Why Do Schizophrenics Hallucinate?

Those familiar furrows on the cerebral cortex—which are known as sulci—are not just a dubious fashion statement. By adding folds that increase the overall surface of the brain, sulci expand the territory for neurons without requiring enlargement of the brain to a cumbersome size. No special prefrontal cortex exercises are required to create these contours—they’re standard in the human brain.

While sulci are a hallmark of greater mental capacity, the size of one in particular may affect one’s ability to distinguish reality from fantasy. Recently, a team of scientists from the United Kingdom found that a shorter paracingulate sulcus (PCS)—a furrow located near the front of each brain hemisphere—is more likely in those with a history of hallucinations. Their study of 153 brain scans of schizophrenia patients and a non-schizophrenic control group found that a one-centimeter reduction in PCS length increased the likelihood of hallucinations by 20%. The PCS in patients with a hallucination history was two centimeters shorter than in the other schizophrenic group, and 3 cm shorter than in the control group. PCS length was not significantly different between the non-hallucinating patients and the controls.

This investigation is the first to identify the difference in size between those with a hallucination history versus those without it. Preceding studies had already shown that variations in the form and structure of the PCS might affect one’s grasp of reality. Reductions in this fold correlate with increases in the surrounding gray matter of the brain, which impairs one’s ability to monitor reality.

As lead study author Dr. Jane Garrison, a Postdoctoral Research Associate at the University of Cambridge, United Kingdom, noted on the University website: “We think that the PCS is involved in brain networks that help us recognize information that has been generated ourselves. People with a shorter PCS seem less able to distinguish the origin of such information, and appear more likely to experience it as having been generated externally.”

The shape of the PCS varies widely between people. It is one of the last folds to form in the cerebral cortex, making its first appearance just before birth (at about 36 weeks into gestation). Shortening of the PCS may be due to genetic factors or a non-genetic disturbance to development of the fold. By compromising connections in the brain responsible for decision-making, this alteration may blur the boundary between what is imagined and what is actually perceived.

The implications of these findings resonate beyond those with a diagnosed psychiatric condition. Many people who aren’t mentally ill also experience hallucinations, and only about 30% of people with schizophrenia report having them. The possible link between a shorter PCS and losing touch with reality may provide a new playing field for predicting and diagnosing a potentially serious brain aberration.