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Fig. 15.6
Creation of new
semantic primitives by means
of internal sensors. Neural
assemblies play the role of
sensors on an internal milieu
of neural activity patterns
15.5.1 New Primitives in Signalling Networks
I came to think about how neural networks might create new primitives from con-
sidering how a signalling network might increase its effective dimensionality. The
simplest way of conceiving this is to assume that each element in a network is capa-
ble of producing and receiving specific signals that are in some way independent of
one another, as with signals consisting of tones of different frequencies. A new com-
munications link is established whenever a tone frequency emitted by one element
can be detected by another. The effective dimensionality of such a network is related
to the number of operating independent communications links. If the elements can
be adaptively tuned to send and receive new frequencies that are not already in the
network, then new signal primitives with new frequencies can appear over time and
with them, new communications links. The dimensionality of the signalling network
has thus increased.
One can conceive of the brain as a large signalling network that consists of a large
number of neural assemblies of many neurons. If each neural assembly is capable of
adaptively producing and detecting specific spatial and temporal patterns of action
potential pulses, then new patterns can potentially arise within the system that con-
stitute new signal primitives. In the brain we can think of Hebb's neural assemblies
(Hebb
1949
, Orbach
1998
) as ensembles of neurons that act as internal sensors on an
analog internal milieu (Fig.
15.6
). The creation of a new neural assembly through an
activity-dependent modification of neuronal synapses and axons can be conceived
as the equivalent to adding a new internal observable on the system. Here a new
concept is a new means of parsing the internal activity patterns within the nervous
system. If an adaptively-tuned neural ensemble produces a characteristic pattern of
activity that is distinguishable from stereotyped patterns that are already found in
the system, then the neural network has created a new signal primitive that can be-
come a marker for the activity of the ensemble and some complex combination of
conditions that activates it.
The remainder of the chapter presents an outline of how a neural system might
utilise this kind of dimensionally open-ended functional organisation. The nature
of the central neural code in the brain is still one of science's biggest unsolved
