In the past decade, methods adapted from experimental physics have transformed our understanding of the nervous system, in areas ranging from optical imaging to large scale electrical recordings. In the future, deeper exploration of massively parallel neural networks in the brain requires the precision, bandwidth, and quantitative analysis that are well-developed in physics. The theme of Neural Interfaces in PHYS-X is optical and electrical interactions with neural circuits for both recording and stimulation. In optical recordings, we are developing novel approaches to monitoring neural activity using interferometric techniques for detection of nanometer-scale cellular deformations associated with changes of the transmembrane electric field. Combined with adaptive optics, interferometric recordings will enable detection of neural activity with single cell resolution in a living human eye. To further our understanding of large neural networks in the nervous system, we are advancing the size, resolution and sophistication of large-scale electrical recordings and stimulation, and using them to develop novel approaches to communication with living neural circuits. For precise control of neural activity, we are developing “electronic synapses” - nanoelectrodes for cell-attached coupling, which may revolutionize electro-neural interfaces by providing continuous modulation of cellular potential for stimulation and inhibition, while reducing the applied currents by many orders of magnitude, as compared to the standard extracellular electrodes. These developments in optical and electronic technologies for neural interfaces will not only further our understanding of the brain and lead to replacement or augmentation of the damaged neural circuitry, such as sensory or motor prosthetics, but may also be used to enhance our cognitive and sensory capabilities.