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

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.