Probing Dendritic Function with Holographic Structured Illumination

Holographic structured illumination has revolutionized techniques to investigate how neurons process information. Neurons receive synaptic inputs via its dendrites, and understanding the processing of those inputs and the influence of the dendrite’s nonlinear properties are key components to decode the neuron’s computing power. Recent breakthroughs to understand dendritic function make use of structured illumination to stimulate and/or record dendritic activity either via photochemical or optogenetic tools. As a stimulator, patterned light resembles multiple synaptic inputs onto dendrites, which can be used to investigate the nonlinear properties of dendrites and the input–output transfer function of neurons. For optical recording, light patterns can excite fluorogenic indicators (calcium or voltage) at multiple sites, and the fluorescence can be collected simultaneously using an image sensor array (e.g., camera). Simultaneous recording of the changes in the fluorescence from multiple sites enables the probing of critical spatiotemporal phenomena occurring in dendrites. The future points to combining the advantages of holographic photostimulation, optical recording, and three-photon excitation with adaptive wavefront correction to enable the visualization of dendritic activity at high spatiotemporal resolution in deep regions of the intact brain. Probing the integrative and nonlinear properties of dendrites will get us closer to understanding of how these neurons function as tiny computers in the brain.