Activity as a function of diet: II. Instrumentalactivity!

G. H. COLLIER, R. L. SQUIBB AND FLORENCE JACKSONRUT GERS, THE STA TE UNIVERSITY

AbstractRa ts fed isocaloric diets va rying in percen tage

protein showed the high es t rate of responding forsugar on a high protetn diet and the lowest levelof r esponding on a low protein diet. When protein wassub stituted as the r einforcer, the level of respondingImmediately dropped but eve ntually showed a trendin the direc tion of the highest r ate of r esponding forthe low protein diet and the lowest r ate of respondingfor the high protein diet.Problem

The voluntary intake of different items of food hasbeen shown to vary a s a function of nutritional defictts(e. g., Lepkovsky, 19·18), but the question of whetherreinforcing properties of di etary components vary in thesame fashion has received little investigation. Thepresent s tudy evaluates the effe ct of isocaloric dietscomple te in all essentials and containing varying a ­mounts of balanced protein on the reinforcingpropertiesof su crose and protein.

Procedures and ResultsThree Iso calozlc diets containing 13.8 . 21.3 (normal

cont r ols), and 41. 3% cr ude protein were us ed; eachcon tained 4.8 ca lor ies per gram of diet, and the knownrequirements of the rat for minerals, vitamins and otheres sen tials. Food and wate r were constantly avail able.

Three groups of 12 weanling r ats eac h wer e con­ditioned on the three exp erimental diets for 60 days .Figure 1 shows the typical growth curves for these diets.Following this period fiv e representative individuals

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from each dietary regimen were trained to bar press(BP) (Collier. & Myers, 1961) for 0.1 ml 32% sucrosereinforcement on a 1 min. FI schedule for 20 min. dailyover an eight- day period. After these sess ions thegroups were then switched from sucrose to a fresh rawliver slurry reinforcement for an addit ional six days.

Figure 2 shows that the rats fed the high proteindiet pressed significantly more for sucrose than thosefed the normal level of protein . On the other hand,the rats raised on the protein deficient diet presseds ignificantl y less than either group. When the liverslurry replaced sucrose as a reinforcer these ob­served differences disappeared and it was not until thefinal days that a trend, matching the supplementalvalue of the reinforcement, appea r ed . Food and waterintake a r e shown in Fig. 3 and were similar to those r e­ported in a prior experiment (Collier, Squibb, & J ack­son, 1965) . Rectal temperatures taken at the end of thefirst 60 days of the dietary regimen, when compared.tocontrol values (101.70F), were s ignificantly higher in therats fed a deficiency of protein (102 .00F) and lower intho se fed the surfeit protein (100 .50F).

DiscussionThe question can be raised as to the degree which the

effec tivenes s of various kinds of reinforcers can be

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Psychon. Sci. , 1965, Vo l. 3 175

determined by the nutritional state of the animal. Thepresent data suggest that animals consuming an adequatediet imbalanced for protein may respond instrumentallywith differential strengths to substances tending to re­store the balance, showing an inverse relation betweenactivity level and instrumental performance (Collier,Squibb, & Jackson, 1965), contrary to the predictionsof conventional drive theory. In the formused, proteinas a reinforcer appeared to be much less effe ctivethan sugar, however. The protein reinforcement im ­mediately changed the level of responding but did notresult in a significant inversion of rates of BP . Thefailure to show a significant separation, as would bepredicated from the deficiencies, may have been dueto the short duration of the experiment (s ix days) and/orthe prior training on sucrose.

R e fere n e e 8Coll ier, G., & Myers , L. Th e loci of rei nforcement . J . ex po P su­

chol . , 1961, 61 , 57-66 .Collier, G. R., Squibb, R. L . , & Jackson , Florence . Activity as a

function of di et: 1. Spontaneous ac tiv ity. Psychon. Sci ., 1965 , 3,173-174 .

Lepkovsky, S. Th e physiological basi s of volu ntary food inta kes(Appe tite). Adv . Foo d Res. I, 1948, 46, 105-14 8.

N oteI. Th e work was sup porte d in part by gra nt MH 10252 from theUnite d States Public Health Service , Natio nal Ins titute of MentalHeal th.

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176 Psychon . Sci. , 1965 , Vol. 3