Recent research led by Christopher Pack, Ph.D., of McGill University, supported in part by his 2008 NARSAD Young Investigator Grant, may help to explain why people with schizophrenia misperceive the world. The new findings, published April 2nd in the Journal of Neuroscience, furthers understanding of what causes people with schizophrenia to interpret hallucinations—seen or heard—as real.
Dr. Pack and team studied a particular mechanism in the brain called the corollary discharge system. Corollary discharges are signals that aid in the integration of sensory and motor signals and make it possible for us to monitor and recognize our own actions.
“A corollary discharge is a copy of a nervous system message that is sent to other parts of the brain, in order to make us aware that we are doing something,” explained Dr. Pack. “For example, if we want to move our arm, the motor area of the brain sends a signal to the muscles to produce a movement. A copy of this command, which is the corollary discharge, is sent to other regions of the brain, to inform them of the impending movement. If you were moving your arm, and you didn’t have the corollary discharge signal, you might assume that someone else was moving your arm. Similarly, if you generated a thought, and you had an impaired corollary discharge, then you might assume that someone else placed the thought in your mind. Corollary discharges ensure that different areas of the brain are communicating with each other, so that we are aware that we are moving our own arm, talking or thinking our own thoughts.”
In the study, patients with schizophrenia and healthy controls were asked to perform a visual task while looking at a computer screen. The researchers found that compared to controls, patients with schizophrenia made larger errors in localizing visual stimuli. The researchers conclude that the patients have a “noisy” corollary discharge—the extra noise interferes with proper functioning of the signal.
Because the circuits that control eye movements are well understood, Dr. Pack is “optimistic that we can work backward from the behavioral data to the biological basis of the corollary discharge effects.”