Each cell in the human brain appears to have an inherent ability to process information, scientists have discovered. By looking at neurons taken directly from human brain tissue, researchers were able to make some of the first electrical recordings of individual cells, which could provide insight into our intelligence.
Brain size has been closely tied to our success as a species—as our brains got bigger, we became more intelligent. However, studying exactly what is going on inside our heads is inherently difficult. Most of what we know about neurons and their function comes almost exclusively from research on rodents.
"Testing hypothesis that human neurons are different to other species is extremely challenging because it's very hard to get living human brain tissue," explained Mark Harnett, an investigator at the McGovern Institute for Brain Research at the Massachusetts Institute of Technology.
We know cortical neurons are larger in human brains than in other species. However, it is not clear how this size affects synaptic integration—the process where an individual neuron processes information and converts it to an output signal.
In a study published in the journal Cell, Harnett and his colleagues looked at how human brain cells work at an extreme level of detail. The brain cells were provided to the team by neurologist Sydney Cash of Massachusetts General Hospital. He extracted them from patients being treated for a type of epilepsy.
This involved operating to remove tissue from deep inside their brains. "To do that we had to remove overlying cortex," Cash said. "That area of the brain [is] thought to be responsible for higher-order cognitive processing. We then took that piece of tissue and placed it into specialized artificial spinal fluid and handed it off to Mark's group."
At MIT, the researchers sectioned the human brains into thin slices and then recorded the electrical activity of individual neurons.
Previous research has shown that human brain cells have much longer dendrites (tree-like structures that receive most inputs) than rats do. After watching the electrical activity, the team discovered that human cells process information differently than rats—and this was largely due to the size differences.
"Those signals had much further to travel in humans than in rats, leading to enhanced signal compartmentalization," study author Lou Beaulieu-Laroche said.
The other difference had to do with ion channels. This is the protein that acts as a pore allowing electrical currents to pass in and out of a cell. Researchers found there were fewer ion channels in humans than in rats, which potentially increases the resistance of human dendrites, making the cell better at processing information.
"The human brain contains approximately 86 billion brain cells called neurons. Neurons are thought to represent elemental units of information processing.… Distinct information-processing capabilities at a level of individual neurons is likely to impact cortical computation in the human brain," Beaulieu-Laroche said.
