TUESDAY, July 24, 2001 (HealthDayNews) -- Schizophrenics, who often have trouble appreciating pleasant odors, seem to filter smells through the analytic part of the brain rather than the normal "gut reaction" part, suggests a new study.
The Iowa researchers say this shift could be the brain's way of making up for the loss of certain emotional aspects of the ability to smell, because recognizing noxious odors is more vital to survival. Such a shift could cause schizophrenics to mistakenly perceive "threatening aspects to stimuli and, in turn, give rise to paranoid thinking," the Iowa researchers add.
Schizophrenics often suffer from a condition known as anhedonia, which is the waning ability to experience pleasure. For example, long-time music lovers lose their interest in song, movie fanatics no longer feel like going, avid socializers give up dating, and pleasant smells lose their intoxication.
The findings, which appear in this week's issue of the Journal of the American Medical Association, offer the most detailed comparison so far of real-time brain differences between healthy people and those with schizophrenic anhedonia in processing the sense of smell, experts say. And although the work doesn't have any immediate implications for treatment, it could help scientists better understand how the debilitating condition affects a sufferer's perception not only of odor but also of the other four senses.
Smell is the most emotionally evocative, because of the olfactory bulbs' prime seat up against the deep limbic, or emotional, areas of the brain. The olfactory bulb begins in the roof of the nasal cavity right above the cranial nerve.
Scientists have known that schizophrenics lose brain volume, particularly in the olfactory bulbs. But what has puzzled them is why schizophrenics lose their enjoyment of pleasing odors yet have no trouble reacting to, sometimes with an over-keen sense of, foul ones.
In the latest work, researchers at the University of Iowa used positron emission tomography, or PET scans, on 18 schizophrenics and 16 healthy people to measure blood flow in the brain during standardized odor tests.
The groups were presented with two sets of scented cotton balls: one smelled like vanilla, the other had a pungent, noxious odor. The people were then asked for their reactions.
The two groups were equally able to identify the intensity of an odor and had generally the same reaction to the offensive one. But the schizophrenics were far less likely to respond to the pleasant scent, the researchers say, and a few even said it was unpleasant.
In addition, the PET scans of the schizophrenics showed that they had suppressed action in several regions of the brain that process emotion in response to odor, the researchers say. And they also had increased blood flow in parts of their frontal cortex, a region involved in thinking and planning, considered more analytical than affective.
In a sense, says Daniel O'Leary, an Iowa University neuroscientist and co-author of the journal article, the schizophrenic patients were filtering the unpleasant odors through analysis instead of responding to them viscerally.
Surprisingly, one of the suppressed sites, the cerebellar vermis, had been previously thought to control only motor processes, not emotional ones.
"We used to think it was sitting back there as a motor brain, but we've been finding the cerebellar vermis is involved in attention, memory, language and emotion," O'Leary says.
Although anhedonia primarily alters a person's ability to perceive pleasure, the researchers found that more deeply psychotic patients may have a heightened reaction to unpleasant odors, O'Leary adds.
Paul Moberg, a schizophrenia expert at the University of Pennsylvania in Philadelphia, says the latest work will help clarify the still-murky picture of brain differences between healthy people and those with schizophrenia, a mental illness that affects about 1 percent of the U.S. population.
The advantage of using olfactory tests, Moberg says, is that the system has a hot line to the brain's emotional centers and can be studied in real-time. Trying to study memory, by comparison, is far more difficult.
What To Do
For more on schizophrenia visit the National Alliance for Research on Schizophrenia and Depression or
this Web site devoted to the condition. You can also try the National Institute of Mental Health.
Curious about the brain? Check into the Virtual Hospital and see where all your thoughts come from.
Here's also a simple and good drawing of the limbic system.
