Cortical networks underlying coordinated movements revealed by magnetoencephalographic beamforming Paul Ferrari a ,* , K.J. Jantzen a , J.A. Scott Kelso a , Douglas O. Cheyne b , Armin Fuchs a a Center for Complex Systems and Brain Sciences, Florida Atlantic University, FL, USA. b Neuromagnetic Imaging Laboratory, Hospital for Sick Children Research Institute, ON, Canada _______________________________________________________________________ Abstract. Event-related beamformer analyses was applied to magnetoencephalographic data from five subjects who performed synchronized and syncopated unimanual motor coordination tasks at rates ranging from 1.25 to 1.75Hz. For syncopation, the stability of the coordination pattern decreased systematically with increasing movement rate. Averaged sensor data revealed the motor field (MF) and motor evoked fields (MEF) I and II. Additionally, we observed an early field (M0) at approximately 160ms prior to peak flexion with polarity opposite to the MF. Beamformer analysis reproduced previous findings that showed the MF activity being generated mainly in precentral gyrus and the activity of the MEFs is distributed across multiple generators in pre and post-central gyrus. For syncopation, additional areas of activation were observed during early M0 and late MEF II time periods which included premotor, frontal, cingulate, and SMA, with the premotor areas exhibiting a dependence on rate. These results provide evidence of the power of MEG beamforming for characterizing the properties of cortical neural activity at a high resolution in space and time. Keywords: Magnetoencephalography, Beamforming, Motor Coordination, Synchronize, Syncopate 1. Introduction Unimanual sensorimotor coordination with an external metronome is stable for synchronization (on-beat) and syncopation (between-beat) tasks when performed at low movement rates. However, under parametric increase in rate, the syncopation pattern becomes progressively destabilized until at some critical frequency subjects switch spontaneously to the synchronized coordination pattern. The inab ility of syncopating at higher rates has been attributed to attentional and timing related demands required for * Corresponding author. Tel: +1 561-297-2230. Fax: +1 561-297-3634. E-mail address: ferrari@ccs.fau.edu ; Center for Complex Systems and Brain Sciences, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA. Manuscript