge. A reference frame for a coffee cup corresponds to a physical object that we can touch and see. However, reference frames can also be used to organize knowledge of things we can’t directly sense. Think of all the things you know that you haven’t directly experienced. For example, if you have studied genetics, then you know about DNA molecules. You can visualize their double-helix shape, you know how they encode sequences of amino acids using the ATCG code of nucleotides, and you know how DNA molecules replicate by unzipping. Of course, nobody has ever directly seen or touched a DNA molecule. We can’t because they are too small. To organize our knowledge of DNA molecules, we make pictures as if we could see them and models as if we could touch them. This allows us to store our knowledge of DNA molecules in reference frames—just like our knowledge of coffee cups.

Reference frames are not an optional component of intelligence; they are the structure in which all information is stored in the brain. Every fact you know is paired with a location in a reference frame. To become an expert in a field such as history requires assigning historical facts to locations in an appropriate reference frame. Organizing knowledge this way makes the facts actionable. Recall the analogy of a map. By placing facts about a town onto a grid-like reference frame, we can determine what actions are needed to achieve a goal, such as how to get to a particular restaurant. The uniform grid of the map makes the facts about the town actionable. This principle applies to all knowledge.

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2. 'Thinking' Consists of Moving Through Reference Frames

I. Another team of scientists, Alexandra Constantinescu, Jill O’Reilly, and Timothy Behrens, used the new fMRI technique for a different task. The subjects were shown images of birds. The birds differed by the length of their necks and the length of their legs. The subjects were asked to perform various mental imagery tasks related to the birds, such as to imagine a new bird that combined features of two previously seen birds. Not only did the experiments show that grid cells are present in frontal areas of the neocortex, but the researchers found evidence that the neocortex stored the bird images in a maplike reference frame—one dimension represented neck length and another represented leg length. The research team further showed that when the subjects thought about birds, they were mentally “moving” through the map of birds in the same way you can mentally move through the map of your house. Again, the details of this experiment are complex, but the fMRI data suggest that this part of the neocortex used grid-cell-like neurons to learn about birds. The subjects who participated in this experiment had no notion that this was happening, but the imaging data were clear.

The method of loci uses a previously learned map, the map of your house, to store items for later recall. In the bird example, the neocortex created a new map, a map that was suited for the task of remembering birds with different necks and legs. In both examples, the process of storing items in a reference frame and recalling them via “movement” is the same.

If all knowledge is stored this way, then what we commonly call thinking is actually moving through a space, through a reference frame. Your current thought, the thing that is in your head at any moment, is determined by the current location in the reference frame. As the location changes, the items stored at each location are recalled one at a time. Our thoughts are continually changing, but they are not random. What we think next depends on which direction we mentally move through a reference frame, in the same way that what we see next in a town depends on which direction we move from our current location.

The reference frame needed to learn a coffee cup is perhaps obvious: it is the three-dimensional space around the cup. The reference frame learned in the fMRI experiment about birds is perhaps a bit less obvious. But the bird reference frame is still related to the physical attributes of birds, such as legs and necks. But what kind of reference frame should the brain use for concepts like economics or ecology? There may be multiple reference frames that work, although some may be better than others. This is one reason that learning conceptual knowledge can be difficult. If I give you ten historical events related to democracy, how should you arrange them? One teacher might show the events arranged on a timeline. A timeline is a one-dimensional reference frame. It is useful for assessing the temporal order of events and which events might be causally related by temporal proximity. Another teacher might arrange the same historical events geographically on a map of the world. A map reference frame suggests different ways of thinking about the same events, such as which events might be causally related by spatial proximity to each other, or by proximity to oceans, deserts, or mountains. Timelines and geography are both valid ways of organizing historical events, yet they lead to different ways of thinking about history. They might lead to different conclusions and different predictions. The best structure for learning about democracy might require an entirely new map, a map with multiple abstract dimensions that correspond to fairness or rights. I am not suggesting that “fairness” or “rights” are actual dimensions used by the brain. My point is that becoming an expert in a field of study requires discovering a good framework to represent the associated data and facts. There may not be a correct reference frame, and two individuals might arrange the facts differently. Discovering a useful reference frame is the most difficult part of learning, even though most of the time we are not consciously aware of it. I will illustrate this idea with the three examples I mentioned earlier: mathematics, politics, and language.

II. Say you are a mathematician and you want to prove the OMG conjecture (OMG is not a real conjecture). A conjecture is a mathematical statement that is believed to be true but that has not been proven. To prove a conjecture, you start with something that is known to be true. Then you apply a series of mathematical operations. If, through this process, you arrive at a statement that is the conjecture, then you have succeeded in proving it. Typically, there will be a series of intermediate results. For example, starting from A, prove B. From B, prove C. And finally, from C, prove OMG. Let’s say, A, B, C, and the final OMG are equations. To get from equation to equation, you have to perform one or more mathematical operations. To a mathematician, equations are familiar objects, similar to how you and I see a smartphone or a bicycle. When mathematicians see a new equation, they recognize it as similar to previous equations they have worked with, and this immediately suggests how they can manipulate the new equation to achieve certain results. It is the same process we go through if we see a new smartphone. We recognize the phone is similar to other phones we have used and that suggests how we could manipulate the new phone to achieve a desired outcome.

III. To be an expert in any domain requires having a good reference frame, a good map. Two people observing the same physical object will likely end up with similar maps. For example, it is hard to imagine how the brains of two people observing the same chair would arrange its features differently. But when thinking about concepts, two people starting with the same facts might end up with different reference frames. Recall the example of a list of historical facts. One person might arrange the facts on a timeline, and another might arrange them on a map. The same facts can lead to different models and different worldviews. Being an expert is mostly about finding a good reference frame to arrange facts and observations. Albert Einstein started with the same facts as his contemporaries. However, he found a better way to arrange them, a better reference frame, that permitted him to see analogies and make predictions that were surprising. What is most fascinating about Einstein’s discoveries related to special relativity is that the reference frames he used to make them were everyday objects. He thought about trains, people, and flashlights. He started with the empirical observations of scientists, such as the absolute speed of light, and used everyday reference frames to deduce the equations of special relativity. Because of this, almost anyone can follow his logic and understand how he made his discoveries. In contrast, Einstein’s general theory of relativity required reference frames based on mathematical concepts called field equations, which are not easily related to everyday objects. Einstein found this much harder to understand, as does pretty much everyone else.

3. Hebbian Learning

The brain remembers a lot of things. You have permanent memories, such as where you grew up. You have temporary memories, such as what you had for dinner last night. And you have basic knowledge, such as how to open a door or how to spell the word “dictionary.” All these things are stored using synapses, the connections between neurons. Here is the basic idea for how the brain learns: Each neuron has thousands of synapses, which connect the neuron to thousands of other neurons. If two neurons spike at the same time, they will strengthen the connection between them. When we learn something, the connections are strengthened, and when we forget something, the connections are weakened. This basic idea was proposed by Donald Hebb in the 1940s and today it is referred to as Hebbian learning. For many years, it was believed that the connections between neurons in an adult brain were fixed. Learning, it was believed, involved increasing or decreasing the strength of synapses. This is still how learning occurs in most artificial neural networks. However, over the past few decades, scientists have discovered that in many parts of the brain, including the neocortex, new synapses form and old ones disappear. Every day, many of the synapses on an individual neuron will disappear and new ones will replace them. Thus, much of learning occurs by forming new connections between neurons that were previously not connected. Forgetting happens when old or unused connections are removed entirely.

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