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
This attention to internal acoustic patterns occurs at the expense of
attention to external voices and sounds, according to a study appearing in the
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
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"
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
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<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>.▪