Auditory hallucinations: Insights and questions from neuroimaging.
BACKGROUND
The human brain has the capacity to hallucinate but rarely, except in severe neuropsychiatric conditions such as schizophrenia, do they naturally predominate. The neural basis of auditory verbal hallucinations (AVHs) has been investigated using structural and functional neuroimaging techniques. So far, no studies have defined a model that explains why auditory hallucinations are perceived in the absence of an external stimulus.


METHODS
A selective literature review was undertaken specifically to focus on: (1) clinical phenomenology; (2) putative brain systems involved in the pathogenesis of auditory hallucinations as suggested by neuroimaging studies; (3) contributions and weaknesses of the neuroimaging findings in potentially bridging the gap between the neuroscience and phenomenology. Throughout, an attempt was made to ask questions as much as to answer them.


RESULTS
Functional domains implicated in the genesis of auditory verbal hallucinations include: (1) hearing and language; (2) "sense of reality", including externality of voices; (3) attention and salience; (4) emotional response; (5) memory; (6) volition and self-monitoring; (7) impulse control. Each of these domains can be mapped onto neural "systems" that comprise components that overlap with brain regions known to activate during the experience of auditory hallucinations.


CONCLUSIONS
In the next phase of neuroimaging research into the pathogenesis of auditory hallucinations we need to examine component processes that lead to the patient's perception of them as real.
Sheffield Cognition abd Neuroimaging Laboratory, University of Sheffield, UK.
P W R
PW
Woodruff