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Introduction
Page 1
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Results
Pages 5 - 6 - 7 - 8 - 9
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Discussion
Pages 10 - 11
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References
Page 12
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Added figures
Pages 13 - 14 - 15
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Figures
Figures 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10
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1. Midbrain cells appearing to mediate affective defense behavior.
The four cells which responded if and only if the cat displayed affective defense fulfilled all the criteria which were tested in this experiment for cells mediating that behavior. Their responses did not appear to be mechanical artifacts caused by tissue movement since there was no diminution of spike amplitude at the beginning or end of firing. They also did not appear to be the result of irritation of the cell caused by movement of the cat since they did not fire when the cat was lifted and dropped and since they began to fire before movement artifacts. The response did not seem to be related to the movement associated with the striking or postural changes of affective defense since they did not fire during leg retraction or dropping of the cat, More recent work with fighting behavior which includes continuous direct measurement of arterial blood pressure suggests that the responses could not have been due to increased blood pressure. Transient increase in blood pressure may sometimes be observed during fighting but only during or after the first movement artifacts (2). Since the cells reached their maxi- mum firing rates during the exact second of affective defense and stopped or diminished in firing rate within a second or two afterwards, it does not seem likely that they were firing in response to circulating hormones such as epinephrine. Also the response did not seem to be related simply to hissing since the cells fired during displays when the cat was only striking as well as trials when there was both striking and hissing. Of course, no matter how many components and concomitants of affective defense are independently tested as control manipulations, some others, such as piloerection, or tactile stimulation of a limited receptive field, remain untested and could be responsible for the cell's response. However, brain stimulation in the region where these cells were found produced an integrated affective defense behavior, and lesions, it is known from the experiments of Hunsperger (8), abolish affective defense for at least several weeks; therefore it seems reasonable to hypothesize that these cells are related to the integrated behavior.
These four cells alone are hardly enough to demarcate precisely the midbrain areas involved in affective defense. However, the fact that they were located toward the center of the region from which affective defense may be elicited by electrical stimulation suggests that the active area may be smaller than the region indicated by stimulation and lesion data and that it may be in the center of that region. Ultimately, it may be possible by the combination of anatomical and physiological techniques to identify the exact cells which mediate affective defense behavior and to catalog their inputs and outputs. It should now be possible to find the inputs of these cells by driving them with electrical stimulation at other points in the brain.
Some of the cells which increased in firing rate 50% more during affective defense than during other manipulations of the cat also might have been involved in the mediation of affective defense behavior. This seems particularly likely for the three cells which were found in the same location as the cells which responded if and only if there was affective defense. The especially great response of these cells to tapping on the partition separating the two cats could have reflected a conditioned response. The movement of the partition had been associated with affective defense on many trials, since the partition was regularly opened just before the attack cat was moved toward the recording cat to provoke affective defense.
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