Potentialtties in the Control of Behaviour 
or deep anaesthesia, i.e. after the circulation of impulses through 
a large number of cortical chains of neurones has stopped.”’ 
He cites evidence obtained by Alexander Mauro and M. B. 
Rosner (unpublished) that memory persists after long-lasting 
total cessation of cortical activity. In hibernating animals corti- 
cal activity, electrically recorded, ceases entirely and cannot be 
elicited by electrical stimulation, however strong. Nevertheless, 
hamsters awakened from such sleep are able to perform pre- 
viously learned tasks just as well after hibernation as before. 
Enduring memory thus appears to be based on some enduring 
chemical changes in the submicroscopic compartments of 
neurones. Lorente de No concludes: “Circulation of impulses 
must precede and be the cause of the establishment of memory, 
but however memory may be stored, in the evocation process 
circulation of impulses must again take place to reproduce the 
sensation caused by the original experience.” 
Studies of maze learning in rats indicate that there are two 
stages of information storage. An initial process presumably 
involves continuity of nerve impulses traversing circuits, and in 
a later process some sort of permanent consolidation of chemical 
traces occurs. Thus, in rats, an electric shock across the head 
after a learning trial impairs learning. And this is also true of 
hypoxia and depressant drugs. The closer the seizure or drug 
administration to the end of a preceding trial, the more severe 
is the learning loss. This is not due to punishment effects since 
electric shocks delivered to the legs have no such results. Elec- 
tric shock across the head does not affect learning if the shock 
is given one hour after the learning trial. Investigators have 
reported that maze learning in rats was impaired when thio- 
pental (thiopentone sodium) was administered one minute after 
the end of each trial but after thirty minutes no such effects 
were noted. McGaugh and co-workers have impressively 
demonstrated that stimulant drugs such as strychnine and picro- 
toxin administered either before or after a learning trial in- 
crease the rate at which learning proceeds. ‘The improved 
learning, when injections are made before the trial, could be 
due to increased motivation, alertness, etc. But their finding 
311 
