Two-photon microscopy has recently demonstrated its capacity to complement classical electrophysiological recordings for exploring brain activity. Applied to calcium imaging, two-photon microscopy allows the measurement of single or multiple action potentials simultaneously in many individually localized neurons. Despite the recent success of this optical approach in neurophysiology, many technical challenges remain. There is a need to increase the 3D volume visulaized by two-photon microscopy, improve the temporal resolution, minimize the light power used for excitation to prevent photo- toxicity… I will present the current development in our lab of a two-photon microscope optimized for low illumination and high frame rate while maintaining wide field imaging. I will also show how this microscope can be applied to the investigation of the detailed functions of the somatosensory cortex. This region of the cortex in rat is considered a model system for the study of a cortical column and is one of the most documented areas of the cortex. Rats use their whiskers to explore their environment. A large fraction of their primary somatosensory cortex is dedicated to the representation of these whiskers. It is organized in “barrels” respecting the same arrangement as the whiskers with a one to one correspondence. A neuron within a given barrel is activated when the associated whisker is moved. Until recently, the dominant paradigm was that each barrel independently processes the tactile information provided by its principal whisker. There is now evidence from anatomy, neurophysiology and behavioral experiments showing that some multi- whisker information is computed in the barrel cortex. Using two-photon calcium imaging of barrel cortex in combination with a matrix of 24 piezoelectric devices manipulating all the whiskers simultaneously, we have explored the encoding of similarity between the movements of the whiskers. I will present new results showing a category of neurons exclusively activated when a perfectly identical motion is applied to all whiskers (possibly serving as global motion detectors) and another category of cells responding to contrasted stimulation, in which a given whisker is deflected in one direction while all surrounding whiskers are deflected in opposite direction (possibly serving as basis for object contour recognition). This example will illustrate how two-photon microscopy is advancing our understanding of the neuronal representation of information in the brain.


Wednesday, December 11, 2013, 10:30. Seminar Room

Hosted by Pablo Loza-Álvarez