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114 Biomimetics: Biologically Inspired Technologies

Figure 3.A.6 The implementation of confabulation in human cerebral cortex. See text for explanation.

the right in Figure 3.A.6. Each assumed fact symbol has knowledge links to multiple symbols
of the answer lexicon; as illustrated by the colored arrows proceeding from each source lexicon
to the answer lexicon. The width of each such knowledge link arrow corresponds to the link
strength; i.e., the value of its p(cjl) probability. Each assumed fact symbol in this example is
assumed to be the sole conclusion of a previous confabulation on its lexicon. Thus, symbols a, b, g,
and d are all active (maximally transmissive).
The symbols of the answer lexicon which receive one or more links from the assumed facts are
denoted by e, l 1 , l 2 , l 3 , and so forth, and for clarity, are grouped in Figure 3.A.6. As discussed in
the previous section, the actual percentage of neurons of each target symbol which receive synaptic
inputs from the assumed fact’s transponder neurons is approximately the same for all symbols (this
is a function of the roughly uniform — at least for each individual answer lexicon — binomial
connection statistics of the locally random cortico-cortical axons implementing each knowledge
link). And as mentioned earlier, this percentage is low (from 1 to 25%, depending on where the
module is located in cortex).
As shown in Figure 3.A.6, symbol l 1 receives only one link (it is a medium-strength link from
assumed fact symbol a). In accordance with Figure 3.A.5, only a fraction of the neurons of the
answer lexicon which represent symbol l 1 , are actually being excited by this input link. These are
shown as green filled circles with a above them (again, for clarity, the target symbol neurons which
happen to receive input excitation from a particular assumed fact, which are actually randomly
located, are grouped together in the figure, and labeled above with the symbol of that assumed fact).
Note that, in the case of this group of green neurons of symbol l 1 receiving input from assumed fact
symbol a, that a medium-sized font a is shown above the group; reflecting the fact that the
knowledge link delivering this assumed fact excitation only has medium strength p(l 1 ja). Simi-
larly, the neurons representing symbol l 2 are also receiving only one medium-strength link; namely
from assumed fact symbol g.