Optical tissue interface method and apparatus for stimulating cells

A method for electrically stimulating a target cell of a living animal in vivo, the method comprising:

• inserting an elongated structure, having a hollow portion, into a narrow passageway in the animal such that an end of the structure is sufficiently near the target cell to deliver stimulation thereto;
• while the elongated structure is in the narrow passageway, delivering a viral vector through the hollow portion of the elongated structure, wherein the viral vector comprises a nucleotide sequence encoding a light-activatable polypeptide having at least 75% amino acid sequence identity to the ChR2 amino acid sequence set forth in SEQ ID NO:1, wherein the nucleotide sequence is operably linked to a target cell type-specific promoter, and wherein said delivering provides for expression of the light-activatable polypeptide selectively in the target cell;
• after delivering the viral vector, inserting an optical fiber through the hollow portion of the elongated structure, and
• stimulating the target cell by using the optical fiber to deliver light to the light-activatable polypeptide expressed in the target cell.