"Connectomics" is an area of neuroscience that aims to map the brain's connections, known as synapses, to gain an understanding of how information flows through the circuits of the brain. With an estimated 100 billion nerve cells, or neurons, in the brain, each connected to thousands of other nerve cells, adding up to an estimated 150 trillion synapses, the creation of such a map is no small task – but a new technique is bringing scientists a step closer to developing a computer model of the brain.
"We first need to understand the function of each neuron and find out to which other brain cells it connects," says Dr Tom Mrsic-Flogel, a Wellcome Trust Research Career Development Fellow at University College London (UCL). "If we can find a way of mapping the connections between nerve cells of certain functions, we will then be in a position to begin developing a computer model to explain how the complex dynamics of neural networks generate thoughts, sensations and movements."
With neurons in different areas of the brain performing different functions, Dr Mrsic-Flogel and his colleagues focused on the visual cortex, which processes information from the eye. Using high-resolution imaging they were able to detect, out of the thousands of neurons in the visual cortex of the mouse brain, which ones responded to a particular stumulus, such as a horizontal edge.
Then, by taking a slice of the same tissue and applying small currents to a subset of neurons, the scientists were able to see to which other neurons they were synaptically connected. Repeating this technique many times allowed the scientists to trace the function and connectivity of hundreds of nerve cells in the mouse's visual cortex.
With results showing that neurons that responded very similarly to visual stimuli tend to connect each other much more than those that respond differently, the researchers say their study has resolved the debate about whether local connections between neurons are random and independent of function or whether they are ordered.
The researchers hope to use the technique to begin generating a wiring diagram of a brain area with a particular behavioral function. While their initial study focused on the visual cortex, they say the technique should also help reveal the functional circuit wiring of the regions of the brain responsible for touch, hearing and movement.
Scientists hope that creating a computer model of the brain will help them understand how perceptions, sensations and thoughts are generated and how diseases such as Alzheimer's, schizophrenia and stroke can cause these functions to go wrong.
"We are beginning to untangle the complexity of the brain," says Dr Mrsic-Flogel. "Once we understand the function and connectivity of nerve cells spanning different layers of the brain, we can begin to develop a computer simulation of how this remarkable organ works. But it will take many years of concerted efforts amongst scientists and massive computer processing power before it can be realized."
The researcher's study entitled, "Functional specificity of local synaptic connections in neocortical networks," appears in the journal Nature.
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