Voice-Identification System May Be Absent in Schizophrenia

Voice-Identification System May Be Absent in Schizophrenia Mark Moran

Patients with schizophrenia appear to lack the normal neurophysiological function of "corollary discharge" by which animals are able to distinguish between external auditory sounds and their own internally generated thoughts and speech.
Functional magnetic resonance imaging (fMRI) appears to confirm that the auditory mechanism of patients with schizophrenia is "tuned in" to their own internal speech and thoughts, causing patients to mistake them for real voices.

This attention to internal acoustic patterns occurs at the expense of attention to external voices and sounds, according to a study appearing in the January Schizophrenia Bulletin.
The left side primary auditory cortex—where voices are processed in the brain—was found to be less responsive to external auditory probes among patients with schizophrenia who experience auditory hallucinations than among patients who do not hear voices and individuals without schizophrenia, according to the study.
The same effect was not found in the right side auditory cortex, underscoring the likelihood that the resources for processing external sounds of patients who hear voices are compromised on the left relative to the right because of the linguistic content of their internal voices.

"Researchers have long tried to understand where the voices patients hear are coming from," said lead author Judith Ford, M.D., in an interview with Psychiatric News. "This kind of study provides some really hard evidence that something is going on in the auditory cortex of patients that is making these voices seem very real."

She is a professor of psychiatry at the University of California, San Francisco.
In the study, whole brain images from 106 patients—including 66 hallucinators and 40 nonhallucinators—and 111 healthy comparison subjects were collected while subjects performed a task requiring them to identify external auditory sounds. Specifically, subjects heard a sequence of standard and target—or "oddball"—tones at periodic intervals and were instructed to press a button when they heard the oddball tone. The data were gathered at nine sites of the Functional Imaging Biomedical Informatics Research Network.

Response to the auditory probes was analyzed at several "regions of interest": the primary and secondary auditory cortex, the auditory association cortex, and the middle temporal gyrus.
Researchers found that healthy controls had greater activation in all of the regions of interest than did the patients, and that nonhallucinating patients had greater activation than did patients who were classified as "hallucinators."

Ford, in her research, has focused on what is known as "corollary discharge," the neurophysiological process by which all animals are able to distinguish between externally and internally produced sounds. This process is faulty in people with schizophrenia, Ford said, and she likens the resulting functional disability to the "line being busy" when the external auditory world tries to "connect" to the patient.

"Every animal has this corollary discharge function, and it is what allows us to know that what we are sensing is coming from us and not from somewhere else," Ford said. "It affects not just inner speech but memories and thoughts that pop up into your consciousness, and it allows you to know that these thoughts are yours. Patients with schizophrenia will often not be able to identify [their own internal voices and thoughts as distinct from the external world] because they are missing this system.

"So in fact they are hearing their own inner musings and obsessions as auditory sounds, and are hearing them louder than they should be. When they do hear sounds from the outside, they are in competition [with the internal sounds]."

Ford added that one implication of the study for clinicians is to underscore the difficulty patients can have in paying attention to and processing what they are told.
"The whole auditory apparatus [of people with schizophrenia who hear voices] is ready to experience internally generated sound and does not have energy to attend to the external auditory world," she said.

Funding was provided by the Biomedical Informatics Research Network.

Information about the Biomedical Informatics Research Network is posted at http://www.nbirn.net/. "Tuning In to the Voices: A Multisite fMRI Study of Auditory Hallucinations" is posted at <http://schizophreniabulletin.oxfordjournals.org/cgi/content/full/35/1/58