Human neurons use highly compartmentalized signaling, study finds

October 19, 2018

Human neurons are much larger than those of mice and rats, so we do not know if it is the size that makes the difference in terms of the computing power of our brain. Now, in a study published October 18 in the newspaper Cell, researchers have shown that unlike other animals, human neurons use highly compartmentalized signaling. Human dendrites – tree-shaped branch structures that function as neural antennae – treat electrical signals differently from dendrites in rodents, the most common model systems for studying neuronal properties.

"The human neuron is basically like a rat neuron, but as it is much longer, the signals have a much longer way to go, so the human dendrites have a different input-output function," says the rats. lead author Mark Harnett, Fred and Carole Middleton Assistant Professor, Department of Brain and Cognitive Science, Massachusetts Institute of Technology. "The dendrites farther away from the body of the cell have fewer ion channels, which controls the signal processing, which was something we were not expecting."

Harnett, who studies how the biophysical characteristics of neurons shape information processing in the brain, believes that our longer, denser dendritic pathways endow human neurons and their respective circuits with improved computing capabilities.

"Human neurons are more electrically compartmentalized and can exploit that," he says. "We think having a low density of ion channels at the ends of the dendrites allows the cell to have as many sub-compartments as possible.The longer the branches are, the more units are independent.You have a lot more units to perform the calculation within a single neuron. "

"Integrating different streams of information in this way could endow individual neurons with the sophistication of small computer networks," Harnett said.

Using a technique called patch-clamp recording, in which tiny glass needles are sealed against the cell membrane to measure detailed electrical properties, researchers for the first time directly recorded dendritic activity in living brain tissue of human origin. Human tissue (from brain surgeries) was obtained from the anterior temporal lobe of patients with epilepsy.

The work could also possibly benefit patients with epilepsy, in which small sections of brain tissue are sometimes harvested to control seizures that do not respond to drugs. "People have been using animal models to think about epilepsy for a long time, but it is clear that there are quite significant differences, at least in dendrites, between humans and rodents," Harnett explains. "The better we understand the ion channels and the membrane excitability, the more we learn about the mechanisms of epilepsy and how to treat them."

Next steps are to determine the relationship between neuron size and electrical properties in other species to better understand the evolution of the cortex.