The study is the first of its kind to review mild cognitive impairment (MCI) associated with Alzheimer's disease in a systematic way and reveal the early indicators, signs and symptoms. Terry Goldberg, PhD, director of neurocognition at the Litwin Zucker Center for Research in Alzheimer's Disease, and his colleagues developed a test to identify any problems with a person's ability to process semantic or knowledge based information.
The results of the test showed that there are a number of semantic impairments that are associated with MCI. In order to prevent adding further confusion to the study, the researchers implemented an element of the test that did not require any verbal response. This part of the test measured a person's ability to make a judgment of two sets of facts by their ability to differentiate size. For example, they would be shown a picture of an ant and a house and asked which was bigger. The time it took for them to answer the question would reveal the extent of their inability to process semantic information.
A total of 122 people were tested, of whom 25 had MCI, 27 had Alzheimer's and the other 70 were cognitively "normal". There was a big difference in the ability to process the information among the MCI and Alzheimer's patients compared to the healthy controls. According to Dr. Goldberg: "This finding suggested that semantic processing was corrupted. MCI and AD (Alzheimer's disease) patients are really affected when they are asked to respond to a task with small size differences."
The researchers then added an element to the task by showing the participants pictures of a big house and small ant and also a big ant and small house. The MCI and AD patients were able to successfully complete the first part of this task but had a lot difficulty (unable to answer or delayed response) when shown the picture where the big ant looked just as big as the small house. The patients with MCI were functioning better than the Alzheimer's patients but not nearly as well as the healthy controls.
They used the UCSD Skills Performance Assessment scale to determine how much of an effect impaired semantic processing has on carrying out everyday functions. It assesses stuff like a person's ability to organize day trips out and write complex checks. The authors of the study said: "The semantic system is organized in networks that reflect different types of relatedness or association. Semantic items and knowledge have been acquired remotely, often over many repetitions, and do not reflect recent learning."
This indicates that it could well be possible to repair semantic processing connections through training. According to Dr. Goldberg: "It tells us that something is slowing down the patient and it is not episodic memory but semantic memory."
David P. Salmon, PhD, of the Department of Neurosciences at the University of California in San Diego, said in an accompanying editorial:
"semantic memory deficit demonstrated by this study adds confidence to the growing perception that subtle decline in this cognitive domain occurs in patients with amnestic mild cognitive impairment. Because the task places minimal demands on the effortful retrieval process, overt word retrieval, or language production, it also suggests that this deficit reflects an early and gradual loss of integrity of semantic knowledge."
He concluded: "second important aspect of this study is the demonstration that semantic memory decrements in patients with mild cognitive impairment may contribute to a decline in the ability to perform usual activities of daily living."
A previous study carried out by researchers from The Australian National University developed a test that was able to predict Alzheimer's disease among middle aged people. The finding, along with this one opens possibilities of early detection and intervention in healthcare settings.