Sigurdson et al. \citep{Sigurdsson2020} focussed on cerebellar morphology and structural connectivity (structural co-variance) in TS and found reduced grey matter volumes in part of the cerebellum involved in motor and cognitive information processing compared top controls. The cerebellum also had abnormal structural connectivity with sensori-motor networks and fontal and cingulate cortices. These finding highlight the importance of the cerebellum in tic pathophysiology. The same approach of structural co-variance was used to study the structural underpinnings of premonitory urges with a specific focus on the right insula \citep{Jackson2020}. The severity of tics and premonitory urges correlated, respectively, with posterior (representing the current physiological state) and anterior (associated with urges for action) sub-regions of the insula. In additions, these sub-regions of insular cortex were related to different structural networks, suggesting that separate networks support tics and PU in TS.  
In one of the largest to date studies on resting state functional connectivity in adults and children with TS,  Neilson et al. \citep{Nielsen2020a} showed that patterns of functional connections alterations were age-dependent: while brain networks in TS children presented features of older age, adult TS brain networks appeared "younger" in comparison to age-matched controls. Overall, these findings underline the differences in TS neurodevelopmental trajectories. 
Finally, O’Neil et al. wrote a comprehensive review about neuroimaging findings on the role of the cingulate cortex in TS, suggesting that at least 6 to 8 different sub-regions of this cortical area might be implicated in different aspects of TS pathophysiology, and are especially involved with premonitory urges \citep{31731911}. Activity in the subgenual and pregenual anterior cingulate as well as in the middle cingulate cortex might represent volitional effort, physical discomfort and emotional distress of premonitory urges; the posterior middle cingulate cortex and dorsal posterior cingulate cortex  might play a role in amplification (build-up) of urges. 
A PET study of 33 adults found that serotonin transporter (SERT) binding in caudate and midbrain was normal in people with tics only or OCD only, but was elevated in people with both tics and OCD \citep{30700759}. This result, if replicated, may suggest a nosological distinction between TS with vs. without OCD, which would be surprising from a clinical viewpoint. 

Clinical and neuropsychological studies

Recent studies indicate that the coordination of bimanual movements may involve a number of brain areas: primary sensorimotor cortex, SMA, premotor cortex, cingulate motor cortex, lateral premotor cortex, basal ganglia, inferior parietal cortex, and the cerebellum (many of which, incidentally, have been reported to be altered with respect to structure and/or function in brain imaging studies of TS). However, it is accepted that interhemispheric transfer is mediated through excitatory and inhibitory transcallosal communications between cortical motor areas and that the corpus callosum therefore plays a major role in the coordination of bimanual movements, particularly asymmetric bimanual movements. A recent study investigated externally paced (cued) and internally paced bimanual tapping in adults with and without TS. Importantly, this study combined behavioral measures of bimanual tapping with MRI-based DTI and probabi­listic tractography of inter-hemispheric callosal connections between the SMA and the left SMA–putamen fiber tract \citep{Martino2019}. TS patients were significantly less accurate than healthy individuals when asked to maintain a previously copied rhythmic tapping speed at time intervals < 1 Hz [42]. Unimanual tapping is the condition requiring the greatest level of interhemispheric inhibition. TS patients also showed altered FA in inter­hemispheric (SMA–SMA) and left-sided SMA–putamen fiber tracts. These findings are consistent with compen­satory processes linked to self-regulation of motor control that may occur through the plastic rearrangement of interhemispheric and cortical-subcortical WM pathways.
Maigaard and colleagues studied the ability of children with TS to suppress quick but inappropriate rewards \citep{31103639}. Not surprisingly, children with ADHD did poorly on this task, but children with TS actually did better than healthy control children. All groups improved their accuracy when a reward was promised for accuracy. One hypothesis to explain these results may be that children with TS have better motor inhibition in certain tasks due to their experience withholding tics in response to premonitory urges due to social pressures. The reward effect may correspond to the known improvement in tic suppression in the presence of immediate rewards \citep{29875706,31241402}.

Treatment

Psychological interventions

In a large study of manualized CBT in children with OCD, anxious and depressive symptoms improved substantially and were not linked to improvements in OCD severity \citep{Rozenman2019}. This result is one more argument in favor of psychotherapy for obsessions and compulsions, which are common in people with tics. A consensus report argues strongly for early intervention in OCD \citep{30773387}. Since early-onset OCD is associated with tics \cite{21820387}, a similar argument could be made for early intervention in tic disorders, especially since effective behavioral treatments without side effects are available. Studies of whether early intervention changes the course of tic disorders are needed. 
One of the most interesting possibilities in delivering behavior therapy for tics has come from the development of internet-based platforms, making these approaches available for a large number of patients, even in remote areas. The BIP-TIC platform, developed in Sweden, allows to use either HRT, ERP or a mixture of both online with a possible intervention of a therapist by phone or email. A first pilot study on 23 patients has shown encouraging results in a rater-blind parallel group trial (including a 12 month follow up) \citep{30772854}. A large (n= +200) UK-based study of ERP using this platform, called ORBIT, will commence shortly \citep{30610027}.  
Another way to increase the number of patients to be reached by CBT is group therapy. A Danish study, using a combined HRT/ERP approach has demonstrated that it is equally effective in a group as in an individual setting with 27 patients per treatment arm \citep{Nissen2019}. This represents a promising and interesting way forward in CBT for tics.

Medication

The American Academy of Neurology (AAN) practice guidelines for TS \citep{31061208}\citep{31061209} are one of the most important publications in our field for the 2019. A detailed analysis goes way beyond the scope of this review but it might be worth noting that the only "high confidence in the evidence" rating was awarded to Comprehensive Behavioral Intervention for Tics (CBIT) and not pharmacological or surgical therapies for tics. This represents a true paradigm shift in the field. Similar conclusions were drawn in another review of evidence-based treatments for TS and CTD \citep{31295410}.
In recent years, cannabis and cannabis-derived products are being considered for the treatment of tics – and a variety of other movement disorders. Milosev et al. \citep{Milosev2019} present results from a retrospective data analysis and an online survey on the use of cannabis-based medicine for tics and comorbidities in TS. Patients (n= 98 and 40) expressed a preference for medical cannabis (rich in THC) over dronabinol and nabiximols. However, results from large randomized trials are still awaited and will help guide therapeutic decisions. These will also depend, obviously, on the availability of different cannabis-based medications across countries.

Neurosurgery

Blocking tics by behavior therapy or botulinum toxin has been hypothesized to interrupt the sensory-motor feedforward loop likely operating in TS, i.e. premonitory sensations triggering tics which then re-inforce premonitory sensations. Kimura et al. \citep{Kimura2019} report on four patients who had undergone thalamic DBS for severe TS. In two, DBS could be completely withdrawn four and seven years after surgery, respectively, without re-increase in tics. This is intriguing and confirms unpublished reports from other centers, including our own (Paris). The authors raise the question of whether some of the tics observed pre-op were functional tics. Alternatively, perhaps some patients with severe tics may need treatment only for several years during development, when tics may have been most severe without treatment. On the topic of functional tics, which are occasionally seen by movement disorder specialists, Ganos et al. \citep{Ganos2019} have published a landmark review which should be compulsory reading in the field.
In a 48 month follow-up of a multicentre trial comprising 16 severe TS patients treated with DBS of the anterior pallidum, it was found that 75% of subjects were treatment responders, that YGTSS (-40%) and global functioning scores decreased significantly, and that self-injurious behaviors ceased in all affected (n=7) patients \citep{Welter2019}. Also, no persistent psychiatric or neurological side effects were noted. However, DBS did not lead to overall decrease in medication. Predictors of long term outcome for DBS in TS are still needed and larger, perhaps international studies will be able to fill that gap. One step towards that was signalled by a report of initial results from an international TS-DBS registry relating DBS active contact location to outcomes \citep{Johnson2019}.

Other treatments

Regarding unusual treatment methods for tics, Murakami et al. \citep{Murakami2019} describe the use of oral splints in 22 patients with TS. Tic decrease was noted in the vast majority of cases and occurred almost instantaneously. The authors suggest a  placebo effect and/or a sensory trick as mechanism of action. The major question here remains how and if such an intervention can work long term and without impairing daily functioning, especially speech.  
 A pilot study evaluated the efficacy of a resource activation program as an alternative intervention for children and adolescents (n=24) with tic disorders \citep{31207850}. Their preliminary results suggests that after 16 treatment sessions, tics were significantly diminished using the YGTSS and other tic-related measures. Larger cohorts and longer follow-up will hopefully establish whether this approach might become an alternative or adjunct to established CBT approaches for treating tics such as HRT and ERP.