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The memory-prediction framework is a theory of
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
function created by
Jeff Hawkins Jeffrey Hawkins is a co-founder of the companies Palm Computing, where he co-created the PalmPilot, and Handspring, where he was one of the creators of the Treo.Jeff Hawkins, ''On Intelligence'', p.28 He subsequently turned to work on neurosc ...
and described in his 2004 book ''
On Intelligence ''On Intelligence: How a New Understanding of the Brain will Lead to the Creation of Truly Intelligent Machines'' is a 2004 book by Jeff Hawkins and Sandra Blakeslee. The book explains Hawkins' memory-prediction framework theory of the brain a ...
''. This theory concerns the role of the mammalian
neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, sp ...
and its associations with the hippocampi and the
thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direct ...
in matching sensory inputs to stored
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remember ...
patterns and how this process leads to predictions of what will happen in the future.


Overview

The theory is motivated by the observed similarities between the brain structures (especially
neocortical The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, sp ...
tissue) that are used for a wide range of behaviours available to mammals. The theory posits that the remarkably uniform ''physical'' arrangement of cortical tissue reflects a single principle or algorithm which underlies all cortical information processing. The basic processing principle is hypothesized to be a feedback/recall
loop Loop or LOOP may refer to: Brands and enterprises * Loop (mobile), a Bulgarian virtual network operator and co-founder of Loop Live * Loop, clothing, a company founded by Carlos Vasquez in the 1990s and worn by Digable Planets * Loop Mobile, an ...
which involves both cortical and extra-cortical participation (the latter from the
thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direct ...
and the hippocampi in particular).


The basic theory: recognition and prediction in bi-directional hierarchies

The central concept of the memory-prediction framework is that bottom-up inputs are matched in a
hierarchy A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important ...
of
recognition Recognition may refer to: *Award, something given in recognition of an achievement Machine learning *Pattern recognition, a branch of machine learning which encompasses the meanings below Biometric * Recognition of human individuals, or biomet ...
, and evoke a series of top-down expectations encoded as potentiations. These expectations interact with the bottom-up signals to both analyse those inputs and generate
prediction A prediction (Latin ''præ-'', "before," and ''dicere'', "to say"), or forecast, is a statement about a future event or data. They are often, but not always, based upon experience or knowledge. There is no universal agreement about the exact ...
s of subsequent expected inputs. Each hierarchy level remembers frequently observed temporal sequences of input patterns and generates labels or 'names' for these sequences. When an input sequence matches a memorized sequence at a given level of the hierarchy, a label or 'name' is propagated up the hierarchy – thus eliminating details at higher levels and enabling them to learn higher-order sequences. This process produces increased invariance at higher levels. Higher levels predict future input by matching partial sequences and projecting their expectations to the lower levels. However, when a mismatch between input and memorized/predicted sequences occurs, a more complete representation propagates upwards. This causes alternative 'interpretations' to be activated at higher levels, which in turn generates other predictions at lower levels. Consider, for example, the process of
vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...
. Bottom-up information starts as low-level
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...
l signals (indicating the presence of simple visual elements and contrasts). At higher levels of the hierarchy, increasingly meaningful information is extracted, regarding the presence of
line Line most often refers to: * Line (geometry), object with zero thickness and curvature that stretches to infinity * Telephone line, a single-user circuit on a telephone communication system Line, lines, The Line, or LINE may also refer to: Art ...
s,
region In geography, regions, otherwise referred to as zones, lands or territories, are areas that are broadly divided by physical characteristics ( physical geography), human impact characteristics ( human geography), and the interaction of humanity an ...
s,
motion In physics, motion is the phenomenon in which an object changes its position with respect to time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed and frame of reference to an observer and m ...
s, etc. Even further up the hierarchy, activity corresponds to the presence of specific objects – and then to behaviours of these objects. Top-down information fills in details about the recognized objects, and also about their expected behaviour as time progresses. The sensory hierarchy induces a number of differences between the various levels. As one moves up the hierarchy,
representations ''Representations'' is an interdisciplinary journal in the humanities published quarterly by the University of California Press. The journal was established in 1983 and is the founding publication of the New Historicism movement of the 1980s. It ...
have increased: * Extent – for example, larger areas of the visual field, or more extensive tactile regions. * Temporal stability – lower-level entities change quickly, whereas, higher-level percepts tend to be more stable. *
Abstraction Abstraction in its main sense is a conceptual process wherein general rules and concepts are derived from the usage and classification of specific examples, literal ("real" or " concrete") signifiers, first principles, or other methods. "An abst ...
– through the process of successive extraction of invariant features, increasingly abstract entities are recognized. The relationship between sensory and motor processing is an important aspect of the basic theory. It is proposed that the motor areas of the
cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...
consist of a behavioural hierarchy similar to the sensory hierarchy, with the lowest levels consisting of explicit motor commands to musculature and the highest levels corresponding to abstract prescriptions (e.g. 'resize the browser'). The sensory and motor hierarchies are tightly coupled, with behaviour giving rise to sensory expectations and sensory
perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
s driving motor processes. Finally, it is important to note that all the memories in the cortical hierarchy have to be learnt – this information is not pre-wired in the brain. Hence, the process of extracting this representation from the flow of inputs and behaviours is theorized as a process that happens continually during
cognition Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, though ...
.


Other terms

Hawkins has extensive training as an electrical engineer. Another way to describe the theory (hinted at in his book) is as a
learning Learning is the process of acquiring new understanding, knowledge, behaviors, skills, values, attitudes, and preferences. The ability to learn is possessed by humans, animals, and some machines; there is also evidence for some kind of lea ...
hierarchy A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important ...
of feed forward
stochastic Stochastic (, ) refers to the property of being well described by a random probability distribution. Although stochasticity and randomness are distinct in that the former refers to a modeling approach and the latter refers to phenomena themselv ...
state machine A finite-state machine (FSM) or finite-state automaton (FSA, plural: ''automata''), finite automaton, or simply a state machine, is a mathematical model of computation. It is an abstract machine that can be in exactly one of a finite number ...
s. In this view, the brain is analyzed as an encoding problem, not too dissimilar from future-predicting error-correction codes. The hierarchy is a hierarchy of
abstraction Abstraction in its main sense is a conceptual process wherein general rules and concepts are derived from the usage and classification of specific examples, literal ("real" or " concrete") signifiers, first principles, or other methods. "An abst ...
, with the higher level machines' states representing more abstract conditions or events, and these states predisposing lower-level machines to perform certain transitions. The lower level machines model limited domains of experience, or control or interpret sensors or effectors. The whole system actually controls the organism's behavior. Since the state machine is "feed forward", the organism responds to future events predicted from past data. Since it is hierarchical, the system exhibits behavioral flexibility, easily producing new sequences of behavior in response to new sensory data. Since the system learns, the new behavior adapts to changing conditions. That is, the evolutionary purpose of the brain is to predict the future, in admittedly limited ways, so as to change it.


Neurophysiological implementation

The hierarchies described above are theorized to occur primarily in mammalian neocortex. In particular, neocortex is assumed to consist of a large number of
columns A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression membe ...
(as surmised also by
Vernon Benjamin Mountcastle Vernon Benjamin Mountcastle (July 15, 1918 – January 11, 2015) was an American neurophysiologist and Professor Emeritus of Neuroscience at Johns Hopkins University. He discovered and characterized the columnar organization of the cerebral co ...
from anatomical and theoretical considerations). Each column is attuned to a particular feature at a given level in a hierarchy. It receives bottom-up inputs from lower levels, and top-down inputs from higher levels. (Other columns at the same level also feed into a given column, and serve mostly to inhibit the activation exclusive representations.) When an input is recognized – that is, acceptable agreement is obtained between the bottom-up and top-down sources – a column generates outputs which in turn propagate to both lower and higher levels.


Cortex

These processes map well to specific layers within mammalian cortex. (The cortical layers should not be confused with different levels of the processing hierarchy: all the layers in a single column participate as one element in a single hierarchical level). Bottom-up input arrives at layer 4 (L4), whence it propagates to L2 and L3 for recognition of the invariant content. Top-down activation arrives to L2 and L3 via L1 (the mostly axonal layer that distributes activation locally across columns). L2 and L3 compare bottom up and top-down information, and generate either the invariant 'names' when sufficient match is achieved, or the more variable signals that occur when this fails. These signals are propagated up the hierarchy (via L5) and also down the hierarchy (via L6 and L1).


Thalamus

To account for storage and recognition of ''sequences'' of patterns, a combination of two processes is suggested. The nonspecific
thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direct ...
acts as a 'delay line' – that is, L5 activates this brain area, which re-activates L1 after a slight delay. Thus, the output of one column generates L1 activity, which will coincide with the input to a column which is temporally subsequent within a sequence. This time ordering operates in conjunction with the higher-level identification of the sequence, which does not change in time; hence, activation of the sequence representation causes the lower-level components to be predicted one after the other. (Besides this role in sequencing, the thalamus is also active as sensory waystation – these roles apparently involve distinct regions of this anatomically non-uniform structure.)


Hippocampus

Another anatomically diverse brain structure which is hypothesized to play an important role in hierarchical cognition is the
hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic syste ...
. It is well known that damage to both hippocampi impairs the formation of long-term
declarative memory Explicit memory (or declarative memory) is one of the two main types of long-term human memory, the other of which is implicit memory. Explicit memory is the conscious, intentional recollection of factual information, previous experiences, and c ...
; individuals with such damage are unable to form new memories of episodic nature, although they can recall earlier memories without difficulties and can also learn new skills. In the current theory, the hippocampi are thought of as the top level of the cortical hierarchy; they are specialized to retain memories of events that propagate all the way to the top. As such events fit into predictable patterns, they become memorizable at lower levels in the hierarchy. (Such movement of memories down the hierarchy is, incidentally, a general prediction of the theory.) Thus, the hippocampi continually memorize 'unexpected' events (that is, those not predicted at lower levels); if they are damaged, the entire process of memorization through the hierarchy is compromised. In 2016
Jeff Hawkins Jeffrey Hawkins is a co-founder of the companies Palm Computing, where he co-created the PalmPilot, and Handspring, where he was one of the creators of the Treo.Jeff Hawkins, ''On Intelligence'', p.28 He subsequently turned to work on neurosc ...
hypothesized that
cortical column A cortical column is a group of neurons forming a cylindrical structure through the cerebral cortex of the brain perpendicular to the cortical surface. The structure was first identified by Mountcastle in 1957. He later identified minicolumns as t ...
s did not just capture a sensation, but also the relative location of that sensation, in three dimensions rather than two (''situated capture''), in relation to what was around it.Cade Metz ''The New York Times'' (15 October 2018) "A new view of how we think" pp.B1,B4
see: 'Clarity Over a Coffee Cup'
"When the brain builds a model of the world, everything has a location relative to everything else" —Jeff Hawkins.


Explanatory successes and predictions

The memory-prediction framework explains a number of psychologically salient aspects of cognition. For example, the ability of experts in any field to effortlessly analyze and remember complex problems within their field is a natural consequence of their formation of increasingly refined conceptual hierarchies. Also, the procession from '
perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
' to '
understanding Understanding is a psychological process related to an abstract or physical object, such as a person, situation, or message whereby one is able to use concepts to model that object. Understanding is a relation between the knower and an object ...
' is readily understandable as a result of the matching of top-down and bottom-up expectations. Mismatches, in contrast, generate the exquisite ability of biological cognition to detect unexpected perceptions and situations. (Deficiencies in this regard are a common characteristic of current approaches to artificial intelligence.) Besides these subjectively satisfying explanations, the framework also makes a number of testable
prediction A prediction (Latin ''præ-'', "before," and ''dicere'', "to say"), or forecast, is a statement about a future event or data. They are often, but not always, based upon experience or knowledge. There is no universal agreement about the exact ...
s. For example, the important role that prediction plays throughout the sensory hierarchies calls for anticipatory neural activity in certain cells throughout sensory cortex. In addition, cells that 'name' certain invariants should remain active throughout the presence of those invariants, even if the underlying inputs change. The predicted patterns of bottom-up and top-down activity – with former being more complex when expectations are not met – may be detectable, for example by functional magnetic resonance imaging (
fMRI Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area ...
). Although these predictions are not highly specific to the proposed theory, they are sufficiently unambiguous to make verification or rejection of its central tenets possible. See ''
On Intelligence ''On Intelligence: How a New Understanding of the Brain will Lead to the Creation of Truly Intelligent Machines'' is a 2004 book by Jeff Hawkins and Sandra Blakeslee. The book explains Hawkins' memory-prediction framework theory of the brain a ...
'' for details on the predictions and findings.


Contribution and limitations

By design, the current theory builds on the work of numerous neurobiologists, and it may be argued that most of these ideas have already been proposed by researchers such as Grossberg and Mountcastle. On the other hand, the novel separation of the conceptual mechanism (i.e., bidirectional processing and invariant recognition) from the biological details (i.e., neural layers, columns and structures) lays the foundation for abstract thinking about a wide range of cognitive processes. The most significant limitation of this theory is its current lack of detail. For example, the concept of invariance plays a crucial role; Hawkins posits " name cells" for at least some of these invariants. (See also Neural ensemble#Encoding for grandmother neurons which perform this type of function, and
mirror neuron A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another. Thus, the neuron "mirrors" the behavior of the other, as though the observer were itself acting. Such neurons ha ...
s for a
somatosensory system In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It is ...
viewpoint.) But it is far from obvious how to develop a mathematically rigorous definition, which will carry the required conceptual load across the domains presented by Hawkins. Similarly, a complete theory will require credible details on both the short-term dynamics and the learning processes that will enable the cortical layers to behave as advertised. IBM is implementing Hawkins' model.IBM tests mobile computing pioneer's controversial Brain Algorithms
accessdate=2015-04-08


Machine learning models

The memory-prediction theory claims a common algorithm is employed by all regions in the neocortex. The theory has given rise to a number of software models aiming to simulate this common algorithm using a hierarchical memory structure. The year in the list below indicates when the model was last updated.


Models based on Bayesian networks

The following models use belief propagation or
belief revision Belief revision is the process of changing beliefs to take into account a new piece of information. The logical formalization of belief revision is researched in philosophy, in databases, and in artificial intelligence for the design of rational ag ...
in singly connected
Bayesian network A Bayesian network (also known as a Bayes network, Bayes net, belief network, or decision network) is a probabilistic graphical model that represents a set of variables and their conditional dependencies via a directed acyclic graph (DAG). Ba ...
s. *
Hierarchical Temporal Memory Hierarchical temporal memory (HTM) is a biologically constrained machine intelligence technology developed by Numenta. Originally described in the 2004 book ''On Intelligence'' by Jeff Hawkins with Sandra Blakeslee, HTM is primarily used today for ...
(HTM), a model, a related development platform and source code by Numenta, Inc. (2008).
HtmLib
an alternative implementation of HTM algorithms by Greg Kochaniak with a number of modifications for improving the recognition accuracy and speed (2008).
Project Neocortex
an open source project for modeling memory-prediction framework (2008). *
Saulius Garalevicius' research page
research papers and programs presenting experimental results with a model of the memory-prediction framework, a basis for the Neocortex project (2007). * a paper describing earlier pre-HTM Bayesian model by the co-founder of Numenta. This is the first model of memory-prediction framework that uses Bayesian networks and all the above models are based on these initial ideas. Matlab source code of this model had been freely available for download for a number of years.


Other models


Implementation of MPF
a paper by Saulius Garalevicius describing a method of classification and prediction in a model that stores temporal sequences and employs unsupervised learning (2005).

a pattern machine for Palm OS that stores pattern sequences and recalls the patterns relevant to its present environment (2007).
BrainGame
open source predictor class which learns patterns and can be linked to other predictors (2005).


See also

*
Vernon Mountcastle Vernon Benjamin Mountcastle (July 15, 1918 – January 11, 2015) was an American neurophysiologist and Professor Emeritus of Neuroscience at Johns Hopkins University. He discovered and characterized the columnar organization of the cerebral co ...
, the neuroscientist who discovered and characterized the columnar organization of the cerebral cortex. *
Adaptive resonance theory Adaptive resonance theory (ART) is a theory developed by Stephen Grossberg and Gail Carpenter on aspects of how the brain processes information. It describes a number of neural network models which use supervised and unsupervised learning metho ...
, a neural network architecture developed by Stephen Grossberg. *
Computational neuroscience Computational neuroscience (also known as theoretical neuroscience or mathematical neuroscience) is a branch of neuroscience which employs mathematical models, computer simulations, theoretical analysis and abstractions of the brain to u ...
* Neural Darwinism *
Predictive coding In neuroscience, predictive coding (also known as predictive processing) is a theory of brain function which postulates that the brain is constantly generating and updating a "mental model" of the environment. According to the theory, such a ment ...
* Predictive learning * Sparse distributed memory


References


Further reading

* Jeff Hawkins (2004), ''
On Intelligence ''On Intelligence: How a New Understanding of the Brain will Lead to the Creation of Truly Intelligent Machines'' is a 2004 book by Jeff Hawkins and Sandra Blakeslee. The book explains Hawkins' memory-prediction framework theory of the brain a ...
'', New York: Henry Holt. Bibliography, Index, 251 pages. {{ISBN, 0-8050-7456-2


External links


Hierarchical vision algorithm source code & data
br> – similar to the Memory-Prediction Framework (fro
MIT Center for Biological & Computational Learning

Group of articles about neuroscience and AI
br> – Group of articles and papers supporting Jeff's MPF theory.
MIT ''Technology Review'' Monday, February 12, 2007: Building the Cortex in Silicon
Belief revision Memory Neural circuits