Neuroscience has come a long way since the days of Aristotle who thought that the main function of the brain was to cool the blood. In the 18th century we learned that externally applied electricity could propagate within neurons; in the 19th century we found out that the cerebral hemispheres of rabbits and monkeys had underlying electrical activity; in the early 20th century the first human electroencephalogram (EEG) was recorded; and less than a decade into the 21st century we already had consumer-based EEG products. Scientists have developed sophisticated methods to read, amplify, and understand neuronal activity in the brain, but complex technical challenges remain. Each cubic millimeter of brain tissue can contain up to 100,000 neurons, so even the most sensitive and miniscule of electrode sensors is still “listening” to hundreds or thousands of often distinct signals.
The field may have just become more precise because scientists at the Norwegian University of Life Sciences have developed “detailed mathematical models revealing the connection between nerve cell activity and the electrical signal recorded by an electrode.” Reported this month in Neuron, the research focused on the spatial distribution of a specific type of low frequency signal called the low field potential (LFP) and the results are summarized here:
The size of the generating region depends on the neuron morphology, the synapse distribution, and the correlation in synaptic activity. For uncorrelated activity, the LFP represents cells in a small region (within a radius of a few hundred micrometers). If the LFP contributions from different cells are correlated, the size of the generating region is determined by the spatial extent of the correlated activity.
In terms of applications, the press release discusses diseases and disorders for which this enhanced model may prove useful:
Better understanding of the electrical brain signals may directly influence diagnosing and treatment of illnesses such as epilepsy.
“Electrodes are already being used to measure brain cell activity related to seizures in epilepsy patients, as well as planning surgical procedures. In the future, LFP signals measured by implanted electrodes could detect an impending epilepsy seizure and stop it by injecting a suitable electrical current,” Einevoll says.
“A similar technique is being used on many Parkinson’s patients, who have had electrodes surgically implanted to prevent trembling,” researcher Klas Pettersen at UMB adds..
Einevoll and Pettersen also outline treatment of patients paralysed by spinal cord fracture as another potential area where the method can be used.
“When a patient is paralysed, nerve cells in the cerebral cortex continue to send out signals, but the signals do not reach the muscles, and the patient is thus unable to move arms or legs. By monitoring the right nerve cells and forwarding these signals to for example a robot arm, the patient may be able to steer by his or her thoughts alone,” Einevoll says.
Press release: Tapping the brain orchestra
Paper in Neuron: Modeling the Spatial Reach of the LFP