Dundedin School of Medicine, University of Otago, New Zealand
The Bayesian brain, phantom percepts and brain implants
Tuesday 09th of December 2014 at 12:00pm
Captain Ahab, following the loss of his leg in a skirmish with the whale Moby Dick perceives phantom pain, and Ludwig von Beethoven, after losing his hearing, perceives tinnitus. The loss of sensory input or peripheral deafferentation triggers changes in the central nervous system resulting in phantom percepts.
Non-invasive neuromodulation studies using tDCS, tACS, tRNS, TMS and LORETA EEG-feedback have been used to transiently reduce auditory phantom perception. For a more permanent result electrodes have been implanted in different parts of the brain in an attempt to alleviate auditory phantom percepts. These target the anterior cingulate, the auditory cortex, the dorsolateral prefrontal cortex as well as the hippocampal area, caudate nucleus and VIM nucleus of the thalamus. These seemingly distant targets have all been partly successful.
Using a Bayesian brain approach, predictions, evidence and prediction errors can be retraced to the implanted areas. And based on data from implanted electrodes, EEG and MEG processed with FFT, ICA, lagged phase synchronization and effective connectivity as well as and cross frequency coupling a Bayesian anatomical and electrophysiological framework can be proposed, creating a unified pathophysiological model for phantom perceptions that can be targeted by both non-invasive and invasive neuromodulation techniques. Novel neurostimulation designs are needed as well as some better brain targets explored to improve treatment outcomes for the enigmatic problem of phantom perception.
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