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January 07, 2007
Excessive Startle Response in Schizophrenia
Read more... Schizophrenia Biology · Schizophrenia Research Journal Articles · Schizophrenia Symptoms
An excessive startle response has been a well-documented phenomenon in many patients with schizophrenia. In the medical arena, prepulse inhibition (PPI) is the term coined to describe the ability most people have to filter out expected stimuli and not get overly startled by it. It has been noted by researchers that people with schizophrenia tend to show a startle response more strongly to an auditory stimulus than control subjects do, even after being given a warning to expect that stimulus.
Researchers have wondered whether the noted deficit in PPI (i.e. the excessive startle response) is a biomarker correlated to other symptoms of schizophrenia, such as deficits in cognition or overall function.
Neal Swerdlow, David Braff and colleagues at the University of California (San Diego) in a study written up in the Archives of General Psychiatry found some interesting information while trying to answer this question.
Men in general, with or without schizophrenia, have better PPI (women startle more). Nicotine increases PPI (i.e., it reduces the startle response), with the PPI significantly greater in heavier smokers.
People were tested with three different intervals - 120ms, 60ms and 30ms - between the warnings and the auditory stimuli. Patients with schizophrenia not taking antipsychotic drugs were quite deficient in PPI at all three interval lengths, whereas antipsychotic medications increased and normalized PPI. However, even with antipsychotic medication, there was still a deficit in PPI noted with the 60ms interval. This interval is significant because 120ms is a time in which information is consciously processed and 30ms is an interval in which information is processed automatically, but 60ms is considered a "transition" interval in-between the two.
No correlation was found between deficits in PPI and deficits in neurocognitive function, but a strong relationship was found between PPI and assessments of life functioning (using Global Assessment of Functioning or "GAF", and the Level of Independent Living or "LIL" scales), with the patients with the best PPI in that 60ms range having the best GAF and LIL scores.
Lastly, but quite importantly, atypical antipsychotics were found to be more effective than typical antipsychotics in improving PPI, thus "normalizing" the startle response. This led the authors to note:
“Because an overwhelming number of patients with schizophrenia are currently treated with atypical APs, it is possible that PPI deficits in this population are a vanishing biomarker.”
Thanks to CuKettle for pointing out this interesting study.
Posted by Jeanie Wolfson at January 7, 2007 01:03 PM
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