Detection and explanation of sentence ambiguity are unaffected by hippocampal lesions but are impaired by larger temporal lobe lesions

We address the recent suggestion that the "hippocampal system" is important for understanding ambiguities in language (MacKay et al.,) Cogn Neurosci 1 998;10:377-394). Seven amnesic patients and 11 controls first decided wheth er a sentence was ambiguous and then tried to explain the ambiguity. Three amnesic patients with damage limited to the hippocampal formation and one a mnesic patient with primarily diencephalic damage performed like the contro ls in all respects. Thus, the ability to comprehend ambiguity is independen t of the hippocampal formation. By contrast, three patients with larger tem poral robe lesions, which extended beyond the medial temporal lobe, were im paired to about the same degree as the noted amnesic patient H.M. las repor ted by Lackner, Neuropsychologia 1974;12:199-207; MacKay et al., J Cogn Neu rosci 1938;10:377-394). Patient H.M., like our 3 impaired patients, has som e damage outside the medial temporal robe. However, patient H.M. also had a dditional difficulties on these and other language tests that the patients with larger temporal lobe lesions did not exhibit. Accordingly, it is possi ble that H.M.'s impairment has a different basis. Hippocampus 2000;10:759-7 70. Published 2000 Wiley-Liss, Inc.dagger.