[en] Alzheimer ; Language ; PET ; Articulation Disorders/etiology/physiopathology/radionuclide imaging ; Brain Mapping ; Cerebral Cortex/pathology/physiopathology/radionuclide imaging ; Female ; Frontal Lobe/pathology/physiopathology/radionuclide imaging ; Humans ; Language ; Language Disorders/etiology/physiopathology/radionuclide imaging ; Language Tests ; Male ; Middle Aged ; Nerve Net/pathology/physiopathology/radionuclide imaging ; Phonetics ; Positron-Emission Tomography ; Predictive Value of Tests ; Semantics ; Speech/physiology ; Speech Perception/physiology ; Temporal Lobe/pathology/physiopathology/radionuclide imaging
[en] The language profile of patients suffering from Alzheimer's disease (AD) is characterized not only by lexicosemantic impairments but also by phonological deficits, as shown by an increasing number of neuropsychological studies. This study explored the functional neural correlates underlying phonological and lexicosemantic processing in AD. Using H(215)O PET functional brain imaging, a group of mild to moderate AD patients and a group of age-matched controls were asked to repeat four types of verbal stimuli: words, wordlike nonwords (WL+), non-wordlike nonwords (WL-) and simple vowels. The comparison between the different conditions allowed us to determine brain activation preferentially associated with lexicosemantic or phonological levels of language representations. When repeating words, AD patients showed decreased activity in the left temporo-parietal and inferior frontal regions relative to controls, consistent with distorted lexicosemantic representations. Brain activity was abnormally increased in the right superior temporal area during word repetition, a region more commonly associated with perceptual-phonological processing. During repetition of WL+ and WL- nonwords, AD patients showed decreased activity in the middle part of the superior temporal gyrus, presumably associated with sublexical phonological information; at the same time, AD patients showed larger activation than controls in the inferior temporal gyrus, typically associated with lexicosemantic levels of representation. Overall, the results suggest that AD patients use altered pathways to process phonological and lexicosemantic information, possibly related to a progressive loss of specialization of phonological and lexicosemantic neural networks.
Centre de Recherches du Cyclotron - CRC ; Centre de Neurosciences Cognitives et Comportementales
Fonds de la Recherche Scientifique (Communauté française de Belgique) - FNRS; EC-FP6 project DiMI; IUAP P6/29