![]() ![]() Nevertheless, a number of investigators have used it successfully, variously reporting that auditory hallucinations are associated with activation of speech production areas (Dierks et al., 1999), primary (Dierks et al., 1999) and secondary auditory cortices, and various polymodal association cortices (Dierks et al., 1999, Shergill et al., 2000, Silbersweig and Stern, 1996).Ī more mechanistic approach that does not rely on timing, patience, cooperation and endurance is the “fundamental deficit” approach (see Silbersweig and Stern, 1996). Symptom capture requires patience from the research team and cooperation and insight from the patient. While this approach is conceptually simple, it is extremely difficult in practice because it relies not only on the timely occurrence of an illusive subjective experience but also on the ability of the patient to reliably report its initiation and completion. One approach to understanding auditory hallucinations is “symptom capture”, a naturalist approach which attempts to image the brain, using electroencephalography (EEG), functional magnetic resonance imaging (fMRI), or positron emission tomography (PET), as patients are experiencing hallucinations. With hemodynamic and electrophysiological brain imaging, we have the opportunity to understand the neural mechanisms underlying this perplexing symptom. They are experienced as voices even though no one is speaking. While these studies have identified ERPs and EEG gamma coherence indices of the efference copy/corollary discharge system and documented abnormalities in these systems in patients with schizophrenia, we have so far had limited success in establishing a relationship between these neurobiologic indicators of corollary discharge abnormality and reports of hallucinations in patients.Īuditory hallucinations are a cardinal symptom of schizophrenia, occurring in about 75% of schizophrenic patients (Nayani and David, 1996). ![]() In this paper, we describe the results of a series of studies in which we have shown that: (1) event-related brain potentials (ERPs) can be used to demonstrate the corollary discharge phenomenon during talking, (2) corollary discharge is abnormal in patients with schizophrenia, (3) EEG gamma band coherence between frontal and temporal lobes is greater during talking than listening and is disrupted by distorted feedback during talking in normals, and (4) patients with schizophrenia do not show this pattern for EEG gamma coherence. While associated with sensorimotor systems, it might also apply to inner speech or thought, regarded as our most complex motor act. Although originally described in the visual system, corollary discharge may exist in the auditory system, whereby signals from motor speech commands prepare auditory cortex for self-generated speech. Failure of corollary discharge, a mechanism for distinguishing self-generated from externally generated percepts, has been posited to underlie certain positive symptoms of schizophrenia, including auditory hallucinations.
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