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FRONTIERS COMMENTARY Nikolenko et al. present an elegant technique , which they call " SLM microscopy, " that combines both of these strategies into a single system. Their system targets two-photon excitation simultaneously to up to several tens of points within the fi eld of view. The authors achieve this feat using a spatial light modulator (SLM), which alters the oscillation phase of the incoming light. A shift in phase does not in itself alter the intensity of the light; however, because of constructive and destructive interference, a change in phase can lead, upon propagation, to a dramatic redistribution of intensity. For example, a microscope objective can be thought of as a device that simply adds a spatially-varying phase to the incident illumination; constructive and destructive interference then causes the phenomenon that we usually think of as focusing to a diffraction-limited point. Nikolenko et al. (and related work Lutz et al., 2008; Papagiakoumou et al., 2008), following in the footsteps of holography pioneer Gabor (1948), deliberately perturb the phase of the input light to the objective. The result, of course, is a microscope that no longer focuses all the incoming light to a single, diffraction-limited spot. Ordinarily, this would not be taken as a step forward. However, the SLM consists of more than a million individually-address-able elements, and thus allows phase to be precisely manipulated in nearly arbitrary spatial patterns. The authors employed a computational algorithm to calculate a phase pattern that, after passage through the objective, illuminated many distinct spots. Crucially, the position of these spots is under the control of the user, and thereby allows one to direct light to many specifi c targets, even ones that are above or below the objective's plane of focus. Rather than the usual photomultiplier tube used when scanning a single point, the emitted light is focused onto a CCD camera, which preserves spatial information about the emission source. Nikolenko et al. demonstrated SLM microscopy's utility with two applications. The fi rst is photostimuluation with caged glutamate. The authors were able to simultaneously stimulate multiple spines on the same neuron, or multiple neurons simultaneously. The high power needed for two-photon uncaging currently acts as a barrier to selecting more than a modest number of spots. Nevertheless, the ability to stimulate multiple spots seems likely to yield advances in our understanding of both single-cell membrane properties and neu-ronal circuits. The second application was …