Rocket Racoon is a stand out character in Guardians of the Galaxy, Marvel’s rebooted comic series, which was adapted into a movie that came out August 1. Rocket Racoon’s backstory is that he—and many of his fellow animal friends—were genetically engineered to become bipedal and to have “human” intelligence. (It’s not clear why they didn’t choose to use a smarter species than ours given everything on offer in the Marvel Universe). Which makes me think of two things—how smart are racoons in first place and could they really be made as smart as humans?
Anyone who has ever watched a racoon do anything generally has the impression that they are pretty smart. According to the comparative psychologist Michael Pettit, in the early 20th century, “Both popular and scientific naturalists had argued that cunning, mischief and curiosity characterized the species.” How raccoons’ intelligence compared with other species was “a topic of debate between 1905 and 1915 within the then-nascent field of comparative psychology.” One study subjected 22 rats, two dogs, four raccoons and five human children to the same delayed-reaction experiment and concluded that while “the same forms of learning governed rats, dogs and raccoons,” only raccoons and human children were able to complete a memory test following distraction. The work drew charges of anthropomorphism, however, and raccoons soon disappeared from the pages of psychology journals.
So, while racoons are undeniably clever creatures, we currently don’t have any on planet Earth that could rival the inter-galactic experiences and ray-gun ability of Rocket Racoon. But that doesn’t mean scientists aren’t working on ways to boost animals’ intelligence. Two years ago, there was a jaw-dropping experiment in neuroscience, in which researchers claimed they had created super-smart mice.
Xiaoning Han and colleagues in the laboratories of Steven Goldman and Maiken Nedergaard at the University of Rochester Medical Center posed an interesting question—can you enhance the processing ability of one species by surgically implanting and grafting cells from the brain of another “smarter” species?
Han and colleagues wanted to see if they could find compatibility in the mouse brain with certain evolutionary adaptations of the human brain. For instance, humans have glial cells called astrocytes that are much bigger and more complex than those found in mice. The conventional thinking is that glial cells, which don’t produce electric signals, form a physiological support and protection network for neurons, but don’t play a role in processing information. Glial cells do transmit signals using calcium signalling, however, and what’s more, human astrocytes do it three times faster than those in mice.
So, of course, Han and colleagues wondered what would happen if you grafted human glial progenitor cells onto the forebrain of immunosuppressed mice. It turned out the human glial cells thrived in the mouse forebrain and had the ability to propagate calcium signals at the rate usually found in the humans. But all this established was that the cells could live in the mice brains and do some similar things. Could they also affect cellular processes like the strengthening of signal transmission between neurons, called long-term potentiation, which underlies learning and memory formation? Again the answer was yes—there was nearly a 10 percent LTP increase in the mice.
The biggest question of all, though, was whether or not all of these adaptations could actually affect behaviors. Behaviors assessed in these kinds of reduced animal experiments include fear conditioning, maze learning, and locating of new objects in the environment. The “enhanced” mice with engrafted human glial cells showed improved performance in all behavioural tests administered. In short, the chimeric mice were made smarter by implantation of human brain cells. Of course, before getting too carried away, it’s important to recognize that this study represents mostly a proof of principle that cross-species grafting technique could be a useful way to study—and modify—the brain. Despite that, there remain many issues to overcome before inferring too much about our ability to boost intelligence with cellular implantation.
The key scientific takeaway for brain evolution on Earth is that contrary to prior wisdom, astrocytes may actually play for role in neural processing. Future work will have to address a key limitation that is involved in all related studies—the need for massive immunosuppression to ensure that the host animal continues to accept the donor tissue. This is not a trivial issue, but further study could end up producing a fundamental shift in the way we study, understand and treat the brain.
Of course this will also help us to better understand the chimeric space aliens comprising the Guardians of the Galaxy when they finally arrive to save us. Hopefully.