Calcium ion (Ca2+) is one of the most important divalent ions in the day-to-day life of any cell, as shown by its involvement as second messenger in virtually all cell types, from life onset to cell death through almost every physiological processes (muscle contraction, heart physiology, coagulation, immune system control, neuronal information processing). Ca2+ concentration can vary by up to 6 orders of magnitude with dynamics in the millisecond range; however, the investigation of its variations has been hindered by the lack of precise control over the dynamics, especially in excitable cells such as neuron. In this project, we propose to first build a new tool to control in real time the variations of intracellular Ca2+ via the combination of two-photon microscopy and dynamic current clamp: the dynamic calcium clamp. Then, we propose to use this tool to investigate two neurophysiological mechanisms: one related to a new form of synaptic plasticity dependent on the rates of activity of both the pre and post synaptic neurons and the other to the integration of the eye velocity signal into an eye position signal. The conception of the dynamic calcium clamp and its first applications would be undertaken in Boston University, USA, since in this institution hosts both one of the leading laboratory in microscopy applied to Neurosciences (BioMicroscopy Lab, outgoing host) and a laboratory developing one of the best dynamic clamp software (NDL, partner). The last part of the project will be lead at the return host, located in Paris 5 University, FRANCE (LNRS-UMR7060). There, the dendritic properties of the neurons of the velocity to position integrator would be studied, with a special focus on the Goldman hypothesis about dendritic hysteresis which would modify the local computing properties. Thus, this project will at the same time provide new tools, better understanding of brain mechanisms and foster the development of the career of the fellow in Europe.