Bihemispheric Language Disorders in Early-Stage Dementia of the Alzheimer Type: Evidence From a Novel Metalinguistic Task

Because dementia of the Alzheimer type (DAT) is commonly characterized by bilateral cerebral atrophy, we examined the issue of higher linguistic abilities lateralized to the right cerebral hemisphere (RH) in earlystage DAT. A modified version of an insertion task was administered to 14 patients with probable DAT, 8 right-hemisphere brain-damaged (RHD) patients, 8 left-hemisphere brain-damaged (LHD) patients, and 28 normal elderly (control, CTR) right-handed subjects. The task consisted of presenting the subjects with 53 well-formed sentences; in each a word or syntagm had to be inserted grammatically. Twenty-eight word/syntagm insertions required grammatical role reassignment of a lexical item in the stimulus sentence (shift, sensitive to RHD); 25 insertions implied only semantic reinterpretation of the target sentence (nonshift, sensitive to LHD). The three pathological groups were relatively and similarly impaired on standard aphasia assessment. The performances of the DAT patients, controlled for global cognitive verbal proficiency, verbal cognitive skills, and mood, were found to be significantly worse than the performances of the CTR group on both insertion subtests, whereas there were no significant differences between the DAT and RHD subjects on the shift items or between the DAT and LHD subjects on the nonshift items. Similarly, no differences were noted between the RHD and CTR nonshift scores, or between the LHD and CTR shift scores. On the other hand, the LHD group outscored the RHD group on the shift insertions. A comparison between the two insertion subtests revealed that only the RHD and DAT groups performed significantly worse on the shift than on the nonshift items. Results are consistent with other anecdotally reported RH-specific language-related disorders in early DAT and replicate previous findings of bihemispheric extralinguistic disturbances in these patients.