A Comparison of Urge Intensity and the Probability of Tic Completion During Tic Freely and Tic Suppression Conditions

Abstract

Tic-suppression-based treatments (TSBTs) represent a safe and effective treatment option for Chronic Tic Disorders (CTDs). Prior research has demonstrated that treatment naive youths with CTDs have the capacity to safely and effectively suppress tics for prolonged periods. It remains unclear how tic suppression is achieved. The current study principally examines how effective suppression is achieved and preliminary correlates of the ability to suppress tics. Twelve youths, ages 10 to 17 years, with moderate-to-marked CTDs participated in an alternating sequence of tic freely and reinforced tic suppression conditions during which urge intensity and tic frequency were frequently assessed. Probability of tics occurring was half as likely following high-intensity urges during tic suppression (31%) in contrast to low-intensity urges during tic freely conditions (60%). Age was not associated with ability to suppress. Intelligence indices were associated with or trended toward greater ability to suppress tics. Attention difficulties were not associated with ability to suppress but were associated with tic severity. In contrast to our “selective suppression” hypothesis, we found participants equally capable of suppressing their tics regardless of urge intensity during reinforced tic suppression. Tic suppression was achieved with an “across-the-board” effort to resist urges. Preliminary data suggest that ability to suppress may be associated with general cognitive variables rather than age, tic severity, urge severity, and attention. Treatment naive youths appear to possess a capacity for robust tic suppression. TSBTs may bolster these capacities and/or enable their broader implementation, resulting in symptom improvement.

Keywords

tic suppression Tourette’s urges tics

Chronic tic disorders (CTDs) are neuropsychiatric conditions that arise in early childhood and are believed to result from dysfunction in the sensory-motor, cortico-striato-thalamo-cortical (CSTC) tracts (Singer, 1997). CTDs are characterized by the presence of involuntary motor and vocal tics (i.e., brief, repetitive movements and/or vocalizations). The landmark comprehensive behavioral intervention for tics study (CBIT; Piacentini et al., 2010) re-envisioned a long extant, yet neglected behavioral approach called Habit Reversal Training (HRT; Azrin & Nunn, 1973) as a central component of a safe and effective non-pharmacological treatment for CTDs. Tic-suppression-based treatments (TSBTs), including CBIT and exposure and response prevention (ERP), hinge on creating effective suppression of tics for prolonged periods. ERP encourages individuals to refrain from ticcing while utilizing cognitive coping strategies to endure (Verdellen et al., 2008), whereas CBIT encourages the use of incompatible behaviors to refrain (Piacentini et al., 2010). Prior research has shown that youth with CTDs can effectively and safely suppress their tics (Piacentini et al., 2010; Specht et al., 2013); however, the pretreatment ability to suppress tics and possible correlates of such ability in TSBT naive individuals has not yet been directly investigated. Examining the ability to suppress tics may yield important clues regarding how tic suppression is achieved through TSBTs. The current study builds on prior research and principally examines the question of how effective suppression is achieved by examining patient demographic, clinical, and cognitive variables related to the ability to suppress in TSBT naive youth.

In addition to tics, most individuals with CTDs who are above the age of 10 years report the presence of accompanying unpleasant somatosensory experiences that precede tics. These sensations are often referred to as “premonitory urges” (Leckman, Walker, & Cohen, 1993; Woods, Piacentini, Himle, & Chang, 2005). Many affected individuals also report that tic completion results in rapid, but not lasting, termination of the unpleasant urge; conversely, not ticcing results in an increase in urge severity (Leckman et al., 1993). As a result of such reports, it has been hypothesized that tics are maintained and exacerbated via a negative reinforcement cycle. Furthermore, it has been proposed that TSBTs serve to interrupt this cycle and allow habituation to the urge to occur, in turn resulting in lasting reductions in tic severity. Despite the important implications of hypotheses with respect to behavioral theory regarding tics, direct examination of the relationship between urges and tics has been largely neglected in the literature. The relationship between urges and tics when ticcing freely and when suppressing tics in treatment of naive youth offers the promise of yielding important insights regarding how TSBTs reduce CTD severity.

TSBT naive children and adolescents appear to have varying capacity to suppress tics, without instruction, for prolonged periods in an environment that differentially reinforces tic suppression (Himle, Woods, Conelea, Bauer, & Rice, 2007; Specht et al., 2013; Verdellen et al., 2008). One study provided evidence to support the negative reinforcement hypothesis of tic maintenance and suggested that, for some youth, urge severity was low when children were allowed to tic freely and comparatively higher when tics were suppressed (Himle et al., 2007). Results of a subsequent study that examined urge ratings during and across sessions of ERP for tics indicated a contradictory pattern with no initial increase in urge severity when tics were suppressed (Verdellen et al., 2008). To further complicate the matter, a tightly controlled study of the effects of tic suppression unexpectedly suggested that urge intensity remained relatively stable, irrespective of whether participants ticced freely, or suppressed tics (Specht et al., 2013). Therefore, the negative reinforcement hypothesis of tic maintenance remains an issue.

Despite the lack of clear evidence in support of the negative reinforcement hypothesis, examination of the hypothesis that tic suppression allows for habituation to the urge has continued. While there is support for the notion that habituation to the premonitory urge occurs within and across ERP session for tics (Verdellen et al., 2008), a non-treatment study that assessed urge severity at more frequent intervals and attempted to control expectancies showed that urges neither increased during initial tic suppression nor decreased with prolonged (40 min) suppression (Specht et al., 2013). Together, these studies suggest a more complex relationship between urges and tics.

Given the previously mentioned research, there appears to be at least three possibilities regarding how tic suppression is achieved. One possibility is that tic completion is immediately reinforcing and tic suppression is difficult and/or aversive, at least initially (Himle et al., 2007). Perhaps the contingent delivery of reinforcement when tics are successfully suppressed for brief periods is necessary to produce sufficient motivation to override the urge to tic. A second possibility is that suppressing tics may have more proximal, but modest intrinsic reinforcing properties. This possibility is supported by data showing no initial increase in the premonitory urge but a gradual, albeit modest, tapering of urge intensity (Verdellen et al., 2008). One final possibility is that there is no intrinsic reinforcement for tic completion or suppression. This possibility is supported by results from one study indicating that urges did not change when tics were completed or were effectively suppressed (Specht et al., 2013). Therefore, motivation for overriding urges to tic may rely solely on extrinsic reinforcement to create effective tic suppression. Considered together, all three possibilities suggest no immediate robust intrinsic reinforcement properties associated with suppression of one’s tics.

In light of the fact that individuals can achieve robust tic suppression without apparent intrinsic benefit, it may be the case that participants in previous studies selectively suppressed or refrained from responding to less-intense (compelling) urges while continuing to tic in response to more intense urges. Therefore, TSBTs may achieve reduction in total tic frequency by creating sufficient incentive for individuals to selectively suppress tics in response to only low-intensity urges while continuing to tic following more intense urges. Another possibility is that reduced tic frequency is achieved because, with sufficient incentive, individuals are capable of suppressing tics irrespective of urge intensity. That is, individuals non-selectively attempt to suppress all tics. Determining whether tic suppression in TSBT naive youths is selective or non-selective with respect to urge severity will inform whether TSBTs should encourage patients to suppress all tics or only those prompted by less-intense urges.

While the precise neurological mechanisms that allow for tic suppression are not known, tic suppression in accordance with HRT principles requires individuals to learn to continually monitor their internal bodily environment for premonitory urges. Then, based on the topographical location of the urge and corresponding tic, individuals must select and enact an appropriate motor sequence to suppress the tic. These motor sequences are termed competing responses, as they are generally incompatible with tic completion. In addition, competing responses must be discrete and ideally allow for persisting with the task at hand (e.g., attending to a teacher’s instruction) while “riding out” the premonitory urge, like a surfer gracefully riding a wave to the beach. Therefore, effective tic suppression can be theoretically considered an attention-demanding task (Conelea & Woods, 2008) that also relies on declarative memory.

Research to date has demonstrated no consistent neurocognitive profile for individuals with uncomplicated CTDs. Attention and executive functioning deficits have been largely limited to individuals with complicated CTD, particularly with comorbid Attention Deficit Hyperactivity Disorder (ADHD) and Obsessive Compulsive Disorder (OCD; Chamberlain, Blackwell, Fineberg, Robbins, & Sahakian, 2005; Osmon & Smerz, 2005). Phenomenological studies suggest a strong trend toward reduced tic severity in the post-pubescent period, which is believed to reflect neurodevelopmental maturation (Church et al., 2009; Mink, 1996) and/or compensation (Mueller, Jackson, Dhalla, Datsopoulos, & Hollis, 2006). Cognitive control, broadly defined as cognitive processes that collectively allow for selecting goal-directed behaviors, has received increased attention with respect to the notion of neurodevelopmental compensation via the lateral prefrontal cortex. In addition, evidence of an association between deficits in procedural learning and increased tic severity, despite intact declarative learning in children and adults with Tourette’s disorder (TD; Marsh et al., 2004) also has possible implications for the notion of neurodevelopmental immaturity and compensation. Together, these lines of research may partially explain how TSBTs create lasting reductions in tics, through encouraging maturation and/or compensation.

Contrary to initial speculation, individuals with CTDs actually out-performed age-matched peers on cognitive control tasks (Jackson, Mueller, Hambleton, & Hollis, 2007; Mueller et al., 2006). Emerging evidence has also demonstrated that faster task switching and response selection were associated with less tic severity (Baym, Corbett, Wright, & Bunge, 2008). It has been suggested that increased cognitive control may be the long-term consequence of efforts by CTD affected youths to suppress tics (Baym et al., 2008; Jackson et al., 2007; Mueller et al., 2006). Therefore, the ability to suppress tics, as opposed to tic severity, may be a better phenotypic behavioral marker of compensatory cognitive control in youths with CTDs.

Prior research has demonstrated intact declarative (what), but poorer procedural (how) memory and association with increased tic severity in individuals with TD compared with healthy controls (Marsh et al., 2004). Therefore, TSBTs may capitalize on intact declarative memory to compensate for deficits in procedural memory. That is, TSBTs may rely centrally on teaching affected individuals what to do to suppress one’s tics, in compensation for a system with a neurodevelopmentally immature procedural how memory. To our knowledge, there has been no exploration of the relationship between the pretreatment ability to suppress tics and neurocognitive variables in TSBT naive individuals. Examining the relationship between the ability to suppress and developmental and phenomenological considerations (e.g., age, tic severity, urge severity) may have important phenomenological implications. For instance, an association between increased age and an increased ability to suppress tics would provide direct support to the neurodevelopmental maturation and compensation hypotheses. In addition, examining the relationship between neurocognitive variables (e.g., attention, cognitive abilities) and ability to suppress may provide important insights regarding how TSBTs work. For example, if verbal intelligence is associated with the increased ability to suppress, it would suggest that tic suppression may be a task that relies on declarative what memory.

The primary purpose of the current study was to build on prior research by examining how robust, stable tic suppression is achieved in youths naive to TSBTs (Specht et al., 2013). Specifically, because individuals with tics often report that their tics are both involuntary and prompted by unpleasant premonitory urges (Leckman et al., 1993), we hypothesized that when participants were told to “tic freely,” the urge-tic ratio would be nearly 1:1, therefore tic completion would be equally likely regardless of reported urge intensity (low, medium, or high). In addition, because previously published data on the same sample suggested robust, stable reductions in tics during tic suppression (Specht et al., 2013), we hypothesized that the probability of tic completion would be significantly lower for all reported urge intensity ratings (i.e., low, medium, and high when contrasting “tic suppression” vs. “tic freely” conditions for each). For example, contrasting the probability of a tic occurring following a low urge rating for tic freely versus tic suppression (i.e., Low Urge/Tic Freely vs. Low Urge/Tic Suppression). Finally, given the “quasi-volitional” nature of tics (Leckman et al., 1993), we hypothesized that participants would selectively suppress tics, such that tic suppression would be significantly easier and thus tic completion would be significantly less likely following low and medium urge intensities in contrast to high urge intensity.

In addition to the aforementioned hypotheses, we explored potential correlates of the ability to suppress tics (tic control) to evaluate its potential as a behavioral marker of cognitive control in affected youth. Given the remitting course of CTDs in the post-pubescent period and associated decreases in tic severity with age (Church et al., 2009), we hypothesized that age would be positively correlated with the ability to suppress. To explore if the ability to suppress tics might mirror findings regarding cognitive control and tic severity (Baym et al., 2008), we hypothesized that tic severity would be inversely correlated with the ability to suppress. Because individuals with CTDs report completing tics to terminate unpleasant premonitory urges (Leckman et al., 1993), we hypothesized that urge intensity would be negatively correlated with increased ability to suppress. Finally, given that active tic suppression theoretically demands attention resources (Conelea & Woods, 2008) and that it likely requires recruitment of declarative memory to compensate for procedural memory deficits and CSTC dysfunction (Baym et al., 2008), we hypothesized that verbal intelligence measures would be positively correlated with increased ability to suppress and that better performance on a neurocognitive measure of sustained attention would be positively correlated with increased ability to suppress tics.

Method

The current study includes follow-up analyses from a previously reported study (Specht et al., 2013). Therefore, the methods described below, while substantially edited, are fundamentally identical to those previously reported with the exception of the data analysis section.

Participants

Children and adolescents (ages 10-17 years) were recruited at Johns Hopkins University, School of Medicine (JHMI) and the University of Wisconsin–Milwaukee (UWM) via clinician referrals, fliers posted on bulletin boards, community seminars, and regional Tourette Syndrome Association newsletters.

Participant eligibility requirements included being generally healthy males or females who met the Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.; DSM-IV-TR; American Psychiatric Association, 2000) diagnostic criteria for a primary CTD (i.e., TD or chronic motor or vocal tic disorder), as diagnosed by a clinical psychologist or psychiatrist. All participants (a) had moderate to severe tic severity determined by a total score of ≥14 for both motor and vocal tics or ≥ 10 for only motor or vocal tics on the Yale Global Tic Severity Scale (YGTSS; Leckman et al., 1989); (b) had no history of more than 3 weeks of treatment for tics in which suppression strategies were a primary component; (c) possessed low-average range or better intellectual functioning defined by a two-scale score of ≥75 on the Wechsler Abbreviated Scale of Intelligence (WASI; Psychological Corporation, 1999); (d) reported the presence of noticeable premonitory urges as indicated by a score of ≥12 on the Premonitory Urge for Tic Scale (PUTS; Woods et al., 2005); (e) were currently exhibiting one or more motor and/or vocal tics at a rate of at least one tic per minute, assessed via 10-min videotaped observation. Severe oppositional defiant disorder or conduct disorder, determined by a clinician severity rating of ≥4 on the Anxiety Disorders Interview Schedule–Research Lifetime Version (ADIS; Silverman & Albano, 2002), were exclusionary. Otherwise, comorbidities (e.g., OCD, ADHD) were not necessarily exclusionary provided all other eligibility requirements were met. Pharmacological tic and/or urge suppression would unnecessarily confound results; therefore, potential participants were excluded if they reported a current regimen that included (a) antipsychotics, (b) anti-hypertensives, (c) benzodiazepines, or (d) selective serotonin reuptake inhibitors.

Materials

Materials utilized to evaluate tic suppression and premonitory urge intensity (also see Specht et al., 2013) were adapted from Woods and Himle (2004) and Himle et al. (2007) and included a tic detector, urge thermometer, computer monitor, and audiovisual recording equipment. During all study conditions, participants sat alone in a room and were situated in front of the tic detector and urge thermometer, while two research assistants were inconspicuously located behind a one-way observation mirror in an adjacent room with the audiovisual recording equipment and the tic detector control unit.

Tic detector

The tic detector is an electronic token dispenser contained within a rectangular box. It has two white lights adjacent to a plastic receptacle attached to the front to gather dispensed tokens. Participants were told that the tic detector, which had a nonfunctioning webcam mounted atop, had the ability to monitor and count tics. They were also told that when the two lights on the front of the tic detector were illuminated, it had begun to count their tics. This deception was necessary in that it allowed research assistants to monitor and count tics while operating the token dispenser without influencing the participant and unnecessarily confounding data, as direct observation may have led to altered tic expression. Parents were aware of this deception and its rationale prior to consenting. After completing the study, the deception was thoroughly explained and demonstrated to the child along with the parent(s), and all children signed a debriefing form providing assent for the researchers to use their data in the study.

Urge thermometer

The urge thermometer is a rating scale adapted from the “feelings thermometer” from the ADIS (Silverman & Albano, 2002), which was automatically presented at 10-s intervals via Microsoft PowerPoint on a computer screen located to the left of the tic detector. During all conditions, urge ratings (URs) were verbally indicated by participants when prompted by the appearance of the urge thermometer on the screen. Responses were recorded with audiovisual equipment, which included a microphone located in front of the computer monitor. The scaling consists of the numbers 0 to 9 with 10 corresponding ascending bars and qualitative descriptions for each number (i.e., “0” = “no urge at all” to “9” = “very, very strong urge”) to indicate urge intensity. To ensure participants’ understanding of the urge thermometer, theoretical urge descriptions were provided prior to experimental conditions for which participants reported theoretical URs within three points of predetermined URs.

Previous studies have used longer intervals (30 s) between UR reports to reduce the possibility that movement required to verbally report ratings may result in or disguise tic symptoms; however, reporting URs did not appear to elicit or obscure tic symptoms (Himle et al., 2007). In the current study, shorter, 10-s intervals allowed for urges to be assessed within each 15-s segment of tic presence or absence. This allowed for a more accurate assessment of the relationship between urge intensity during intervals in which a tic did or did not occur.

Audiovisual equipment

A video camera, located behind a one-way mirror, was used to record participants during all experimental conditions. A microphone located in the room with the participant was used for audio recording. All audiovisual equipment was operated by two research assistants in the room behind the one-way mirror.

Procedure

Eligible participants were identified via phone screen and subsequently completed study procedures on two separate occasions, approximately 1 week apart.

Visit 1: Assessment

During the first visit, participants and their parents provided informed assent and consent and completed: (a) demographics, medical history, medication history, and behavioral treatment history form; (b) the ADIS (Silverman & Albano, 2002); (c) the YGTSS (Leckman et al., 1989); (d) the WASI (Psychological Corporation, 1999); (e) the PUTS (Woods et al., 2005); (f) the Conners’ Continuous Performance Test, Version II (CPT-II; Conners & Staff, 2000); (g) the verbal confirmation from parent and child to establish sufficient tic rate (at least one tic per minute). This series of assessments is consistent with the procedures in Himle et al. (2007), and they have been shown to be the best-available diagnostic and evaluation methods for CTDs and psychological comorbidities in children.

Visit 2: Experimental conditions

The second visit consisted of an ABABA reversal design during which the children participated in an altering sequence of two conditions: a 10-min baseline (BL) control, or tic freely period, and a 40-min differential reinforcement of zero-rate behavior (DRO), or tic suppression period. The entire sequence was 110 min long and consisted of three BL periods and two DRO periods (BL1-DRO1-BL2-DRO2-BL3).

In addition to verbal confirmation of tic frequency from parent and child, a 10-min videotaped observation was done as part of the initial experimental condition to ensure the participant exhibited one tic per minute.

Baseline (BL)

During the BL conditions, participants sat across from the tic detector and were instructed to “tic freely,” as much or as little as needed. The lights were not illuminated on the tic detector indicating that it was not monitoring tics. Tokens were not dispensed during BL conditions. Participants were instructed to state aloud their URs (from 0-9) when prompted by the appearance of the urge thermometer on the computer screen at 10-s intervals.

DRO

During DRO conditions, participants were asked to suppress all tics. They were not provided any instructions regarding how to suppress tics and were told they only needed to remain seated in their chair and facing the tic detector. They were told that when the lights were illuminated on the tic detector, it had begun to count their tics. Again, participants stated aloud their URs when prompted by the appearance of the urge thermometer. They were told that a token would be dispensed into the receptacle for each 15-s period in which they did not complete a tic. Participants were told they could exchange tokens for money or a gift card following the experiment. In actuality, all participants received the same remuneration regardless of their performance. Once one research assistant explained the instructions and left the participant’s room, the other research assistant simultaneously began the timer and turned on the tic detector lights indicating that the detector had begun to count tics.

Reinforcement delivery

To properly dispense tokens, the research assistants utilized a list of operational definitions of tics specific to each child. These definitions were established by the child, parents, and principal investigator via the YGTSS during the first visit and were reviewed by the child and research assistants prior to beginning experimental procedures and during the 10-min video observation during the second visit. Because there was no clock in the room with the participant, he or she was unaware of precisely how much time had elapsed between tics and tokens; therefore, he or she was unable to knowingly suppress tics just long enough to receive a token after each 15-s period.

Manipulation checks and accuracy evaluations

To ensure participants understood and followed instructions, manipulation checks were conducted before and after each of the five conditions. Following each of the two DRO periods, an accuracy evaluation was completed to establish the participant’s perceived accuracy of the tic detector. This accuracy rating was on a scale from 1 to 5 (i.e., 1 = not accurate at all to 5 = extremely accurate). For both DRO periods, all participants rated the tic detector as “somewhat” accurate or better. In fact, 71% of participants rated the tic detector as “very” or “extremely” accurate during the first DRO period, and 86% of participants said it was “very” or “extremely” accurate during the second DRO period.

Data Collection

Age was calculated based on date of birth collected from the demographics form and the date of the visit two. The WASI (Psychological Corporation, 1999) is a psychometrically sound intelligence assessment with norms for administration of two subscales. The two subscales’ scores were used as the best estimate of overall intellectual functioning (full scale IQ; FSIQ). The two subscales’ scores consist of the vocabulary and matrix reasoning subtests, resulting in verbal IQ (VIQ) and performance IQ (PIQ) scores. The CPT-II (Conners & Staff, 2000) is a computer-based test of sustained attention and provides indexes of inattention (omission errors) and impulsivity (commission errors). The CPT-II possesses adequate internal consistency and reliability (Conners & Staff, 2000).

All videotapes for each condition were coded for the presence of tics using the Multi-Option Observation System for Experimental Studies computer program, which provides a timestamp corresponding to the occurrence of an event (i.e., a tic or an urge rating). The tapes were first coded for tics per minute (TPM), URs, and the number of tokens rewarded. The tapes were then coded again for URs and a dichotomous “yes” or “no” for tic completion within 15-s intervals. If two URs occurred within the same interval, the average of the two ratings was coded; however, the majority of consecutive URs were the same.

Quality Assurance

Identical experimental procedures were utilized at both JHMI and UWM. Quality assurance between the two sites was achieved via post hoc examination of videotapes by the principal investigator. Inclusion and exclusion decisions were discussed via teleconference and were ultimately made by the principal investigator. All data were analyzed at JHMI.

Inter-Rater Reliability

Two research assistants independently coded all videotaped sessions. Procedures for inter-rater reliability followed those in Piacentini et al. (2006) and Himle et al. (2006). These studies suggest high within-site inter-observer agreement for the event-frequency method (M = .76, r = .58-.99; Himle et al., 2006).

For calculations, all conditions were divided into 10-s segments and the number of tics coded by each research assistant was counted. For each segment, the lower of the two numbers of tics counted was divided by the higher number and multiplied by 100. Then, the average agreement of the segments for each subject was determined.

Videotapes were re-coded by both research assistants for those conditions with low inter-rater reliability (<65%). To improve subsequent accuracy, both research assistants first watched these tapes together to identify specific tics and resolve discrepancies about the presence of tics. Once tics were agreed on, each research assistant independently re-coded the conditions.

The principal investigator evaluated videotapes for correct implementation of study protocol and participant compliance to ensure the consistency of procedure and independent variable integrity.

Data Analysis

In this study, the independent variables were chronological age, tic severity (YGTSS Total Tic Severity Score), urge severity (PUTS), general intelligence (WASI FSIQ), verbal abilities (WASI VIQ), nonverbal abilities (WASI PIQ), attention/concentration abilities (CPT-II Clinical Confidence Index), condition (BL or DRO), and urge intensity ratings. Urge intensity ratings were classified into three categories based upon severity: low severity (0-3), medium severity (4-6), and high severity (7-9). Dependent variables were tic probability and ability to suppress.

All analyses were performed using IBM SPSS Statistics for Windows, Version 19.0 or, when indicated, STATA 9 (StataCorp, 2005).

Tic probability

Tic probability was calculated by first determining if a tic occurred (yes = 1) or did not occur (no = 0) during the subsequent 15-s interval. For each participant, tic probability was calculated by summing the 15-s intervals in which a tic occurred and dividing by the number of intervals subsumed in each urge intensity category (low, medium, high) and condition (BL and DRO). As a result, each participant had six tic probability scores (i.e., BL: Low, Medium, High and DRO: Low, Medium, High). Paired-samples t tests were used to examine tic probability within each condition across urge severity levels (low, medium, and high). This data analytic strategy was used because the sphericity assumption of ANOVA was violated. Paired-samples t tests were also used to determine significant differences in tic probability between conditions (BL vs. DRO) for each urge severity level. The non-parametric test of trend (nptrend) was used to evaluate if there was a significant trend across the levels of urge intensity separately for BL and DRO conditions.

Ability to suppress

To measure each participant’s ability to suppress, TPM were first calculated by dividing the number of tics observed within each condition by the duration of the interval sampling period (i.e., TPM = # tics / time). Each participant then received an ability to suppress score, which was calculated with the following equation: ([DRO tics per minute / BL tics per minute] − 1) × − 1. Pearson product–moment correlations were used to examine the relationship between the ability to suppress and age, general intelligence, verbal abilities, nonverbal abilities, and attention/concentration abilities.

Results

Clinical Characteristics

Fifteen participants were enrolled in the current study. One participant passed the initial screen, but was subsequently determined to be ineligible because he did not exhibit at least one tic per minute. Two participants did not complete all experimental conditions due to equipment malfunctions.

Twelve (n = 12) participants ages 10 to 17 years (M = 13.77 years, SD = 2.25, median = 13.91) ultimately completed and tolerated all study procedures and were used in the following analyses (unless otherwise indicated). Visits occurred approximately 12 days apart (M = 11.60, SD = 9.35). Average inter-rater agreement was high (M = 78%, range = 65%-90%). Participants were mostly upper-middle-class Caucasian (83%) males (ratio 11:1) who met DSM-IV-TR TD criteria (91%). Participants reported moderate-to-marked (Leckman et al., 1989) tic severity (YGTSS Total Tic Score M = 27.67, SD = 8.78; Total Score M = 55.00, SD = 14.28), with tics occurring at a rate in excess of one per minute and with noticeable premonitory urges (PUTS Total Score M = 24.67, SD = 4.82). None had previously received behavioral treatments in which tic suppression was a component.

Psychiatric Comorbidity

Common co-occurring psychiatric conditions included ADHD (18%), OCD (18%), and specific phobia (18%). Less common diagnoses included moderate oppositional defiant disorder (8%), social anxiety disorder (8%), separation anxiety disorder (8%), enuresis (8%), and learning disability (8%). One of the two children who met DSM-IV-TR criteria for ADHD was adhering to a psychostimulant medication regimen.

Cognitive Variables

In cases of missing data, participants were excluded from the following analyses. Participants (n = 10) were of slightly above average intelligence (WASI FSIQ M = 109.25, SD = 10.28). There were no significant differences between the WASI Vocabulary T-score (M = 56.50, SD = 7.99) and Matrix Reasoning T-score (M = 54.80, SD = 7.63), t(9) = 0.59, p = .57.

Participants (n = 9) demonstrated performance profiles more consistent with ADHD youths (CPT-II Clinical Index scores M = 57.32%, SD = 15.31) and were equally likely to commit errors of commission (CPT-II commission error T-score M = 52.45, SD = 11.84) as omission (CPT-II omission error T-score M = 48.98, SD = 5.60), t(8)= −0.89, p = .40.

Primary outcome: Relationship between urge intensity and ability to suppress tics

Paired-samples t tests were used to examine differences in tic probability between BL and DRO for each urge intensity category (low, medium, high). There were significant differences between BL and DRO with respect to low, t(11) = 5.28, p < .001; medium, t(11) = 7.32, p < .001; and high, t(11) = 3.94, p < .01, urge severities (see Figure 1).

Figure 1.

Average percentages of tic probabilities within each urge severity category (low = 0-3, medium = 4-6, high = 7-9) during aggregated conditions (BL = baseline, DRO = differential reinforcement of zero-rate behavior).

During BLs, there was no significant difference between the probability of a tic occurring following medium or high urge intensity ratings, t(11) = −0.02, p = .98. The probability of a tic occurring following low-intensity urges was significantly lower (M = 59.6%, SD = 25.3%) than following medium intensity urges (M = 76.2%, SD = 20.9%); t(11) = −2.59, p < .05. While tic probability following low urge intensity in contrast to high intensity (M = 76.5%, SD = 30.2%), was not statistically significant, t(11) = −1.43, p = .18, there was a significant increasing non-parametric trend regarding probability of a tic occurring for low (rank = 161), medium (rank = 245), and high (rank = 261) urge intensities (z = 1.96, p < 0.05).

During DRO conditions, the probability of a tic occurring did not vary across low (M = 24.5%, SD = 15.6%) and medium (M = 29.1%, SD = 20.1%), t(11) = −0.77, p = .46, urge ratings, nor low and high (M = 30.9%, SD = 30.1%); t(11) = −1.30, p = .22, urge ratings. Likewise, there was no significant difference between the probability of a tic occurring following medium or high urge intensity ratings, t(11) = −1.23, p = .24. The non-parametric trend regarding probability of a tic occurring for low (rank = 199), medium (rank = 218), and high (rank = 249) urge intensities (z = 0.97, p = .33) was not significant.

Secondary outcomes: Predictors of ability to suppress tics

Percent reduction in TPM between BL and DRO conditions was used as an indication of ability to suppress. Participant ability to suppress was robust with a dramatic decrease in TPM during DRO conditions (M = 74.8%, median = 78.7%, SD = 19.28%, range = 36%-97%). Counter to our hypotheses age, tic severity, and urge severity were not correlated with ability to suppress. However, the WASI VIQ score was associated with a greater ability to suppress, r(8) =.65, p < .05, whereas the WASI two-scale FSIQ score, r(6) = .69, p = .058, and WASI PIQ score, r(8) = .56, p = .09, approached significance.

Counter to our hypotheses, variables of attention (inattention and impulsivity) assessed via the CPT-II, were not associated with ability to suppress. However, the Clinical Confidence Index was correlated with increased YGTSS tic severity, r(8) = .75, p < .05.

Discussion

Despite the demonstrated efficacy and safety of TSBTs for CTDs, they remain underutilized. Underutilization is partially driven by questions regarding the mechanism by which TSBTs produce durable tic reduction. Previously reported data, obtained from the same sample used in the current study, explored if TSBT naive youths can effectively and safely suppress their tics. Results from that study demonstrated that participants achieved a robust, stable reduction in tic frequency (72%) for prolonged periods (i.e., 40 min) when contingently reinforced for effective tic suppression. The current study builds on that prior study and was designed to address the important remaining question regarding factors related to successful tic suppression, which has important phenomenological and treatment implications.

Given the quasi-volitional nature of tics, we hypothesized that youth with tics might adopt a strategy of selectively suppressing tics associated with less-intense (i.e., less compelling) urges, while continuing to tic in response to more intense urges. Considering the robust and stable tic suppression previously reported (Specht et al., 2013), tic probably was significantly lower when participants were contingently reinforced for effective tic suppression. Contrary to our “selective suppression” hypothesis, however, we found that participants were equally effective in suppressing tics regardless of urge intensity during the reinforced tic suppression condition. In addition, tics were much less likely to occur following the highest intensity urges during tic suppression (≈31%) in contrast to the lowest intensity urges during tic freely conditions (≈60%). We did, however, find some evidence for selective suppression or, alternatively, preferential responding, during “tic freely” conditions. There was a trend such that participants were significantly less likely to respond to low-intensity urges (≈60%) in contrast to medium- or high-intensity urges (≈76%). This trend suggests that there may be a significant association between urge intensity ratings and tics.

While the current findings were achieved in a well-controlled experimental paradigm and may have limited generalizability outside the lab, they do suggest that when ticcing freely, youth with tics are less compelled to tic in response to low-intensity urges and more compelled to tic in response to high-intensity urges. In stark contrast, the present study demonstrated that youths are able to withhold tics regardless of urge intensity when contingently reinforced for tic suppression. This finding, when considered with evidence that tic suppression may not be intrinsically reinforcing, at least not initially, demonstrates an ability to suppress with extrinsic reinforcement irrespective of urge intensity.

Given that there is relatively high variability in the degree to which children were able to suppress their tics (range = 36%-97%), we also explored developmental and neurocognitive correlates of the ability to suppress. Although we appreciate the limitations of small samples, the current study is, to our knowledge, the first to examine possible correlates of the ability to suppress tics in TSBT naive youths. Contrary to our hypotheses, the current findings preliminarily suggest that age, urge and tic severity, as well as attention/concentration, are not be associated with the ability to suppress one’s tics in an environment that reinforces tic suppression. Interestingly, consistent with prior research regarding cognitive control (Baym et al., 2008), higher tic severity in the current study was associated with poorer attention/concentration.

As hypothesized, increased capacity to suppress tics was associated with measures of VIQ. Considered in conjunction with prior research demonstrating intact declarative memory, but procedural memory deficits, in individuals with TD compared with healthy controls (Marsh et al., 2004), these suggest that, theoretically, TSBTs might capitalize on intact declarative what memory to compensate for deficits in procedural how memory. However, these findings are very preliminary and will require additional exploration with larger samples and more specific neurocognitive measures of verbal abilities.

This study represents a lock-step in a line of research examining the relationship between urges, tics, and the capacity to suppress tics. The strength of this study rests on its careful assessment of urges and tics in tightly controlled and alternating conditions. Moreover, a concerted effort was made to control the effects of gender, ethnicity, medication, and comorbidity through recruitment and screen procedures. However, given its relatively small sample size, conclusions reached may not be directly generalizable to all individuals with CTDs. Although one of the strengths of this study was the use of relatively short coding intervals (15 s) in comparison with similar studies, the use of dichotomous, yes or no coding of tic completion is a limitation. Because we used a dichotomous (“yes”/“no”) rather than a frequency count of tics during each coding interval, the current findings do not necessarily rule out a direct link between urge intensity and tic frequency. This possibility will require additional investigation.

Although the current study suggests that youths are equally capable of suppressing tics in the moments following urges regardless of intensity, there are limitations associated with our assessment of urge intensity. Despite the fact that most individuals with CTDs above the age of 10 years report experiencing premonitory urges as unpleasant, varying in intensity, and preceding tics (Leckman et al., 1993), biological markers of the presence and intensity of premonitory urges have not yet been established. In lieu of the direct physiological assessment of premonitory urges, as is often the case with psychological constructs, we utilized a well-established self-report methodology to assess premonitory urges (Himle et al., 2007). It is possible that obtaining frequent urge ratings may have increased the salience of urges for participants resulting in artificially inflated urge ratings. However, given that urge ratings were obtained in the same manner across conditions, this potential confound should have been effectively controlled. In calculating tic probability as a function of urge intensity, we also made the assumption that reported urge ratings represented a pre-tic baseline; however, it is possible that ratings were adulterated by the completion of a tic in the seconds prior to when the urge rating was collected. Because tic completion theoretically results in a temporary decrease in urge intensity, it is possible that, in some cases, urge ratings may have been lowered by the completion of a tic in the seconds prior to the urge rating. While this potential confound would have been stable across conditions and therefore effectively controlled, it is possible that contrasts between urge intensity categories (low, medium, and high) may have been affected. Finally, with respect to our exploratory findings, we appreciate the limitations of our small sample size. However, given the relative paucity of published data regarding factors associated with effective tic suppression in contrast to those associated with tic severity, our findings represent the first foray into a relatively unexplored, yet potentially fruitful area of research.

In summary, the current study was not intended to address either the negative reinforcement hypothesis of tic maintenance nor the urge habituation hypothesis as a means through which TSBTs produce decreased tic severity. Instead, this study focused on more fundamental questions regarding the basic relationship between urge intensity and tic completion when youth with CTD were allowed to tic freely compared with when they were reinforced for tic suppression. In contrast to our “selective suppression” hypothesis, we found that youth were equally capable of suppressing their tics regardless of urge intensity during reinforced tic suppression. Therefore, a decrease in the overall probability of tics occurring during tic suppression was not simply achieved by refraining from ticcing when urge ratings were low. Instead, tic suppression was achieved with an across-the-board effort to resist urges to tic, even when urge ratings were high. In fact, the probability of a tic occurring following a high urge rating when suppressing tics was about half as likely as the probability of a tic occurring following a low-intensity urge rating when ticcing freely. Preliminary data from the current study also suggest that ability to suppress may be associated with verbal abilities rather than age, tic severity, urge severity, or attention. Treatment naive youths appear to possess a capacity for robust tic suppression regardless of urge intensity; TSBTs may bolster these capacities and/or enable broader implementation, resulting in symptom improvement.

Footnotes

Author’s Note

The current study represents follow-up analyses from a previously reported study (Specht et al., 2013). Therefore, the methods described above, while substantially edited, are fundamentally identical to those previously reported with the exception of the data analysis section.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Dr. Specht also received payment from the Tourette Syndrome Association for speaking engagements. The terms of this arrangement are being managed by the Johns Hopkins University in accordance with its conflict of interest policies. Doug Woods has received book royalties from Guilford Press, Oxford University Press, Springer Press, and New Harbinger Publications. Dr. Woods has received grants from the Tourette Syndrome Association, Trichotillomania Learning Center, and the National Institutes of Health. Dr. Woods has received speaking honoraria from a partnership program between the Tourette Syndrome Association and Centers for Disease Control. Marco Grados has received payment from the Tourette Syndrome Association for a speaking engagement. John Walkup collects less than US$500 annually in royalties from books on Tourette’s syndrome. Dr. Walkup receives travel expenses from the Tourette Syndrome Association for medical and scientific advisory board meetings. Dr. Walkup also receives honoraria and travel expenses from the Tourette Syndrome Association funded by the Center for Disease Control to do education and training for medical and allied professionals.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Matt W. Specht has received funding for the current study from the Tourette Syndrome Association. This research was supported by a grant from the Tourette’s Syndrome Association.

Author Biographies

Matt W. Specht is an Assistant Professor in the Division of Child and Adolescent Psychiatry at the Johns Hopkins University School of Medicine. He is Co-Founder and Co-Director of the Pediatric OCD and Tourette’s Disorder Specialty Clinic (POTSC), a comprehensive, multidisciplinary clinical and research program.

Cassandra M. Nicotra received her B.A. in Cognitive Science and Psychology from the Johns Hopkins University and her M.S. in Medical Science from the University of South Florida. She conducted research on pediatric psychological disorders for three years, and she is currently researching diabetes and obesity in nonhuman primates before attending medical school.

Laura M. Kelly received her B.A. in Psychology from Johns Hopkins University. She conducted research on pediatric psychological disorders for three years.

Douglas W. Woods is a Professor and Head of Psychology at Texas A&M University. His research interests include the development, testing and dissemination of behavioral treatments for tic disorders, trichotillomania, and other OC-spectrum disorders in children and adolescents.

Emily Ricketts is a Clinical Psychology doctoral student at the University of Wisconsin-Milwaukee, working under the mentorship of Douglas Woods, Ph.D. Her research interests include the dissemination of behavioral treatments, stigma reduction, and the role of family factors in tic disorders and body-focused repetitive behavior disorders.

Carisa Perry-Parrish is an Assistant Professor in the Division of Child and Adolescent Psychiatry at the Johns Hopkins University School of Medicine. Her research focus is on links between emotion regulation and developmental psychopathology (e.g., ADHD, anxiety).

Elizabeth Reynolds is an Assistant Professor in the Division of Child and Adolescent Psychiatry at the Johns Hopkins University School of Medicine. Her experimental research focuses on basic processes in the development and maintenance of health risk behavior among children and adolescents.

Jessica C. Hankinson is an Instructor in the Division of Child and Adolescent Psychiatry at the Johns Hopkins University School of Medicine. Her clinical and research interests are in pediatric psychology and application of behavioral modification principles with children with comorbid medical and psychological issues.

Marco A. Grados is an Associate Professor in the Department of Psychiatry and Behavioral Sciences at Johns Hopkins University School of Medicine. His research interests include the genetic epidemiology of obsessive-compulsive disorder and Tourette’s syndrome and the clinical phenotype of both disorders in relation to attention-deficit hyperactivity disorder.

Rick S. Ostrander is an Associate Professor and Director of Pediatric Medical Psychology in the Division of Child and Adolescent Psychiatry at the Johns Hopkins University School of Medicine.

John Walkup is Professor of Psychiatry, DeWitt Wallace Senior Scholar, the Vice Chair of Psychiatry, and Director of the Division of Child and Adolescent Psychiatry, Weill Cornell Medical College and NewYork-Presbyterian Hospital.

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