A verbal long term memory deficit in frontal lobe damaged patients.

The retention performance for learned words was compared in two groups of cortically damaged patients: A group of 14 patients with uni- or bilateral damage to the frontal lobes (group F), and a group of 14 patients with postrolandic damage. The patients learned three lists of words each of which had to be reproduced after 15 min. and after 1 day: one list under free recall, one under cued recall, and one under a recognition condition. While the performance of the two groups of patients was similar under all three conditions when tested after 15 min., group F was significantly inferior in the one day free recall retention test. We interpret this deficit as related in part to the classic "frontal" symptomatology (reduced attention and lack of initiative, drive, and concentration), and in part to a distinct disturbance of long term memory. We base this conclusion on the similar performance levels of frontal and non-frontal patients under all other conditions of testing, in particular under the free recall condition after the 15 min. delay. Reasons are given why attentive and drive related components might be mediated by prefrontal cortical neurons themselves, while mnemonic components might be mediated by mediodorsal thalamic neurons projecting to the prefrontal cortex. No or only minor differences could be established between the side of damage or between uni- versus bilateral frontal damage.