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    Brain Waves Are Time And Voltage
    By News Staff | December 17th 2013 06:30 AM | 1 comment | Print | E-mail | Track Comments

    In a Neuron paper,
    Institute of Science and Technology Austria
    post-doctoral fellow Alejandro Pernía-Andrade and Professor Peter Jonas outline the synaptic mechanisms underlying oscillations at the dentate gyrus, the main entrance of the hippocampus).

    Building on that work, the researchers suggest a role for these oscillations in the coding of information by the dentate gyrus principal neurons. 

    Brain oscillations are rhythmic changes in voltage in the extracellular space, referred to as electrical brain signals associated with the processing of information. These electrical signals are similar to those seen in electro-encephalographic recordings (EEG) in humans. Pernía-Andrade and Jonas observed these oscillations in the hippocampus in behaving rats, and recorded oscillations occurring in this area using extracellular probes.

    To understand how oscillations are generated and which synaptic events trigger these oscillations, the researchers looked at synaptic transmission in granule cells (principal cells at the main entrance of the hippocampus) from both the extracellular (oscillations) and the intracellular perspectives (synaptic currents and neuronal firing), and then correlated the two.

    They discovered that excitatory and inhibitory synaptic signals contributed to different frequencies of oscillations, with excitation from the entorhinal cortex generating theta oscillations and inhibition by local dentate gyrus interneurons generating gamma oscillations. Together, excitation and inhibition provide the rhythmic signals of oscillations.



    Prof. Peter Jonas and post-doc Alejandro Pernía-Andrade with workshop head Todor Asenov sitting in front of screen. Credit: © IST Austria, 2013


    It has been speculated that oscillations may help the dentate gyrus to encode information by acting as reference signals in temporal coding. Pernía-Andrade and Jonas now show that granule cell neurons send signals only at specific times in the cycle of oscillations. This so-called "phase locking" is necessary if oscillations are to function as reference signals in temporal coding.


    How information is processed and encoded in the brain is a central question in neuroscience, as it is essential for high cognitive function such as learning and memory. Theta-gamma oscillations are associated with information processing during exploration and spatial navigation. 

    The precise, high-resolution recording from granule cells necessary for these discoveries was possible only through technological innovations by Pernía-Andrade and Jonas, as previously no equipment was available to record synaptic signals in active rats in such high resolution. They are the result of a collaboration with the Miba machine shop, IST Austria's electrical and mechanical SSU (Scientific Service Unit).

    Adapting commercially available equipment and custom-designing tools, Pernía-Andrade, Jonas and Todor Asenov, manager of the Miba machine shop, produced the first tools for precise biophysical analysis in active rats. This research is therefore not only a scientific advance but also represents a significant technological and conceptual progress in the quest to understand neuronal behavior under natural conditions. 


    Citation: Alejandro Javier Pernía-Andrade, Peter Jonas, 'Theta-Gamma-Modulated Synaptic Currents in Hippocampal Granule Cells In Vivo Define a Mechanism for Network Oscillations', Neuron 12 December 2013. 10.1016/j.neuron.2013.09.046. Source: Institute of Science and Technology Austria

    Comments

    A simple question. Sensory input is transformed into a series of electrical pulses over an applicable network of neurons. For example, the eye beholding an apple will be represented by a set of pulses over an activated network. These pulses travel from center to center (eg to optical thalamus and eventually on to optical cortex). Eventually, these pulses ground into the surrounding fluid and disappear. So where is the content, that is the shape, texture, color etc. of the object held? Is it in the pattern of the pulses generated or in the pattern of the networks activated?
    We need to understand such basic things first. Does anyone know? It's very easy to conjecture about consciousness etc. cuz it sounds cutting-edge.