P1‐410: Neocortical disconnectivity disrupts semantic binding in Alzheimer's disease
Elena K. Festa, Brian R. Ott, Geoffrey N. Tremont, William C. Heindel · Alzheimer s & Dementia · 2011
Real world objects (particularly living items) are characterized by a set of multimodal perceptual features that define their stored representations within semantic memory, and that are represented in a distributed fashion across relevant cortical areas. The semantic memory impairments observed in AD may be directly attributable to the disruption of functional connectivity among cortical areas underlying these distributed representations. This study investigates the degree to which sensory binding of semantic object representations is disrupted in early AD, and whether performance measures on these tasks could serve as effective diagnostic markers of the disease. Very mild AD patients and elderly controls were administered two tasks assessing both unimodal (visual) and crossmodal (audiovisual) binding of semantic object representations. In the unimodal task, subjects were presented with pictures of real world objects in typical or atypical colors, and asked to name the presented color as quickly as possible. In the crossmodal task, subjects were presented with pictures of objects along with congruent or incongruent auditory sounds, and asked to identify whether the picture and sound belonged to the same object. In both tasks, half the stimuli were of living objects and half non-living objects. Changes in binding integrity are reflected in changes in the pattern of response times and accuracies across conditions. In the unimodal task, accuracy was high and did not differ across conditions for the elderly group but was selectively impaired in the strongest binding condition (i.e., living) for the AD group, suggesting that conditions that mandatorily activate sensory binding of distributed representations are most affected in AD. Similarly, in the crossmodal task, the AD but not the elderly group showed a selective impairment only in the strongest binding condition. When the maximal binding measures were entered into a discriminant function, each measure predicted group membership at 75% accuracy separately, and at 93.3% accuracy combined. Results suggest that sensory binding of distributed semantic object representations is disrupted at the earliest stages of AD due to decreased functional connectivity across cortical regions. Development of markers for this binding impairment could lead to effective diagnostic tools for early detection and treatment of AD.