BEHAVIOR AND CNS INTEGRATION 199 



feasibility and advantages of these techniques should help place current find- 

 ings in their proper perspective. 



Unlearned or Natural Responses 



In the literature on mammals, the testing of unlearned, or natural, responses 

 typically involves the postoperative study of visual following or avoidance. 

 While these may involve only eye movement, they more often include 

 movement of the limbs or of the entire body. Regardless of the exact nature 

 of the chosen response, this type of visual assessment has several advantages 

 that make it potentially valuable for use with sharks. 



A primary consideration is the "built-in" nature of the response, which 

 allows highly repeatable and easily elicitable behaviors to be monitored on a 

 continuing basis almost immediately after completion of surgery. This per- 

 mits greater flexibility in research design and yet requires less of the investi- 

 gator's time per animal than usually demanded by rigorous training proce- 

 dures. It also reduces the total amount of time before and after surgery that 

 the experimental animal must spend captive in a laboratory setting. In 

 planning shark research this time can be an important health and cost-related 

 consideration (Clark 1963). Moreover, the technology for stimulating and 

 observing unlearned responses is typically simpler than that for testing 

 learned responses. This makes it more feasible to conduct shark neurological 

 studies in less formal laboratory settings, reducing cost and allowing for a 

 more realistic, natural test situation. The latter consideration assumes 

 particular importance in the study of sharks because of the real-life hazards 

 they pose and the need for data to help reduce their threat. In this respect 

 the investigator can benefit by studying experimentally induced changes in 

 an animal's normal behavioral repertoire, rather than studying changes in 

 learned behavior patterns. Interpretive pitfalls are less likely, and findings 

 can be more meaningfully related to behavior outside the laboratory. 



Despite the potential advantages of testing unlearned visually guided, or 

 elicited, responses after surgery, only a few investigators have done so. Steiner 

 (1886) was the first to carry out nonsystematic general observations of 

 swimming behavior following selective ablation of the telencephalon, dience- 

 phalon, or mesencephalon of sharks (Scyliorhinus canicula). Similar experi- 

 ments were subsequently conducted by Loeb (1891), Bethe (1899), and 

 Polimanti (1911, 1913). They reported on the fish's postoperative ability to 

 maintain normal balance and to move spontaneously in the aquarium 

 without bumping into the sides. Rizzolo (1929) extended these observations 

 to Galeus canis and showed that forebrain removal did not disturb righting 

 ability or posture while resting. Except for two studies concerning the role 

 of the tectum in maintaining balance (Rizzolo 1929, Ten Cate 1931), there 

 has been no subsequent use of purely observational techniques for assessing 

 the consequences of damage to the shark forebrain or mesencephalon. 

 Although all these early reports are limited by the sole use of dogfish, their 

 findings will be discussed later in relation to other, more recent, findings 

 about the functions of these two areas. 



