W. R. ADEY 585 



task, and just as quickly resume their 'resting' character. It is a matter for 

 regret that the tedium of preparation of card-punched data has greatly 

 limited the examination of many closely related aspects of these problems. 



DISCUSSION 



Returning briefly to the general problem of the functions of the hippo- 

 campal formation, it may be noted that the hippocampal cortex occupies 

 a dorsomedial position in the hemisphere of all vertebrate brains, hi his 

 Arris and Gale lectures to the Royal College of Surgeons in London 50 

 years ago, Elliot Smith indicated that the discharge from this hippocampal 

 cortex to subcortical structures through the fornix was one of the first 

 great efferent pathways to appear in the evolution of the forebrain. Thus, 

 it would not be surprising if the hippocampus did, in fact, have functions 

 in planned motor performance, rather than, perhaps, in memory or 

 emotional activity. We are further encouraged in this point of view by the 

 recent observation by Hess (1959) that damage to this cortex in birds leads 

 to the permanent loss of imprinting behaviour. 



Now it may be asked what significance might attach to such phase 

 shifts in intrahippocampal rhythms in the course of the learning process. 

 Any answer must be entirely speculative, but perhaps not unfruitful, 

 particularly if we accept the need to seek basically different ways of 

 examining neural processes in the course of learning. It may be suggested 

 that the informational coding of some neural signals may be on the basis 

 of certain phase-comparator mechanisms, which would allow an exceed- 

 ingly subtle and finely graded scries of changes to be each differen- 

 tially integrated in determining the output of either an individual neurone 

 or of the more complex output of a highly organized neural tissue, such 

 as the hippocampus, or cortical structures generally. Aspects of informa- 

 tional coding on the basis of such phase-comparison techniques are well 

 known to communication engineers as, for example, in the transmission 

 of chrominance values in colour television signals, and in phase modulation 

 of telemetry signals. 



Can any evidence be adduced to support the existence of a phase- 

 comparator mechanism in the hippocampal systems studied here? No 

 definite answer is possible, but if we turn for a moment to the anatomical 

 organization of the densely packed hippocampal pyramidal cells, it is 

 apparent that they receive afferent fluxes from two main sources, one 

 from the entorhinal cortex via the temporo-ammonic tracts, and the 

 other from septal areas (and, thus, indirectly from the reticular thalamic 

 areas) via the axons of the dentate granule cells. Both these aflcrcnt paths 



