Although the concept of cognitive human knowledge - something which is acquired, stored, and then used - has been in widespread use for millennia, even today there is no understanding of the mechanisms involved (other than the persistent suspicion that Hebbian synaptic modification might somehow be involved) or of the nature of knowledge. Confabulation theory (see Figs. 1.4 and 1.5) specifies precisely what cognitive knowledge is, how it is acquired, how it is stored, and how it is used in thinking (Sect. 1.3.3).
Cerebral Cortex symbol (neuron collection) representing color red symbol (neuron collection) representing word apple thalamocortical module describing the name attribute of mental world objects unidirectional neuron collection-to-neuron collection knowledge link thalamocortical module''
describing the color attribute of mental world objects
Fig. 1.4. A cognitive knowledge link. Here, a human subject is viewing and considering a red apple. A visual thalamocortical module is expressing a symbol for the color of the apple. At the same time, a language thalamocortical module is expressing a symbol for the name of the apple. Pairs of symbols which meaningfully co-occur in this manner have unidirectional axonal links, termed knowledge links (each considered a single item of knowledge), established between them via synaptic strengthening (assuming that the required axons are actually present - this is determined by genetics). The average adult human has billions of knowledge links, most of which are established in childhood. The rate of human knowledge acquisition often exceeds one link per second of life
Fig. 1.5. Billions of pairs of symbols are connected via knowledge links. The set of all knowledge links joining symbols belonging to one specific source module to symbols belonging to one specific target module is termed a knowledge base. In the human brain, knowledge bases take the form of huge bundles of axons termed fascicles, which together make up a large portion of each cerebral hemisphere's ipsilateral white matter. Each module also typically has a knowledge base to its contralateral "twin" module (and perhaps to a few others near its twin) - which together constitute the corpus callosum fascicle linking the two cerebral hemispheres. Here, reciprocal knowledge links (red arrows), only some of which are shown, connect each expressed symbol representing an attribute of an apple pairwise with other such symbols. When an apple is currently present in the mental world, it is its collection of knowledge-link-connected symbols which are currently being expressed. There is no binding problem because all of these symbols are mutually "bound" by their previously established pairwise knowledge links. Shockingly, confabulation theory contends that such knowledge links - formed exclusively on the basis of meaningful symbol pair co-occurrence - are the only type of knowledge used (or needed) in cognition! Knowledge links are the second of the four key elements of confabulation theory
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