***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The effects of deep brain stimulation ( DBS ) on balance in people with Parkinson 's disease ( PD ) are not well established . This study examined whether DBS r and omized to the subthalamic nucleus ( STN ; n = 11 ) or globus pallidus interna ( GPi ; n = 10 ) improved compensatory stepping to recover balance after a perturbation . The st and ing surface translated backward , forcing subjects to take compensatory steps forward . Kinematic and kinetic responses were recorded . PD-DBS subjects were tested off and on their levodopa medication before bilateral DBS surgery and retested 6 mo later off and on DBS , combined with off and on levodopa medication . Responses were compared with PD-control subjects ( n = 8) tested over the same timescale and 17 healthy control subjects . Neither DBS nor levodopa improved the stepping response . Compensatory stepping in the best-treated state after surgery ( DBS+DOPA ) was similar to the best-treated state before surgery ( DOPA ) for the PD-GPi group and the PD-control group . For the PD-STN group , there were more lateral weight shifts , a delayed foot-off , and a greater number of steps required to recover balance in DBS+DOPA after surgery compared with DOPA before surgery . Within the STN group five subjects who did not fall during the experiment before surgery fell at least once after surgery , whereas the number of falls in the GPi and PD-control groups were unchanged . DBS did not improve the compensatory step response needed to recover from balance perturbations in the GPi group and caused delays in the preparation phase of the step in the STN group BACKGROUND Low-frequency , bilateral stimulation of the subthalamic nucleus can improve axial symptoms of advanced Parkinson 's disease ( PD ) , but it is not particularly effective for segmental symptoms . METHODS The optimal contacts for low-frequency ( 60 Hz ) and high-frequency ( 130 Hz ) single monopolar stimulation were determined . Then , in a r and omized , double-blind , prospect i ve crossover manner , 60-Hz and 130-Hz stimulations via the respective optimal contacts were compared for immediate efficacy in improving the motor function of patients with PD .  RESULTS The optimal contacts for 60-Hz stimulation were situated more ventrally than those for 130-Hz stimulation ( P = 0.038 ) . Under the respective optimal , single monopolar stimulation , 60 Hz provided superior efficacy over 130 Hz in improving the total Unified Parkinson 's Disease Rating Scale motor score ( P < 0.001 ) and the akinesia ( P = 0.011 ) and axial motor signs ( P = 0.012 ) subscores without compromising the therapeutic effect on tremor and rigidity . CONCLUSIONS Low-frequency stimulation via the optimal contacts is effective in improving overall motor function of patients with PD OBJECT Difficulty with step initiation , called " start hesitation , " is related to gait bradykinesia and is an early hallmark of gait freezing in Parkinson disease ( PD ) . Authors of this study investigated the effects of deep brain stimulation ( DBS ) and levodopa on step initiation before and 6 months after DBS surgery in 29 patients with PD who were r and omized to either the bilateral subthalamic nucleus ( STN ) or globus pallidus internus ( GPi ) as the DBS site . METHODS The authors measured the amplitude and duration of anticipatory postural adjustments ( APAs ) , the feed-forward postural preparation that precedes the onset of voluntary step initiation , based on center-of-pressure displacements on a force plate . They also measured the length and velocity of the first step using a motion analysis system to study kinematics . Some of the patients ( 22 ) were from a large , multicenter , double-blind clinical trial , and all patients in the study ( 29 , PD-DBS group ) were r and omized to  DBS in either the bilateral STN ( 15 patients ) or bilateral GPi ( 14 patients ) . Differences in step initiation were investigated in 2 conditions before surgery ( off/on levodopa ) and in 4 conditions after surgery ( off/on levodopa combined with off/on DBS ) . Twenty-eight elderly healthy control volunteers ( CTRL group ) were also tested , and 9 control volunteers with PD who met the criteria for DBS ( PD-C group ) were tested at baseline and 6 months later . RESULTS Patients in the PD-DBS group had smaller amplitudes and longer duration s of APAs compared with those in the 28 healthy control volunteers in all conditions . Before surgery , APAs improved with levodopa . After surgery , the APAs were significantly worse than in the best-treatment state before surgery ( DOPA condition ) , and responsiveness to levodopa decreased . No differences in APAs were detected between the STN and GPi groups . A comparison with PD control volunteers who did not undergo DBS surgery confirmed that a deterioration in step preparation was not related to disease progression . Step length and velocity were smaller in the PD-DBS group than in controls in all conditions . Before surgery , levodopa improved the length and velocity of the first step . Both step length and velocity were unchanged in the best-treatment state before surgery ( DOPA condition ) as compared with after surgery ( DBS+DOPA ) , with only step velocity in the STN group getting worse after surgery . CONCLUSIONS Six months of DBS in the STN or GPi impaired anticipatory postural preparation for step initiation , the opposite effect as with levodopa . Deep brain stimulation disrupted postural preparation more than step execution , suggesting independent motor pathways for preparation and execution of gait . Although turning the stimulators on after surgery combined with levodopa benefited the postural preparation to step , a comparison of pre- and postsurgery conditions suggests that either the surgery itself or 6 months of continuous stimulation may lead to an alteration of circuits or plastic changes that impair step initiation BACKGROUND High frequency stimulation ( HFS ) of the subthalamic nucleus ( STN-DBS ) has been shown to have little impact on postural control and gait improvements in Parkinson 's disease ( PD ) . There is a lack of consensus and quantitative evidence to suggest that stimulating STN at a lower frequency ( LFS ) as compared to HFS will be superior in improving symptoms . OBJECTIVE /HYPOTHESIS To determine if postural control and gait characteristics of persons with PD improve at an LFS ( 60 Hz ) compared to HFS ( > 100 Hz ) . We hypothesized that persons with PD would perform better on postural control and gait measures at LFS . METHODS Nineteen participants with bilateral STN-DBS underwent UPDRS , static and dynamic postural control using gait initiation , and gait evaluations in three stimulation conditions ( baseline voltage stable across conditions : OFF , LFS of 60 Hz , and HFS of > 100 Hz ) . Additionally 10/19 participants were also stimulated at 30 Hz and 60 Hz and at higher voltages . A one-way ANOVA was performed to compare the conditions . RESULTS Total UPDRS-III score , step length and velocity during gait initiation , and gait speed significantly improved during 60 Hz and > 100 Hz conditions when compared to the OFF condition ( P < 0.05 ) . There were no significant differences between 60 Hz and > 100 Hz conditions . Using LFS at higher voltage showed no improvement over > 100 Hz condition . CONCLUSIONS The positive effects of both LFS and HFS on postural control and gait were similar and clinical changes were relatively small . LFS may not help improve postural control , and gait particularly for persons with PD who do not develop gait-related disorders after HFS Postural instability is a sign of progression of Parkinson 's disease ( PD ) and often resistant to levodopa treatment . To explore the effect of bilateral deep brain stimulation ( DBS ) of the subthalamic nucleus ( STN ) on postural stability and gait , full body gait analyses were performed without medication , OFF and ON DBS in eight PD patients and 12 healthy age-matched controls . DBS setting was changed at least 3 hours before gait analysis . To describe asymmetry most and least affected sides ( MAS and LAS ) were rated with the Unified Parkinson 's Disease Rating Scale , motor part and quantitative gait analysis with the Vicon 612 gait analysis system . Stride length and gait velocity but not cadence improved ON DBS . The distances between the heel markers and center of mass ( COM ) were asymmetric and reduced OFF DBS . STN DBS  increased the distances significantly and reduced asymmetry . The improvement in heel to COM distance was larger on the MAS compared with the LAS . OFF DBS knee momentum asymmetry was inversed so that LAS was more impaired than MAS . ON DBS asymmetry improved . PD patients OFF  DBS place the heel too close to COM . The most affected body side has the most impaired swing and the result is a smaller knee moment on the opposite and least affected body side and an asymmetric gait pattern with disturbed balance OFF STN DBS . The asymmetry OFF DBS improved ON DBS . We suggest that DBS facilitates symmetric gait and thereby improves balance during gait Deep brain stimulation of the subthalamic nucleus represents the most important innovation for treatment of  advanced Parkinson 's disease .  Prospect i ve studies have shown that although the beneficial effects of this procedure are maintained at 5 years , axial motor features and cognitive decline may occur in the long term after the implants . In order to address some unsolved questions raised by previous studies , we evaluated a series of 20 consecutive patients who received continuous stimulation for 8 years . The overall motor improvement reported at 5 years ( 55.5 % at Unified Parkinson 's Disease Rating Scale-motor part , P < 0.001 compared with baseline ) was only partly retained 3 years later ( 39 % , P < 0.001 , compared with baseline ; -16.5 % , P < 0.01 , compared with 5 years ) , with differential effects on motor features : speech did not improve and postural stability worsened ( P < 0.05 ) . The preoperative levodopa equivalent daily dose was reduced by 58.2 % at 5 years and by 60.3 % at 8 years . In spite of subtle worsening of motor features , a dramatic impairment in functional state ( -56.6 % at Unified Parkinson 's Disease Rating Scale-Activities of Daily Living , P < 0.01 ) emerged after the fifth year of stimulation . The present study did not reveal a predictive value of preoperative levodopa response , whereas few single features at baseline ( such as gait and postural stability motor scores and the preoperative levodopa equivalent daily dose ) could predict long-term motor outcome . A decline in verbal fluency ( slightly more pronounced than after 5 years ) was detected after 8 years . A significant but slight decline in tasks of abstract reasoning , episodic memory and executive function was also found . One patient had developed dementia at 5 years with further progression at 8 years . Executive dysfunction correlated significantly with postural stability , suggesting interplay between axial motor deterioration and cognition . Eight years after surgery , no significant change was observed on scales assessing depression or anxiety when compared with baseline . At 8 years , there was no significant increase of side-effects when compared with 5-year follow-up . In conclusion , deep brain stimulation of the subthalamic nucleus is a safe procedure with regard to cognitive and behavioural morbidity over long-term follow-up . However , the global benefit partly decreases later in the course of the disease , due to progression of Parkinson 's disease and the appearance of medication- and stimulation-resistant symptoms Gait and balance disturbances typically emerge in advanced Parkinson ’s disease with generally limited response to dopaminergic medication and subthalamic nucleus deep brain stimulation . Therefore , advanced programming with interleaved pulses was put forward to introduce concomittant nigral stimulation on caudal contacts of a subthalamic lead . Here , we hypothesized that the combined stimulation of subthalamic nucleus and substantia nigra pars reticulata improves axial symptoms compared with st and ard subthalamic nucleus stimulation .  Twelve patients were enrolled in this 2 × 2 cross-over double-blind r and omized controlled clinical trial and both the safety and efficacy of combined subthalamic nucleus and substantia nigra pars reticulata stimulation were evaluated compared with st and ard subthalamic nucleus stimulation . The primary outcome measure was the change of a broad-scaled cumulative axial Unified Parkinson ’s Disease Rating Scale score ( Scale II items 13–15 , Scale III items 27–31 ) at ‘ 3-week follow-up ’ . Secondary outcome measures specifically addressed freezing of gait , balance , quality of life , non-motor symptoms and neuropsychiatric symptoms . For the primary outcome measure no statistically significant improvement was observed for combined subthalamic nucleus and substantia nigra pars reticulata stimulation at the ‘ 3-week follow-up ’ . The secondary endpoints , however , revealed that the combined stimulation of subthalamic nucleus and substantia nigra pars reticulata might specifically improve freezing of gait , whereas balance impairment remained unchanged . The combined stimulation of subthalamic nucleus and substantia nigra pars reticulata was safe , and of note , no clinical ly relevant neuropsychiatric adverse effect was observed . Patients treated with subthalamic nucleus and substantia nigra pars reticulata stimulation revealed no ‘ global ’ effect on axial motor domains . However , this study opens the perspective that concomittant stimulation of 
    Output:
    
This meta- analysis showed a robust improvement of gait and FOG  by STN-DBS for more than 4 years in the Med-Off/Stim-On condition .
No beneficial effect was found for the On state of medication .
Pre-operative levodopa responsiveness of global motor performance ( UPDRS-III ) is the strongest predictor of the effect of deep brain stimulation on gait