Brain response to complex visual stimuli in Parkinson's patients with hallucinations: a functional magnetic resonance imaging study.

Visual hallucinations (VH) in Parkinson's disease (PD) have been associated with gray matter reductions in visual associative areas and with abnormal patterns of brain activation in posterior and frontal regions. However, all previous fMRI studies have used simple visual stimuli. The objective of our study was, therefore, to compare the pattern of brain activation during a one-back face detection task. We examined 10 PD patients with VH, 10 PD patients without VH, and 10 controls matched for age and education. The fMRI task consisted in three blocks of 21-face stimuli (activation condition) and three blocks of 21-colored mosaics (control condition). Subjects were asked to press a key when two identical stimuli were presented consecutively. During the face condition, compared with patients without VH, hallucinating PD patients showed significant reductions in the activation of several right prefrontal areas, such as the inferior (BA 10,47), superior (BA 6/8), middle frontal (BA 8), and anterior cingulate gyrus (BA 31/32). In the control condition, we found a hyperactivation in the hallucinating PD sample compared with the nonVH patients in the right inferior frontal gyrus. A dysfunction of the frontal areas associated with the control of attention could predispose to VH through an abnormal processing of relevant and irrelevant visual stimuli.