Children with Tourette's syndrome are much quicker at certain mental grammar skills than are children without the disorder, suggests a new study by researchers from the Georgetown University Medical Center. "These children were particularly fast, as well as largely accurate, in certain language tasks. This tells us that their cognitive processing may be altered in ways we have only begun to explore, and moreover in a manner that may provide them with performance that is actually enhanced compared that of typically-developing children," reported the study's senior investigator, Michael Ullman, in the journal Neuropsychologia.
About 200,000 Americans have the most severe form of Tourette's syndrome, but as many as 10 percent of all Americans have a milder form. The most common initial symptom is a facial tic, and other tics - sudden, rapid, repeated movement or vocalization - may follow. Tics can include eye blinking, repeated throat clearing or sniffing, arm thrusting, kicking, shoulder shrugging or jumping. Coprolalia, the involuntary use of obscene words, is only rarely associated with Tourette's syndrome.
The disorder is linked to structural and functional abnormalities in the basal ganglia and frontal cortex area of the brain, which result in decreased inhibition of frontal activity, leading to hyperkinetic behaviors. The disorder is also associated with abnormalities in the way that chemical substances, such as hormones and neurotransmitters, mediate communication between cells.
Ullman explained that the two basic aspects of language - "rule governed" and "idiosyncratic" knowledge - depend on distinct neurobiological processes. Rule-governed knowledge involves the procedural memory system that depends on frontal/basal-ganglia area circuits in the brain; in language, it is used to combine parts of words together according to the grammatical rules of the language. In contrast, idiosyncratic knowledge depends on declarative memory, and is learned and processed in the hippocampus and other temporal lobe areas in the brain. This kind of memory allows us to learn that a word is linked to an object.
In this new study, eight children, aged 8-17, with Tourette's syndrome and eight typically developing children of the same ages without the disorder were given tasks that included producing past-tense forms. All of the children had a normal IQ. The investigators found that the children with Tourette's syndrome were significantly faster than the control group in producing rule-governed past tenses (like "slip" and "slipped") that depend on grammar and procedural memory but not in producing irregular or other unpredictable past tenses (such as "bring" and "brought") that are stored in declarative memory.
"This may mean that the brain abnormalities we see in Tourette's syndrome may lead not only to tics but also to a much wider range of unsuppressed and rapid behaviors," Ullman speculated. The researchers are now developing new language and memory tests for patients with Tourette's syndrome.
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Source: Georgetown University Medical Center
