Abstract
Hallucinations occur in both normal and clinical populations. Due to their unpredictability and complexity, the mechanisms underlying hallucinations remain largely untested. Here we show that visual hallucinations can be induced in the normal population by visual flicker, limited to an annulus that constricts content complexity to simple moving grey blobs, allowing objective mechanistic investigation. Hallucination strength peaked at ~11 Hz flicker and was dependent on cortical processing. Hallucinated motion speed increased with flicker rate, when mapped onto visual cortex it was independent of eccentricity, underwent local sensory adaptation and showed the same bistable and mnemonic dynamics as sensory perception. A neural field model with motion selectivity provides a mechanism for both hallucinations and perception. Our results demonstrate that hallucinations can be studied objectively, and they share multiple mechanisms with sensory perception. We anticipate that this assay will be critical to test theories of human consciousness and clinical models of hallucination.
Highlights
Hallucinations occur across a wide range of pathologies and are common in non-clinical populations (Barrett, 1993; 1994)
Visual hallucinations are thought to arise in exceptional circumstances when external stimuli are overwhelmed by internally generated spontaneous patterns of neural activity
We modeled the region of visual cortex that was stimulated by the flickering annulus as a ring of tissue in one spatial dimension (Figure 3A)
Summary
Hallucinations occur across a wide range of pathologies and are common in non-clinical populations (Barrett, 1993; 1994). Visual hallucinations are thought to arise in exceptional circumstances when external stimuli are overwhelmed by internally generated spontaneous patterns of neural activity This situation occurs when the parameters governing normal visual function are altered due to changes in brain anatomy or physiology (Ffytche, 2008; Butler et al, 2012), state changes such as dreaming or migraines (Llinas and Ribary, 1993; Aurora and Wilkinson, 2007), psychotropic drugs that temporarily perturb normal cortical function, or empty full field luminance flicker (Passie et al, 2008; Billock and Tsou, 2012). This stimulus effectively constrained the hallucinated forms to one spatial dimension
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