“Man had always assumed that he was more intelligent than dolphins because he had achieved so much — the wheel, New York, wars and so on — whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man — for precisely the same reasons….In fact there was only one species on the planet more intelligent than dolphins, and they spent a lot of their time in behavioural research laboratories running round inside wheels and conducting frighteningly elegant and subtle experiments on man. The fact that once again man completely misinterpreted this relationship was entirely according to these creatures’ plans.” – Douglas Adams, The Hitchhiker’s Guide to the Galaxy

As tempting as it may be to believe the science fiction version of the intelligence rankings, real-life science has spoken and suggests (much to my displeasure) that humans may actually be the highest on the intelligence scale.

Glia are non-neuronal cells found in the brain mainly described as performing “housekeeping” functions, for example, providing structural support to neurons, and providing them with nutrients. Astrocytes are a specific type of glia, and as one might hypothesize, they are bigger in humans than in mice. Was this just a consequence of humans having more complex brains, or do these astrocytes have different functions in humans beyond the basic housekeeping functions? To test this, scientists grafted human astrocyte progenitor cells into developing mouse brains to create chimeric mice.

Human astrocyte (green) and mouse astrocyte (red)

The human astrocytes that matured successfully matured as human cells; characteristics such as their size were unaffected by being in a mouse environment. But they did not remain completely foreign – they successfully formed electrical connections with the mouse cells. Their differing cellular properties were thus propagated into the mouse neural networks. Of particular interest is the hippocampus, the brain region important for learning and memory. Chimeric hippocampal slices had a higher level of baseline excitatory activity, and long-term potentiation (LTP), or synapse strengthening, was much greater. At the molecular level, this can be explained because the human cells express higher levels of a protein that promotes an increased number of glutamate receptors at the synapse.

There were also clear differences in the behavior of chimeric mice. Experiments were performed to test learning and memory abilities to corroborate the cellular results observed in the hippocampus. A classic fear conditioning experiment involves pairing a tone with a foot shock; mice learn to associate the two and exhibit freezing behavior after hearing a tone. Chimeras learned the association after only one tone/shock pairing. The learning persisted for several days, during which time control animals did not learn the initial association. The experiment was repeated as context fear conditioning, meaning that the mice were placed in different chambers that had varying floors and odors. Chimeric mice were able to differentiate between chambers significantly better than their control counterparts. In other learning and memory tasks, these mice learned their way through mazes faster and were better at familiar object recognition in novel contexts.

The results of this study show that glial cells have much more function beyond their basic housekeeping properties. A single cell graft manipulation was enough to significantly improve mouse performance on learning and memory tasks. Complexity of these cells has evolved with the brain, and this provides important new insight on how exactly this complexity has come to be. Future experiments could involve grafting chimpanzee or macaque glia, any differences observed could be key in outlining how our processing abilities evolved from our monkey fathers (I additionally support research with dolphin glia grafts, keeping on the theme of the three most intelligent species). Unfortunately, without the higher processing abilities made possible by human cells, mice likely cannot achieve the tasks and level of status they exhibit in the science fiction. It seems as though man has indeed correctly interpreted his relationship with the mouse.

So long, and thanks for all the fish.

-Reena Clements

References:

Human Brain Cells Boost Mouse Memory – ScienceNOW

Forebrain Engraftment by Human Glial Progenitor Cells Enhances Synaptic Plasticity and Learning in Adult Mice – Cell Stem Cell

Ever wonder why people still “talk with their hands” when they’re on the telephone? We often use hand gestures while speaking even at times when the listener cannot see them. Gestures are processed in the same areas of the brain as speech (think sign language): the left inferior frontal gyrus (Broca’s) and the posterior middle temporal gyrus (Wenicke’s area). Hand movements help us to communicate more efficiently and emphasize certain points of the message we are trying to convey to our conversational partners. They’re an indication of our thought process throughout the discussion. Evolutionary insight proposes that the language brain regions, which originally supported the pairing of body language and meaning, have been adapted in humans for spoken language; however, we still don’t know precisely the reason why people gesture, and more interestingly, why some people use gestures more often than others.

A team of German researchers recently conducted a study suggesting a strong relationship between gesturing, fluid intelligence, and brain development. The scientists at Humboldt-Universität zu Berlin selected fifty-one 11th graders gifted in math and science for their experiment and separated them into groups of high and average fluid intelligence, which is responsible for learning and recognizing patterns. They asked both groups to solve analogy tasks that involved pairing sets of geometric configurations correctly. The students with higher fluid intelligence obviously performed better on the task than the students with average fluid intelligence, but they also produced more representational hand and arm gestures while describing how they solved the problems.

All of the students verbally explained the same method to solve the problems, but the students’ intelligence could be distinguished by simply observing their hand movements. The researchers considered that specifically the motion of hands rotating around an imaginary axis (a strategy that was never mentioned in the students’ accounts of the problems) was a reflection of mentally rotating the shapes and using spatial reasoning. Participants with higher fluid intelligence therefore engaged in more active mental representation during problem solving.

Furthermore, fMRI scans of the students’ brains showed that individuals with higher fluid intelligence and who had demonstrated more hand gestures showed greater cortical thickness in Broca’s areas and other areas in the left hemisphere such as the superior frontal cortex.

Both gesture and speech appear to be founded on the same underlying system of simulated action in mental imagery. We haven’t concluded whether gestures facilitate the development of fluid intelligence or whether the gestures themselves are its product. However, since young children are shown to gesture when learning new concepts and expressing new ideas, the activity may facilitate in cognitive development by simulating thought.

Show Your Hands – Are You Really Clever? Reasoning, Gesture Production and Intelligence – Linguistics: An Interdisciplinary Journal of the Language Sciences