Towards a General Theory of Cerebral Neocortex

................................................................................................................................................. 9 Introduction ......................................................................................................................................... 11 The Neocortex as a Uniform Cognitive Architecture ...................................................................... 13 2.1 Computation and the Brain ..................................................................................................... 13 2.2 Cognitive Architecture ............................................................................................................ 15 2.3 The Importance of the Cortex in Cognition ............................................................................ 18 2.4 Anatomical Uniformity of the Cortex ..................................................................................... 20 2.5 The Fundamental Hypothesis ................................................................................................. 29 2.6 Some Objections to the Hypothesis ........................................................................................ 31 2.6.1 Modular Anatomy and Localization of Function .......................................................... 31 2.6.2 Diversity of Functional Properties of Cortical Neurons ................................................ 32 2.6.3 From Uniform Neural Circuitry to Uniform Cognitive Architecture ............................ 34 2.7 Summary ................................................................................................................................. 36 A General Theory of the Neocortex ................................................................................................... 38 3.1 The Model Cortical Neuron .................................................................................................... 38 3.2 Population Coding .................................................................................................................. 42 3.3 The Local Circuitry ................................................................................................................. 44 3.4 Feedforward Activation in Layers 2–4 ................................................................................... 47 3.5 Motor Production in Layer 5 .................................................................................................. 51 3.6 Feedback Activation From Layer 6 ........................................................................................ 55 3.7 Lateral Activation in Layers 2–4 ............................................................................................ 60 3.8 Plasticity ................................................................................................................................. 61 3.8.1 Properties of Cortical Plasticity ..................................................................................... 61 3.8.2 Weight Modification Rules ............................................................................................ 63 3.8.3 Molecular Mechanisms .................................................................................................. 67 3.9 Large-Scale Organization of the Cortex ................................................................................. 69 3.10 The Focusing Mechanism ..................................................................................................... 72 3.10.1 Properties of the Mechanism ....................................................................................... 73 3.10.2 Anatomical Substrate ................................................................................................... 78 3.11 Summary ............................................................................................................................... 80 Early Visual Processing ...................................................................................................................... 82 4.1 Review of the Subcortical Visual System ............................................................................... 83 4.1.1 Luminance Processing in Retina and LGN.................................................................... 85 4.1.2 Wavelength Processing in Retina and LGN .................................................................. 85 4.2 Overview of Early Processing ................................................................................................ 87 4.3 Luminance .............................................................................................................................. 88 4.3.1 Simple and Complex Receptive Fields .......................................................................... 89 4.3.2 Laminar and Columnar Organization ............................................................................ 93 4.3.3 The End-Stopping Property ........................................................................................... 94 4.3.4 Plasticity of Receptive Field Properties ......................................................................... 94 4.4 A Model of Simple and Complex Receptive Fields ............................................................... 95 4.4.1 Description of the Model ............................................................................................... 95