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One goal of researchers in neuroscience, psychology, and artificial intelligence is to build theoretical models that can explain the flexibility and adaptiveness of biological systems. How to Build a Brain provides a guided exploration of a new cognitive architecture that takes biological detail seriously while addressing cognitive phenomena. The Semantic Pointer Architecture (SPA) introduced in this book provides a set of tools for constructing a wide range of biologically constrained perceptual, cognitive, and motor models.

Examples of such models are provided to explain a wide range of data including single-cell recordings, neural population activity, reaction times, error rates, choice behavior, and fMRI signals. Each of the models addressed in the book introduces a major feature of biological cognition, including semantics, syntax, control, learning, and memory. These models are presented as integrated considerations of brain function, giving rise to what is currently the world´s largest functional brain model.

The book also compares the Semantic Pointer Architecture with the current state of the art, addressing issues of theory construction in the behavioral sciences, semantic compositionality, and scalability, among other considerations. The book concludes with a discussion of conceptual challenges raised by this architecture, and identifies several outstanding challenges for SPA and other cognitive architectures.

Along the way, the book considers neural coding, concept representation, neural dynamics, working memory, neuroanatomy, reinforcement learning, and spike-timing dependent plasticity. Eight detailed, hands-on tutorials exploiting the free Nengo neural simulation environment are also included, providing practical experience with the concepts and models presented throughout.



Table of Contents

1 The science of cognition
1.1 The last 50 years
1.2 How we got here
1.3 Where we are
1.4 Questions and answers
1.5 Nengo: An introduction
Part I. How to build a brain
2 An introduction to brain building
2.1 Brain parts
2.2 A framework for building a brain
2.2.1 Representation
2.2.2 Transformation
2.2.3 Dynamics
2.2.4 The three principles
2.3 Levels
2.4 Nengo: Neural representation
3 Biological cognition - Semantics
3.1 The semantic pointer hypothesis
3.2 What is a semantic pointer?
3.3 Semantics: An overview
3.4 Shallow semantics
3.5 Deep semantics for perception
3.6 Deep semantics for action
3.7 The semantics of perception and action
3.8 Nengo: Neural computations
4 Biological cognition - Syntax
4.1 Structured representations
4.2 Binding without neurons
4.3 Binding with neurons
4.4 Manipulating structured representations
4.5 Learning structural manipulations
4.6 Clean-up memory and scaling
4.7 Example: Fluid intelligence
4.8 Deep semantics for cognition
4.9 Nengo: Structured representations in neurons
5 Biological cognition - Control
5.1 The flow of information
5.2 The basal ganglia
5.3 Basal ganglia, cortex, and thalamus
5.4 Example: Fixed sequences of actions
5.5 Attention and the routing of information
5.6 Example: Flexible sequences of actions
5.7 Timing and control
5.8 Example: The Tower of Hanoi
5.9 Nengo: Question answering
6 Biological cognition - Memory and learning
6.1 Extending cognition through time
6.2 Working memory
6.3 Example: Serial list memory
6.4 Biological learning
6.5 Example: Learning new actions
6.6 Example: Learning new syntactic manipulations
6.7 Nengo: Learning
7 The Semantic Pointer Architecture (SPA)
7.1 A summary of the SPA
7.2 A SPA unified network
7.3 Tasks
7.3.1 Recognition
7.3.2 Copy drawing
7.3.3 Reinforcement learning
7.3.4 Serial working memory
7.3.5 Counting
7.3.6 Question answering
7.3.7 Rapid variable creation
7.3.8 Fluid reasoning
7.3.9 Discussion
7.4 A unified view: Symbols and probabilities
7.5 Nengo: Advanced modeling methods
Part II. Is that how you build a brain?
8 Evaluating cognitive theories
8.1 Introduction
8.2 Core Cognitive Criteria (CCC)
8.2.1 Representational structure
8.2.1.1 Systematicity
8.2.1.2 Compositionality
8.2.1.3 Productivity
8.2.1.4 The massive binding problem
8.2.2 Performance concerns
8.2.2.1 Syntactic generalization
8.2.2.2 Robustness
8.2.2.3 Adaptability
8.2.2.4 Memory
8.2.2.5 Scalability
8.2.3 Scientific merit
8.2.3.1 Triangulation
8.2.3.2 Compactness
8.3 Conclusion
8.4 Nengo Bonus: How to build a brain - A practical guide
9 Theories of cognition
9.1 The state of the art
9.1.1 ACT-R
9.1.2 Synchrony-based approaches
9.1.3 Neural Blackboard Architecture (NBA)
9.1.4 The Integrated Connectionist/Symbolic Architecture (ICS)
9.1.5 Leabra
9.1.6 Dynamic Field Theory (DFT)
9.2 An evaluation
9.2.1 Representational structure
9.2.2 Performance concerns
9.2.3 Scientific merit
9.2.4 Summary
9.3 The same...
9.4 ...but different
9.5 The SPA versus the SOA
10 Consequences and challenges
10.1 Representation
10.2 Concepts
10.3 Inference
10.4 Dynamics
10.5 Challenges
10.6 Conclusion
A Mathematical notation and overview
A.1 Vectors
A.2 Vector spaces
A.3 The dot product
A.4 Basis of a vector space
A.5 Linear transformations on vectors
A.6 Time derivatives for dynamics
B Mathematical derivations for the NEF
B.1 Representation
B.1.1 Encoding
B.1.2 Decoding
B.2 Transformation
B.3 Dynamics
C Further details on deep semantic models
C.1 The perceptual model
C.2 The motor model
D Mathematical derivations for the SPA
D.1 Binding and unbinding HRRs
D.2 Learning high-level transformations
D.3 Ordinal serial encoding model
D.4 Spike-timing dependent plasticity
D.5 Number of neurons for representing structure
E SPA model details
E.1 Tower of Hanoi
Bibliography
Index