A Theory of Cerebral Cortex (1998)

A theory of the function of cerebral cortex and thalamus is sketched. 1. Introduction This report sketches the author’s theory of cerebral cortex and thalamus; incorporating relevant discoveries, improvements, changes and updates as of the issue date. The main focus is to provide a coherent, integrated picture of that portion of the theory which provides answers to the following questions: What is cortical knowledge and how is it acquired and stored?, and How is cortical knowledge used to carry out thinking? The theory’s explanation for another key aspect of cortical and thalamic function – the moment-by-moment selection, evaluation, and execution of the action commands that control waking brain activity and muscle movement – is also briefly addressed. This theory proposes the first cogent answers to these questions and therefore should be of interest to both scientists and technologists. In particular, the theory’s characterizations of knowledge and thinking are radically different from the ‘reasoning’ approaches that others have considered; and, given their efficacy (as demonstrated herein via computer thinking experiments), these deserve attention on their own merits. The reader is warned that this theory is not a simple ‘sound bite’ discovery; as is today’s fashion. The pieces of this theory emerged gradually over decades (I began research in computational neurobiology in 1968). However, these pieces only came together as a whole late in 2003. Thus, this report must introduce and relate a number of novel concepts and show how they fit together. To keep the discussion accessible, detailed mathematical models of feature attractors and knowledge links are not discussed. The mathematics of confabulation is so simple that it is included. The basic claim of the theory is that the cerebral cortex and thalamus implement thousands of lexicons, each containing thousands of symbols. These constitute the terms of reference used to describe the objects and actions of the mental universe. Each such lexicon is postulated to be implemented by a single, modular, thalamocortical neuronal circuit called a feature attractor (each symbol of the lexicon is represented by a distinctive population of co-active neurons). Each cortical item of knowledge (of which the average human has billions) is hypothesized to take the form of a unidirectional neuronal linkage between the neurons representing one symbol in one lexicon to neurons representing a second symbol in a second lexicon. Simultaneous inputs from (potentially) thousands of knowledge links to a feature attractor cause many of the neural ensembles representing symbols of its lexicon to become partially excited. The feature attractor then operates; extinguishing all of these excited neurons except those of the single most excited symbol ensemble. This simple, fast, ‘winner-take-all’ information processing operation, termed confabulation, is postulated to be the fundamental mechanism of vertebrate cognition. The next section of this report (derived from a stand-alone article that has not yet been published) discusses an idealized mathematical description of confabulation. This discussion illustrates, largely sans biology, the essence of cortical knowledge acquisition, knowledge storage, and thinking. The third section then overviews how these mechanisms of knowledge storage and confabulation are implemented in biological tissue. This