Motivation and learning in mice after goldthioglucose-induced hypothalamic lesions

Psychon. Sci. Motivation and learning in mice after goldthioglucose-induced hypothalamic lesions 1,2 JERI A. SECHZER STEVEN G. TURNER ROBERT A. LIEBELT Shock-avoidance training was given to normal mice and to mice with goldthioglucose-induced lesions in the ventromedial region of the hypothalamus. The lesioned mice learned faster than the control mice. Lesions in the ventromedial region of the hypothalamus may alter the emotionality of an animal and thus its motivation during learning. - this study. Comparison of lesioned to normal mice is presented according to strain. The results shown here clearly indicate that regardless of strain, the goldthioglucose-lesioned mice reach criterion in ap­ proximately half the number of trials as their controls. Discussion One possible explanation of these present findings requires the assumption of a change in the emotionality of the animal as a result of the ventromedial lesions. Our observations of the mice throughout the experi­ ment support this hypothesis. The first observation was a marked increase in sensitivity to shock (pain) in the goldthioglucose-lesioned mice. Shock thresholds were found to be consistently lower than those of the control mice. Although each mouse was trained at its own shock threshold, latencies of response were shorter in the lesioned mice. In addition, the normal mice showed more "freezing" behavior both during shock and during the 5 sec. interval. "Freezing" was usually accompanied by urination and defecation. On the other hand, the lesioned mice tended to escape from shock quite readily and consequently showed much less "freezing" with a marked decrease in urination and defecati ')n. The results and observations presented here strongly suggest that ventromedial hypothalamic lesions alter the emotionality of the animal, affecting its motivation during learning under noxious conditions. Elimination of "freezing" and the resultant shorter latencies in the goldthioglucose-lesioned mouse appeared to help the animal during learning. In contrast, the normal mouse "froze" almost immediately and appeared im­ mobilized in the presence of shock or a signal of on­ comiJ;lg shock. Consequently. this animal may have taken longer to learn because it had to first over­ come this emotional response to the noxious situation. It must be emphasized that although our results appear to be significant no generalization can be. made from the mouse to other species such as the rat or cat. We also cannot state at this time whether our results are independent of goldthioglucose and whether similar results would be obtained after electrolytic lesions in this area of the hypothalamus. Finally, further studies are necessary with food­ reward training to determine whether this phenomenon is a general one or is related only to negative rein­ forcement situations. Anand. B. K .. & Brobeck , J. R. Hypothalamic control of food intake . Yale J. Bioi. Med .. 1954 , 24 . 123 - 140 . Evans , W. O. A new technique for the investigation of some analgesic drugs on reflexive behavior in the rat . Psycholpharmacol., 1961 , 2 , 318 . Flexner , J. B. , Flexner , L. B. , & Stellar , E. Memory in mice as affected by intracerebral puromycin . Science . 1963 , 141 , 57 - 59 . Hetherington , A. W. , & Ranson , S. W. Experimental hypothalami cohypophysial obesity in the rat . Proc. Soc . E.rp. BioI., 1939 , 41 , 465 - 466 . Liebelt , R. A. , & Perry , J. H. Hypothalamic lesions associated with goldthioglucose-induced obesity . Proc. Soc. E.rp. Bioi. Mcd. . 1957 , 95 , 774 - 177 . Stellar , E. The physiology of motivation . Psychol . Rev., 1954 , 61 , 5 - 22 . Teitelbaum. P. Sensory control of hyperphagia . J. compo physiol. Psychol .. 1955 , 48 . 156 - 163 . 1. Research supported by U.S.P.H.S. Grants No. MH-I0792-01 and AM-1230. 2. A portion of this paper was presented at the American Physiological Society meeting , Los Angeles, California in August, 1965 ; abstract published in The Physiologist 8 , 292 ( 1965 ). 3. Courtesy of Schering Corp., Bloomfield , N. J. (...truncated)