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Deeper insight into the activity of the cortex

Max Planck Scientists can image the processing of information deeper in the cortex with the help of a new multiphoton microscope design


Left is an image of a cross-section through the whole mammalian brain that shows both brain hemispheres (solid white outline) as well as the overlaying cerebral cortex which is made up of many layers (I – VI). On the right hemisphere are brain cells, neurons, labeled with a genetically encoded fluorescent marker that reports back the cells activity by fast changes in brightness. This image has been taken from a brain slice post mortem where the lower limit of the cortex can be seen (dotted white line). Right, this image shows the same deep layer V brain cells (red box) labeled with the genetically encoded fluorescent marker but actually imaged non-invasively from a living animal using a modified multiphoton microscope, or RAMM approach. This allows scientists to study activity in neuronal populations deep in the cortex of an awake behaving animal and will lead to a deeper understanding of how cortical networks perform computations. Picture: Wolfgang Mittmann, Jason Kerr / Max Planck Institute for Biological Cybernetics. Tübingen, 12. July 2011. Visual and tactile objects in our surroundings are translated into a perception by complex interactions of neurons in the cortex. The principles underlying spatial and temporal organization of neuronal activity during decision-making and object perception are not well understood yet. Jason Kerr from Max Planck Institute for Biological Cybernetics in Tübingen, in collaboration with Winfried Denk from the Max Planck Institute for Medical Research in Heidelberg, now investigated how different sensations are represented by imaging activity from neuronal populations deep in the cortex. The scientists further developed a method, using multiphoton imaging, with which they can study the neuronal activity in some of the deepest layers of the cortex in rodents, something that has not been possible up until now.  

The cerebral cortex, or just cortex, is the outermost sheet of neural tissue of the mammalian brain and is made up of several layers which all are thought to play different, yet an undefined, role in memory, perceptual awareness and consciousness. The cortex receives and processes information from the senses, such as sight, touch or smell and the principles underlying these processes are not fully understood yet. Jason Kerr, research group leader of the Network Imaging Group at the Max Planck Institute for Biological Cybernetics in Tübingen and his colleagues from the same group, Wolfgang Mittmann, Damian Wallace und Uwe Czubayko managed to image neuronal activity simultaneously from many neurons with single cell resolution in deep cortical layers, over twice as deep as previously achieved. In collaboration with Winfried Denk from the Department Biomedical Optics at the Max Planck Institute for Medical Research in Heidelberg and scientists from the Howard Hughes Medical Institute in Ashburn, Virginia they studied the neural cell activity in layer L5b in the adult rodent, which, as well as being one of the output layers of the cortex, it is also only one layer away from the corpus callosum, which is where the cortex ends.  

Up until now, most imaging studies were restricted to the upper third of the cortex in the so-called layers L2 and L3. Deeper layers could only be studied using electrodes or by damaging the cortex using optical fibers or prisms. The Max Planck scientists developed a method, with which they can see exactly which cell is active and importantly, what cells are not active during a stimulus, up to one millimeter from the cortical surface. This has enabled the scientists to measure the spatiotemporal organization of activity in these deeper layers.  

“We express a bright genetically encoded fluorescent activity reporter in the neurons of interest and with this we can measure the activity of many neurons at the same time”, explains Jason Kerr. Changes in brightness of the fluorescent marker are relative to the activity of the neuron. Jason Kerr and his team combined regenerative amplification multiphoton microscopy (RAMM) with genetically encoded calcium indicators to extend multiphoton imaging of neuronal population activity to the deeper layers of the cortex. Using this approach, they found, that RAMM could be used to record and quantify spontaneous activity and activity evoked by sensory stimulation in neuronal populations located in layers L5a and L5b.  

The goal of their research is to record activity from populations of neurons located in all cortical layers, from layer 6 to layer 1. In combination with genetically encoded activity indicators, the team plans to investigate the spatial temporal organization of neuronal activity from all cortical layers in trained animals. Further, they want to address the question of whether the deeper layers also show spatiotemporal re-organization similar to that shown for the upper cortical layers during learning. With these technical advances the scientists aim to gain insights into cortical circuits involved in decision making in the awake, behaving cortex, and how these circuits are functionally modified during learning.    


Original Publication:
Wolfgang Mittmann, Damian J Wallace, Uwe Czubayko, Jan T Herb, Andreas T Schaefer, Loren L Looger, Winfried Denk & Jason N D Kerr. (2011) Two-photon calcium imaging of evoked activity from L5 somatosensory neurons in vivo. Nature Neuroscience doi:10.1038/nn.2879    


Contact:
Jason Kerr
Phone: +49 (0) 7071 601-1721
E-mail: jason(at)tuebingen.mpg.de  

Stephanie Bertenbreiter (Presse- & Öffentlichkeitsarbeit)
Phone: +49 (0) 7071 601-472
E-mail: presse(at)tuebingen.mpg.de


The Max Planck Institute for Biological Cybernetics works in the elucidation of cognitive processes. It employs about 300 people from more than 40 countries and is located at the Max Planck Campus in Tübingen, Germany. The Max Planck Institute for Biological Cybernetics is one of 80 research institutes that the Max Planck Society for the Advancement of Science maintains in Germany and abroad. 


Left is an image of a cross-section through the whole mammalian brain that shows both brain hemispheres (solid white outline) as well as the overlaying cerebral cortex which is made up of many layers (I – VI). On the right hemisphere are brain cells, neurons, labeled with a genetically encoded fluorescent marker that reports back the cells activity by fast changes in brightness. This image has been taken from a brain slice post mortem where the lower limit of the cortex can be seen (dotted white line). Right, this image shows the same deep layer V brain cells (red box) labeled with the genetically encoded fluorescent marker but actually imaged non-invasively from a living animal using a modified multiphoton microscope, or RAMM approach. This allows scientists to study activity in neuronal populations deep in the cortex of an awake behaving animal and will lead to a deeper understanding of how cortical networks perform computations. Picture: Wolfgang Mittmann, Jason Kerr / Max Planck Institute for Biological Cybernetics.

Left is an image of a cross-section through the whole mammalian brain that shows both brain hemispheres (solid white outline) as well as the overlaying cerebral cortex which is made up of many layers (I – VI). On the right hemisphere are brain cells, neurons, labeled with a genetically encoded fluorescent marker that reports back the cells activity by fast changes in brightness. This image has been taken from a brain slice post mortem where the lower limit of the cortex can be seen (dotted white line). Right, this image shows the same deep layer V brain cells (red box) labeled with the genetically encoded fluorescent marker but actually imaged non-invasively from a living animal using a modified multiphoton microscope, or RAMM approach. This allows scientists to study activity in neuronal populations deep in the cortex of an awake behaving animal and will lead to a deeper understanding of how cortical networks perform computations. Picture: Wolfgang Mittmann, Jason Kerr / Max Planck Institute for Biological Cybernetics.

This image shows the same deep layer V brain cells (red box) labeled with the genetically encoded fluorescent marker, but actually imaged non-invasively from a living animal using a modified multiphoton microscope, or RAMM approach. This allows scientists to study activity in neuronal populations deep in the cortex of an awake behaving animal and will lead to a deeper understanding of how cortical networks perform computations. Picture: Wolfgang Mittmann, Jason Kerr / Max Planck Institute for Biological Cybernetics.

This image shows the same deep layer V brain cells (red box) labeled with the genetically encoded fluorescent marker, but actually imaged non-invasively from a living animal using a modified multiphoton microscope, or RAMM approach. This allows scientists to study activity in neuronal populations deep in the cortex of an awake behaving animal and will lead to a deeper understanding of how cortical networks perform computations. Picture: Wolfgang Mittmann, Jason Kerr / Max Planck Institute for Biological Cybernetics.