Table 1. Comparison of light targeting strategies.

Targeted light strategy	Number of neurons addressed	Pros	Cons	Biological questions addressed	Representative references
1P full field	100 - 1000	Many neurons activated simultaneously, high temporal resolution	Low spatial resolution using viral transfection	Circuit analysis of cell types	47, 52
1P full field + sparse labeling	1 - 100	High spatial and temporal resolution; can identify cells individually	Only suitable for low numbers of neurons	Single to many-neuron computation	34
1P fiber	100 - 1000	Can be used in freely moving animals	Low spatial resolution	Effect of cell types on behavior	104
1P directed beam	10 - 100	Spatial resolution ~50 µm	Cannot activate individual neurons	Mapping anatomical features of cell types and projections	25, 105
1P DMD	100 - 1000	Commercially available	Low spatial resolution	Effect of activation of cell types in spatial patterns	71, 72, 103, 106
1P SLM	100 - 1000	Holographic patterns enable photostimulation in three dimensions	Low spatial resolution	Effect of activation of cell types in spatial patterns	107, 108
2P directed beam	1	Single cell spatial resolution	Only one neuron at a time	Mapping inputs from individual neurons	76, 83, 84, 109
2P SLM	~50	High-resolution holographic patterns can activate multiple individual neurons	Low temporal resolution	Manipulation of neural coding at the individual neuron level	78, 84
2P temporal focusing	1 - 10	High spatial and temporal resolution: can activate multiple individual neurons	Few neurons at a time given high laser power required for each neuron	Manipulation of neural coding at the individual neuron level	77, 78
2P AOD	1 - ?	High spatial and temporal resolution: can activate multiple neurons sequentially over very short intervals	Untested	Manipulation of neural coding at the individual neuron level	None