| Abstract No.: | B-C2103 |
| Country: | Canada |
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| Title: | AUDITORY HALLUCINATIONS AND GAMMA BAND SYNCHRONY IN RESPONSE TO AUDITORY STIMULATION AND SPEECH IN SCHIZOPHRENIA |
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| Authors/Affiliations: | 1 Crystal Villeneuve*; 1 Derek Fisher; 1 Alain Labelle; 1 Verner Knott;
1 Institute of Mental Health Research, Ottawa, ON, Canada
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| Content: | Objectives: Gamma band oscillations (fast electrical frequencies in the range of 30-50 cycles per second) are recognized as an objective tool for investigating brain connectivity. Gamma frequencies have been associated with multiple cognitive domains, and particularly with the sensory encoding and processing of auditory information. Their presence in the brain is widespread, and reflects the activity of GABA-driven inhibitory interneurons, which are themselves modulated by synaptic dopamine and glutamate. Although many studies to date have observed reduced gamma activity in schizophrenia, findings for this band appear to be dependent upon the syndrome or symptom being studied. Positive symptoms, for example, appear to be associated with excessive gamma. This finding may reflect a hyperconnectivity, which in turn could be associated with excessive processing and impaired sensory integration. Given this background, the general purpose of this study was to use gamma band oscillations to examine inter-regional synchrony in hallucinating (HP) and non-hallucinating (NP) patients during passive recording conditions. We were also interested in examining how these inter-regional synchronies varied with the increasing of hallucinations. As a number of studies have suggested that hallucinations worsen in the presence of speech and especially in the presence of unintelligible speech, the study also examined gamma band oscillations in response to external speech presented during background noise conditions, as well as during a silence condition.
Materials and Methods: There were three groups of 12 participants: hallucinating patients, non-hallucinating patients, and healthy controls. EEG recordings were taken under 3 sound conditions presented in random order, and a separate recording under silent conditions. The sound conditions consisted of frequent and rare consonant-vowel syllables being presented once very half-second during no-noise or simultaneously with white noise or traffic noise.
For each of these 4 conditions, electrical activity was recorded from the scalp with a 40-channel system and artifact free activity was submitted to spectral analysis for computation of amplitudes in the gamma band, which were plotted across the scalp.
Expected Results: Relative to non-hallucinating patients, we expect greater gamma band oscillations and greater gamma band oscillation synchrony in hallucinating patients, and we expect this pattern to be more evident in the speech/noise conditions.
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