EEG dynamics of the frontoparietal network during reaching preparation in humans J.R. Naranjo, a,b A. Brovelli, a,c R. Longo, d R. Budai, e R. Kristeva, b, ⁎ and P.P. Battaglini f a Cognitive Neuroscience Sector, International School for Advanced Studies (SISSA), Trieste, Italy b Cortical Motor Control Laboratory, Department of Neurology, University of Freiburg, Breisacherstr. 64 D-79106 Freiburg, Germany c Institut de Neuroscience Cognitives de la Méditerranée, CNRS-Université de la Méditerranée, Marseille, France d Department of Physics, University of Trieste, Trieste, Italy e Santa Maria della Misericordia Hospital, Udine, Italy f BRAIN Center, University of Trieste, Trieste, Italy Received 6 March 2006; revised 20 July 2006; accepted 26 July 2006 Available online 27 December 2006 Visuomotor transformation processes are essential when accurate reaching movements towards a visual target have to be performed. In contrast, those transformations are not needed for similar, but non- visually guided, arm movements. According to previous studies, these transformations are carried out by neuronal populations located in the parietal and frontal cortical areas (the so-called “dorsal visual stream”). However, it is still debated whether these processes are mediated by the sequential and/or parallel activation of the frontopar- ietal areas. To investigate this issue, we designed a task where the same visual cue could represent either the target of a reaching/pointing movement or the go-signal for a similar but non-targeting arm movement. By subtracting the event-related potentials (ERPs) recorded from healthy subjects performing the two conditions, we identified the brain processes underlying the visuomotor transforma- tions needed for accurate reaching/pointing movements. We then localized the generators by means of cortical current density (CCD) reconstruction and studied their dynamics from visual cue presentation to movement onset. The results showed simultaneous activation of the parietal and frontal areas from 140 to 260 ms. The results are interpreted as neural correlates of two critical phases of visuomotor integration, namely target selection and movement selection. Our findings suggest that the visuomotor transformation processes required for correct reaching/pointing movements do not rely on a purely sequential activation of the frontoparietal areas, but mainly on a parallel information processing system, where feedback circuits play an important role before movement onset. © 2006 Published by Elsevier Inc. Keywords: Reaching movements; Visuomotor transformation; Frontoparietal network; EEG; Cortical dynamics; Cortical current density reconstruction Introduction The correct execution of reaching movements involves the activation of cortical areas widely distributed in a frontoparietal network, the so-called “dorsal visual stream”. One of the principal roles of the frontoparietal network is to translate the information about the position of objects that have to be reached in the peripersonal space into motor commands (Battaglia-Mayer et al., 2003). Electrophysiological recordings in behaving monkeys have demonstrated the presence of visuomotor-related neurons within the parieto-occipital (Galletti et al., 1996; Fattori et al., 2001, 2005) and intraparietal sulci (Grefkes and Fink, 2005), the premotor dorsal (PMd) and premotor ventral (PMv) cortices (Hoshi and Tanji, 2004a,b). Despite the invaluable information provided by neuronal recording in monkeys, it is still partially unclear how the visual, parietal, premotor, and motor cortex interact during visually guided arm movements in humans (Culham and Kanwisher, 2001). Neuroimaging studies in humans reported activation of dorsal occipital, parietal, premotor, motor areas, and the supplementary motor area (SMA) as well as cingulate cortex and the cerebellum during reaching and grasping (Grafton et al., 1996). Furthermore, during pointing preparation, the inferior (IPL) and superior parietal lobule (SPL), precuneus, the posterior superior temporal sulcus, the dorsal premotor and anterior cingulate cortex were activated (Astafiev et al., 2003). PET and fMRI techniques provide a high spatial resolution, but are limited by the unknown relationship between functional imaging signals and the underlying neuronal activity. Therefore, they cannot accurately elucidate the fast temporal dynamics of co-activating frontal and parietal areas during a visuomotor task. Electroencephalography (EEG) is a valuable tool to study the temporal pattern of cortical activity on a milliseconds scale. Thus, by using event-related potential (ERP) methods, high sensor arrays and advanced electromagnetic source analysis techniques, it is possible to localize and separate the underlying neural sources of www.elsevier.com/locate/ynimg NeuroImage 34 (2007) 1673 – 1682 ⁎ Corresponding author. E-mail address: kristeva@nz11.ukl.uni-freiburg.de (R. Kristeva). Available online on ScienceDirect (www.sciencedirect.com). 1053-8119/$ - see front matter © 2006 Published by Elsevier Inc. doi:10.1016/j.neuroimage.2006.07.049