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o 2000 oP^ (os.fts hbrùrr^ a$oiùn) N v

I PHYSIOLOGICAL TREMOR: DOESI HANDEDNESS MAKE A DIFT'ERENCE?

ANNE BEUTER4q*, RODERICK EDWARDS'and ANNIE BOUCHERb

" Cosniliv Neatuyience Cenîe (D5,5719), Unircnilr .,f euebec at Maûrcat,?O Box 8838 Station C.hie t i e. Mùnieat ec HJC 3pB. Cdha.ta:o Deparîment oI Kinanlhrc?otosie, Uniwrsb) ;f euehet at Aontui:'Depdrtnent af Mathematics ahd Slatisii.s, Urirùsitr o[ r/i.1oria,

pO Box 3415, t/ictatia BC V8tit 3p4. Caradd

(Re.eitu4 2 Jnc t99c )

Tbc !ù4'ose of rhh srMy was ro qlaDtify with tecjsion rhc chèræt€risrics ofromalphysioloeical tÉnor in tle doninânr and Dondoninant land of â eroùp of rishr-handedllnâles. 'twenly

two rignl harded fenalês (ased 20 ro 40) gare infomed;osùr btâilicipate Manùal dominancc detmined wnn a qùesrionûajÉ had ro be €qùi to, orîbov . ,0 " " . to r s rô ie r , ro De. .c1-a ed n rbe n rd r w0 te fc .ub( ! r r ten h , , e \ ..tu.ed. r"mo. rr. r"ordeo .mr rrre.ùdj ,û rhc qo (\Frded ;de^ h;*._ d;""4 0 . P e ù d n e b e ê o r a i r g o t p o s L r â t I e n o r t h - e { ù - D . . , o d d u r n l r l ù r h L h ;. L b t e ( r . $ e e â \ < Ê d r o r l î r ' , . r ' o t c o r d i l o r ) . o e \ e . r a t , " , . . . * , r t , , : " o , o o . "ôngers otr two sbain g.ùses (static cotrdnion)j or io pless on and ofl wiih borb irdexingers on two srrain gèus6 (dtmmic cordirion) Each condition was .æordcd rwiæsfth two helium neon !Èlôcity lâsen This p.oæture ùâs repeated afrer Dermtation ofûe lâss, ûrùs a ioral ol twelve sccps of daia wcre rÈcorded. Sder paranerers w€reused io analyTi the renôr signal irclûding neàsùr€s ofhamonicily, mêdian Irequency,lrolortrotrâl power in the ? 12Hz rùgq amlli1ùde, wavetom morybology. enrropy.ârd nonlineùry. Signili@r! differcnæs bè1veù hands w€re fonnd in rhree ;arancùs(nedian fr.qlency. povff in ? 12 Hz and mtrôpy) blt nor in irenor anpftdde (RMSI.r i d d . l r o n . . i c 1 i t i c r ' o r - c r . r ' e . r e r e o u n d r t n e o l r o t . c v e n ( h - d . . ; i , i c ! b ( . $ æ ncondilions. 'Ihcse

rsults sùeeest lhat neùromolor activirl, lræÈding lbc æcording ofr tmor !{s a signitcarr inflncn* or renor chaiacterisric and ltDt sonc of thseI cha@1etutcs â.e signifrcdtly ditrerenr berwæn the rigti and hft hard in rigbt-handed

Ke:t\|ùtlt: Eandednùsj lhysiolosicat trmor tâteratily: neùrotnolor actvity marùalJ"ntun-e

icorespondilc allbôr. Faa: (5141 987 8952, èmai1: beùrer.ânne@uqan.ca

9

l0 A. BEtnER r, d.

Tremor, defined as an irregular involunlary oscillatory motion presentin a body segment. is ubiquitous ât resl and during motion (Lakie,i995). In healtày sùbjecis it is hârd1y visibte in the extremities âûd is anormâl phenomenon (Eshner, 1897). It cân be influenced by numer-ous factors. Wâchs and Boshes (1961) have identiûed thirty seven fac-tors including liûb temperâtur€, breathing, posture, etc. The fùnctionalmle of tlemor, however, is ùnclear. Ac.ording to Goodman ând Kelso(1983) tremor could facilitâte the initiation of voluntary movementsby decreasing the initial inertia.

Hand dominance is not symm€trical in huralls. According tovârious studies, up to 90% of nolmâl adults are found to be right-handed (Briggs and Nebes, 1975;Hardyck, Goldman and Petrinovich,1975). Int€rcstingly this percentage is only âbout 60% in schizophrcnicpatients (Green et al.,1989). Males, âs â whole, tend to exhibit lessright-hând preference âs compâred to females (Rymar et al., 1984).Rymâr aiso found that 90% of 72s €lementary and junior high schoolstudents w€rc rig'ht-handed, and only about 55% were righl-eyed. How-ever, hand preference was found to be negligibly correlated with eye

Only few studies hav€ explored the relationship betw€€n tremor andhand dominarce. Eshner (1897) was tÏe tust to evoke the possibility ofsuch a relationship. He reported an average peâk ftequency of 6.7 Hzfor the left hând and 7 Hz for the .ight hand. However, this âuthor didnot repon the hand doninance of tlle pârticipants nor tlte methodùsed io câlc late tremor amplitude ând frequency. Later, Fnedlander(1956) ùsed â tremorgraph to examine trcmor in ih€ iirdex ûûgers ofa

$oup of subjects ând did not report sig licani differcnces betweenhands in amplitude but âdmiited that his technique was not preciseenough. Marsden €r al (1969) found no significânt differcnces in trem-or amplitûde or frequency between the two hands in heâlthy subjectsusing acceleromete$. These âuihors applied cross-spectral.analysisto trcmor of the outstretched tngers recorded simullaneously ftomboth hands of 18 heâltly subjects and at repeated intervals in twoirained subjects and found no consistent phase relâtionship betweenthe treûror of the t\to hands, i.?., tlle coherence was negLigible. Morerecenlly Semmler and Nordstrom (1995) found no significant differ-enc€s between hands for tremor RMS amplitude or for the peak freqù-ency in tÏe power spectrùm for tremor force bÙt noted thât tremoi at

l l

the pcak ftequency was higher in the nondominant side of right_handed subjecls. Lâkie (1995) found thal caretul analysjs ofthe pooted'pectml d" tâ of )45 healrhy 'ubiecr. ,hoqed lha r . on a\ erdge. \ubjecrçhâd slightly more tremor on the right side. The difference, however,was 'Lust sjgniûcanr in some ofrhe (higher frequency) bands,' (p. 165).

In subjects with essential tremor, Biary and Kolter (1985) hâveshown that 83% oft}le pâtients were righr-handed and t7% were lefr-handed. In the dght-handed group, 47% of rhe pârienrs had grearerright-sided tremor measured wirh an acceleromerer and only 5% hadgreater leftsided lremor. Furtlermore, tlcse authors nored a higherincidence of left-handedness in patients with essential tremor thân incontrol subjects. In this study, however, tremor amplitude wâs notquantified in heàlthy control subjects.

The goal of the presert study was to investigate ihe relationship be_tween treùror ând handedness wirh precise laser systems and derâiledanalysis methods developed in our lâboratory. Therefore, postùraltremor iû a groùp of young righr handed subjecrs was quartified ândanalyzed to determine if there was â sigdficânt difiercnce betweendominant ând rondomimnt hands ir terms of tremor amplitude,ftequency, and moæhology- Since â number of studies have reporredthat females are more strongty lâreralized than males (Annelr, 1970,1972; Yen, 1975) this study examined females onty.

METHODS

Subj€cts

Twenty two healrhy femâles aged between 20 and 40 recruited throughâclvertrement gave informed consent to participate to this study afterthe nature of the procedure was fully explained. Exctusion crireriaincluded diabetes, migraines, ho.monal problems, ûeurologicàl pro_blems, anxi€ty, essential tremor or taking neuroleptics. Maûual domin_ance was determined from a l0-question qrestionmire modified fromOldfield (1971) and Rieal (1995) and using a five-point Likerr scale(always left, ofien left, no preference, ofren right, elways right). Theselected subjects had to have right preference scores between 90 and100% to be accepted in rhe srudy. Subjects werc asked ro refrainfrom dinkirg caffeine or atcohol for l2hours before being rested, to

PHYSIOLOCICAL TREMOR

A. BEtnER ., al.

avoid smoking or ergaging in intense physical exercise for tbree hoùrsbefore being tested. Care was taken !o ensùre thâi the laboratory waswârm, quiet and empty of persons other than the subject and themvestrgator.

Before each testirg session the lasers were calibratôd- Strâin gaùgeswere calibrated using 2009 weights co[esponding to one volt on theoscilloscope. Each subject sât on a comfortable chair adjustâb1e inheight and was given a settle down time of 5 min (Ito, 1961). The sub-ject was then asked to remove her watch. The subje,rt had her elbowsa! approximately 90" and her foreams rested on foam pads on a ta-ble. Hcr pâ1ms rcsted on a molded support in such a way that the in-dex metâcarpophalangeal joinl did not touch the support. The indexfingers did not touch any other finger. A small piece of reflecljve tâpe(weight less ihân I g) was placed on the flngernail of each index finger.ln lhe control cordition, tbe sùbject rested ând then atteûpted tomaintain the index frngers outstretched but not hypeæxtended witheyes closed for 40s. ln the static conditioû lhe same 40s recording waspreceded by a pressùre of the two index fingers on two sûair gâugesfor 30 s. A diodevisible by the subject wâs turned on when the pressureproduced by the subject was between 1.6 ard 2.2N. ln ihe dynamiccondition tl1e same 40s recording was preceded by periodic pressure

by both index fingers timed by a metronome (50 times in 60 s, or âbout0.83 Hz) for 60s. ln âll conditions the recording of postural tfemorstarted ûve seconds afler the subjsrt was askcd 10 plâce her irdex fingels in position. The effects of fatigue and learning were avoided byrândomiziûg the conditions. Al1 subjecls sta ed by the control con-dition (tremor preceded by a resi period), then eleven sùbjects executed the static condition (t.e., piessure of the index fingers) beforetle dynamic condition (t.e., periodjc pressure of the indexet and theother eleven subjects executed the dynamic condition before the staticcondition. Each test was executed twice and bctween eâch test a twominute r€st pedod was given to the subject. After permutation ofthe two lasers, the three conditons were repeated twice in tle rewconliguation. A grand totâl of 12 sweeps of data were recorded forcach subject.

PHYSIOLOCICAL lREMOR l l

Eqripment

Physiological tremor wâs recorded with two helium rcon velocitylase$, type 3544 (Brùel and Kjaer Canada Limited,90 Leacock,Pointe Claire, QC). Recorded data from the lase$ were amplifiedard digitized using â dâta acquisition system at a frequency o1200Hzper channel (Datawave Technologies, 380 Main Streer, suite 209,Longnont, CO). The lasers were plâced ar 26cm ftom rhe reflectivemârker in a slightly oblique position (âbour 18'). This inclinarion cre-âies a 5% underestimâtjon of velocity âmplitudes, bur thjs is u form

For the static and dymmic conditions two strain gauges rvere used10 produc€ a lbrce between i.6N ând 2.2N. A visual feedback wâsprovided to the subject rra â diode which wâs rurned ofi wh€n thesubject was ùnder or above the desired force intervâI. The subjecr wasâsked to use tlis visùal feedback to âdjust her force.

An additionâl six sweeps ofdâiâ wcre recorded âfter the two iase$were inverted to cancel the potentiâl elTect of slight calibration difi€r-ences between the two laser systerns,

Dâta Processing

Thc raw data werc converted to ASCIL The first 1000 poinrs wereremoved to âvoid contamination by trànsients. Then, noise presentin the form of occasional spikes produ€ed by the laser sysremwas removed using ân âlgoritlûr which interpolated isolâted pojnrswlth iarge values, which could not correspond ro a physical 6ngermovement. The criteria for interpolation were that the differencebetween a point and its two neighbours was lârger than a threshold(0.005m/s), tlat the difi-erenc€ between the two neighbouring pointswas less t}lâr the threshold, and that the poirt wâs further from themean of the liûe series tlan either of its neighbours. The signâl wasthen (lowpâss) filtered at 20H2. For the calculatior of one of rhemeasures (wobble)l displac€ment dâta were oblained by numericatintegrâtion ând (highpâss) frltered below 2Hz, ând accelerarion darawere obtained by numerical differentiation andr (lowpass) frlreredahove 20 Hz.

Sev€n tremor characteristics were calculated for each sweep of data.These included a meâsure of velocity amplitude. the root mean squâre

oî the ûlter€d datâ, in m/s (ttre logarilbm was used lor statistical anâ-lysis âs âmplitude has â rougl y log-normal distributior); two measures ofpower iû Lhe frequency spectrâ, mediân frequency (F50), in Hz,and proportional power in the '7 l2Ez tungq. one measurô of'harmonicity' which meâsùres how concentrâted spectrâl power is orthe frequency axis (Hm cenlre of mass of the power spectrùm âfier itsfrequency bins are sorted in order ol d€creasing power); one meâsùreof morphology, wobblô (the nùmber of oscillâtions jn accelerâtionover the number ofoscillalions in displacemeno;entropy, which meâs-ures "disorder" in the distribution of data points, pârljcularly dùe inthis context to amplitude fluctuations; and a measure ofasymmetry inthe decây of the autocorrelation function (ACF) which is associatedwith nonlineârity ofunderlyins dynamics (ADACF the masnitude ofthe first maximun minus tle magnitude of tle tust minimum of theACF). Detailed description of these characteristics cân be found inEdwards and Beùter (1999) and Beuter ard Edwârds (1999). In addi-tion, coherence between ihe tremor ofthe two hands was calculated.

No two of the abov€ characteristics were highly correlated with eachother (> 0.75)- For each châracteristic in each condition, the averageover the four lrials wâs used in the following anâlysis-

RXSULTS

Means ând stândard deviâtions of the seven charâcteristics and thethre€ experimental conditions ùsed to analyze physiological tremorare presented in Table L A univariate ANOVA for each characteristic

TABLE I Mca.s ând standard deviâriom ol rhe s€ven cha.æFnsiics ol teror

S1ttj. Dlrmic Dtwicright left nchl

F50 7.00+0.811 12Hz 0.39+0.09RMS 0.r4 + 0 05(x 100)

4.1?: l0 .31 4.0110.35?.23:t0.?2 6.66 + 1.030.41+0.09 0.37+0.090 r4+0.07 0.14+0.05

1.823 +0.16 1.926 + 0.201.36+0.04 135+005

-0.00t 0.011

4 03+0.15 4. +0.10 4.15+0.317.0?+0.1! |4 6.93+ l .0 l ? .26+0.8 i0.4r +0.10 0.38 +0.09 0.41+0.090.14+0.05 0.13+0.04 0.13 +0.05

I 3 ? 0 + 0 t 3 1 3 2 9 + 0 . t 6 t . 8 4 5 + 0 . 1 ?r .36+0.04 1.14+0.06 1.36+0.05

0.024 0.022 0.004+0.09 +0.09 +0.09

l 5

TABLE ll _ R6ùlts of rhe analysis of variênce for rhe seven chalactensrics, 1be twohands and lhe rbrce Èrpe.imentâl conditions (haràclc4 in bold rcflect staristicalty sig-

P}TSiOLOGICAL TREMOR

7 1 2 H 2

RMS

t37l l 2 l

5 . t i l5 2 90.534.48

I 09

0.026

0.i94

0.r0212.003.414.4600 000

0 . 1 7 7

1.649

0.000

0.0250,0040 591

0.1800.1440.8?l0.0000.8250_752

0.0420.0.t6

0.612

0,0t)70.204

using a mixed efects model rev€aled the presence of significânt djffer_ences betwe€n the two hands for median frequency, power in 7 12H2,ând entropy (see Tab- II) as wôIl as signiûcant differences berweenconditions for harmo city, median freqùency, amplitude, wobble, ândnsymmerric decây ofrhe ACF (Tab_ II). There lvas a signifi€ant inrer,action between hand ând condition for wobbte (Tâb. II).

Maximum coherence values between the tremor of the two hanalswere for the most part between 0.2 ard 0.4 with a few values between0.4 and 0.5.

DISCUSSION AND CONCLUSION

The results of the pæsent srudy reveal signiûcanr dift-erenc€s ûor onlybetween hands but âlso between conditions for several cha.âcleristics.But given the relatively small sample size, our datâ should be inler_preted wirh caution.

I6 A. BEUTER ?t ,/.

The dominant side (right) hâs more fluctuations in amplitude(entropy), more power in the 7 12Hz rar|'ge and a larger medianfrequency rcga.dless of the €ordition examined, but does not havehigher amplitude or more harmonic tremor. The larger median frequ-ency is ir agreement with tïe results reported by Eshner (1897). The0.3 Hz difference between right and left sides repo ed by tbis âuthor isobserved in the three conditions of tÏe present study. Our resulis,however, do not ùgfee with those reported by Semmlerând Nordstrom(1995) who measuled tremor force and found that the peak frequencyin the power spectrum was not influenc€d by hàndedness.

The type of activity employed beforc tÏe recording o1- postuml

tr€ûor (rest, static, dynamic) also significânt1y affects ifemor but indifierent wâys. The static (isoûetric) condition produces a lowcr fie-quency, more harmonic and more morphologicâlly distinctive tremorthân the contrcl (rest) condilion, wher€âs the dynamic (periodic) con-dilion produces a lower amplitude but more nolrlin€ar tremor (in thesense oî âsymmetric decay of the ACF). Wobble, which is a measure oftbe morphology of tremor oscillations, is the or y characleristic lbrwhich thcre is ân int€Éction between hands and conditions. This resultindicates lhat the shâpe of the osciilatory movement dùring ttre test isâfiected difierently in the dominant and notdominant hands by theactivity preceding the recording of tremor. As cân be seen in Table Iwobble folows a reverse pâttern in ihe static condilion than in thecontrol or dynamic conditions.

Using the method proposed by Marsden el d/. (1969) we foùnd thatthe coherence vâlues between the two hânds were low in generâI.

However, these values arc higher tlan those reported by these âuthors.This is due to the fact that they reported àverage coherence valuescalculated betwôen one and twenty cycles per second- These valuesrânged between 0.108 ând 0.008 and exceeding Îârely tlte spuriouscoherence inevitable iû statisticâl airalysis of a ûnite sample. In thepresent study. we used maximum coherenc€ values over the entircfrequency range. Although calculated diiTerently our values are low.Mârsd€n and his coileagrres (1969) found ûo moment to moment linkbetween the shapes of the tremor wave forms of the two hânds andconcluded that tremor amplitude and frequency of the two hards areprobâbly not detemined by some coûrmon pacemaker locâted in thecentrâl n€rvous system. Tremor miglt be determined by two separate

PHYSIOLOCICAL TREMOR 17

pâcemàkers, one for each hand, sincc the 8 12Hz component ofphysiologicâl tremor is suppos€d ro be of central origin (Elble ardKoner, 1990).

Surprisingly, no signi{icanr differences in tremor amplirude wer€lbund belween hânds and this resutt agreôs with r.hose oblained bySemmler and Nordstrom (1995). However, ttese results are differentfrom those reported by Latie (1995) who investigated rremor in thetwo middle fingers simultaneoùsly with accelercmeters and calculatedthe size of acceleration ât the peak and the mean acceleralion l€vel ineach ofnine bards ofâbout 1.5H2 widrh berween 3 ând 15H2. How_ever, Lakie (1995) fouûd differences in amplihrde only in some higherT.equency bands ând this rnight be in accord wirh our observatior ofâhigher prcportionâl powef in rhe 7 12Hz band for the right hand(RMS arnplitude efe€tivell measures torat amplitude h a frequenciesât once). Tremor âmplitude, however, was significanrty difiercnl acrossconditions wirh rhe lowesr values associared wirh rhe dynamiccondition (periodic pressure). Entropy, lvhich is particutarly sensitiveto amplitrde fluctuatior, was highe. in the dominânt hand âcross allconditions. Therc is no previous report of this measure and thisprecludes us ftom making comparisons.

Until we rcplicate our srudy with lett-handed females we can onlyspeculate âbout the mechanisms rhat mây accounr for the relationshipbetween tremor and handedness. However, if handedness can be takenas â sjgn ofcerebral dominanæ it can be hyporhesized rhat a differenceexists between dominant and nondominant hemispheres for righrhanded females. Semmler and Nordstrom (1995), sludying dischargeproperlies of motor units in the ûrst dorsal interosseoùs mùscle ofright and left handed jndividuais, nored rhat moror unir alischarge rateand variability were sinilar in nght ând left hânits but the strengthof motor unil synchronization (expæssed as rhe frequency of extrastmchronous discharges above chance) was weâker in the domjnanthând of right-handers compared to left-handers. These authors inter_pret their results as "reffecting a more restricted distributjon of directprojections from motor corticai neurcns within the first dorsal interosseous motoneuron poot or reduced excitability of the cortical ncu_rons durins the task" (p. 115).

Recently, differences between right ard left hands hâve been exlen_sively exploæd for votuntâry movements of rhe fingers using newty

I I J A. BEUTER er a/.

devetoped c€rebral imaging techniques For example, Reichenbâch

el a1. (199u) found thar in right handed subjects, moving rhe nondoml-

nàni thùmb wâs âssociâted with a more bilaleral âctivation pattern

in both putamen and cerebellar regions Kim cr l]l (1993) noted

an hemispheric âsymmetry in the fLrnctional activâtion of the humân

motor cortex during contralât€ral and ipsilateral finger movements

especially in right-handed subjects. Finallv, Mattav ?r dL (1998) in a

similar study concluded that nondominânt hand novements which

tend to be less automatic, appear to rcquire morc cortical activtty

similar to compiex tâsks with the dominant hand. The âreas actlvaied

for volÛntary movements ale similar to those activated during

pathological tremor nnd il is not excluded that asyllmelries that we

observe in physiological rremor are related, in som€ yet unknown way'

to as),nmetries present in voluntâry finger movementsPractically, tlese results can be us€d to improve lhe eârly detection

ofa nunber of neufological conditions which have a very progessive

onset and in which the eârly signs ofabnormalities are unilateral (? g 'Parkinson's disease). As indicated by Marsden er d/. (1969) tlere is

some practical importance to know the relation of tremor of one hand

to thât of thc other. When the early eff€cts of a chronic exposure to

neufotoxic substances are being explored, forexample' it is important to

be able to separate the changes associated wittr handedness from those

associated with the slow (preclinical) onset ofa neùological disorder.

Annetl, M. {1970) A dasnlicâlion of hând !refcrenæ bv associalion analvsis Brirltr

JôûtMl oJ Pslchalost, 61, fO] 332.Anndi M. ( | 9?2i The disûbnrior of nannal asvmrelry. a/ itish J@ûal of Psv(hÔtagj.

63, 141 358.Beutd. A. & Edwards. R. (1999) Usins lrtqùcncv doiain charucterlstics ro discnn!

i;re physiologiul ând parkinsoalû rt.mos- Jaut,al of Clinicul NeurcPhvtiokst

Biary, fi. & (oller, W. (1985) Handedrcs ald esentiâl rreûor' atchiv.s aj Neùroksr'42. loriz 1083.

Briggs, G. G. & Nebes, R. D. {1975) Pâftcrns ofhand pref€rdæ in â srudentlopÙlaûonCortex,11.230 Ba

Edwùds, R. & Beùtcr, A. (1999) Usitrs tifre donâin clâradenslics to discnrinâtephysiologiù] alrd Parkinsoniân tmôn Journat of Electro.n1lhdloqruPhf and

clinical N eûophyt iolôst (n@pred)Elbl€, R J. & K;I;r. w. c. 0990) Dfl,.. Thc Jobns HopkiN UnivÙsitv Pr*s

(BajtinoÉ). Eshner. A. A. (1897) A grapnic srùdv ol trenor' Joutnal o1 ExlÙi'nental Me.li.ke. 2, l0\ 112.

l 9

Friedlander, W. J (19561 Claracterhtic ofpo(ural trcmor in nomal and in varioùsnbDorftl statcs. ùelrolrAl, 6, 716 724

Goodnù, D. & Kelso, J A. S. (1981) Ëxplôring the tunclional siCnincènce of phy-sorosical rr€nor. A biospectrosopic approach. trpcltn.,ra1 sruk R6eû.h, 49,4 1 9 4 3 i .

Grcen, M. F., Satz, P., SniLh, C. ., aa (t9ll9) h theÉ âryli@l haDdedrcs iùeh\zoptuûia7 J.ùnal oI Abnot dl Ps!.holosr, 9a. 51 6t.

Ha.dyck, C., Goldnan, R & Pelrinovich, L. (1975) Hândedness, rex, race .nd ase.Huhon BiolaEj. 47(.3),169 315.

I1o. K. (1962) Scltle down tine of hùnan ninor rrenor. yônuso Actd Medjca, se).90 95.

Kim, S. C, Ashe, J.. Hcndrich, K., Ellemann. J. M., Mer}te, H.. Uglrbil, K.& Ceoleo!ôùlos, A. P (1993) Functonal nasnelic resoûræ inâsing of mo-ror cort€x: hcmisphe.ic asymetn/ and iandedness. S.r,.?, 261, 615 1?.

tlkie, M. (1995)Is e$cûtialhenor physiologial? (pp.165 183) tn: Findtày. L. J. ând(oller, N. C. (1995) sdlôook an Trcnù Di\or4ers.Nq york : Maût DelLer,

Masdeù, C. D., Meadows, J. C.. Lanee, c. W. & Warson. R. S. (1969) Thc rclatioiberwær physioloeical irtuor of the rwo hands in heaftny sùbjècrs. Ete.baetæ-Phalogapht md Cliniùl Neuopb'sioloA|t,27, 119 185.

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PHYSIOLOCICAL TREMOR