Brain mapping could aid picture of neural networks

A computer model for analysing conditions such as Alzheimer’s and schizophrenia could be in the pipeline thanks to a new brain-mapping technique.

Researchers at University College London (UCL) have developed a way of mapping both the connections (synapses) and functions of nerve cells in the brain together for the first time.

By mapping these connections — and hence how information flows through the circuits of the brain — scientists hope to understand how perceptions, sensations and thoughts are generated in the brain and how these functions go wrong in diseases such as Alzheimer’s, schizophrenia and stroke.

‘We first need to understand the function of each neuron and find out to which other brain cells it connects,’ said Dr Tom Mrsic-Flogel, who has been leading the research.

‘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.’

There are estimated to be one hundred billion nerve cells (neurons) in the brain, each connected to thousands of other nerve cells — making an estimated 150 trillion synapses.

The UCL team focused on the visual cortex, which processes information from the eye. For example, some neurons in this part of the brain specialise in detecting the edges in images; some will activate upon detection of a horizontal edge, others by a vertical edge.

In a study published online in the journal Nature, the team described how it used a high-resolution imaging technique on the brains of mice to detect which of the visual cortex neurons responded to a particular stimulus, for example, a horizontal edge.

It then took a slice of the same tissue and applied small currents to a subset of neurons to see which other neurons responded — and hence which of these were synaptically connected.

By repeating this technique many times, the researchers were able to trace the function and connectivity of hundreds of nerve cells in visual cortex.

The study addressed the issue of whether neurons are ordered or connected randomly by proving that neurons responding to visual stimuli tend to connect to each other much more than those with different functions.

‘We are beginning to untangle the complexity of the brain,’ said 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 among scientists and massive computer processing power before it can be realised.’

The research was supported by the Wellcome Trust, the European Research Council, the European Molecular Biology Organisation, the Medical Research Council, the Overseas Research Students Award Scheme and UCL.