A new study suggests that people who eventually develop Alzheimer’s disease may have problems early on in processing some information.
While clinicians have observed other types of cognitive problems in patients with Mild Cognitive Impairment (MCI) — including some who were perplexed by even the most simple task — no one had studied in it a systematic way, according to Terry Goldberg, Ph.D., a professor of psychiatry and behavioral science at the Hofstra North Shore-LIJ School of Medicine.
In setting out to test the semantic processing system, Goldberg said he and his colleagues needed a task that did not involve a verbal response. That would only confuse things and make it harder to interpret the results, he noted. They decided to use size to test a person’s ability to use semantic information to make judgments between two competing sets of facts.
“If you ask someone what is bigger, a key or an ant, they would be slower in their response than if you asked them what is bigger, a key or a house,” said Goldberg, explaining that the greater the difference in size between two objects, the faster a person can recognize the difference and react to the question.
Investigators recruited 25 patients with MCI, 27 patients with Alzheimer’s, and 70 cognitively fit people for testing. They said they found large differences between the healthy people and the MCI and Alzheimer’s patients.
“This finding suggested that semantic processing was corrupted,” said Goldberg. “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 tweaked the task by showing pictures of a small ant and a big house or a big ant and a small house. This time, the MCI and AD patients did not have a problem with the first part of the test — they were able to choose the house over the ant when asked what was bigger.
But if the images were incongruent — the big ant seemed just as big as the small house — they were confused and they answered incorrectly or took longer to arrive at a response.
Patients with MCI were functioning somewhere between the healthy people and those with AD, the researcher noted. “When the decision was harder, their reaction time was slower,” he said.
The research team then wondered if a damaged semantic system would have an effect on everyday functions.
To answer this question, they turned to the UCSD Skills Performance Assessment scale, a tool that they have been using in MCI and AD patients that is used to identify functional deficits in patients with schizophrenia. The test taps a person’s ability to write a complex check or organize a trip to the zoo on a cold day.
This is actually a good test to figure out whether someone has problems with semantic knowledge, according to the researchers, who said semantic processing has its seat in the left temporal lobe.
“The semantic system is organized in networks that reflect different types of relatedness or association,” the investigators wrote in their study, which was published in the American Journal of Psychiatry.
“Semantic items and knowledge have been acquired remotely, often over many repetitions, and do not reflect recent learning.”
Goldberg said the study’s finding is important because it may be possible to strengthen these semantic processing connections through training.
“It tells us that something is slowing down the patient and it is not episodic memory but semantic memory,” he said, noting the researchers will continue to study these patients over time to see if these semantic problems get worse as the disease advances.