Visualizing the Brain at the Cellular Level: How Microscopy Changed Neuroscience

Visualizing the Brain at the Cellular Level how microscopy changed neuroscience -1850 Camillo Golgi developed a new method that used silver nitrate to stain a few cells of the nervous system at random Golgi believed the brain was continuous. made up of an uninterrupted reticulum, a single mesh Reticular Theory drawing by Golgi of a hippocampus stained with silver nitrate Santiago Ramon y Cajal used the Golgi stain, but argued that neurons were self-contained. and that the brain was a network of distinct, interconnected units Neuron Doctrine beginning of modern neuroscience visually mapping the brain's circuits progressed slowly until Osamu Shimomura F1900 isolated Green Fluorescent Protein (GFP) from a jellyfish that glowed green when exposed to blue light Golgi and Cajal win Martin Chalfie Nobel Prize inserted the DNA that encoded for GFP into neurons of a worm so that when these cells were illuminated with a blue light. they glowed green Roger Tsien genetically altered GFP so that it emitted other colors of light. like yellow. blue, and red. which allowed neuroscientists to distinguish individual cells Jean Livet created DNA molecules that incorporated into the genes of neurons. Red. green, yellow and orange fluorescent proteins were randomly expressed in each neuron, creating a rainbow of colored neurons Brainbow using confocal microscopy. each protein color could be imaged independently and 1950 then combined together in a computer to form the brainbow fluorescent proteins revolutionized how the brain was studied. and imaging techniques had to keep up to visualize the inside of cells. Ernst Ruska &Moax Knoll invented electron microscopy EM uses an electron beam (instead of light) to illuminate a specimen. producing a detailed and magnified image Although the images EM creates have amazing resolution. the tissue sample is not living and has to be cut into incredibly thin sections Marvin Minsky traditional microscopes cannot observe a structure inside a biological sample without also detecting out-of-focus objects above and below it (left) 2000 confocal microscopy uses scanning lasers and sophisticated optics to image a single focal plane (right) Shimomura. Chalfie, and Tsien win Winfried Denk Nobel Prize two-photon microscopy illuminates only the structures that fall within a tiny focal point Confocal Two-photon two-photon microscopes use infrared light. which can travel across tissue more easily than visible light. so neurons can be imaged through a live animal's thinned-down skull to bypass the diffraction limit of microscopy and achieve better resolution. Stefan W. Hell developed STED microscopy Conf STED (stimulated emission depletion) STED functions by depleting specific regions of a sample while leaving a center focal +20501spot active to emit fluorescence excitation spot (2D. left), doughnut-shape de-excitation spot (center) and remaining area allowing fluorescence (right) the current microscopy technologies are approaching the physical limits of light microscopy future advances. like CLARITY, will help neuroscientists continue to look deeper into the brain without breaking the laws of physics References: Portraits of the Mind: Visualizing the Brain from Antiquity to the 21st Century by Carl Schoonover Abrams. New York 2010. Images adapted from aperfectworld.org. Wikimedia Commons, microscopy.berkeley.edu, and conncoll.edu. Illustration by Kate Jones knowingneurons.com