Online Transcranial Magnetic Stimulation Protocol for Measuring Cortical Physiology Associated with Response Inhibition.

We describe the development of a reproducible, child-friendly motor response inhibition task suitable for online Transcranial Magnetic Stimulation (TMS) characterization of primary motor cortex (M1) excitability and inhibition. Motor response inhibition prevents unwanted actions and is abnormal in several neuropsychiatric conditions. TMS is a non-invasive technology that can quantify M1 excitability and inhibition using single- and paired-pulse protocols and can be precisely timed to study cortical physiology with high temporal resolution. We modified the original Slater-Hammel (S-H) stop signal task to create a "racecar" version with TMS pulses time-locked to intra-trial events. This task is self-paced, with each trial initiating after a button push to move the racecar towards the 800 ms target. GO trials require a finger-lift to stop the racecar just before this target. Interspersed randomly are STOP trials (25%) during which the dynamically adjusted stop signal prompts subjects to prevent finger-lift. For GO trials, TMS pulses were delivered at 650 ms after trial onset; whereas, for STOP trials, the TMS pulses occurred 150 ms after the stop signal. The timings of the TMS pulses were decided based on electroencephalography (EEG) studies showing event-related changes in these time ranges during stop signal tasks. This task was studied in 3 blocks at two study sites (n=38) and we recorded behavioral performance and event-related motor-evoked potentials (MEP). Regression modelling was used to analyze MEP amplitudes using age as a covariate with multiple independent variables (sex, study site, block, TMS pulse condition [single- vs. paired-pulse], trial condition [GO, successful STOP, failed STOP]). The analysis showed that TMS pulse condition (p<0.0001) and its interaction with trial condition (p=0.009) were significant. Future applications for this online S-H/TMS paradigm include the addition of simultaneous EEG acquisition to measure TMS-evoked EEG potentials. A potential limitation is that in children, the TMS pulse sound could affect behavioral task performance.

Parent and Patient Perceptions of Functional Impairment Due to Tourette Syndrome: Development of a Shortened Version of the Child Tourette Syndrome Impairment Scale.

The Child Tourette Syndrome Impairment Scale (CTIM) rates 37 problems in school, social, and home domains separately for tics and for comorbid diagnoses. However, a shorter version would be easier to implement in busy clinics. Using published data from 85 children with Tourette syndrome, 92 controls, and parents, factor analysis was used to generate a "mini-CTIM" composed of 12 items applied to tic and comorbid diagnoses. Child- and parent-rated mini-CTIM scores were compared and correlated across raters and accounting for clinician-rated tic severity and presence of attention-deficit hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD). The mini-CTIM achieved domain Cronbach alphas ranging from 0.71 to 0.94 and intra-item correlation coefficients ranging from 0.84 to 0.96. The resulting scale correlated with clinician-rated tic severity and reflected the presence of ADHD and OCD. The mini-CTIM appears promising as a practical assessment tool for tic- and non-tic-related impairment in children with Tourette syndrome.