When people hear voices others can't, the prevailing scientific model describes this as psychosis due to brain abnormality, chemical imbalance, or other affliction. But scientists have now reliably induced auditory hallucinations in some people not diagnosed with psychosis.
The technique uses good old classical conditioning developed by Pavlov. They repeatedly showed four groups of subjects a grid pattern while playing a tone, then showed the grid without the tone. Many still heard the tone. The study led by Yale neuroscientist Albert Powers says:
Using functional neuroimaging and computational modeling of perception, we identified processes that differentiated voice-hearers from non–voice-hearers and treatment-seekers from non–treatment-seekers and characterized a brain circuit that mediated the conditioned hallucinations. These data demonstrate the profound and sometimes pathological impact of top-down cognitive processes on perception and may represent an objective means to discern people with a need for treatment from those without.
They conclude: "Our observations support an explanation of hallucinations based on strong perceptual priors. They suggest precision treatments for hallucinations, such as targeting cholinergically mediated priors, and interventions to mollify psychosis more broadly, such as cerebellar transcranial magnetic stimulation."
• Pavlovian conditioning–induced hallucinations result from overweighting of perceptual priors (Science)
Image: Bill Strain