What have neuropsychological studies contributed to the understanding of the pathogenesis of Tourette syndrome (TS) and other tic disorders?

Updated: May 30, 2019
  • Author: William C Robertson, Jr, MD; Chief Editor: Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP  more...
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Neuropsychological studies have been conducted to study specific areas of cognitive function. Among other goals, this purpose may inform our understanding of the genesis of tics. (The interested reader can consult an excellent review by Como in 2001. [89] )

Independent studies found that patients with TS performed worse than controls on a weather-prediction task that involved habit learning. In this task, cues predict outcomes at probabilities between 0 and 100%; the subject gradually learns to predict outcomes correctly even though feedback to the subject appears to be inconsistent. Worse performance on this task correlates with more severe illness. [90, 91]

In animal and human studies, habit-learning tasks require a healthy striatum. Other forms of memory, including other kinds of procedural learning, are generally normal in TS. [92]

Intentional and reflexive eye movements were studied in TS; the results are summarized as being consistent with the hypothesis that the ability to inhibit or delay planned motor programs is significantly impaired in TS. Altered cortical-basal ganglia circuitry may lead to reduced cortical inhibition, making it harder for TS subjects to withhold the execution of planned motor programs. [93]

Startle reflexes can be studied in a repeatable way and are abnormal in TS, as in OCD. Advances that allow the study of such reflexes in the functional MRI environment and in preclinical models offer hope for rapid screening of potential treatments. [66]

Immune studies related to group A streptococcal infections are discussed below. In addition, a large longitudinal study suggests that 2 cytokines, interleukin-12 and tumor necrosis factor-alpha, are associated with recrudescences of symptoms in patients with TS. [94] Whether these are markers specifically for TS symptoms remains to be determined.

Although a pilot microarray study of gene expression in TS peripheral blood did not find a statistically different pattern of expression, the 6 genes with increased expression in TS were all related to immune function. [95] However, none of these same genes were detected in a microarray study of post mortem putamen tissue, suggesting that further study is required in this area. [96]

The high male-to-female ratio in TS (up to 10:1 in some prevalence studies) suggests a possible androgen-mediated effect, perhaps occurring during prenatal development. A study that examined gender identity and gender role behavior in males and females with tic disorders offered some support for this hypothesis: in this study, females demonstrated more gender dysphoria, increased masculine play preferences, and a more typically "masculine" pattern of performance, while males reported increased masculine play preference. [97]


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