Functional changes in brain activity during priming in Alzheimer's disease

Patients with Alzheimer's disease (AD) are often impaired on certain forms of implicit memory, such as word-stem completion priming (WSCP). Lesion dat a suggest that deficient WSCP may be associated with abnormal functioning i n the posterior neocortex. Using positron emission tomography (PET), we her e provide direct support for this view. Compared with normal old adults, AD patients showed reduced priming timing on a word-stem completion task. The normal old showed decreased activity in right occipital cortex (area 19), whereas the AD patients showed increased activity in this region during pri ming. To the extent that decreased activity during priming reflects an expe rience-dependent reduction of the neuronal population involved, these resul ts indicate that shaping of the relevant neurons is slower in AD, possibly as a result of inadequate initial-stimulus processing.