Mental representation of knowledge following frontal-lobe or postrolandic lesions

The aims of this study were to examine the role of the prefrontal cortex in the representation of familiar activities using scripts, and to compare both Shallice's [Phil. Trans. Roy. Soc. Lond. B. Vol. 298, pp. 199-209, 1982] and Grafman's [Integrating Theory and Practice in Clinical Neuropsychology, pp. 93-138, Lawrence Erlbaum, Hillsdale, New Jersey, 1989] models of schematic representation of knowledge. Twelve patients with frontal-lobe damage, nine with postrolandic lesions, and 13 normal control subjects were asked to generate actions belonging to six different scripts in a forward condition, and to two others in a backward condition. The latter condition was included to test Shallice's hypothesis that damage to the frontal lobes would only affect the execution of non-routine tasks. The results showed that patients with frontal-lobe lesions produced scripts that were deprived of contextual elements and made more sequencing errors in the forward condition than matched normal control subjects, hence suggesting that the frontal cortex contributes to the production of an adequate mental representation of routine events. By contrast, the performance of the two clinical groups did not differ from the control subjects in their ability to generate scripts in the backward condition, although these three groups of subjects generated fewer actions in the latter condition. Further qualitative analyses demonstrated that patients with parietal-, but not with temporal-lobe lesions, produced sequencing errors in both forward and backward conditions. The latter findings suggest that the frontal lobes, together with the parietal cortex, may play a special role in establishing the spatio-temporal position of events within a script. The results of this study are discussed in terms of the recent models developed by Shallice and Grafman concerning the contribution of the frontal lobes in the mental representation of knowledge.