seciton 11.5 Flashcards
Gaffen and Miskin & Delacour
showed that monkeys with bilateral medial temporal lobectomies have major problems forming long-term memories for objects encountered in the delayed nonmatching-to-sample tests. In this test, a monkey is presented with a distinctive object (the sample object), under which it finds food. Then, after a delay, the monkey is presented with two test objects: the sample object and an unfamiliar object. The monkey must remember the sample object so that it can select the unfamiliar object to obtain food concealed beneath it. These monkeys had major obkect-recognition deficits.
Combined bilateral lesions of rats’ hippocampus, amygdala, and medial temporal cortex produce
major retention deficits at all but the shortest retention intervals.
In monkeys, the hippocampus is usually removed by aspiration via
the inferior surface of the brain, thus destroying substantial amounts of rhinal cortex.
In rats, aspiration of the hippocampus is usually performed via the
dorsal surface of the brain, thus destroying small amounts of the parietal neocortex.
Bilateral surgical removal of the medial temporal cortex consistently produces
severe and permanent deficits in performance on the delayed non-matching-to-sample test and other tests of object recognition.
In contrast, bilateral surgical removal of the hippocampus produces only
moderate deficits, and bilateral destruction of the amygdala has no effect.
Damage to brain structures other than the hippocampus contributes to the amnesia observed in patients following
global cerebral ischemia. Although the most obvious damage following cerebral ischemia is in the CA1 subfield of the hippocampus, there is substantial damage to other areas that is more diffuse and thus more difficult to quantify.
Allen
found that ischemic patients with a greatly reduced hippocampal volume were much more likely to suffer from anterograde amnesia, however, these same patients also tended to have extensive neocortical damage.
