Soma-targeted (somatic) opsin

An opsin fused to a trafficking / localization motif (for example from the Kv2.1 channel or the ankyrinG-binding domain) that restricts its expression to the neuronal soma and proximal dendrites, keeping it out of axons and the surrounding neuropil. This is essential for two-photon holographic stimulation: without it, a focal spot aimed at one cell also illuminates the dense mesh of passing axons and dendrites belonging to other neurons, producing off-target spikes and destroying single-cell specificity.

Soma-targeting sharpens the effective spatial resolution of optogenetic write-in toward the single cell, which is why it is a prerequisite for credible all-optical control. It is not perfect: residual neuropil expression, out-of-focus two-photon absorption, and imperfect trafficking mean true single-cell resolution is approached, not guaranteed, and must be characterized empirically.