PET and SPECT findings in patients with hallucinations

Hallucinations remain one of the most intriguing phenomena in psychopathology. The development of neuroimaging techniques has enabled investigators to examine the neural underpinnings of hallucinatory symptoms present in schizophrenia and other disorders. Here we provide an overview of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) neuroimaging studies in patients with hallucinations. The majority of these studies have been in schizophrenia patients with auditory verbal hallucinations, and show increased metabolism or blood fl ow in auditory cortex and speech perception areas. A number of studies also implicate non-sensory brain regions such as the anterior cingulate cortex that may be involved in top-down attentional and speech monitoring processes. In patients with neurological disorders who experience visual hallucinations reduced activation in the ventral visual pathway is reported, again implicating a fundamental role for the modality-specifi c sensory cortex. In conclusion, fi ndings from PET and SPECT neuroimaging studies might suggest that ‘imbalances’ between bottom-up sensory activation and topdown attentional modulation are the primary neurocognitive dysfunction that underpins the hallucinating brain.