248 Information Storage and Neural Control 



regions. Other workers have reported that assimilation of the 

 rhythm appears only in the training situation and is not observed 

 when the animal is in his home cage. Such observations demonstrate 

 that the brain has the capacity to generate temporal patterns of 

 potentials which are substantially the same as those elicited by a 

 previously experienced stimulus. Although obtained under different 

 experimental conditions, the phenomena described by Morrell and 

 his colleagues in studies of cortical conditioning (17, 20, 21) and 

 by Stern et al. (24) in their studies of trace conditioning provide 

 additional evidence of this capacity. It is of interest that one can see 

 these assimilated rhythms appearing with apparent simultaneity in 

 regions relatively distant from each other, as if an anatomically 

 extensive system were activated. One might reasonably ask whether 

 such sustained patterns in the absence of a previously experienced 

 stimulus do not reflect neural processes which represent that ex- 

 perience. These endogenously generated potentials may be a mani- 

 festation of the elusive "memory trace." 



ASSIMILATED RHYTHMS AND GENERALIZATION 



Some evidence presented earlier by Killam and me is com- 

 patible with a functional role for such endogenously generated 

 frequency-specific patterns. We observed that an animal trained 

 to perform a conditioned avoidance response to a ten per second 

 flickering light characteristically displayed twenty per second po- 

 tentials in the visual cortex, as seen in Figure 2. On presentation of 

 a seven per second flicker after the animal reached criterion to the 

 ten per second flicker, the animal showed evidence of generaliza- 

 tion by repeatedly performing the conditioned response to the 

 new stimulus frequency. Examination of the electrical records 

 showed that the response of visual cortex to the seven per second 

 flicker was a twenty per second potential, as is visible in Figure 3A. 

 The arrow denotes the beginning of the behavioral response. 

 After repeated presentation of the seven per second flicker, the 

 animal no longer performed the generalized response but sat 

 quietly. At this time, the seven per second flicker elicited pre- 

 dominantly seven per second activity in the visual cortex. Presenta- 

 tion of the original ten per second conditioned stimulus at this 

 point failed to elicit performance of the conditioned response for 



