Differential cognitive effects of colloid cysts in the third ventricle that spare or compromise the fornix

A series of twelve cases, all of whom had received surgery for the removal of a colloid cyst in the third ventricle, was examined on a series of memor y tests. The only consistent predictor of poor memory performance that coul d be detected from MRIs was the presence of bilateral interruption of the f ornix, which occurred in three of the subjects. Although these three cases were poor on tests of learning and recall, there was evidence that recognit ion was less impaired. The subjects were also tested on a set of recognitio n and concurrent discriminations that closely matched tests given to non-hu man primates. Clear parallels were found between the apparent effects of fo rnix damage in these clinical cases and those observed following more selec tive surgery in non-human primates. These findings not only indicate that f ornix damage is sufficient to induce anterograde amnesia but also support t he validity of recent animal tests that are thought to capture aspects of e pisodic memory.