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creases the likelihood of activity in all assemblies with which it is negatively associated. Positive association between a pair of cell assemblies increases whenever they are active at the same time. Negative association is asymmetrical in that one cell assembly may be negatively associated with a second, while the second is not necessarily negatively associated with the first; this negative association increases each time the first assembly is active and the second is inactive. (The underlying neural assumption here is that, if neuron n2produces a pulse immediately after it receives a pulse from neuron n1,then n1is better able to elicit a pulse from n2in the future; contrariwise, if n2produces no pulse upon receiving a pulse from n1,then n1is more likely to inhibit n2in the future. It is usually assumed that this process is the result of changing synapse levels. The same process can be invoked in explaining the origin of cell assemblies.) It should be noted that, under this assumption, there is a tendency for cell assemblies to become active in fixed combinations, at the same time actively suppressing alternative combinations. (Because a cell assembly involves only a minute fraction of the neurons in a CNS, a great many can be excited at any instant, different configurations corresponding to different perceived objects, etc.) Temporal association (i.e., probable action sequences) can occur via appropriate asymmetries; e.g., assembly a can arouse b via positive association while b inhibits a through negative association. Thus the action sequence is always ab, never the reverse. |
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4. At any instant the response of the CNS to sensory input is determined by the configuration of active cell assemblies. (Overt behavior such as eye movement, activation of reflexes, release of voluntary muscle sequences, and so on will accompany most sensory events. Via the mechanisms of (3), neurons involved in this behavior will tend to become components of cell assemblies active at the same time. Since pulse trains from the active cell assemblies dominate overall CNS activity, overt behavior will thus be determined by the active configurations. In effect, the sensory input modulates the ongoing activity in the CNS to produce overt behavior.) |
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5. Cell assemblies involved in temporal sequences yielding "need satisfaction" (satisfaction of hunger, thirst, etc.) have their associations enhanced; the greater the "need," the greater the enhancement. ("Needs" are internal conditions in the CNS-controlled organism, conditions primarily concerned with survival, which set basic restrictions on CNS |
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