In the first MRI study we present morphometry (VBM) data on grey matter density in patients and healthy controls, as well as an analysis of cortical thickness. ( 1999) assessing the ability to explicitly focus attention on either the left or right ear stimulus in the dichotic listening situation in hallucinating patients, with the hypothesis that this ability would be impaired in the patients. In Study IV we review data presented in Løberg et al. In Study III we present new data on the relationship between frequency of hallucination and dichotic listening performance. ( 2004) examining whether or not ongoing auditory hallucinations have more detrimental effects on dichotic listening performance than having had a previous history of auditory hallucinations. In Study II we review data presented in Løberg et al. ( 1994) on hallucinating and non-hallucinating patients, adding a new healthy control group. In Study I we have re-analyzed the data presented in Green et al. We finally suggest a model for the understanding of auditory hallucinations as instances of perceptual phenomena, possibly related to deficient glutamate regulation, and with a genetic origin. For this purpose we present data from four behavioral studies using a dichotic listening (DL) paradigm to assess impairment of lateralized speech sound processing in hallucinating and non-hallucinating patients compared with healthy controls, and structural and functional brain imaging data from two MRI studies. The aim of the article is to present the results in a common frame of reference so that it hopefully “tells a coherent story”. In this article we summarize empirical work related to auditory hallucinations 1 in patients with schizophrenia conducted in our laboratory over the last 15 years. Ongoing fMRI studies are focused on the underlying synaptic and molecular mechanisms by investigating the effects of the glutamate antagonist drug memantine on auditory perception and speech lateralization, and examination of temporal cortex-specific gene expression in the left peri-Sylvian region. Hallucinating patients also failed to show a right ear advantage in the dichotic listening test. The behavioral DL data are substantiated in two MR morphometry studies that revealed significant reductions in grey matter density in the left peri-Sylvian region in hallucinating patients, and patients with reduced left temporal lobe grey matter density. Moreover, we have found that schizophrenia patients fail to shift attention to the left ear stimulus, when explicitly instructed to focus on the right or left ear stimulus only, thus showing a deficit in inhibition of attention and response-inhibition. The results also revealed that patients with ongoing auditory hallucinations were more impaired than patients with previous hallucinations, and that a higher score on the hallucination item in a standard symptom rating scale (BPRS) correlated negatively with number of correct reports for the right ear stimulus. Absence of a right ear advantage is indicative of a functional deficit in the left peri-Sylvian region. Across a series of behavioral experiments, we have shown that patients with schizophrenia who experience frequent auditory hallucinations fail to demonstrate an expected right ear advantage on the dichotic listening test. From this we predict that hallucinating patients should have problems identifying a simultaneously presented external speech sound, as measured through performance on the dichotic listening (DL) paradigm with consonant–vowel syllables, since this technique lateralizes the stimulus input. We here advance the hypothesis that auditory hallucinations are internally generated speech perceptions that are lateralized to the left temporal lobe, in the peri-Sylvian region. Auditory hallucinations are among the most common symptoms in schizophrenia, affecting more than 70% of the patients. The review consists of both previously published and new data that for the first time is presented together in a cohesive way. In this article we review research in our laboratory on auditory hallucinations using behavioral and MRI measure.
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