The Behavior of Cats (Felis Catus L.) With Lesions in the Caudal Midbrain Region

Abstract

1. An ablation study of the caudal midbrain region in cats is reported. Two lesion groups were prepared by stereotaxic surgery. In one lesion group, the group, most of the tegmentum and the tectum were destroyed at an intercollicular level. In the other lesion group, the group, an area ventral and lateral to the T lesion was destroyed so that the medial lemniscus, pons, and adjacent tegmentum were involved. The two lesions overlapped in the ventral tegmentum. 2. The behavioral changes that were found are summarized in Table II. The cats with the T lesion (Figure 5) persisted in performing one of three prey behaviors: 1. approaching prey, 2. carrying prey, and 3. fishing or mousing. These three behaviors are illustrated in Figure 2. 3. Since the cats with the T lesion performed these parts of prey behavior all the time, it follows that other behavior that is sometimes seen in the laboratory never appeared: these cats never searched or scratched before or after micturition or defecation; they never ingested food in the normal manner (all the food that they ingested was incidentally swallowed during prey-carrying behavior) ; they never groomed; they never exhibited other components of prey behavior. 4. In the other lesion group (the VL group, Figure 6) there were changes in both prey and grooming behavior. In addition to these prey and grooming changes that were common to all members of this group, some members possessed other abnormalities: overeating and obesity, and a loss of responses to a dangerous situation. a. The grooming acts that are seen in normal cats are briefly described. b. The changes in grooming behavior consisted of the appearance of certain of the grooming movements to light tactual stimulation of the body surface: biting, scratching, and licking were elicited by light tactual stimuli and occurred without any of the orienting movements which are normally associated with these behaviors. These same cats groomed themselves excessively. c. In addition to the grooming changes, the cats with the VL lesion killed and ate rats, mice, chicks, and frogs in a normal manner. The other lesion group would not kill or eat prey, nor would cats without lesions that were currently living in the laboratory. d. Some of the modified behaviors reverted to normal after nine months or more. 5. A neurological examination revealed general hyporeflexic conditions; the two lesion groups did not differ systematically on this examination. 6. The cats with the largest lesions were mute, and performed poorly on learning tasks. 7. The thyroid glands of both lesion groups were hyperplastic. 8. The discussion points out that these results are consistent with previous work on the caudal midbrain region and that this region of the brain is therefore significantly implicated as important for instinctive behaviors. 9. The importance of the caudal midbrain region may be due mostly to its connections with other parts of the central nervous system. Thus concepts which are supplementary to the concept of centers are briefly discussed. 10. The change in grooming may be viewed as a simple quantitative increase in behavior and is therefore classified as a super-positive change. The increased sensitivity of partly denervated central nervous system structures that receive input from the skin may be involved in the production of this grooming modification. 11. Because the lesions are rather large and involve many structures, no specific neuroanatomical explanation is possible at the present time. 12. Some fiber systems may be eliminated as critically involved because destruction of these fiber systems at more rostral levels has not produced any behavioral changes. Some of the fiber systems not eliminated interconnect the midbrain with the hypothalamus and subthalamus, and interconnect the superior colliculus with more ventral and caudal parts of the brain stem. The relationships between the midbrain and hypothalamus are emphasized. 13. Some of the changes in behavior that were found here may be produced separately by smaller lesions. 14. The modified grooming and prey bites are compared. Each modified bite was produced by a different lesion. The modifications are similar: both bites have reflex-like properties and may be elicited without the orienting components that normally occur. This dissociation between fixed action patterns and appetitive behavior, together with the dissociation between major instinctive systems (grooming and prey), support the ethological categories of analysis and suggest a high degree of specificity in the structural bases of the behavior involved.