The size and complexity of brain cells called astrocytes is what differentiates a human brain from that of a mouse, a new study has found.
"Our astrocytes signal faster, and they're bigger and more complex. This has big implications for how our brains process information," said study co-author Nancy Ann Oberheim, of University of Rochester, who has completed her doctoral thesis on astrocytes.
The study is one of the most extensive examinations yet of the astrocyte. Oberheim and co-authors discovered a previously unknown form of the cell, a varicose projection astrocyte, in the human brain but not in the rodent brain.
University of Rochester Medical Centre (URMC) scientists found that human astrocytes, cells that were long thought simply to support flashier brain cells known as neurons that send electrical signals, are bigger, faster, and much more complex than those in mice and rats.
The team also found that the most abundant type of astrocyte, protoplasmic astrocytes, are approximately 2.6 times larger than their rodent counterparts, and that the human cells have about 10 times as many "processes", or structures designed to connect to other cells.
"We have not really been able to understand why the human brain is so much more capable than that of any other animal," said neuroscientist Maiken Nedergaard, who led the study.
"Some people have thought that it's simply that a bigger brain is a better brain, but an elephant's brain is bigger than a person's, for example, but it's not nearly as powerful. So that's not the answer.
"It may be that humans have a much higher brain capacity in large part because our astrocytes are more sophisticated and have more complex processing power," added Nedergaard, according to an URMC release.
"Studies in rodents show that non-neuronal cells are part of information processing, and our study suggests that astrocytes are part of the higher cognitive functioning that defines who we are as humans."
"Dogma is slow to change, and one of the dogmas of neuroscience is that astrocytes are support cells that don't do much themselves," said Oberheim.
"The view is slow to change, but scientists are coming around. Astrocytes are now acknowledged as active participants in brain function and sensory processing," she added.
These findings appeared in the March 11 issue of the Journal of Neuroscience.