Manipulation
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Optical and acoustic forces for biomedical applications
Exerting controlled forces in a non-contact way is important in biomedical investigations which require holding, moving, or mechanically probing biomedical samples. Optical and acoustic manipulation of microscopic samples both play a prominent role among suitable technologies. The differences in the physical laws and in the typical length scales governing acoustic and optical forces make them complementary: Acoustic forces can levitate large and heavy particles, which optical tweezers could not handle without adverse high-power effects, while optical forces cover subcellular scales. The talk will contrast the two modalities, and identify situations where one or the other is favorable, or when a combination of both is the best choice.
Holographic control of neuronal circuits
Genetic targeting of neuronal cells with activity reporters (calcium or voltage indicators) has initiated the paradigmatic transition whereby photons have replaced electrons for reading large-scale brain activities at cellular resolution. This has alleviated the limitations of single cell or extracellular electrophysiological probing, which only give access to the activity of at best a few neurons simultaneously and to population activity of unresolved cellular origin, respectively. In parallel, optogenetics has demonstrated that targeting neuronal cells with photosensitive microbial opsins, enables the transduction of photons into electrical currents of opposite polarities thus writing, through activation or inhibition, neuronal signals in a non-invasive way. These progresses have in turn stimulated the development of sophisticated optical methods to increase spatial and temporal resolution, light penetration depth and imaging volume. Today, nonlinear microscopy, combined with spatio-temporal wave front shaping, endoscopic probes engineering or multi scan heads design, enable in vivo in depth, simultaneous recording of thousands of cells in mm 3 volumes at single-spike precision and single-cell resolution. Joint progress in opsin engineering, wave front shaping and laser development have provided the methodology, that we named circuits optogenetics, to control single or multiple target activity independently in space and time with single- neuron and single-spike precision, at large depths. Here, we will review the most significant breakthroughs of the past years, which enable reading and writing neuronal activity at the relevant spatiotemporal scale for brain circuits manipulation, with particular emphasis on the most recent advances in circuit optogenetics.
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