The neural mechanisms of hallucinations: A quantitative meta-analysis of neuroimaging studies

Abstract

Activation likelihood estimation meta-analysis of functional neuroimaging data was used to investigate the neural mechanisms underlying auditory-verbal and visual hallucinations (AVHs and VHs). Consistent activation across studies during AVHs, but not VHs, in Wernicke's and Broca's areas is consistent with involvement of speech and language processes in the experience of hearing voices when none are present. Similarly, greater activity in auditory cortex during AVHs and in visual cortex during VHs supports models proposing over-stimulation of sensory cortices in the generation of these perceptual anomalies. Activation across studies in the medial temporal lobe highlights a role for memory intrusions in the provision of content for AVHs, whereas insula activation may relate to the involvement of awareness and self-representation. Finally, activation in the paracingulate region of medial prefrontal cortex during AVHs is consistent with models implicating reality monitoring impairment in the misattribution of self-generated information as externally perceived. In the light of the results, the need for unified theoretical frameworks that account for the full range of hallucinatory experiences is discussed.

Pavlovian conditioning–induced hallucinations result from overweighting of perceptual priors

“…2C, Table S6). A meta-analysis of symptom-capture-based studies examining neural activity of AVH highlighted similar regions (17) (Fig. 2D).…”

“…C. Whole-brain analysis during conditioned hallucinations (FDR-corrected, P < 0.05). D. Clusters derived from a meta-analysis (17) of AVH experiences during functional imaging. E–F.…”

Brain Mechanisms of Reality Monitoring

“…Auditory and visual hallucinations are the most common forms, with a prevalence of around 59% and 27% in schizophrenia, respectively [51], but olfactory, tactile, somatic, and gustatory hallucinations have also been reported [52][53][54]. Activity associated with hallucinations is often observed in sensory processing areas, such as the superior temporal gyrus during auditory hallucinations and extrastriate cortex during visual hallucinations [55], suggesting that separable modality-specific impairments contribute to different types of hallucinations across patients. One possibility is that hallucinations primarily reflect unusually vivid internally generated experiences [ 3 0 1 _ T D $ D I F F ] represented in one or more of these modality-specific [ 3 0 2 _ T D $ D I F F ] processing areas, experiences that are so vivid that they seem to be external events.…”

Hallucinations in Healthy Older Adults: An Overview of the Literature and Perspectives for Future Research

“…This multiplicity is stimulating more detailed examination of the similarities and differences in the combination of factors driving hallucinations in healthy and clinical samples (Badcock and Hugdahl, 2012) though age and clinical status are often confounded in these comparisons. For example, a recent meta-analysis of neuroimaging data on psychosis, Parkinson's disease, Charles Bonnet Syndrome and healthy hallucinators showed significant cross-study activation in auditory and visual cortices, pointing to similar mechanisms of sensory over-stimulation in the genesis of hallucinations (Zmigrod et al, 2016). The most common explanations for this increase in activation include disturbances in cortical inhibition and neurotransmitter function arising from a reduction of sensory input (Roberts et al, 2010; Pang, 2016).…”