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.
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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.
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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)