February 19, 2002
By Cameron Johnston
Special to DG News
TORONTO, ON -- Central executive abilities appear to be the main working memory deficit seen in patients with multiple sclerosis (MS).
In a presentation at the annual meeting of the International Neuropsychological Society, held in Toronto, Ontario, Canada, Jean Lengenfelder, PhD, presented the results of a study that aimed to identify the source of the working memory deficit. Dr. Lengenfelder is a clinical neuropsychologist at the Kessler Medical Rehabilitation and Research Corp, West Orange, New Jersey, United States.
Her study used an auditory n-back task and the Paced Auditory Serial Addition Test (PASAT) in a group of 13 patients with MS and no cognitive impairment; 18 MS patients who were cognitively impaired, and 17 healthy controls. The auditory n-back task assesses the patient's ability to store and rehearse/maintain information with three memory loads (1-back, 2-back, 3-back). The PASAT assesses the same abilities as the n-back test but also evaluates the patient's central executive abilities.
The Central Executive component of Baddeley's working memory model is the temporary memory used for tasks involving planning or decision making, trouble-shooting, new situations, dangerous or technically difficult situations, or situations involving a strong habitual component.
Dr. Lengenfelder explained that the cognitive gap is not part of an auditory deficit - that is, the patient hears the instructions or hears what a person is saying. Rather, these patients do not process correctly the information, so that they appear not to hear what is being said or they are very slow to react to the information.
The problem is not one of "retrieval" because long-term memory is intact, as is their ability to perform many activities of daily living. Instead, the problem is one of "acquisition", that is, the information is not processed correctly in the brain, she said.
This cognitive gap is important in the clinical setting because two-thirds of patients with MS eventually develop some degree of cognitive impairment in areas such as memory, processing of information and executive abilities, Dr. Lengenfelder said in an interview.
These patients are therefore unable to understand their doctor's instructions on medication being prescribed, she explained. The patients, in effect, "are able to hold on to one piece of information, but they are not able to manipulate it," she said. "This is very difficult for people, in their daily lives, especially the young mom who has kids [asking for things] or if she's trying to make all the plans that are needed for running a household. It's very difficult, hanging on to this kind of information."
Results from her study showed that MS patients with cognitive impairment performed significantly worse than did the other two groups on the PASAT (p<0.01). MS patients with cognitive impairment also did worse on the 2-back task, (p<0.01). The results showed that the MS patients with cognitive impairment heard what was being said, but took significantly longer to respond to stimuli than the other patients.
"Results suggest that central executive abilities are the primary difficulty for MS subjects," according to the researchers. MS patients with cognitive impairment also "appear to have some difficulty with storage and rehearsal as memory load increases."
Dr. Lengenfelder said her research is not designed to deal with specific treatments for this cognitive impairment, but it is important for the family doctor to confirm that there is cognitive impairment. "Especially early in MS [development], the cognitive impairment is subtle and sometimes not easily captured, so a full cognitive evaluation is something that might capture this."
"If somebody does have memory impairment,
you'll want to start thinking of some kind of rehabilitation for this impairment,"
she explained. Rehabilitation hospitals that offer memory retraining strategies
may be an option for these patients, she added.
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