Functional Brain Imaging of Hallucinations: Symptom Capture Studies

Abstract

Hallucinations are defined as erroneous percepts that occur without any external sensory input. For decades, brain imaging has been extensively used to explore the neural substrates of hallucinations and propose new pathophysiological hypotheses for the schizophrenia spectrum. A reappraisal of the functional imaging procedures developed in the field allows conceptual distinction between two main study categories. Cognitive studies comparing hallucinators with nonhallucinators (i.e., trait studies), and state studies conducted during hallucinatory episodes; the latter category (e.g. capture studies) is of particular significance for our purpose because these studies directly measure brain activation associated with the onset of hallucinations. Because the available findings are difficult to summarize, here we report findings from a recent coordinate-based meta-analysis of the existing functional data on hallucinatory states. This quantitative review provides evidences for increased activity within the language network and the hippocampal formation during psychotic auditory verbal hallucinations. The role of primary and associative auditory cortices in hallucinations is critically discussed, and future research directions are considered.