Activation of Regional Cerebral Blood Flow by a Memorization Task in Early Parkinson's Disease Patients and Normal Subjects

Task-induced changes in regional cerebral blood flow (rCBF) during memory activation were compared in 18 right-handed patients with early Parkinson's disease (PD) and 20 normal volunteers using the same activation paradigm. We used single-photon emission computed tomography and ¹³³Xe in 21 regions of interest during rest, passive listening of a word list, and memorization of another word list, which was followed by a free recall test immediately after completion of the rCBF measurement. The average performance on free recall was not significantly lower in PD patients than in controls. In normal subjects, five left-sided regions (anterior middle frontal, posterior inferior frontal, superior middle temporal, thalamic, and lenticular) showed a significant increase in memorizing compared to passive listening. This pattern of activation suggests the existence of a verbal rehearsal strategy during the memorization task in normals. In PD patients, increases in these regions did not reach significance, whereas significant activations were noted in superior prefrontal regions. Such alterations in the pattern of activation in PD patients, despite a memory performance similar to that of controls are viewed as a consequence of an early dysfunction of the articulatory loop system and of compensatory mechanisms in other parts of the frontal lobe emerging in the early stages of the disease.