Do Patients With Tourette Syndrome Jump to Conclusions?

Tourette syndrome is characterized by involuntary movements and vocalizations (motor and vocal tics). The exact pathophysiology of Tourette syndrome is still unknown, although it is thought to involve dysfunction in frontostriatal dopaminergic pathways. Patients with Tourette syndrome can sometimes exhibit mild deficits in executive functions, especially inhibition.¹ Studies have also indicated changes in social² and probabilistic³ reasoning.

The beads task is a probabilistic reasoning task used in the neuropsychological assessment of psychiatric conditions, particularly disorders characterized by dopaminergic dysregulation such as schizophrenia.⁴ In this task, participants are shown two jars, one with a greater proportion of one color bead (e.g., 60% red beads and 40% blue) and the other jar with the opposite proportions (e.g., 60% blue and 40% red). The jars are then obscured from view. The experimenter removes beads one by one, until the participant feels they have seen enough beads and can decide which jar the beads are coming from. Healthy participants base their decision on the proportion of beads revealed of the two colors (e.g., mostly blue beads means the 60% blue jar is more likely). Patients with schizophrenia require fewer beads before making a decision, exhibiting a jumping to conclusions (JTC) bias.

Schizophrenia is associated with dopamine dysfunction treatable with dopamine antagonists, and similar agents can be helpful in Tourette syndrome.⁵ If neurochemical dysregulation is linked to the JTC bias, then patients with Tourette syndrome could show a similar JTC bias to that seen in schizophrenia. Furthermore, a tendency to JTC could be linked to impulsivity or compulsivity. Impulsive and compulsive behavioral problems (including attention deficit, hyperactivity, and obsessive-compulsive symptoms) are common in Tourette syndrome,⁶ and these tendencies could be linked to a greater propensity to JTC on the beads task.

We compared the beads task performance of patients with Tourette syndrome and matched healthy control subjects. As previous studies highlighted a link between beads task performance and executive functions,⁷ measures of inhibition, verbal fluency and working memory were also used. Standard Tourette syndrome symptom scales, including measures of impulsive and compulsive behaviors frequently associated with Tourette syndrome [attention deficit hyperactivity disorder (ADHD; obsessive compulsive disorder (OCD)] were also taken for patients. We explored differences between the groups in terms of the number of beads drawn to decision, executive performance, and symptom scores for the Tourette syndrome group.

Methods

Patients and Procedure

Fifteen patients with Tourette syndrome agreed to participate in this study and were compared with 15 matched control subjects (Table 1) who had no psychiatric diagnoses. Tourette syndrome is often complicated by comorbidities, and OCD and ADHD scales were administered to assess the presence of comorbid symptoms and relationships with task performance. Eight patients were taking medication (aripiprazole = 2; risperidone = 2; sulpiride = 1; clonidine = 1; paroxetine = 1; and citalopram = 1).

The study was approved by the local National Health Service Research Ethics Committee, and all participants gave written informed consent. Both patients and control subjects completed the beads task and executive tasks in pseudorandomized order. For patients with Tourette syndrome, their treating consultant provided an assessment of tic severity, and patients completed scales assessing OCD and ADHD.

Tasks and Symptom Scales

Beads Task.⁸

Participants were shown two jars, one with 60% blue beads and 40% white and the other jar with the colors in opposite proportions (60% white and 40% blue). The jars were then obscured from view. The experimenter removed beads from one jar, one-by-one. The participant was asked to keep a written record of the color of the beads they had seen. After each bead was shown, they were asked to decide if they wanted to see another bead or were ready to decide which jar (mostly blue/mostly white) all beads were coming from. The sequence of beads drawn was preset (e.g., blue, white, white, etc.) and identical for all participants. Scores reflect the number of bead draws to decision (DTD).

FAS Test.⁹

This standard executive task involved generating as many different words as possible in 1 minute beginning with a given letter. Scores were totaled for the letters F, A, and S. Names of people were not allowed.

Digit Ordering Test—Adapted.¹⁰

The experimenter read strings of three to eight digits in a mixed order that had to be spoken back in ascending order. Scores represent the longest string responded to correctly.

Hayling Test.¹¹

For the baseline condition, the experimenter read sentences that cue a final word, and participants were asked to complete each sentence with an obvious word. For the test condition, the sentences still cued particular words, but participants were asked to avoid saying the word that seems most obvious and use a different word. Inhibition was assessed by comparing time and error differences across conditions.

Yale Global Tic Severity Scale.¹²

Tics were rated in terms of number, frequency, intensity, complexity, and interference. Here we used only the total tic scale score and not the more subjective impairment score.

Obsessive Compulsive Inventory—Revised.¹³

This scale was used to assess the severity of obsessive-compulsive symptoms, and scores range from 0 to 72.

Adult ADHD Self-Report Scale.¹⁴

We used the ADHD Self-Report Scale subscale recommended for diagnosing ADHD, and scores can range from 0 to 24.

Results

Nonparametric analyses were appropriate given group sizes and distributions. The groups did not differ for age or education. Task and scale scores are shown in Table 1, along with the results of between-group comparisons. Patients with Tourette syndrome selected significantly fewer beads than control subjects before making a decision on the beads task (DTD score was lower). Both groups made no errors on the Hayling Test, but patients did exhibit inhibitory deficits in comparison to control subjects according the Hayling Task time measures. There were no group differences for verbal fluency or working memory measures.

Within-group comparisons investigated correlations between beads task DTD, executive tasks, and symptom scales, indicating that OCD symptoms (Sr = −0.457, p=0.019) and ADHD symptoms (Sr = −0.709, p=0.007) were negatively related to DTD. Beads task selections were not significantly related to tic symptoms, education, or any other executive measure.

Discussion

This controlled study investigated probabilistic reasoning on the beads task in Tourette syndrome. When compared to controls, patients showed a tendency to select fewer beads before making a decision, indicating a possible JTC bias. There were limited differences between the groups for executive functions, and as shown in previous studies,¹ there was only a mild deficit in inhibition in Tourette syndrome. It is therefore unlikely that broader cognitive impairments such as memory difficulties can explain the group difference on the beads task. Indeed, there were no relationships between DTD on the beads task and executive performance in Tourette syndrome.

Significant relationships were apparent between DTD and symptoms of OCD and ADHD, such that when these symptoms were more severe, fewer beads were needed before patients made a decision. There was no relationship with tic severity. However, this measure was clinician rated, whereas the Obsessive Compulsive Inventory—Revised and ADHD Self-Report Scale were self-report. One previous study¹⁵ reported a difference between patients with delusions and controls on the beads task, but not between patients with OCD and control subjects. However, our findings imply that the tendency to JTC in Tourette syndrome is likely to be related to impulsivity and/or compulsivity.

Taking together the beads task performance of patients with Tourette syndrome and patients with schizophrenia, a link between dopamine dysregulation and JTC seems all the more likely. Interestingly, schizotypal traits also appear to be overexpressed in Tourette syndrome and can be related to OCD.¹⁶ A JTC bias in Tourette syndrome could have implications in other areas of reasoning including social cognition.²

The limitations associated with the current study include the relatively small sample of patients from one specialist clinic; therefore, further work is needed to establish whether the tendency to JTC in TS is a robust effect. It is also difficult to draw comparisons with other studies as there are often variations in how the beads task is designed (e.g., the proportions of different colors and sequence of beads drawn).

In conclusion, patients with Tourette syndrome exhibit a possible bias toward JTC on a probabilistic reasoning task. This appears to be linked to the presence of impulsive and compulsive traits rather than tics or executive deficits. Future studies should investigate this task in larger samples of patients without symptoms of OCD or ADHD and evaluate the possible contribution of dopamine dysregulation.