BEHAVIOR AND CNS INTEGRATION 211 



cephalon, slightly more medially than those found by Cohen et al. in the 

 nurse shark and as predicted by the anatomical findings of Ebbesson and 

 Schroeder (1971). The authors conclude that the absence of telencephalic 

 visual responses in Scyllium is due to functional, not morphological, dif- 

 ferences since they simultaneously confirmed the presence of the crossed 

 thalamo-telencephalic pathway by recording evoked potentials in response 

 to stimulation of the contralateral dorsal thalamus. 



Past Behavioral Studies --In accordance with the early anatomical 

 literature, the belief that the telencephalon plays no role in shark vision is 

 fairly well supported by the findings of previous behavioral studies (Healey 

 1957). All investigators who have examined the effects of telencephalic 

 ablation have reported that there are no postoperative disorders in vision, 

 locomotion, or equilibrium (Bethe 1899, Karamian 1956, Loeb 1891, 

 Polimanti 1911, 1913, Rizzolo 1929, Steiner 1886, 1888). Thus, Aronson 

 (1963, p. 220) has stated that "on the basis of general observations in an 

 aquarium, it is hardly possible to distinguish an operated from an intact 

 individual. " 



While these investigations were limited solely to nonsystematic descriptive 

 observations, there is no reason to question their basic validity. The key to 

 understanding the lack of visual deficits that they describe may lie in the fact 

 that all their experiments were conducted on various species of dogfish, 

 most often Scyllium. The findings of Veselkin and Kovacevic (1973) imply 

 that these sharks may be unique among elasmobranchs and lack the physio- 

 logical basis for telencephalic visual involvement. 



In view of the unexpected findings that resulted from using instrumental 

 conditioning to analyze tectal lesions, we thought that a similar approach 

 might prove equally revealing in reassessing the effects of telencephalic 

 ablation. 



Telencephalic Ablation and Visual Discrimination 



Postoperative Learning of Novel Tasks— The initial experiment was 

 designed along the lines of the previously described tectal study. Two groups 

 of juvenile nurse sharks were trained postoperatively to discriminate black 

 from white (BW) and horizontal from vertical (HV) black and white stripes. 

 One group received bilateral suction lesions aimed at destroying most of the 

 central telencephalic nuclei, especially the posterior portion known to 

 receive input from the visual area of the thalamus. The other group under- 

 went bilateral aspiration of the anterior telencephalon and thus served as an 

 operated control group. The training and histological procedures were 

 identical to those already described for the tectal experiment, with only one 

 shark (NS-191) receiving any preoperative experience in the training situa- 

 tion. 



The operated control subjects exhibited no substantial behavioral deficits 

 other than anorexia in the first two weeks after surgery. However, none mani- 

 fested any subsequent motivational deficits during training. Their learning 



