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Activation of the cerebellum in co-ordinated eye and hand tracking movements: an fMRI study - page 11 / 12

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ed the anterior parts (the anterior portion of the quadran- gular lobule), the same area strongly activated in the eye-hand task in our study.

We also took care to balance the visual inputs within the four conditions of experiment 1, and sensory inputs associated with eye or hand movement would not be ex- pected to differ in these tasks. The spatial separation be- tween ocular and manual targets on the screen (Fig. 1) is not expected to affect the cerebellum. Clower et al. (1996) reported only activity in area PEG of the posteri- or parietal lobe, and not cerebellum, due to the re- integration and alignment of visual and proprioceptive representations of the hand distorted by prism lenses.

The cerebellum has been proposed to be concerned with error detection or error processing, and in motor learning (see Clower et al. 1996; Cordo et al. 1997; Kitazawa et al. 1998). However, our subject’s perfor- mance in these tasks was stable over time and similar across conditions (Fig. 3). Hence, there is no reason to suppose differential cerebellar activation because of tracking errors in the different conditions, nor significant motor learning during scanning. The equivalent perfor- mance across the tasks also suggests that the contrast be- tween the conditions is not likely to be confounded by the increase in difficulty moving from single tasks to du- al tasks. The final aspects of the task that would be ex- pected to sensitively activate the cerebellum are tracking speed and velocity errors. We can estimate these from the total mouse movement and tracking errors (cumula- tively measured every 4.4 s), which were not significant- ly different in the two tasks. In fact, the total mouse mo- tion was smaller in the eye-hand condition than in the hand-only condition, and thus the difference in average speed is of the wrong sign to explain the increased cere- bellar activity observed.

Thus, we argue that the cerebellum is particularly concerned with inter-communication between different motor effectors, to allow co-ordinated control. Visually guided control of the arm involves communication from oculomotor centres carrying information about the posi- tion and velocity of the eye motion, as these define the target’s motion. Likewise, signals from the arm-control centres provide information that allows the eyes to accu- rately track the hand through visual space. So one might expect that the oculomotor site, active in eye tracking, would be more active in eye and hand tracking, if it then receives and processes information from the hand con- trol site. The same would be expected for the hand- control areas. However, there are no direct connections between the cerebellar cortical regions shown to be acti- vated by these experiments. Hence, the communication must involve extra-cerebellar relays, perhaps including areas in the premotor cortices or the cortical eye fields. It is our aim to now test cerebral areas in the same tasks to challenge this point.

Acknowledgements This work was funded by a Wellcome Trust Senior Research Fellowship. We very gratefully acknowledge the use of the imaging facilities of the CRL Laboratory, Tokyo, and also the facilities of the FMRIB Centre, Oxford. We thank Edwin

Robertson for comments on the manuscript and also the research teams at CRL, Tokyo and ERATO, ATR, Kyoto. In particular, we would like to thank Professor Mitsuo Kawato for his help and sup- port.

References

Abrams RA, Meyer DE, Kornblum S (1990) Eye-hand coordina- tion: oculomotor control in rapid aimed limb movements. J Exp Psychol 16:248–267 Allen G, Buxton RB, Wong EC, Courchesne E (1997) Attentional activation of the cerebellum independent of motor involve- ment. Science 275:1940–1943 Bastian AJ, Martin TA, Keating JG, Thach WT (1996) Cerebellar ataxia: abnormal control of interaction torques across multiple joints. J Neurophysiol 76:492–509 Beppu H, Nagaoka M, Tanaka R (1987) Analysis of cerebellar motor disorders by visually guided elbow tracking movement. II. Contribution of the visual cues on slow ramp pursuit. Brain 110:1–18 Biguer B, Prablanc C, Jeannerod M (1984) The contribution of co- ordinated eye and head movements in hand pointing accuracy. Exp Brain Res 55:462–469 Blouin J, Gauthier GM, Vercher JL, Cole J (1996) The relative contribution of retinal and extraretinal signals in determining the accuracy of reaching movements in normal subjects and a deafferented patient. Exp Brain Res 109:148–153 Brown SH, Kessler KR, Hefter H, Cooke JD, Freund HJ (1993) Role of the cerebellum in visuomotor coordination. I. Delayed eye and arm initiation in patients with mild cerebellar ataxia. Exp Brain Res 94:478–488 Carter N, Zee DS (1997) The anatomical localization of saccades using functional imaging studies and transcranial magnetic stimulation. Curr Opin Neurol 10:10–17 Clower DM, Hoffman JM, Votaw JR, Faber TL, Woods RP, Alexander GE (1996) Role of posterior parietal cortex in the recalibration of visually guided reaching. Nature 383:618–621 Cordo PJ, Bell CC, Harnad S (1997) Motor learning and synaptic plasticity in the cerebellum. CUP, Cambridge Coull JT, Nobre AC (1998) Where and when to pay attention: the neural systems for directing attention to spatial locations and to time intervals as revealed by both PET and fMRI. J Neuro- sci 18:7426–7435 Culham JC, Brandt SA, Cavanagh P, Kanwisher NG, Dale AM, Tootell RBH (1998) Cortical fMRI activation produced by at- tentive tracking of moving targets. J Neurophysiol 80:2657– 2670 Dettmers C, Fink GR, Lemon RN, Stephan KM, Passingham RE, Silbersweig D, Holmes A, Ridding MC, Brooks DJ, Frackowiak RSJ (1995) Relation between cerebral activity and force in the motor areas of the human brain. J Neurophysiol 74:802–815 Duvernoy HM (1995) The human brainstem and cerebellum: sur- face, structure, vascularization and three dimensional sectional anatomy with MRI. Springer, Wien New York Ebner TJ, Fu Q (1997) What features of visually guided arm movements are encoded in the simple spike discharge of cere- bellar Purkinje cells? Prog Brain Res 114:431–447 Ellerman JM, Siegal JD, Strupp JP, Ebner TJ, Ugurbil K (1998) Activation of visuomotor systems during visually guided movements. A functional MRI study. J Magn Reson 131:272– 285 Flament D, Ellermann JM, Kim SG, Ugurbil K, Ebner TJ (1996) Functional magnetic resonance imaging of cerebellar activa- tion during the learning of a visuomotor dissociation task. Hum Brain Map 4:210–226 Friston KJ, Frith CD, Liddle PF, Dolan RJ, Lammertsma AA, Frackowiak RSJ (1990) The relationship between global and local changes in PET scans. J Cereb Blood Flow Metab 10:458–466

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