Cognitive processing speed in Lyme disease.

Objective: The goal of this study was to more precisely define the nature of the cognitive processing deficits in the patients with Lyme disease.

Background: Lyme disease has been associated with cognitive disturbances.

Method: Sixteen patients who met the Centers for Disease Control's case definition for Lyme disease and 15 age- and education-matched control subjects completed two computerized assessments. The first was a matching procedure that assessed perceptual/motor speed. The second task was an alphabet-arithmetic (AA) test that measured the speed of mental arithmetic. On the matching task, subjects judged as true or false simple identity equations (e.g., B + 0 = B). On the AA task, subjects indicated the veracity of equations of the same form as those of the matching task but which required mental arithmetic (e.g., A + 3 = D). The use of this paradigm permits sensory or motor slowing to be distinguished from slowed cognitive processing speed. Also, the tests do not involve automated or overlearned responses.

Results: Lyme disease patients and healthy controls did not differ in perceptual/motor speed. However, Lyme disease patients' response times were significantly longer than those of healthy controls during the AA task, demonstrating specific impairments in mental activation speed.

Conclusions: These results suggest that Lyme disease patients show specific deficits when initiating a cognitive process. These impairments are independent of sensory, perceptual, or motor deficits.