EFFECT OF ABLATING THE PYRIFORM-AMYGDALOID AREAS AND HIPPOCAMPI ON POSITIVE AND NEGATIVE OLFACTORY CONDITIONED REFLEXES AND ON CONDITIONED OLFACTORY DIFFERENTIATION

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Abstract
To determine the effects of certain temporal lobe lesions on olfaction, the following tests were made after and before and after the operations: a, establishment of a conditioned foreleg reflex to clove vapor; b, transference of the clove reflex from one foreleg to the other; c, establishment of a negative conditioned reflex (absence of foreleg response) for asafetida and conditioned differentiation, which involved a decision in 7 secs. whether to respond positively or negatively to the vapor inhaled, irrespective of any order in which it might come; d, food from no food discrimination by smell. With one exception, considered in the discussion, unilateral extirpation of the pyriform-amygdaloid areas produced little or no effect on a, b, c or d with either the contralateral or the homolateral foreleg. Bilateral extirpation of the pyriform-amygdaloid areas or severance of their isocortex connections had little or no effect on a, b or d, but abolished c in every instance in which elimination was complete. The inclusion of the hippocampi (95 to 100%) to the pyriform-amygdaloid ablations resulted in no additional effects on a, b or d. Other purely olfactory vapors such as anis and xylol were substituted for asafetida in the differential tests with the same results. Consideration was given in the discussion to: 1, the relationship of the pyriform-amygdaloid areas to the afferent side of conditioned olfactory differentiation; 2, certain temperamental variations noted in c; 3, the likelihood of the mammillo-thalamic bundle furnishing important afferent olfactory impulses for a conditioned reflex. Deletion of the pyriform-amygdaloid-hippocampal areas produced no effect on the taste responses elicited from solns. of sugar, salt, quinine and acetic acid dropped on the tongue.

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