Genetic tools to manipulate MRI contrast.

Advances in molecular biology in the early 1970s revolutionized research strategies for the study of complex biological processes, which, in turn, created a high demand for new means to visualize these dynamic biological changes noninvasively and in real time. In this respect, MRI was a perfect fit, because of the versatile possibility to alter the different contrast mechanisms. Genetic manipulations are now being translated to MRI through the development of reporters and sensors, as well as the imaging of transgenic and knockout mice. In the past few years, a new molecular biology toolset, namely optogenetics, has emerged, which allows for the manipulation of cellular behavior using light. This technology provides a few particularly attractive features for combination with newly developed MRI techniques for the probing of in vivo cellular and, in particular, neural processes, specifically the ability to control focal, genetically defined cellular populations with high temporal resolution using equipment that is magnetically inert and does not interact with radiofrequency pulses. Recent studies have demonstrated that the combination of optogenetics and functional MRI (fMRI) can provide an appropriate platform to investigate in vivo, at the cellular and molecular levels, the neuronal basis of fMRI signals. In addition, this novel combination of optogenetics with fMRI has the potential to resolve pre-synaptic versus post-synaptic changes in neuronal activity and changes in the activity of large neuronal networks in the context of plasticity associated with development, learning and pathophysiology.