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## Pathophysiology
A rodent model was used to determine to what extent cortical input and striatal input affected the temporal and spatial properties of motor tics \cite{26674861}. Biccuculline injections into the anterior striatal motor region produced focal tics in the forelimb area. The medium spiny neurons and the fast spiking interneurons exhibited increased activity during tics. Almost all of the MSNs were only active during the tics while a minority of the FSIs exhibited a decrease in activity. About half of the globus pallidus neurons demonstrated increased activity during the tic while the rest showed only inhibition or a combination of inhibition and excitation. Short bursts of high-frequency stimulus pulses were applied at random intervals to the region of the primary motor cortex representing the forelimb. Stimulation was provided before and after the bicuculline injections. The results suggested that the precise timing of tic occurrence was related to the summation of incoming excitatory cortical input and the time since the previous tic. These results supported the idea that the corticostrial network is fundamentally associated with tic occurrence.
### Pathological studies
In a rodent model removing about half of the cholinergic interneurons in the dorsolateral striatum produced increased fragmented grooming behavior in response to a repeated unpredictable acoustic startle stimuli and increased repetitive sniffing in response to D-amphetamine challenge \citep{25561540}. Ablation in This important study \citep{25199956} follows up on the
dorsomedial striatum did not produce similar deficits. None of autopsy results from the
experimental conditions produced a change in prepulse inhibition.
A detailed review \cite{26275849} describes Vaccarino lab by comparing RNA transcripts from the
involvement basal ganglia of
histaminergic modulation 9 TS and 9 matched control subjects. The most strongly associated set of
downregulated transcripts involved striatal
function by interneurons, consistent with the
tuberomamillary nucleus autopsy studies. The leading set of upregulated transcripts involved immune-related genes even though none of the
hypothalamus. The roles described for histamine are that it suppresses both TS subjects met the
thalamic and cortical drive to medium-spiny projection neurons (MSNs), modulates thalamostriatal synapses resulting in diagnostic criteria for pediatric autoimmune streptococcal-associated neuropsychiatric disorders or pediatric acute onset neuropsychiatric syndrome. There was a
facilitation lack of
thalamic input, overlap between the results obtained in the present study using brain tissue and
suppresses lateral feedback inhibition. previous studies using blood samples. The authors
suggest conclude that
during wakefulness and increased attention the striaum will be more responsive to thalamostriatal input and feedforward inhibition will predominate(?). The role of histamine in TS was discussed their results "strongly [implicate] disrupted interneuron signaling in
terms the pathophysiology of
a rare mutation involving histamine synthesizing enzyme histidine decarboxylase in one severe TS
human adult and
decreased prepulse inhibition of startle responses and an increase in a variety of stereotypies which decreased in response suggests that metabolic alterations may be linked to
histamine infusion their death or
use of haloperidol. Effects were thought to occur as a result of the histaminergic control of the lateral GABAergic inhibitory connections between MSNs and ongoing research on histaminergic treatment for TS was discussed. dysfunction."
A collaborative genetic study \citep{25735483} demonstrated an association of TS with 33 genes related to glycolysis or glutamine metabolism. None of the individual genes would have survived correction for multiple testing and the results were consistent with a combined effect of many genetic variants of small effect. These results narrow the hunt for genes that may contribute to the development of TS and they also suggest a new direction for future electrophysiological, imaging and pharmacological studies. ### Animal models
This important study \citep{25199956} follows up on the autopsy results from the Vaccarino lab by comparing RNA transcripts from the basal ganglia of 9 TS and 9 matched control subjects. The most strongly associated set of downregulated transcripts involved striatal interneurons, consistent with the autopsy studies. The leading set of upregulated transcripts involved immune-related genes even though none of the TS subjects met the diagnostic criteria for pediatric autoimmune streptococcal-associated neuropsychiatric disorders or pediatric acute onset neuropsychiatric syndrome. There was In a
lack rodent model removing about half of
overlap between the
results obtained cholinergic interneurons in the
present study using brain tissue dorsolateral striatum produced increased fragmented grooming behavior in response to a repeated unpredictable acoustic startle stimuli and
previous studies using blood samples. The authors conclude that their results "strongly [implicate] disrupted interneuron signaling increased repetitive sniffing in response to D-amphetamine challenge \citep{25561540}. Ablation in the
pathophysiology dorsomedial striatum did not produce similar deficits. None of
severe TS and suggests that metabolic alterations may be linked to their death or dysfunction." the experimental conditions produced a change in prepulse inhibition.
The GABA-A antagonist picrotoxin Another rodent model was
injected used to determine to what extent cortical input and striatal input affected the temporal and spatial properties of motor tics \citep{26674861}. Biccuculline injections into
targets throughout corticostriatal regions the anterior striatal motor region produced focal tics in
adult mice \cite{25597650}. Infusions into the
central forelimb area. The medium spiny neurons and
dorsolateral striatum produced intermittent non-rhythmic stereotyped lifting the fast spiking interneurons exhibited increased activity during tics. Almost all of the
front or hind paw or head jerks. Infusions into MSNs were only active during the
dorsomedial striatum did not have tics while a
significant behavioral effect. Infusion into the ventral striaum produced locomotor activation with sterotypical sniffing and wall licking. Infusions into minority of the
sensorimotor cortex produced similar movements FSIs exhibited a decrease in
addition to exploration activity. About half of the
cage. sniffing and occasional licking. When an NMDA receptor antagonist was infused into the dorsolateral striatum prior to infusing picrotoxin into globus pallidus neurons demonstrated increased activity during the
same location, tic
frequency decreased significantly thus demonstrating while the
role rest showed only inhibition or a combination of
glutamateric activity in tic generation. Infusion inhibition and excitation. Short bursts of
a GABA-A antagonist into high-frequency stimulus pulses were applied at random intervals to the
sensorimotor region of the primary motor cortex
10 minutes representing the forelimb. Stimulation was provided before
picrotoxin infusion into and after the
dorsolateral striatum also resulted in significant bicuculline injections. The results suggested that the precise timing of tic
suppression.EEG recordings allowed experimenters occurrence was related to
determine whether the
infusions were causing seizures or not. The interpretation summation of
these incoming excitatory cortical input and the time since the previous tic. These results
was supported the idea that the
tic-like movements were generated from enhanced striatal responsivity to afferent glutamatergic synaptic input rather than to autonomous striatal activity. corticostrial network is fundamentally associated with tic occurrence.
The
brain circuits underlying tics were studied using GABA-A antagonist picrotoxin was injected into targets throughout corticostriatal regions in adult mice \citep{25597650}. Infusions into the
first genetically engineered mouse model central and dorsolateral striatum produced intermittent non-rhythmic stereotyped lifting of
TS+OCD ("Ticcy" D1CT-7) transgenic mice \cite{26453289}. In these mice the front or hind paw or head jerks. Infusions into the dorsomedial striatum did not have a
small region of dopaminoceptive D1+ somatosensory cortical significant behavioral effect. Infusion into the ventral striaum produced locomotor activation with sterotypical sniffing and
limbic neurons is chronically potentiated which results wall licking. Infusions into the sensorimotor cortex produced similar movements in
cortical and amygdalar glutamatergic excitation addition to exploration of
striatothalamic, striatopallidal the cage. sniffing and
nigrostriatal subcircuits. Tics were occasional licking. When an NMDA receptor antagonist was infused into the dorsolateral striatum prior to infusing picrotoxin into the same location, tic frequency decreased
by significantly thus demonstrating the
use role of
drugs that acted at different points glutamateric activity in
tic generation. Infusion of a GABA-A antagonist into the
"hyperglutamergic cortico-striato-thalmo-cortical circuit". Excitatory forebrain serotonin and norepinephrine activity was blocked by ritanserin and prazosin respectively. In contrast, downstream glutamate-triggered target striatothalamic neurons' GABA output and downstream glutamate-triggered target nigrostriatal neurons' co-modulatory dopamine output sensorimotor cortex 10 minutes before picrotoxin infusion into the dorsolateral striatum also resulted in significant tic suppression.EEG recordings allowed experimenters to determine whether the infusions were
blocked by moxonidine and bromocriptine respectively. All four causing seizures or not. The interpretation of these
drugs decreased tic frequency and results was that the tic-like movements were
considered generated from enhanced striatal responsivity to
be "circuit-breakers" for the hyperglutateric CSTC tic circuit. afferent glutamatergic synaptic input rather than to autonomous striatal activity.
The brain circuits underlying tics were studied using the first genetically engineered mouse model of TS+OCD ("Ticcy" D1CT-7) transgenic mice \cite{26453289}. In these mice a small region of dopaminoceptive D1+ somatosensory cortical and limbic neurons is chronically potentiated which results in cortical and amygdalar glutamatergic excitation of striatothalamic, striatopallidal and nigrostriatal subcircuits. Tics were decreased by the use of drugs that acted at different points in the "hyperglutamergic cortico-striato-thalmo-cortical circuit". Excitatory forebrain serotonin and norepinephrine activity was blocked by ritanserin (a serotonin 2a/2c antagonist) and prazosin (an \( \alpha_{1} \) adrenergic antagonist) respectively. In contrast, downstream glutamate-triggered target striatothalamic neurons' GABA output and downstream glutamate-triggered target nigrostriatal neurons' co-modulatory dopamine output were blocked by moxonidine (an imidazoline receptor subtype 1 agonist) and bromocriptine (a dopamine agonist) respectively. All four of these drugs decreased tic frequency and were considered to be "circuit-breakers" for the hyperglutamatergic CSTC circuit.
### Neuroimaging and electrophysiology studies
An important (though frustrating) recent finding was that even very small head movements can cause artifactual findings in structural MRI \citep{25498430} . Neroimaging scans were performed on 12 healthy adults while they were still or engaged in specific types of movements including nodding, headshaking and a movement that they invented and then repeated during the scan run. Even during scans when subjects remained still, there was an average of 3 mm/s RMSpm (RMS displacement per minute), but it was significantly higher during the motion conditions. In general there was a 1-3% local volume loss for each 1 mm/s RMSpm increase. The greatest thickness reductions were found in the pre- and post-central cortex, in the temporal lobes and pole, and enthorhinal and parahippocampal regions. Increased thickness associated with motion was seen in regions associated with deep sulci such as the medial orbital frontal and lateral frontal areas. Recommendations were made to reduce head motion during scans as much as possible and then control for motion in the statistical analysis, along with using correlational analyses to determine the associations between head motion and the predictors of interest. A more recent article \citep{26654788} described the development of a system for motion tracking and prospective motion correction, and mentions similar systems that are available for other scanner platforms. The challenges using neuroimaging techniques to study pediatric and clinical subjects are described in detail along with various strategies that can be used to collect high-quality data
\cite{26754461}. \citep{26754461}.
Many researchers have used a variety of experimental paradigms to study motor response inhibition since tic expression seems related to motor inhibition. In healthy adults performance on a stop-signal task and a continuous performance task was examined using positron emission tomography to measure striatal D1- and D2-type receptor availability \citep{25878272}. Stop-signal reaction time was negatively correlated with both D1- and D2-type receptor activation in both the associative striaum and the sensory motor striatum. Neither D1- nor D2-type receptor activation was associated with Go reaction time or Stop signal reaction time on the continuous performance task suggesting that these two tasks are associated with different neurochemical mechanisms related to motor response inhibition.
...
A whole brain analysis of cortical gray matter found reduced gray matter thickness in the insula and sensorimotor cortex for TS children and young adults compared to a matched control group \cite{26538289}. In addition, Premonitory Urge for Tics Scale scores were negatively correlated with grey matter thickness in these areas.
Several studies examined dopamine receptors. Positron emission tomography was used to investigate striatal D2/D3 dopamine receptors using a D2/D3 receptor antagonist and an agonist with preferential binding to D3 dopamine receptors \cite{25788222}. As expected, binding potential for the D3 preferential agonist was greater in the ventral striatum while it was greater for the D2/D3 receptor antagonist in the motor and associative regions of the dorsal striatum. However, no differences were found for these 3 regions when the TS subjects were compared with the controls and there were no significant correlations between binding potentials and tic severity.
Dopamine receptors and motor response inhibition \cite{25878272}|Stop-signal reaction time was negatively correlated with D1- and D2-type activation in the dorsal, but not ventral, striatum. No significant correlations involving the continuous performance task were found suggesting that different inhibitory mechanisms are involved in these two tasks. Another study examined D1 and D2 involvement in healthy adults and found that learning from positive outcomes was positively correlated with D1 receptor binding in the putamen and caudate while there was an inverted U-shaped relationship between learning from negative outcomes and D2R binding in the putamen\citep{25562824}. A dietary manipulation that reduced dopamine precursor levels significantly improved learning from negative outcomes. These results were interpreted as providing evidence that dopamine acts as a reward prediction error signal rather than as a saliency signal.
Resting-state functional magnetic resonance imaging identified greater functional connectivity between the right dorsal anterior insula and the bilateral supplementary motor area in TS adults compared to controls \cite{25855089}. Post-hoc analyses found significant correlations between PUTS scores and both right dAI-right SMA2 and right dAI-left SMA1 connectivity suggesting that these regions might be involved in the increased awareness of body sensations that tend to be associated with premonitory urges.
KEVIN--does this have adequate control for movement? Average maximum displacement for controls was .7 mm for controls and .9 mm for patients.
Local field potentials were studied in 3 patients who had DBS surgery \cite{25435514} along with EMG recordings to identify the muscle contractions associated with spontaneous tics. In all 3 patients repetitive thalamo-cortical coherent activity Stop-signal reaction time was
present from 800 to 1500 msec prior to the muscle contraction related to spontaneous motor tics. The frequency range affected varied among the patients negatively correlated with D1- and
there was also ongoing intermittent intra-thalamic coherences that were D2-type activation in the dorsal, but not
synchronized to ventral, striatum \citep{25878272}. No significant correlations involving the
tics continuous performance task were found, suggesting that
different inhibitory mechanisms are involved in
TS. It was pointed out these two tasks. Another study examined D1 and D2 receptors in healthy adults and found that
DBS targets may not matter as much as the target is part of learning from positive outcomes was positively correlated with D1 receptor binding in the
striato-pallido-thalamo-cortical network. Since these patients were older putamen and
had very severe caudate while there was an inverted U-shaped relationship between learning from negative outcomes and
complex tics, D2R binding in the
authors mention putamen \citep{25562824}. A dietary manipulation that
it is not clear at this point to what extent these reduced dopamine precursor levels significantly improved learning from negative outcomes. These results
would generalize to the TS population were interpreted as providing evidence that dopamine acts as a reward prediction error signal rather than as a
whole. saliency signal.
Resting-state functional magnetic resonance imaging identified greater functional connectivity between the right dorsal anterior insula and the bilateral supplementary motor area in TS adults compared to controls \cite{25855089}. Post-hoc analyses found significant correlations between PUTS scores and both right dAI-right SMA2 and right dAI-left SMA1 connectivity suggesting that these regions might be involved in the increased awareness of body sensations that tend to be associated with premonitory urges. The authors paid attention to head movement and removed high-movement frames, but recent analyses suggest that the motion threshold of 0.4mm and the lack of global signal regression in this analysis may have introduced some artifactual correlations between brain regions due to residual small head movements during the scan \citep{25462692}.
Local field potentials were studied in 3 patients who had DBS surgery \citep{25435514} along with EMG recordings to identify the muscle contractions associated with spontaneous tics. In all 3 patients repetitive thalamo-cortical coherent activity was present from 800 to 1500 msec prior to muscle contractions related to spontaneous motor tics. The frequency range affected varied among the patients and there were also ongoing intermittent intra-thalamic coherences that were not synchronized to the tics. The authors concluded that specific DBS targets may not matter as much as whether the target is part of the striato-pallido-thalamo-cortical network. Since these patients were older and had very severe and complex tics, the authors acknowledge that it is not clear at this point to what extent these results generalize to the TS population as a whole.
| **Title** | **Comment** |
|:----------|:------------|
| |Motor execution and motor imagery
\cite{26566185}|An \citep{26566185}| An exploratory study found neural hyperactivation for both types of tasks when TS adults were compared to controls. Interestingly, the exception to this was that basal ganglia and thalamic activation was smaller in the TS subjects than the controls. Premotor activation during the motor imagery tasks was correlated with tic severity. |
|
|Brain structural MRI in pediatric Tourette syndrome
\citep{TSANIC:VBM:London}|A \citep{TSANIC:VBM:London}| A large multisite study found TS children had greater gray matter volume in the posterior thalamus and hypothalamus-midbrain in addition to decreased white mater volume in the orbital prefrontal cortex and the anterior cingulate.|
|
|DTI and the corpus callosum
\cite{26747579} \citep{26747579} |Axial diffusivity
(AD) was reduced in treatment-naive boys with "pure TS" compared to controls. AD was negatively correlated with tic severity although this result did not reach significance after Bonferroni correction. |
|Tourette syndrome and chronic tic disorder \citep{26531497} |Event-related potentials
recordings, recordings during a stimulus-response compatibility
task, task revealed increased parietal and central activation for both patient groups compared to the control group. The two patient groups were not significantly different from one another.|
|
|Event-related topography and the effect of comorbidities \citep{Germain_2015}|P300 amplitude in the frontal region was reduced for TS patients with comorbid symptoms compared to control subjects while a medication-naive TS group with no comorbid conditions was similar to the control
group
| group.|
|Magnetoencehalography and beta rhythms
\cite{26649991}. \citep{26649991}. |TS adults exhibited less beta suppression in the sensorimotor region and increased beta power in parieto-occipital brain regions during a Go/NoGo
task with task. YGTSS motor scores negatively correlated with average beta power and beta power increases over time suggesting that compensatory mechanisms to control tics might involve both increased motor inhibitory processes and visuomotor attentional processes.|
### Clinical and neuropsychological studies
The effects of comorbidities on a variety of measures was examined in TS children and adolescents \cite{25631951}. Compared to age-matched controls the TS group did significantly worse on the parent-rated Social Responsiveness Scale which measures social skills impaired in autism. They also took significantly longer to complete forms of the Trail Making Tests. However, of the 31 TS subjects, 11 had OCD, 18 had ADHD and 9 had an anxiety disorder. Once these co-occurring conditions were taken into account, the group differences on the Trail Making Tests and the Social Responsiveness Scale were no longer significant.
The issue of how comorbidities Many factors affect
a variety tic frequency and two studies examined the effects of
measures attention on tic frequency. The role of attention on tic frequency was
seen examined under several conditions /citep{25185800}. In the first study mean tic frequencies were significantly higher for 12 TS subjects compared to baselines when they were alone in a room. Then they were recorded while looking at themselves in a
mirror. A second study
of TS children and adolescents \cite{25631951}. Compared was performed to
age-matched controls determine whether the
TS group did significantly worse on increase in frequency was due to increased attention to the
parent-rated Social Responsiveness Scale which measures social impairment. They also significantly longer tics themselves or due to
complete forms of increased self-awareness in general. In addition to the conditions from the first study, the
Trail Making Tests. However, 16 subjects were also shown videos of
themselves while they were not ticcing. Tic frequency was again lower during the baseline compared to the
31 mirror condition. Tic frequency was lower when subjects were watching the video of themselves while not ticcing. The authors suggest that future treatments stress attention to states when patients experience fewer tics. Another study of TS
subjects, 11 had OCD, 18 had ADHD and 9 adults \cite{25486384} compared tic frequency while subjects were engaged in tasks that involved attending to particular fingers, colored circles, or whether a tic had
an anxiety disorder. Once these co-occurring conditions occurred during a specific 2 second interval during tic suppression or free ticcing conditions. Not surprisingly, more tics were
taken into account seen during a baseline free ticcing condition. During the
group differences attention tasks, tic frequency was greatest while they focused on their tics, decreased on the
Trail Making Tests color attention condition, and
decreased further on the
Social Responsiveness Scale were no longer significant. finger attention condition. When subjects suppressed their tics, they reduced their baseline tic frequency similarly across all attention conditions. These authors suggested that behavioral treatment might be more effective if it focused on teaching patients to focus on external events and voluntary actions when they are in situations that are most likely to result in ticcing.
Many factors affect tic frequency and two studies examined the effects of attention on tic frequency. The role of attention on tic frequency A three-stage instrumental-learning paradigm was
examined under several conditions /citep{25185800}. In the first study mean tic frequencies were significantly higher for 12 used to compare antipsychotic-medicated and unmedicated TS
adults with a control group \citep{26490329}. First, subjects
compared learned to
baselines when they were alone in a room. Then they were recorded while looking at themselves in associate six different stimuli with six specific outcome pictures and a
mirror. A specific response (i.e., left or right key press). During the second
study stage, subjects were presented with two outcomes with an indication that one outcome was
performed to determine whether the increase in frequency devalued so that it was
due to increased attention no longer associated with point rewards and subjects had to
press the
tics themselves or just due key associated with the outcome that would still generate points. During the third stage (i.e., "slip-of-action" stage) the six outcomes were presented simultaneously with indications that two were devalued so that responding to
increased self-awareness. In addition the associated stimuli would no longer be rewarded with points. Subjects were instructed to
press the
conditions from key associated with stimuli associated with the
first study still valued outcomes and withhold the
16 subjects were response for stimuli associated with devalued outcomes. Subjects also
shown videos did a Go-No Go task in which two of
themselves while they six cueing stimuli were
not ticcing. Tic frequency was again lower during the baseline compared devalued with instructions to
withhold the
mirror condition. Tic frequency was lower key press response when
subjects were watching the
video devalued stimulus was presented. This task determined whether excessive "slips of
themselves while not ticcing. The authors suggest that future treatments stressing attention action" were related to
states when patients experience fewer tics. Another study a working memory deficit or deficient response inhibition rather than outcome devaluation insensitivity. There were no group performance differences for the first two stages of
TS adults \cite{25486384} the instrumental learning task or on the baseline Go-NoGo task. However, unmedicated patients showed a significantly higher response rate to devalued outcomes compared
tic frequency to controls (in Bonferroni-corrected post hoc analyses) while
there was no difference between medicated subjects
were engaged and controls. In addition, in
tasks that involved attending to particular fingers, colored circles, or whether a tic had occurred during a specific 2 second interval during unmedicated subjects tic
suppression severity was correlated with response rates to devalued outcomes and
free ticcing conditions. Not suprisingly was also correlated with stronger structural connectivity between the
greatest tics were seen during a baseline free ticcing condition. During right supplementary motor cortex and the
attention tasks, tic frequency posterior putamen. The influence of comorbidities was
greatest while they focused on their tics and decreased tic frequency on reduced by excluding subjects with ADHD from the
color attention condition and study. In addition, the
greatest decrease results obtained in this study contrasted with results on
the finger attention condition. When subjects suppressed their tics, they reduced their baseline tic frequency and they exhibited similar
frequencies across all attention conditions. These tasks obtained with subjects with pure obsessive-compulsive disorder without tics. The authors
suggested argued that
behavioral treatment might be more effective if it focused on teaching patients to focus over-reliance on
external events and voluntary actions when they are habits in pure OCD is associated with impaired knowledge of response-outcome associations, while this type of learning was intact in
situations both TS groups in this study. They also concluded that
are most likely to result habit formation is enhanced in
ticcing. unmedicated TS subjects.
A three-stage instrumental-learning paradigm was used to compare antipsychotic-medicated and unmedicated TS adults with a control group \citep{26490329}. First, subjects learned to associate six different stimuli with six specific outcome pictures and a specific response (i.e., left or right key press). During the second stage, subjects were presented with two outcomes with an indication that one outcome was devalued so that it was no longer associated with point rewards and subjects had to press the key associated with the outcome that would still generate points. During the third stage (i.e., "slip-of-action" stage) the six comes were presented simultaneously with indications that two were devalued so that responding to the associated stimuli would no longer be rewarded with points. Subjects were instructed to press the correct key associated with stimuli associated with the still valued outcomes and withhold the response for stimuli associated with devalued outcomes. Subjects also did a Go-No Go task in which two of six cueing stimuli were devalued with instructions to withhold the key press response when the devalued stimulus was presented. This task provided determined whether excessive "slips of action" were related to a working memory deficit or deficient response inhibition rather than outcome devaluation insensitivity. There were no group performance differences for the first two stages of the instrumental learning task or on the baseline Go-NoGo task. However, unmedicated patients showed a significantly higher response rate to devalued outcomes compared to controls in Bonferroni-corrected post hoc analyses while there was no difference between medicated subjects and controls. In addition, in unmedicated subjects tic severity was correlated with response rates to devalued outcomes and was also correlated with stronger structural connectivity between the right supplementary motor cortex and the posterior putamen. The influence of comorbidities was minimized by excluding subjects with ADHD from the study. In addition, the results obtained in this study contrasted with results on similar tasks obtained with subjects with pure obsessive-compulsive disorder without tics. Delorme et al. argued that over-reliance on habits in pure OCD is associated with impaired knowledge of response-outcome associations while this type of learning was intact in both TS groups in this study and concluded that unmedicated TS subjects tend to engage in enhanced habit formation. Sustained attention, using a continuous performance test, was examined in 48 children who had OCD alone, tic disorders (TD) alone or both OCD and
TD. The challenges of trying to separate out the effects due to comorbidities is evident in this study TD \cite{25296570}. A high rate of ADHD was seen in all groups (i.e., 62% of the OCD+TD group, 27% in the TD alone group, and 20% in the OCD alone group. Anxiety was also commonly seen (i.e., 77% in the OCD+TD group compared to 49% for the other two groups combined). The OCD+TD group had more errors of omission and did more poorly on other measures of sustained attention compared to the other two groups. Although an attempt was made to examine the specific effect of ADHD in the OCD+TD group,the subgroups were quite small (i.e., 8 in the OCD+TD+ADHD, 5 in the OCD+TD-ADHD) thereby limiting the power to detect additional differences. However, reaction time variability, which is commonly seen in ADHD was higher in the OCD+TD group than for the groups with OCD alone or TD alone.
This study exemplifies the challenges of trying to separate out the effects of comorbidities in children with TS.
*Title** | **Comment** |
|:----------|:------------|
| Anthropomorphic triangles \citep*{26177119} | This clever study results from Dr. Eddy's research on social cognition in TS. People with TS and controls demonstrated intact mentalizing when observing animated triangles demonstrating simple and complex interactions. However, people with TS
also tended to attribute human-like intentions when the two triangles were moving randomly. This tendency was not explained by other constructs such as executive function, alexithymia or clinical symptoms.|
|
| The eyes have it \citep{26175694} | A measure of cognitive control explained half of the variance in tic severity. Blink rate—related to dopamine—was higher in children with TS than in controls. Pupil diameter—related to norepinephrine—was correlated with anxiety. |
|
Postural |Postural stability
\cite{25683311} \citep{25683311} | TS children with "pure TS" had significantly greater difficulty maintaining postural
stability stability, especially when they had to use only vestibular cues (rather than visual or somatosensory cues).
|
Normal |Normal sensory thresholds
\cite{26818628} \citep{26818628} | Thresholds for externally applied sensory stimuli were similar in adults with "pure" TS and
controls suggesting controls. Like a previous study \cite{22038938}, these results suggest that sensory abnormalities seen in TS are related to abnormalities in interoceptive awareness or central sensorimotor processing.
|
