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THE LANCET Neurology Vol 1 May 2002 http://neurology.thelancet.com 5

Newsdesk

Canadian researchers may have shedlight on a syndrome that is more thana pain in the neck. Eliana Klier, and ateam led by J Douglas Crawford (YorkUniversity, Toronto, Ontario), havepinpointed a key structure in thecontrol of head movement—findingsthat could be relevant to some patientswith torticollis.

In cervical dystonia—a commonform of torticollis—abnormal headpositions are often maintained byinvoluntary sustained neck-musclecontractions, explains neurosurgeon

Joachim Krauss (University Hospital,Mannheim, Germany). But little isknown about the control of headmovement and why it fails in suchpatients. Clinical evidence hasimplicated “impairment in the basalganglia circuitry, but also dysfunctionof the vestibular system and vascularcompression of the spinal accessorynerve have been discussed”, he notes.

Previously, Crawford and col-leagues found that the interstitialnucleus of Cajal (INC) acts as amidbrain “neural integrator” to

control eye movements. INC inputsinclude signals from the vestibularapparatus whereas the interstitiospinaltract that controls neck muscles is akey output. So, Crawford’s teaminvestigated the role of the INC inhead movement.

Four alert macaque monkeys hadhead and eye movements recordedafter electrical stimulation andmuscimol-induced inactivation ofmidbrain sites. INC stimulation led to the tilted head positions seen in torsional torticollis. Muscimolinjections into the INC, but notadjacent sites, also caused progressivetorsional torticollis. One-sidedinactivation of the INC caused head-tilt toward the opposite side whereas stimulation produced a same-sided tilt (Science 2002;295: 1314–16).

“The authors demonstrate con-vincingly that the INC is not only aneural integrator for eye movementsbut also for head orientation”, saysKrauss. The INC seems to convertvestibular and volitional inputs duringgaze shifts into muscular commandsthat dictate final head position,suggests Crawford. So, any disorderthat affects the bilateral balance of INCactivity—either direct damage or aninput imbalance—could cause dystonictorticollis.

If an INC activity imbalance couldbe identified, Crawford speculates,deep brain stimulation might re-setthis imbalance. Krauss, whose unitpioneered bilateral stimulation of theglobus pallidus as an effectivetreatment for cervical dystonia, isunsure. He points to human studiesfrom 1970 when neurosurgeons atTeikyo University (Tokyo, Japan)found that unilateral INC stimulationcaused head retroflexion rather thantorsion. INC lesioning was beneficialin some patients with cervicaldystonia, he notes. However, “it wasnot pursued further and it was sooncompletely abandoned and forgotten”.Crawford’s team now aims to explorein more depth how the INC andrelated areas control neck-muscleactivity and thus head position. Kelly Morris

“Neural integrator” may go awry in torticollis

US scientists have devised a simplebrain-computer interface that alloweda monkey to move a cursor apparentlyusing neural signals alone.Importantly, the monkey was able touse “thought control” to direct thecursor immediately. Such “neurallybased control of movement mayeventually be feasible in paralysedhumans”, suggest the authors.

Previously, cortical signals havebeen used to drive a robot that canmimic a monkey’s arm movement inreal time. Now, John Donoghue’s team(Brown University, Providence, RI,USA) has found that goal-directedbehaviour can be achieved withoutarm movement, using motorcommands from as little as sixneurons. Initially, monkeys fitted withmultiple intracortical electrodes used ajoystick to move a cursor towards atarget for food reward. When neuralsignals were also used to update cursorposition, the team observed that onemonkey was achieving the task withoutmoving its arm—thus, suggestsDonoghue, “the brain activitysubstituted for the hand-motionsignal”. Subsequent tests confirmedthat neural control could substituteimmediately for hand control, andnearly as accurately (Nature 2002; 416:141–42).

First author Mijail Serruya explainsthat the current device, which haspotential for human use, is based on asimple linear regression algorithm.

These findings indicate “that humanprosthetic devices will not require largeamounts of data or lengthy training tobecome functional”, he says. But oneconcern for José del Millán (EC JointResearch Centre, Lausanne,Switzerland) is whether feedback fromthe monkey’s arm movements isnecessary for stable neural control overtime. If the monkey could not move,Millán believes that similar resultsmight still be achieved by using mutuallearning strategies—“Where thesubject and the machine learn fromeach other”—together with moresophisticated estimation of controlparameters.

So did the monkey will the cursorto move? Donoghue acknowledgesthat the monkey could have discoveredsome other subtle action that wasgetting the cursor to move. “What wasreally going on remains a mysterybecause we can not readily interrogatethe monkey”, he says. Serruya believesthat “we’ll learn more whenneuromotor prosthetics areimplemented in people”. However, forMillán, who directs development of anon-invasive brain interface forparalysed people, the challenge is to seewhether it is possible to obtain similarresults with non-invasive technologiesusing mutual learning and appropriatecontrol techniques to compensate forthe lower resolution of recorded brainsignals.Kelly Morris

Can a cursor be moved by thought alone?