Abstract In order to assess the role played by area V6A in visuomotor control, two adult green monkeys (Cerco- pithecus aethiops) were subjected to small, bilateral le- sions in the anterior bank of the parieto-occipital sulcus. Before and after the lesions, monkeys were tested for naturally designed reaching, grasping and picking-up pieces of food from various positions on a plate and from a differently oriented narrow slit. All movements were recorded with closed circuit TV and analysed offline on a single-photogram basis for defective reaching and wrist orientation. V6A lesions provoked parietal weak- ness, reluctance to move, and specific deficits in reach- ing, wrist orientation and grasping. Recovery from the observed deficits was rapid, even after a second, contra- lateral lesion was given, creating a bilateral lesion. Thus, together with previous anatomical and electrophysiologi- cal data, these results directly support the hypothesis that area V6A is part of the network involved in the control of reaching movements and wrist orientation. Keywords Superior parietal lobule · Posterior parietal cortex · Parieto-occipital cortex · Lesions · Reaching · Grasping · Wrist orientation Introduction Area V6A is located in the posterior parietal cortex, dor- sally in the anterior bank of the parieto-occipital sulcus and contains both visual neurons and neurons which are insensitive to visual stimulation (Galletti et al. 1999). It strongly projects to premotor frontal areas (Matelli et al. 1998; Shipp et al. 1998) likely supplying the frontal cor- tex with the visuospatial information required for visual control of arm-reaching movements. It also receives aff- erences from the premotor cortex that likely supply it with the copy of motor output related to the arm move- ment (Galletti et al. 2001; Fattori et al. 2001). Hence it seems obvious to suppose that this area is somehow in- volved in the control of arm movements. As a matter of fact, clinical data show that lesions in the posterior parietal cortex provoke various symptoms like optic ataxia, visual disorientation, and a range of difficulties in object reaching, grasping, and manipulation (Perenin and Vighetto 1988; Jeannerod et al. 1994). Recently, Rushworth et al. (1997a, 1997b, 1998) lesioned restrict- ed areas in the posterior parietal cortex of monkeys, showing that the ventral part of the posterior parietal lobe (areas 7a, 7ab and LIP) is essential for spatial coor- dination of visual motor transformation, while its dorsal part (areas 5 and MIP) is involved in the spatial coordi- nation of arm movements that depend upon propriocep- tive and efference copy information. Similar conclusions have also been reached by Stein (1978), who compared the effects of cooling area 5 (dorsal posterior parietal cortex) versus area 7 (ventral posterior parietal cortex). However, in all these reports, lesions were relatively large and involved mainly the exposed cortical surface and/or the cortex hidden in the intraparietal sulcus. The anterior bank of the parieto-occipital sulcus was not in- volved. Moreover, postoperative testing was performed 1–2 weeks after surgery, so as to allow local networks to reorganize and mask the possible involvement of highly interconnected regions. In order to verify the role of area V6A in the control of arm movement, we confined le- sions to this area and postoperative testing was initiated P.P. Battaglini ( ✉ ) · A. Muzur B.R.A.I.N. Center for Neuroscience, University of Trieste, Via A. Fleming 22, 34127 Trieste, Italy e-mail: battagli@units.it Tel.: +39-40-5587183, Fax: +39-40-567862 C. Galletti · P. Fattori Department of Human and General Physiology, University of Bologna, Piazza di Porta San Donato, Bologna, Italy M. Skrap Department of Neurosurgery, General Hospital, Udine, Italy P.P. Battaglini · A. Brovelli Cognitive Neuroscience Sector, International School for Advanced Studies (ISAS-SISSA), Via Beirut 2–4, 34013 Trieste, Italy Exp Brain Res (2002) 144:419–422 DOI 10.1007/s00221-002-1099-4 RESEARCH NOTE Piero Paolo Battaglini · Amir Muzur · Claudio Galletti Miran Skrap · Andrea Brovelli · Patrizia Fattori Effects of lesions to area V6A in monkeys Received: 8 November 2001 / Accepted: 13 March 2002 / Published online: 25 April 2002 © Springer-Verlag 2002