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Misfire in brain tied to auditory hallucinations.

CHICAGO -- A miscommunication between the frontal and temporal lobes may account for auditory hallucinations in patients with schizophrenia, Judith M. Ford, Ph.D., said at the annual meeting of the Society for Psychophysiological Research.

Communication between the frontal lobes, where speech and thoughts are generated, and the temporal lobes, where they are perceived, may occur through the action of a corollary discharge.

Data suggest that in schizophrenia, corollary discharge fails to alert the temporal lobes that these thoughts are self-generated, leading to the misattribution of inner speech to external sources and producing the experience of auditory hallucinations, said Dr. Ford, director of the Laboratory of Clinical Neurosciences, Stanford (Calif.) University.

Corollary discharge is a mechanism for distinguishing self-generated from externally generated percepts and has been well described in the visual system. Early EEG studies of the auditory system have found that the response of the temporal lobe seems to be dampened when subjects are talking and yet robust when hearing ambient sounds in a room.

Dr. Ford and her associate Dr. Daniel H. Mathalon of Yale University in New Haven hypothesized that speaking generates a corollary discharge of motor speech commands that are transmitted to the auditory cortex, suppressing or dampening its response to self-generated speech sounds.

Event-related potentials (ERPs) were used to test whether failures of corollary discharge during speech contribute to the pathophysiology of schizophrenia.

Seven healthy subjects and seven patients with schizophrenia (DSM-IV) were asked to say the vowel sound "ah" into a microphone.

The N1 component of the ERP was recorded when the vowels were spoken and also when replayed for the subjects.

In healthy subjects, the N1 elicited by vowels as they were being spoken was smaller than the N1 elicited by those same vowels, recorded, and played back. As predicted, the patients with schizophrenia showed no difference in ERPs to the vowels when talking or listening, Dr. Ford said.

Similar results were found when the experiment was repeated with patients speaking whole sentences or imagining speaking those sentences.

Dr. Ford said the N1 ERP component amplitude reduction reflects dampening of auditory cortex responsivity during talking and inner speech in controls but not in patients.

Analysis of EEG coherence measures also revealed differences between groups. Dr. Ford conducted t-tests that compared the coherence during talking and listening for 20 electrode pairings for each group--10 from the right hemisphere and 10 from the left.

In healthy controls, the coherence was greater during talking than listening for almost every pair of electrodes tested.

Coherence during talking was even greater over the left than over the right hemispheres.

This also was true for patients who do not hallucinate.

However, patients who hallucinate did not show a difference in coherence during talking and listening.

The coherence between the activity in the frontal and temporal lobes during talking was almost twice as large in controls (coherence 0.53) as it was in the hallucinating schizophrenic (coherence 0.30).

Dr. Ford said this indicates greater communication and interdependence of activity in the frontal speech production and temporal speech reception areas during talking in healthy controls, but is not true in patients who hallucinate.

Analysis is beginning on coherence data from a new set of subjects to determine whether frontal lobe activity drives temporal lobe activity, she said.


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Article Details
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Title Annotation:Neuropsychiatric Medicine
Author:Norton, Patrice G.W.
Publication:Clinical Psychiatry News
Geographic Code:1USA
Date:Mar 1, 2004
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