Eirini Papagiakoumou
  • E-mail :[email]
  • Phone : +33153462702
  • Location : Paris, France
Last update 2021-02-16 16:20:08.329

Eirini Papagiakoumou PhD Physics

Course and current status

Under-graduate studies: Theoretical study of fiber lasers (University of Ioannina, Physics Department, Greece, Supervision: Assoc. Pr. A. Lyras).

PhD & early post-doc employment (National Technical University of Athens, Greece, Lasers and Applications Group, Supervision: Pr. A.A. Serafetinides, Assoc. Pr. M.I. Makropoulou):

Study of light propagation in tissues by use of an integrated sphere for estimating tissue optical properties.

Light Induced Fluorescence spectroscopy in hard and soft tissues.

Laser radiation transmission through waveguides and fibers for medical use.

Laser Ablation on hard dental tissues.

Optical tweezers: study of optical trapping mechanisms, measurement of optical trapping forces.

Study Bessel beams' reformation properties for the identification of cancer cells, cell sorting in the optical potential of a Bessel beam (Optical Trapping Group, Univ. of St. Andrews, Supervision: Pr. K. Dholakia).

Post-Doc employment (Wavefront Engineering Microscopy Group, V. Emiliani Lab, Paris France): Two-photon fluorescence microscopy.

Development of advanced optical techniques for the photoactivation of living cells: techniques based on wavefront shaping by using Spatial Light Modulators (SLMs) (holographic illumination, Generalized Phase Contrast method) combined with temporal focusing of ultrashort laser pulses.

Researcher position (Wavefront Engineering Microscopy Group, V. Emiliani Lab, Paris France): Development of advanced optical methods for neuronal photoactivation in biological preparations in vivo or in vitro. Application in optogenetics for all-optical interrogation of neural circuits by simultaneous stimulation and monitoring of Ca2+ neuronal responses. Methods based on three-dimensional light patterning through spatial light modulators in combination with temporal focusing.

Scientific summary

The use of light for imaging or stimulation of neurons has become an indispensable tool for neuroscientists over the last 20 years, thanks to its advantages over electrode stimulation: light is less invasive, enables superior spatial and temporal specificity, considerable flexibility and multisite stimulation. Unraveling how behavior or pathology are causally related with neural activity patterns necessitates the ability to selectively perturb individual neurons, while monitoring the neural network activity in vivo, in awake and behaving animals. The development of efficient genetically encoded activity sensors (e.g. GCaMP calcium (Ca2+) indicators, or voltage sensors), able to detect single action potentials (APs) or even subthreshold activity in vivo, and optogenetic actuators (light-sensitive proteins; opsins), allowing to control neuronal activity with millisecond (ms) time precision, as well as the combination of these molecular-level revolutions with advanced microscopies in two-photon excitation, allows “all-optical” readout and manipulation of neural circuits with single-cell precision.

Two-photon excitation provides the advantages of reduced scattering into the brain and axial optical sectioning. In the Wavefront Engineering Microscopy group, we specialize in developing parallel light-patterning strategies, optimizing the efficiency of multiphoton neuronal stimulation for applications extending, but not limited, to photolysis of caged neurotransmitters, optogenetics and voltage imaging. Based on light-wavefront shaping on liquid-crystal spatial light modulators (SLMs), we create excitation patterns ranging from multi-diffraction-limited spots to arbitrary shaped beams configured in 3D, able to excite simultaneously several cells or sub-cellular compartments (axons, dendrites, spines, etc.) in a scanless manner. We control pattern’s lateral shape by two complementary methods: Computer Generated Holography (CGH), a Fourier transform-based method, and Generalized Phase Contrast (GPC), an interferometric phase visualization technique. Both methods are flexible in generating a variety of excitation configurations, without need of modification of the optical setup in order to change the stimulation pattern, and are implementable in two-photon excitation.

The axial width of two-photon excitation patterns is controlled independently of the excitation area by combining CGH (or GPC) with temporal focusing (TF), an imaging technique proposed for the first time in 2005 for suppressing out-of-focus two-photon fluorescence. Using parallel light-patterning we achieved scanless activation of the optogenetic actuator channelrhodopsin-2 (ChR2) in neurons up to ~300 µm-deep in brain slices, using a Ti:Sapphire laser, and demonstrated a unique strategy for multicell scanless depth resolved 3D-CGH excitation, with TF. We have also pioneered the use of industrial ultrafast Yb3+-doped fiber chirped pulse amplifiers for delivering high-energy, low-power activation pulses via CGH for in vitro and in vivo ms-temporal resolution AP-generation, in neurons expressing several opsins, independently of the opsin kinetics. These findings allowed the use of the developed optical methods in biological projects, like following brain complexity in the visual cortex in vivo at high spatiotemporal resolution, and understanding how the visual information is transmitted from the bipolar to the ganglion cells in the retina.

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