FREEMAN, W. J. 
This force of pull was integrated, and divided by the duration of 
pulling to get the average force. We knew velocity of approach; force 
times velocity gave the power or rate of work which the animal did 
to reach food. We then correlated this value with the amplitude of 
electrical activity generated concomitantly by this cortex. 
In general, we found a three-to-one ration such that for every 
one per cent increase in amplitude there was a three per cent in- 
crease in rate of work (Fig. 6). There was a dip in the upper half 
of the curve which was of considerable theoretical interest, but on 
the whole, it was apparent thatthere was a positive relationship be- 
tween amplitude and the rate of work done by the animal. 
It was known from previous work that the amplitude of electrical 
activity could be increased artificially by direct electrical stimu- 
lation of the cortex. Since the amplitude was related to work, one 
would presume that the increase brought about by stimulation would 
increase the rate of work done by the animal. We therefore increased 
the amplitude of electrical activity by direct electrical stimulation 
and measured the rate of work that the animal did during stimulus 
periods as compared to alternating non-stimulus runs. We found that 
there was no increase in rate of work. 
Again, something went wrong. We thought about it for a while 
and decided that our m istake was to equate the increase in amplitude 
of this electrical activity with an increase in output of the cortex. 
We went back through our records to find if there were any circum- 
stances under which we could get either positive or negative effects 
and, in fact, it turned out that this was the case. When we had first 
started out with our naive animals, there was a positive effect. 
Stimulation did increase the amount of work, but only for the first 
four days. Subsequently, this positive effect was averaged out to 
zero by a negative effect through most of the subsequent three weeks 
of measurement. In order to get a good measure of these changes, 
we started off with a fresh series of cats and found that, again, 
during the first four days of stimulation, as long as we were care- 
ful not to stimulate too hard or too often, stimulation would increase 
the rate of work done by these animals by some five to ten per cent, 
but that after four or five days, this effect dwindled to zero. We then 
found rather unexpectedly that we could increase the stimulus 
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