Patients with chronic fatigue syndrome (CFS) report cognitive
difficulties (impaired attention, memory and reasoning).
Neuropsychological tests have failed to consistently find
cognitive impairments to the degree reported by CFS patients.
We tested patients with CFS and sedentary controls in
protocols designed to measure sensory reactivity and
acquisition of the classically conditioned eyeblink response.
Patients with CFS exhibited normal sensitivity and
responsivity to acoustic stimuli. However, CFS patients
displayed impaired acquisition of the eyeblink response using
a delayed-type conditioning paradigm. Sensitivity and
responsivity to the airpuff stimulus were normal. In the
absence of sensory/motor abnormalities, impaired acquisition
of the classically conditioned eyeblink response indicates an
associative deficit. These data suggest organic brain
dysfunction within a defined neural substrate in CFS patients.