STRATEGIE CATEGORIALI IN COMPITI DI APPRENDIMENTO E AREA 9 DI BRODMANN: STUDIO DI CORRELAZIONE ANATOMO-FUNZIONALE.

INTRODUCTION: impairments in memory skill have been described in frontal lobe lesions subjects. Depending on the frontal cortical area involved, frontal lobe patients can present different patterns of dysfunctions in memory task; such as, working memory or source memory impairment. About this, the role of dorsolateral prefrontal cortex in organizational strategy during learning has received particular attention from many researchers. It seems that the dorsolateral prefrontal cortex lesions, in particular the most dorsomesial part (area 9 of Brodmann), can impair the ability of optimizing learning through organizational strategies (such as, semantic categorization and subjective organization). AIMs: our aim is to evaluate the organizational capacity during learning in frontal lobe lesion patients compared to normal subjects and prove if there are differences among frontal lobe patients depending of the lesion site within the lobe. MATERIALS AND METHODS: we have tested 29 frontal lobe patients and 29 matched controls with two learning tasks presented without and with external cues about the presence of semantic categorization of the items. The two tasks were both word-list learning tests in which the items belong to 6 different semantic category (3 for each list) and were presented randomly. In the first one, the semantic categories were not declared, while in the second list, the examiner manifest their presence to the participants at the beginning of the trail. We also wanted to verify different pattern of learning impairment depending on the frontal lobe lesion localization. So we wanted to map frontal lobe lesions of our patients to determine the exact cortical localization through MRIcro and identify two groups: the Gr9+ group composed by subject with lesion involving area 9 of Brodmann and GR9- group composed by those subject in which this area were spared. Considering just left hemispheric lesions, our groups were composed by 6 subjects in GR9+ e 14 subjects in GR9-. ANALYSIS AND RESULTS: Frontal lobe patients reveal learning deficits and less degree of stimuli organization when compared with controls in both conditions (without and with external cues). These results show verbal learning impairment in frontal lobe patients which is not sufficiently corrected by external cue to became similar to normal controls’ performance. Comparing frontal lobe patients groups (Gr9+ vs Gr9-), we do not reveal any differences between the two groups, but the t test power is really small (5%). Looking the performance’s means of the two groups, we can see a trends of the data in favor of a more impairment of categorization ability in the group with area 9 impaired. We also carried out a voxel-based lesion-symptom mapping analysis using MRIcron and NPM in all frontal lobe patients to examine the relationship between lesion localization and impairment of organizational strategy and learning. We verify a trend of voxels of dorsolateral prefrontal cortex (approximately near area 9 left of Brodmann) to correlate with categorization impairment. DISCUSSION AND CONCLUSION: Our frontal lobe lesion subjects showed verbal learning impairment mainly due to poor utilization of organizational strategy. Even if external cues are given, our frontal lobe patients can improve their performance but with less degree compared to normal controls. We could not verify a significant differences in learning performance or in organizational ability within the frontal lobe patients divided by the lesion localization, but the very small power of the test cannot allow us to assert any results. We could observe trends towards an involvement of the medial aspect of the dorsolateral prefrontal cortex in organization capacity during learning tasks. Our results give other evidences that dorsolateral prefrontal cortex play a role during verbal learning, in particular in the use of organizational strategy based on semantic clustering.