32ournal ofNeurology, Neurosurgery, and Psychiatry 1995;58:312-319

Kinematic properties of upper limb trajectories in

idiopathic torsion dystonia

Rivka Inzelberg, Tamar Flash, Edna Schechtman, Amos D Korczyn

AbstractThe kinematic properties of upper limbtrajectories of simple reaching move-ments have been analysed in patientswith idiopathic torsion dystonia (ITD).The velocity profiles differed from thoseof neurologically healthy subjects bybeing less symmetric. In several patientsmovement execution was slow due to alonger deceleration time. This phenome-non was even more conspicuous in theabsence of visual feedback from the limband was accompanied by a significantdecrease in the final accuracy. Thesefindings show that patients with ITD havedeficits in central motor mechanismsbeyond abnormal muscle activation pat-terns. Similarities between kinematicproperties of patients with ITD andpatients with Parkinson's disease includ-ing the deterioration of motor perfor-mance in ITD in the absence of visualfeedback from the limb, suggest the exis-tence of abnormalities in sensorimotorintegration in both diseases.

(7 Neurol Neurosurg Psychiatry 1995;58:312-319)

Keywords: kinematic properties; upper limb trajecto-ries; idiopathic torsion dystonia

Department ofNeurology, Tel-AvivMedical Center,Tel-Aviv, IsraelR InzelbergA D KorczynDepartment ofApplied Mathematicsand ComputerScience, TheWeizmann Institute ofScience, Rehovot,IsraelR InzelbergT FlashComputer Center,The WeizmannInstitute of Science,Rehovot, IsraelE SchechtmanCorrespondence to:Dr Tamar Flash,Department of AppliedMathematics and ComputerScience, The WeizmannInstitute of Science,Rehovot 76100, Israel.

Received 15 March 1994and in revised form29 July 1994.Accepted 26 August 1994

Idiopathic torsion dystonia (ITD) is charac-terised by abnormal movements and postures.Despite advances in the understanding of thegenetics of ITD,' 2 several domains in thepathophysiology of this disease remain sub-jects for research.3 The exact anatomical siteaffected in dystonia is unknown, althoughsymptomatic dystonias4 point to the putamen,caudate, or thalamus as the major affectedstructures. Muscle activation patterns in ITD,investigated by the analysis of EMG signals,have shown that instead of normal alternatingagonist-antagonist contractions, patients withITD exhibit prolonged EMG bursts in theactivated muscles, abnormal cocontraction ofantagonistic muscles, and spread to unrelatedmuscles.5-8The mechanisms postulated to underly

such abnormal muscle activation includedefective reciprocal inhibition, which mightreflect abnormalities at spinal or supraspinallevels,-for example, of descending com-

mands to spinal inhibitory interneurons.9-'2The functional state of hierarchically higherstructures enrolled in the programming ofmovement and causing the abnormal muscle

activities in ITD remains obscure. Moreover,a previous kinematic study analysing rapidelbow movements, has shown normal kine-matic properties of this single joint movementin ITD.13

Whereas single joint movements are rela-tively simple, most daily activities employsimultaneous movements about several joints.An important review has stressed that theanalysis of multijoint and complex move-ments might contribute to the understandingof the mechanisms underlying the pathophysi-ology of basal ganglia diseases.'4 Thus wewere interested in studying multijoint move-ments in ITD.When multijoint movements of the upper

limb are considered, a distinction between thehand path and hand trajectory should bemade.'5 "Path" is defined as the geometricalcurve that the hand follows in space, and"trajectory" refers both to the path and to thetime course of position along the path.'5 Innormal subjects, hand paths of planar hori-zontal reaching movements are roughlystraight and the speed first increases and thendecreases resulting in bell shaped velocity pro-files.'6 The durations of the two componentsare roughly equal,'6 although under strictaccuracy demands the decelerative part mightbe longer.'7 This division into accelerative anddecelerative phases relates to a proposal madea century ago by Woodworth,'8 who statedthat a movement is composed of an "initialimpulse", believed to be preplanned, and asubsequent "current control", which is cor-rected by sensory feedback.

Recent data suggest the existence of anabnormal dependency on visual informationfor accurate motor performance in Parkin-son's disease, a prototypical basal ganglia dis-order.'920 The effect of visual feedback onmotor performance has not been previouslyassessed in ITD. The present study thereforehas focused on kinematic analysis of two jointarm trajectories in ITD with special emphasison the effect of visual feedback on the move-ment characteristics. Only movementsdirected toward distally and proximallylocated targets (with respect to shoulder posi-tion) are analysed in the present work, whichfollows previous analysis of the kinematicproperties of upper limb trajectories inParkinson's disease. '9

MethodsSix control subjects and eight patientswith ITD were retrieved from a population

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Table 1 Characteristics ofpatients

Duration of Involved Severity ofSubject Age Sex disease (y) Treatment* body parts dystonia

Si 19 F 8 Trihexyphenidyl UL, trunk ModerateS2 20 M 2 None UL MildS3 37 F 27 None UL, trunk, neck ModerateS4 28 F 18 Trihexyphenidyl UL, LL ModerateS5 24 F 15 Carbamazepine Neck, UL MildS6 43 M 15 Trihexyphenidyl Neck, UL, trunk ModerateS7 34 M 23 None UL, LL, neck MildS8 32 M 13 Trihexyphenidyl UL, spasmodic Mild

Diazepam dysphonia

*Treatment was withdrawn at least 24 hours before the study. Median age for patients with ITM (n = 8) was 28; Median age(range) for controls (n = 6) was 30 (17-36); UL = Upper limbs; LL = Lower limbs.

identified in a countrywide study on the clini-cal course of the disease in Israel.21 They wereall Ashkenazi who carry the 9q DYT genemutation.22 Table 1 summarises their charac-teristics. The diagnosis was based on thepresence of a progressive dystonic posture ormovement, and exclusion criteria includedperinatal jaundice or anoxia, metabolic dis-orders, brain trauma or infection, and expo-sure to drugs that could possibly inducedystonia, as well as the existence of sensory,cognitive, cerebellar, pydramidal, or peri-pheral nerve pathology. Patients had nomedication for at least 24 hours before theexperiment and gave informed consent forparticipation in the study.

EXPERIMENTAL APPARATUSThe experimental apparatus consisted of a 60x 60 cm horizontal digitising table and apen-like stylus (fig 1). This table, which waslinked to a micro PDP computer allowedaccurate localisation of the stylus position at arate of 100 Hz. During each trial, two lightemitting diodes beneath the transparent sur-face of the table were used to mark origin anddestination points for the hand movements.

Figure I The apparatus. The initial and destination points are marked by the solidcircles. Target location with respect to a Cartesian coordinate system located at the shoulderand the distance between the targets are shown. The origin and destination targets aremarked by Ti and T2 respectively.

Targets were 1 0 cm in diameter and the sub-ject was instructed to move the stylus fromone target to the other. Figure 1 shows thetarget positions with respect to the subject'sshoulder. The sequence of target illuminationwas controlled by a computer, which was alsoused for storing and further analysis of themovement records, including visualisation ofthe trajectories on a graphic display terminal.

EXPERIMENTAL DESIGNSubjects were tested while seated, holding thestylus in their right hand (all were righthanded). The shoulder was restrained and thewrist braced, so that the movements wereconfined to elbow and shoulder rotations in ahorizontal plane at the level of the subject'sshoulder. The experiment was performedwhile the room was illuminated, with the sub-jects able to see both the target and the movinglimb (visual feedback condition). The sameprocedure was repeated in darkness. In thissituation (no visual feedback condition) sub-jects wearing red tricolor gelatine filter glasseswere unable to observe the moving limb, butcould see the light emitting diodes, whichremained on throughout the movement.

Subjects were told that the target lightemitting diodes would be first illuminated(duration 800 ms), then turned off (for 300ms) and subsequently turned on again, andwould then remain on throughout the move-ment. They were instructed to move immedi-ately on the second target illumination and toperform a movement the duration of whichwas to be roughly equal to the duration of thefirst illumination-that is, 800 ms. No specificinstructions with regard to accuracy weregiven. Back and forth movements between thesame pair of targets were repeated 10 times.

DATA ANALYSISWith appropriate computer analysis pro-grams, the following variables were derivedfrom the recorded data:

Spatial and kinematic properties(a) The trajectory path and the velocity profile;(b) final position error. The final position ofeach movement corresponded to the endpointof the hand path. The spatial coordinates ofthe final position for all movements werecombined to calculate the mean final position.The final error was represented by the mag-nitude (FEM) and the direction (FED) of a

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vector originating from the target to the meanfinal position. (c) The peak velocity (PV) wasdetermined at the point in time at which thetangential acceleration became zero. (d) Theinitial peak acceleration (IPAV) was defined asthe acceleration value of the first peak in theacceleration profile.

Temporal propertiesThe temporal properties were defined as (a)the reaction time (RT): the time elapsingbetween the second illumination of the desti-nation target and movement initiation; (b)movement time (MT): the time interval elaps-ing between movement initiation and untiltangential velocity first became zero; (c) MTwas further divided into the acceleration time(AT): the time elapsing from movement initia-tion and until the acceleration first becamezero and the subsequent deceleration time (DT)lasting until movement termination; (d) accel-erationldeceleration time ratio (AT/DT): theratio between AT and DT; (e) initial peakacceleration time (IPAT): the time elapsing

from movement initiation and until the firstacceleration peak.

STATISTICAL ANALYSISThe various spatial, kinematic, and temporalparameters were analysed to divide them intogroups of correlated variables. The relatednon-independent variables (namely, RT, AT,DT, AT/DT, MT, PV, IPAT, and IPAV)were then analysed with SAS statistical soft-ware, first by multivariate analysis of variance(MANOVA) to analyse the effect of group,visual feedback, and target location on thevector of dependent variables and then by aunivariate analysis of variance (ANOVA) toanalyse the effect of these factors on eachvariable individually. The independent vari-ables (FEM, FED) were analysed only byANOVA. For both analyses, a logarithmictransformation was employed to stabilise thevariances.The model included four main effects

(three fixed and one random), three two wayinteractions and one three way interaction.23

Figure 2 Examples ofpathological behaviour inpatients with ITD. Handpaths, velocity, andacceleration profiles ofproximally aimedmovements are shown fortwo patients with ITD(Si, S2) and an agematched control (Ci).Upper and lower panelsshow respectivelymovement records obtainedunder visualfeedback andno visualfeedbackconditions. The controlsubject showed straightpaths and bell shapedsymmetric velocity profiles.The paths for patients withITD were not straight.Their velocity profiles wereasymmetric, showing alonger deceleration phase.This asymmetry fuirtherdeteriorated in the novisualfeedback conditions.

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The fixed effects were group (patients/con-trols), visual feedback condition (vision/novision), and target location with respect to thesubject (distal/proximal). The random effectwas the subject, which was nested within thegroup.We used a three factor ANOVA (2 x 2

x 2) with repeated measures on the lasttwo effects23: for each visual feedbackcondition/target location combination we hadsix control subjects and eight patients, whereeach subject repeated each combination 10times. Univariate analyses of variance for eachof the two subject groups (controls and dysto-nia) were also performed separately.

ResultsQUALITATIVE RESULTSFigure 2 shows examples of hand paths andthe corresponding acceleration and velocityprofiles of individual responses recorded fromone control and two patients with ITD. Themovements shown in this figure are alldirected toward the proximal target. Theupper panel in fig 2 displays movements per-

formed in the presence of visual feedback(vfb), and the lower panel displays move-ments performed in the no visual feedbackcondition (nvfb). Figure 3 shows distallydirected movements recorded from the samesubjects under both visual feedback condi-tions.Under the vfb condition, control subjects

performed straight hand paths with roughlysymmetric bell shaped velocity profiles.Qualitatively, the hand paths of the move-ments generated by patients with ITD wereoften not as straight as those of neurologicallyhealthy controls. Their velocity profiles wereasymmetric and the decelerative part waslonger. Under nvfb conditions-that is, whenthe subject could see the target but not themoving limb-the velocity profiles of patientswith ITD but not of control subjects showedgreater asymmetry due to further prolonga-tion of the decelerative part compared withthe vfb condition (figs 2, 3).

In patients with ITD, but not in controls,the final errors were substantially larger undernvfb conditions than under vfb conditions(fig 4).

Figure 3 Examples oftrajectory records fordistally aimed movementsin the same subject groupas in fig 2. See fig 2forlegend description.

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Figure 4 Final errorvectors for ITD and agematched controls. Thinlines correspond to controlsubjects'final error vectorand thick lines to those ofpatients with ITD. Solidlines represent the visualfeedback condition anddotted lines the no visualfeedback condition. Thelength of the arrow isproportional to the errormagnitude. Note theincrease in the final errormagnitude under the novisualfeedback conditionin patients with ITD.

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QUANTITATIVE RESULTS

Table 2 summarises the values of the tempo-ral and spatial variables and table 3 sum-

marises the results of the analysis of the twoway ANOVA (with factors: visual feedbackcondition and target location) of control sub-jects and patients with ITD separately.

Group effectOverall in the group x visual feedback x tar-get location analysis, the main differencebetween control subjects and patients withITD was manifested by the AT/DT ratio,which was significantly smaller in patientswith ITD (0-56 in ITD v 0-76 in controls, p <

0-01, table 2). This result reflects the greaterasymmetry of the velocity profiles of patientswith ITD previously mentioned in the qualita-tive description of the movement characteris-tics (see previous section and figs 2, 3). TheATs were similar between groups (table 2),whereas the DTs were longer in patients withITD; this difference was only marginally sig-nificant (1021 ms v 666 ms, 0-05 < p < 0-1).The total MT did not differ in a statisticallysignificant way between groups, although itwas longer in patients with ITD (1492 ms v

1112 ms, table 2). This lack of statistical sig-

nificance between values which are arithmeti-cally so different may be due to the large vari-ability in the subjects' performances (table 2).

The visualfeedback effectIn the group x visual feedback x target loca-tion analysis, the effect of visual feedback was

seen on the AT/DT ratio, which was smallerduring the nvfb condition than during the vfbcondition (0-60 v 0-67, p = 0 057) thus indi-cating that the velocity profiles became lesssymmetric under nvfb conditions. The finalerror magnitude (FEM) was larger in the nvfbconditions than in the vfb conditions (0-71 cmv 0-46 cm, p = 0-052, table 2).The separate analysis of the performances

of the two groups indicated that the visualfeedback effect was manifested in the AT/DTratio only in patients with ITD and not incontrols. This ratio decreased significantlyduring nvfb (0-61 during vfb v 0-51 duringnvfb, p < 0.05). Whereas AT was not influ-enced by vfb, DT was longer in nvfb condi-tions (936 ms v 1106 ms, p = 0071). TheMT was slightly longer in nvfb conditions(1556 ms v 1428 ms) but this difference didnot reach statistical significance. The finalerror magnitude was greater during the nvfb

Table 2 Temporal and kinematic variable values (mean (SD))

Distal target Proximal target

Variable Group vfb nvjb vfb nvflb

RT (ms) Control 383 (95) 408 (125) 342 (98) 347 (109)ITD 384 (119) 448 (226) 363 (122) 343 (103)

MT (ms) Control 1156 (188) 1138 (247) 1124 (170)' 1028 (251)ITD 1395 (557) 1547 (672) 1460 (624) 1564 (711)

AT (ms) Control 457 (116) 442 (135) 486 (105) 437 (103)ITD 437 (158) 462 (199) 546 (165) 489 (220)

DT (ms) Control 699 (170) 693 (214) 635 (159) 591 (204)ITD 958 (445) 1137 (621) 914 (536) 1076 (580)

AT/DT Control 0-71 (0 35) 0 70 (0 29) 0-82 (0 28) 0-80 (0-30)ITD 0-51 (0 22) 0-49 (0-40) 0-71 (0 29) 0 52 (0 24)

PV (ms) Control 48 (11) 50 (11) 46 (11) 48 (10)ITD 46 (19) 48 (21) 45 (21) 48 (22)

IPAT (ms) Control 749 (131) 761 (154) 782 (107) 739 (93)ITD 781 (172) 793 (215) 785 (135) 755 (117)

IPAV (m/s2) Control 190 (68) 220 (84) 175 (64) 206 (67)ITD 234 (159) 234 (163) 164 (128) 209 (158)

FEM (cm) Control 0 34 (0-18) 0 43 (0-18) 0-52 (0-45) 0-61 (0-54)ITD 0-36 (0 26) 1-02 (0 89) 0-60 (0-51) 0-72 (0-43)

FED (degrees) Control 151 (93) 101 (67) 165 (95) 164 (124)ITD 214 (64) 177 (116) 236 (97) 185 (113)

RT = Reaction time; MT = movement time; AT = acceleration time; DT = deceleration time; PV = peak velocity, IPAT = initialpeak acceleration value; IPAV = initial peak acceleration time; FEM = final error magnitude; FED = final error direction; vfb =visual feedback condition; nvfb = no visual feedback condition.

900

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Table 3 Temporal, spatial, and kinematic variables: data derivedfrom ANOVAperformed separately in controls and patients with ITD

Factors

VisualfeedbackVariable Visualfeedback condition Target location target location

Control ITD Control ITD Control ITDRT - - + + - +MT - - - - -

AT - - - ++ - ++DT - + - - -

AT/DT - + - + -PV - - - - _IPAT - - - - -IPAV - - - + ++FEM - + - - -FED - - - - -

+ + = p < 0-01; + = p < 0 05; + = 005 < p < 0 1; -= non-significant.For abbreviations see table 2.

conditions than in the vfb conditions (0-87cm v 0O48 cm, p < 0 05; table 2, fig 4).

Target location effectOverall in the group x visual feedback xtarget location model, a significant effect oftarget location was seen on RTs. Distallyaimed movement RTs were longer than thoseof proximally aimed ones (409 ms v 350 ms,p < 0.01). This effect was also seen in bothgroups when separately analysed.The AT/DT ratio was significantly larger

for proximally aimed movements (0f69 v

0O59, p < 0O01); ATs of proximally aimedmovements were significantly longer than dis-tally aimed ATs (p < 0.01) whereas DTs were

not influenced by target location. A significantinteraction was found between group and tar-get location (p < 0 05). Whereas ATs of prox-imally aimed movements were also longer incontrols, this prolongation was more promi-nent in patients with ITD. The PVs were

higher for distally aimed movements (48 m/s v

46 m/s, p < 0.05) as well as the IPAVs whichwere higher for distally aimed movements(223 m/s2 v 189 m/s2, p = 0 055, tables 2, 3).The RTs of distally aimed movements were

significantly longer than those of proximallyaimed movements both in controls and inpatients with ITD. Final errors were notaffected by target location (tables 2, 3).When groups were analysed separately for

the effect of target location, statistically signif-icant effects on AT/DT, AT, and IPAV were

found only in patients with ITD and not incontrols. The ATs and AT/DT ratios of prox-imally aimed movements were larger, andIPAVs were greater in distally aimed move-

ments (tables 2, 3).

DiscussionIn the present study we have presented a kine-matic analysis of upper limb trajectories inpatients with ITD and age matched neurolog-ically healthy controls. This analysis hasmainly focused on the effects of visual feed-back from the limb and of movement direc-tions on the temporal, spatial, and kinematicparameters characterising the movements.Our findings showed normal reaction times

in patients with ITD, indicating that move-

ment preparation is normal in this disease. Onthe other hand, although their movementtimes were not significantly longer than nor-mal as a group, in some patients with ITDmovement execution was much slower than incontrol subjects. This variability and slownessof movement execution in ITD is in agree-ment with findings in a previous study con-cerned with elbow movements in ITD."I Inthis respect, our results are also reminiscent ofthe well known bradykinesia of Parkinson'sdisease24 and Huntington's disease.25Slowness of movement seems therefore torepresent a more generalised feature of basalganglia diseases, despite different symptomsof either hypokinesia or hyperkinesia such aschorea or dystonia.

Focusing closer on the velocity profiles weattempted a more detailed analysis of the tra-jectories by further examining the accelerativeand decelerative phases of the movement.The generation of roughly symmetric bellshaped velocity profiles in healthy subjectsreflects the fact that the durations of bothcomponents are almost equal, although thedecelerative phase might be longer undermore stringent accuracy demands.'7 In fact,the mean AT/DT ratio in our normal controlsubjects was 0-76, and 0-56 in ITD. Themajor abnormality in the trajectories of thepatients was the long decelerative component,which became even longer when visual feed-back from the limb was withdrawn. Thesefindings could suggest a specific defect in thesecond part of the movement-that is, in theintegration of "corrective" information intothe motor plan. The validity of this interpreta-tion can be investigated in several ways. Oneapproach might involve the comparison of thekinematic properties of fast and slow move-ments. The rationale of such an approach isthat the dependency on feedback informationis of relatively less significance during fastmovements, as such movements operatemostly under "open loop" conditions, by con-trast with slower movements, which are sub-ject to a mode involving continuous feedbackbased corrections. Indeed, Van Der Kamp etal," who have analysed the kinematic proper-ties of rapid elbow movements in ITD, havenoted equal durations of the acceleration anddeceleration phases in such movements andhave concluded that motor programmesinvolved in the execution of rapid movementsare relatively preserved in ITD. This symmetryof the velocity profile in relatively fast move-ments compared with the asymmetry wefound in relatively slow movements, mighttherefore indicate deficits in the integration offeedback corrections in patients with ITD orthe use of a strategy based on verifying theirperformance (see later). In the present study,we used another approach by analysing motorperformance under conditions in which themovement is more dependent on kinaestheticinformation-that is, in darkness.Among the various sensory modes influenc-

ing the preparation and execution of move-ments, visual, proprioceptive, and possiblyefferent copy information26 play important

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parts. Visual information is necessary for thelocalisation of the target and for the compari-son of hand and target positions during themovement, particularly in the final adjust-ment stage. When vision of the moving limb isnot available, the magnitude and direction ofthe required movement amplitude is deter-mined by comparing the target positionderived from vision with kinaesthetic informa-tion enabling the assessment of the limb'sposition. In primates and healthy humans,inability to see the moving limb does not sig-nificantly affect the temporal features ofreaching movements27 as was also noted in thepresent study. On the other hand, we notedthat in the absence of visual feedback, thevelocity profiles of patients with ITD showedincreased asymmetry due to a longer decelera-tive phase and a deterioration of the finalaccuracy.

Possibly the slowing in the decelerationphase is due to the inability of patients withITD to rely on afferent information. Whenvision of the limb is available, they can verifytheir progress by comparing their hand posi-tion against the target location and obtainaccuracy levels similar to controls. Whenvision of the limb is withdrawn, they movemore slowly to compensate for the lesseramount of information. The fact that the finalaccuracy deteriorates without visual feedbackonly in patients with ITD and not in controlsubjects, despite the relative decrease inmovement speed, might also suggest a deficitin the integration of proprioceptive or efferentcopy information into the descending motorcommand.A new finding that emerged from this study

relates to the similarities between the move-ment characteristics in ITD and Parkinson'sdisease. For example the abnormal depen-dency on visual cues from the moving limb, aswas shown here in patients with ITD, waspreviously reported in monkeys with lesions inthe substantia nigra and in patients withParkinson's disease. A significant increase infinal errors occurred in the absence of visualfeedback from the limb.'920 The deteriorationof performance in ITD, however, seems tooccur mostly in the decelerative part of themovement and in the final error, whereas inParkinson's disease, both the accelerative anddecelerative phases are affected by theabsence of visual feedback.'9 Thus it seemsthat in ITD, the integration of sensory infor-mation into the motor plan is disturbed,whereas in Parkinson's disease, in addition tosimilar abnormal processes, the planning ofthe initial acceleration is also deficient.

Other similarities between ITD andParkinson's disease relate to spatial effects. Anew finding consists of the differences thatexist in RT as a function of movement direc-tion. Van Sonderen et aF8 found longer RTsin healthy young controls when movementswere directed away from the body, than inthose directed toward the body. Our findingsin both normal controls and in patients withITD were similar. We have previously shownprolongations of RTs for distally aimed move-

ments in elderly healthy subjects and pro-nounced prolongations in patients withParkinson's disease.'9 In patients with ITD,however, the magnitude of the effect of targetlocation on RT was similar to that seen incontrols.The effect of direction of movement was

also reflected in the values of movementacceleration in patients with ITD. Initial peakaccelerations were higher and accelerationtimes were shorter for distally aimed move-ments compared with movements aimedtowards the body in patients with ITD but notin controls. Similar results were found by usin patients with Parkinson's disease'9 and byCamarata et at9 in monkeys treated with 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine.It is possible that in ITD and in Parkinson'sdisease, deficits in the evaluation of limb con-figuration and subsequent abnormalities inthe ability to generate appropriate muscleforces in accordance with the variations inlimb inertia as a function of arm configura-tion, result in the inadequacies in initial accel-erations reflected by these findings. Similarabnormalities were reported in deafferentedpatients.30

Another analogy between patients withITD and deafferented patients is the deterio-ration of motor performance in patients withITD in the absence of visual feedback,expressed by the increase in final errors andthe prolongation of deceleration time underthese conditions. For example, Teasdale et al 31

studied drawing movements by a deafferentedlimb and noted that in the absence of visualfeedback the shape of drawn figures remainsconsistent, whereas their spatial locationdrifts. Still, the deficits occurring in ITD,although reminiscent of findings in deaffer-ented patients, are of smaller magnitude.Conscious proprioception is probably normalin ITD, as are the anatomy and innervation ofmuscle spindles.32 A central deficit in subcon-scious assessment of proprioceptive informa-tion, however, seems to exist, requiring extrareliance on visual feedback, as shown in thisstudy.Thus ITD might not necessarily be a pure

motor disorder but may involve complexdeficits in sensorimotor integration. Thereported similarities between the kinematicabnormalities of limb movements of patientswith ITD or Parkinson's disease, and theeffects of visual feedback and movementdirection on motor performance, may indicatethat similar functional pathways enrolled insuch functions are affected in Parkinson'sdisease and ITD.

This work was supported in part by the Yeda Fund of theWeizmann Institute of Science, by grants Nos 85-00395 and88-00141 from the United States-Israel Binational ScienceFoundation (BSF), Jerusalem, Israel, and by the IsraelMinistry of Health, Chief Scientist.

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7 Sheehy MD, Marsden CD. Writer's cramp, a focal dysto-nia. Brain 1982;105:461-80.

8 Yanagisawa N, Goto A. Dystonia musculorum deformans.Analysis by electromyography. J Neurol Sci 1971;13:39-65.

9 Ghez C, Gordon S, Hening W. Trajectory control in dys-tonia. Adv Neurol 1988;50:141-55.

10 Nakashima K, Rothwell JC, Day BL, Thompson PD,Shannon K, Marsden CD. Reciprocal inhibitionbetween forearm muscles in patients with writer's crampand other occupational cramps, symptomatic hemidys-tonia and hemiparesis due to stroke. Brain 1989;112:681-97.

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12 Panizza ME, Lelli S, Nilsson J, Hallett M. H-reflex recoverycurve and reciprocal inhibition of H-reflex in differentkinds of dystonia. Neurology 1990;40:824-48.

13 Van Der Kamp W, Berardelli A, Rothwell JC, ThompsonPD, Day BL, Marsden CD. Rapid elbow movements inpatients with torsion dystonia. _J Neurol NeurosurgPsychiatry 1989;52: 1043-9.

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17 Georgopoulos AP. On reaching. Ann Rev Neurosci 1986;9:147-70.

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19 Flash T, Inzelberg R, Korczyn AD. Kinematic propertiesof upper limb trajectories in Parkinson's disease. ExpNeurol 1992;118:215-26.

20 Viallet F, Trouche E, Beaubaton D, Legallet E. The roleof visual reafferents during a pointing movement: com-parative study between open-loop and closed-loop per-formances in monkeys before and after unilateralelectrolytic lesion of substantia nigra. Exp Brain Res1987;65:399-410.

21 Inzelberg R, Kahana E, Korczyn AD. Clinical course ofidiopathic torsion dystonia among Jews in Israel. AdvNeurol 1988;50:93-100.

22 Korczyn AD. Genetics of idiopathic torsion dystonia inAshkenazi Jews. In: Bonne-Tamir B, Adam A, eds.Genetic diversity among Jews. Oxford: Oxford UniversityPress, 1992:194-201.

23 Winer. Statistical principles in experimental design. McGraw-Hill, 1971.

24 Marsden CD. The mysterious motor function of the basalganglia: the Robert Wartenberg lecture. Neurology 1982;32:514-39.

25 Thompson PD, Berardelli A, Rothwell JC, Day BL, DickJPR, Benecke R, Marsden CD. The coexistence ofbradykinesia and chorea in Huntington's disease and itsimplications for theories of basal ganglia control ofmovement. Brain 1988;111:223-44.

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Thomas Sydenham and Richard Bright onchorea

Thomas Sydenham, known as "The BritishHippocrates" wrote little of neurological diseases, buthis description of chorea' is a classic.

"There is a kind of convulsion, which attacks boysand girls from the tenth year to the time of puberty.It first shows itself by limping or unsteadiness in oneof the legs, which the patient drags. The hand can-not be steady for a moment. It passes from one posi-tion to another by a convulsive movement, howevermuch the patient may strive to the contrary. Beforehe can raise a cup to his lips, he does make as manygesticulations as a mountebank; since he does notmove it in a straight line, but has his hand drawnaside by the spasms, until by some good fortune hebrings it at last to his mouth. He then gulps it off atonce, so suddenly and so greedily as to look as if hewere trying to amuse the lookers-on."Chorea (Greek: dance), was used to describe the

dancing manias. During an outbreak in 1418 suffererswere regarded as hysterics. They were enjoined torepair to the chapels of St Vitus at Zabern nearStrasbourg to plead for the Saint's intervention. ASicilian martyr under Diocletian (AD 303), St Vitus'sremains were moved to France, and, because he waspatron of dancers and actors, his altar was used to seek

relief from the dancing plague. The dancing mania wasa source of great terror: Burton's Anatomy of melan-choly (1621) refers to "Chorus Sancti Viti ... they thatare taken with it can do nothing but dance till they bedead, or cured."

Sydenham's account made no mention here, nor inchapter 10 "On Rheumatism" that he recognised theassociation with rheumatic fever. Indeed this associa-tion was forged in 1831 by Richard Bright(1797-1858)2:"A general irritation which so strongly markschorea" The acute form primarily affected children,in which "we have seen that rheumatism is so inti-mately connected . . . a peculiar connection." Thework of Germaine See in 1850 distinguishedSydenham's chorea from paralysis agitans, thoughmis-citing Parkinson as "Patterson."

J M S PEARCE

1 Sydenham T. On St Vitus's dance. The works of ThomasSydenham, MD. Translated from the Latin edition of DrGreenhill with a life of the author by RG Latham MDVol 2. London: The Sydenhain Society, 1850:257-9.

2 Bright R. Reports of medical cases. Vol 2 Disease of the brainand nervous system: selected with a view of illustrating thesymptoms and cure of diseases by reference to morbidanatomy. London: Longman, 1831:493.

3 Brown J. Locke and Sydenham and other papers. Edinburgh:David Douglas, 1882:33-135.

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