Atypical functional network activity of default mode network and auditory cortices predispose to auditory hallucinations
Auditory hallucinations, hearing voices without external stimulation, constitute one of the most frequent symptoms in debilitating psychotic disorders such as schizophrenia. While in psychotic disorders auditory hallucinations are associated with other symptoms such as delusional thinking and emotional disturbances, and typically their hallucinations are of psychologically disturbing and threatening nature (e.g., voices commanding the patient to commit suicide), there are also healthy persons who have benign auditory hallucinations. Given that auditory hallucinations in healthy subjects are present as an isolated symptom, such individuals offer a very interesting possibility to study the neural basis of auditory hallucinations as an isolated phenomenon.
In their recent study, Lutterveld et al. (2013) obtained resting-state (i.e., without any sensory stimuli or tasks) functional magnetic resonance imaging data in healthy subjects with auditory hallucinations and in control subjects who do not experience auditory hallucinations. The authors specifically scanned the subjects when they were not experiencing hallucinations to exclude hallucination-related transient hemodynamic responses. Functional connectivity patterns (i.e., brain networks) of these two subject groups were then compared with complex network analysis methods.
The authors observed that temporal (auditory) cortical areas and posterior-parietal cortex constituted stronger functional “hub” regions in subjects with auditory hallucinations, as compared with the control subjects. Given that the posterior parietal cortex is an essential part of the so-called “default-mode network” hypothesized to be involved in, e.g., self-referential thinking, these highly exciting results suggest that atypical functioning of the default mode network and auditory cortices underlie predisposition to auditory hallucinations.
Reference: van Lutterveld R, Diederen KMJ, Otte WM, Sommer IE. Network analysis of auditory hallucinations in nonpsychotic individuals. Human Brain Mapping (2013), e-publication ahead of print. http://dx.doi.org/10.1002/hbm.22264