1 The power of magnetoencephalography (MEG) a When someone moves their fingers, clusters of neurons in the brain’s primary motor cortex are rendered active, and the resulting current passing through them generates magnetic fields. The component of this field that is radial to the head can be measured by MEG. In the visualization (left), red represents a field going away from the head, blue represents a field going into the head. Via a mathematical modelling process, called source reconstruction, we can use these fields to construct 3D images showing moment-to-moment changes in neural current (right). The yellow blobs show areas of fluctuating neural current during the finger movement. With MEG, brain activity can be resolved not only in space but also in time. Electrical brain activity can be broken down into oscillations at characteristic frequencies (known as neural oscillations or brain waves). These figures show modulation of the amplitudes of electrical oscillations at different frequencies over time, occurring in the primary motor cortex as someone moves their finger. Blue shows a decrease in a neural rhythm relative to baseline, red shows an increase. While a subject moves their hand there is a decrease in beta (~20 Hz) oscillations, which then returns to baseline, post movement, via a ‘rebound’ (i.e. the signal goes above baseline). This rebound is abnormal in patients with schizophrenia and likely indicates a lack of communication between the primary motor cortex and other brain regions in patients (Courtesy: Elena Boto, University of Nottingham; CC BY 4.0 Robson et al. adapted from NeuroImage: Clinical 12 869).
Taken from the February 2021 issue of Physics World, where it appeared under the headline "Quantum sensing the brain". Members of the Institute of Physics can enjoy the full issue via the Physics World app.
Novel technology in healthcare based on fundamental physics saves millions of lives every year but while these machines have revolutionized medicine, the next generation must meet even greater challenges. Hannah Coleman and Matt Brookes are hoping that the University of Nottingham’s new quantum-enabled MEG scanner will herald a new dawn in the study of human brain function
In most types of medical imaging, the aim is to gain information on the internal structure of the body, looking for growths, tumours or other abnormalities. In doing so, medical practitioners gain critical information that can be used in treatment.
However, for many illnesses we must move beyond simple structure and learn about the way in which an organ functions. This is particularly important for assessing disorders of the brain – such as epilepsy, dementia or mental health problems – where a structural image, no matter how detailed, often looks “normal”, even in patients with profound difficulties. In such instances it is the function of the brain that is perturbed. To gain insight, we must therefore develop technologies that image what the brain is doing, which means developing ways to assess the electrical activity of its 90 billion or so neurons.
For many illnesses we must move beyond simple structure and learn about the way in which an organ functions.
One method of imaging brain function is magneto-encephalography (MEG) – a relatively new technology in which we measure the magnetic fields generated by current flowing through neuronal assemblies. Mathematical modelling of these fields generates 3D images showing moment-to-moment fluctuations in neural current (figure 1a). In this way, MEG is a safe and non-invasive way of imaging brain networks as they form and dissolve to support cognition. By letting us probe brain function, MEG is used extensively in research to investigate and understand both the healthy brain, and its perturbation by disease (figure 1b).
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