J. Hyönä, D.P. Munoz, W. Heide and R. Radach (Eds.) Progress in Brain Research, Vol. 140 © 2002 Elsevier Science B.V. All rights reserved CHAPTER 20 Cortical frames of reference for eye–hand coordination Paul van Donkelaar * , Ji-Hang Lee and Anthony S. Drew Department of Exercise and Movement Science, Institute of Neuroscience, University of Oregon, Eugene, OR OR 97403-1240, USA Abstract: To reach for an object the brain must transform visual input from the eye into motor output of the arm. Recent neurophysiological experiments have shown that this transformation maps onto a network of brain areas including the posterior parietal (PPC) and premotor (PMC) cortices. In this chapter, we review evidence from our own experiments which demonstrate that this network can only partially complete the transformation when the eye and limb movement amplitudes are dissociated. We also discuss the effects of disrupting either the PPC or PMC using transcranial magnetic stimulation (TMS) on the ability to carry out the transformation successfully. Introduction The ease with which we perform the act of reaching out to point at or grasp an object belies the fact that this behavior requires a complex transformation of visual input into a coordinated motor response of the eyes and hand. How this process is carried out in the brain has been the focus of much recent investigation within neuroscience. At the heart of this issue is how the initial visual input coded with respect to the retina is transformed into appropriate oculomotor and manual motor output and how sig- nals related to responses in each of these effectors interact with each other to produce the coordinated movements that are observed. A specific question that arises is how the oculomotor signals based in an eye-centered frame of reference influence the manual motor responses that are of necessity generated in a limb-centered frame of reference. We propose that if compensation for the eye-centered frame of refer- ence is not complete by the time the manual response * Correspondence to: P. van Donkelaar, Department of Ex- ercise and Movement Science, Institute of Neuroscience, University of Oregon, Eugene OR 97403-1240, USA. Tel.: +1-541-346-2687; Fax: +1-541-346-2841; E-mail: paulvd@darkwing.uoregon.edu is generated, this should be apparent and quantifiable in the characteristics of the reaching movement. In a series of recent experiments we have examined this issue in relation to the conditions under which compensation occurs and the areas of the cortex that are responsible for it. Neurophysiological studies A growing body of literature from single unit neuro- physiological studies in awake behaving non-human primates has demonstrated that parts of the poste- rior parietal cortex (PPC) code for oculomotor and manual motor output in an eye-centered frame of ref- erence. Within the medial portion of the PPC there exists the parietal reach region (PRR) which con- tains arm movement-related cells that encode targets with respect to eye position (Batista et al., 1999). A large proportion of these reach-selective cells also fire around the time of saccade generation (Snyder et al., 2000). Such cells could play an important role in the coordination between eye and limb movements to visual targets. The PPC sends strong projections to the premotor cortex (PMC; Wise et al., 1997) and this latter area has also been shown to be involved in eye–hand interactions during reaching movements. The PMC is traditionally thought of as an area whose activity is strongly related to the coding of CICERO/GALAYAA B.V./HYÖNÄ20: pp. 301-310