Some people close their eyes when they listen to music, others wear earplugs when they read in noisy places. Both serve to block out inappropriate sensory stimulation, something that happens automatically when we concentrate. A study by Alexander Drzezga and colleagues (of the Technical University Munich, Germany) to be published in the international open access journal PLoS Medicine now shows that this focusing process is defective in people with Alzheimer disease (AD).

Earlier brain imaging studies have shown how the focusing process works in healthy people: When they undergo tasks that depend exclusively on visual clues, they not only activate the areas of the brain involved in visual processing but also de-activate those areas that have to do with auditory processing. The reverse activation/deactivation pattern is seen when the clues are exclusively auditory. The phenomenon, called "cross-modal auditory/visual deactivation," is thought to help with focusing the information processing capacities of the brain on the relevant areas.

To test whether cross-modal inhibition is affected in AD, Drzezga and colleagues examined the activation and deactivation patterns in the brains of patients with AD and individuals with mild cognitive impairment (MCI). The researchers tested 32 participants: 11 healthy individuals, 11 individuals with mild cognitive impairment, and 10 individuals with moderate AD. The participants were trained to perform a navigation task, based exclusively on visual clues, in a virtual reality environment. All participants understood the task and the clues. They then each completed 12 separate PET scans, 8 during active navigation (finding their way from a start point to a specific destination) and 4 under control conditions (traveling along a never-ending pathway). The tasks were performed in complete silence.

The three groups differed in their performance--measured by the time needed to reach the destination--as would
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Contact: Paul Ocampo
press@plos.org
415-624-1224
Public Library of Science
19-Sep-2005

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