While neuropsychological test material is commonly used by speech therapists to positively diagnose a Demence of Alzheimer's Disease (DAT), other brain-imaging methods such as CT and MRI have been employed to ensure the absence of other disorders. Further, several research groups are presently investigating whether neuropsychological measures can be used to provide additional diagnostic information.
From a neurophysiological point of view, event-related potentials (ERPs) seem to yield the most interesting results. This is particularly true for the P300 component whose latency and amplitude is closely associated with cognitive processes and cholinergetic functions. In Alzheimer patients, increases in latency and decreases in amplitude of this component could be found even at the early stage of the disease. An additional finding is that patients suffering from Alzheimer’s disease or age-associated dysmnesia showed decreases in P300 latencies when under medication with nootropics.
Nonetheless, the clinical importance of the P300 for the differential diagnosis of Alzheimer’s disease will be and has to be critically discussed. This discussion will stress the fact that, as a single measure, alterations in the P300 cannot provide reliable information for a differential diagnosis of DAT as there is a great overlap between the latency and amplitude values of patients suffering from DAT and age-matched controls. It is assumed that in an Alzheimer's Disease - and only here - working processes, that are related to a P300, are selectively slowed down. Accepting this aspect, it will be logical to correlate the latencies of a N100 to the P300: the difference in latency from P300 to N100 might be typical for an Alzheimer's Disease.
However, we make the point that, when used as an additional tool, the P300 can provide useful information that goes beyond the results obtained from neuropsychological measures. From a scientific standpoint, this additional information on the alterations of the P300 might also provide new perspectives in the search for the causes of Alzheimer’s dementia.
This contribution shall show scientific concepts, but before ending our project, no first data can be published.