The turbulent fluctuations of the edge plasma in fusion experiments are characterised by large-amplitude events in the plasma potential and pressure. These electrostatic events are considered the main cause of anomalous particle transport both in RFP (1) and tokamak (2) experiments and so a great effort is concentrated on their investigation. To this purpose the Gas Puffing Imaging Diagnostic (GPID) system (3) has been installed on RFX-mod device. The system consists of a gas-puffing nozzle and 32 optical channels divided into 3 fans to measure the localHeI (667.8 nm) emission from the puffed neutral gas. The optical lines are 5 mm spaced and cover an area of 70 mm along the toroidal direction and 50 mm in the radial one; so the plane normal to the local magnetic field (that is poloidal in the edge of the RFPs) is observed. Signals are sampled at 10 Msample/s and the effective bandwidth of electronics is 2 MHz. Being a non-invasive diagnostic, the GPID is used to study plasma edge also for high plasma current pulses when the Langmuir probes cannot be inserted. In this paper results obtained in RFX-mod device (R=2m, a=0.5m) (4) are described for discharges at 500-600 kA plasma current and "Virtual Shell" operation. In particular the connection between edge plasma fluctuations and core MHD phenomena is analysed. This MHD activity is mirrored in the periodic fluctuations of the reversal parameter ( )/ F B a B