Electrophysiological exploration of hallucinations (EEG, MEG)

Abstract

Hallucinations are an often disabling symptom occurring not only in psychiatric but also in neurological diseases. This chapter highlightens the findings of the past years on auditory verbal hallucinations (AVH) in schizophrenia, epilepsy, and brain injury focusing on the methods of electroencephalography and magnetoencephalography. It has been postulated that hallucinations in a certain modality are generated in the brain areas, which normally are responsible for information processing of that given modality. Even though this hypothesis was mostly investigated and supported in research on schizophrenia, there also is sustained support for this assumption in patients with epilepsy or brain injury. Today's findings suggest that a disturbed interplay of speech production and speech perception areas may form the pathophysiological basis of AVH: When inner speech is produced, the auditory cortex is co-activated in patients suffering from AVH–instead of dampened as in healthy subjects. It may well be that the mechanisms leading to this false co-activation differ between various pathological categories. However, most probably this co-activation plays an essential part in characterizing the hallucinations by giving the self-generated thoughts a more physical character, providing the attribute of coming from an alien source, a sensation that is being termed as hallucination.