INTERHEMISPHERIC DISCONNECTION SYNDROME AND WHITE MATTER DAMAGE IN ALZHEIMER'S DISEASE: NEUROPSYCHOLOGICAL TASKS AND CONTRASTIVE CASE STUDIES

ABSTRACT

There is a wide consensus on the fact that memory and executive function deficits are cognitive markers of early Alzheimer's disease (AD). However one can not differentiate AD from other types of dementia relying solely on these neuropsychological descriptors. Therefore, a combined approach of neuropsychological tasks and neuroimaging may constitute a powerful and reliable tool in the early diagnosis of AD. A plethora of recent studies suggest that the declarative memory deficits in AD are attributable not only to limbic-to-frontal gray matter progressive atrophy, but also to the early degeneration of white matter structures, such as corpus callosum (CC). In the present study, we adapted two tasks, that is, tactile localization task (TLT) and paired object comparison task (POCT) in order to assess the integrity of intrahemispheric and interhemispheric processing on mild and severe AD subjects, by comparison to frontotemporal dementia, and controls respectively. The neurodegenerative status was analyzed through cranial X-ray computer tomography (CT) and magnetic resonance imaging (MRI). We report here preliminary evidence showing: (i) a significant interhemispheric transfer deficit present on both mild and severe conditions of the disease; (ii) a circumscribed declarative memory deficit with left hemisphere predominance; (iii) a reliable correlation between this pattern of neuropsychological decline and gray matter (e.g., hippocampus and Heschl's gyrus and planum temporale) and white matter (e.g., splenium of corpus callosum) atrophy. Our results suggest that interhemispheric communication and declarative memory deficits, correlated with white matter damage, limbic-to-frontal progressive atrophy, and asymmetrical hemispheric degeneration with left side predominance can reliably circumscribe AD.

KEYWORDS: Alzheimer's disease, interhemispheric disconnection syndrome, declarative memory, splenial corpus callosum atrophy