A neural mechanism for the immediate recall of sequences

Summary Lashley's suggestion that serial behavior has a dual organization, central facilitation of the entire sequence plus scanning of the individual movements, is taken as the starting point for the construction of a model to illustrate in more detail how the nervous system might work during such behavior.Two stages in the learning of a sequence are distinguished: 1. immediate reproduction of a presented sample, and 2. reproduction of habitual responses by association, without the necessity of recent access to the original sample. The model is primarily concerned with performances of the first type.Neurons of a scanning chain, which always fire one another in the same order, acquire temporary connections with the movements to be recalled. The connections fade rapidly with disuse so that the same scanning chain can be used again with different combinations of movements.The same mechanism will also permit the recall of sequences of words, or other habitual movement complexes, as if they were individual movements. It is assumed that such habitual motor patterns as words are under the control of higher-order cell assemblies which regulate the sequences of movements within the response, and thus substitute for the general scanning mechanism. This leaves the scanner free to form temporary associations with the higher-order cell assemblies for the words.It is suggested that the scanning mechanism is actuated only by unpredictable inputs so that the elements within a habitual series do not acquire unnecessary connections with the scanning neurons. The arousal system is known to have this characteristic of not being disturbed by the expected, and it seems likely that the two systems are intimately related.