BACKGROUND: The purpose of this article is to point out significant differencesin how mental images are processed by post-stroke patients with left and right hemisphere damage. Theissues involved are of theoretical importance because of the light shed on the modularity of cerebralfunctions, especially the imagination, and of clinical importance due to the better understanding ofthe underlying pathomechanism.
MATERIAL AND METHODS: The research involved 82 right-handed patients witha lesion in the left hemisphere (Group L), 82 right-handed patients with a lesion in the right hemisphere(Group R), and, as a control group, 82 patients with musculo-skeletal disorders not affecting the centralnervous system (Group C), matched by age and sex. Image processing of complex notions was examined byusing selected items from the Simple Neurolinguistic Test.
RESULTS: In the control group, the majorityof the patients responded to most of the prompts with polymodal associations of various types. In GroupL, responses were dominated by isolated elements of the complex situation, while in Group R the associationswere mostly verbal (lexical) and highly restricted in scope.
CONCLUSIONS: The results indicate that theloss of LH functions interferes with the ability to assemble pieces of polymodal image information intosensible strings, while the loss of RH functions leaves strings to which little information is attached.

Keywords: Stroke, mental imagery, complex notions, cerebral hemisphere specialization