This week’s task of deciphering the Journal of Neuroscience has felt much easier than the previous attempt. There were two articles in the July 31, 2013 issue that leapt off the screen, into my download file. They are both about memory, a topic I have been considering deeply as I read Suzanne Corkin’s book about H.M., Permanent Present Tense. Incidentally, I love this book, and I plan to write to Dr. Corkin and thank her profusely for writing it.
The first article about memory is from Zhang and Little and their colleagues. They examined cellular changes that correspond to memory formation in flies. Yes, much of what we understand about genetic control of cell function comes from research on fruit flies. Next time you swat one of those pests, remember to thank it first. In this study the researchers measured the flies’ ability to remember that a particular odor was a signal for shock. Then they measured the ability of a protein called Notch to cause accumulation of a protein called CREB, which gets manufactured in the cell and then moves into the cell’s nucleus, where it convinces specific genes to be transcribed. These genes then produce even more proteins, which act to link cells together and promote their ability to communicate. It is clearly established that long-term memory depends on physical changes in cells so that they establish connections with each other, but the mechanisms and signals inside the cell that initiate the new connections are still being worked out. This research shows that the CREB production happens in a cycle, which the authors propose allows the circuit that was activated by the odor + shock situation to get re-stimulated every half hour or so, which strengthens the circuit and allows the fly to remember the next day that that particular odor is bad news.
It’s always fun to try deciphering a fly article—fly researchers like to be creative with the names they give genes and proteins. The article mentions Klingon (attaches neurons to glial cells). You can learn anything on the Web, so I looked it up and found an alphabetical list including armadillo, bag pipe, big brain, blown fuse, and cappuccino (I stopped at C). See The Interactive Fly for more! More importantly, the mechanisms in fruit flies are remarkably similar to what is happening in our own cells, so this type of work has provided important information about human brain function.
While fruit flies have been invaluable tools for sleuthing out the cellular mechanisms of memory, brain imaging techniques have provided a window into the neural basis of memory in humans, even while they are learning. Magnetic resonance imaging (MRI) provides very clear and precise pictures of areas of brain cells (gray matter), and a new form of MRI, called diffusion tensor imaging (DTI), allows one to see the connectivity (white matter) between these areas of cells. Hofstetter and colleagues used DTI to examine a specific area after humans AND rats learned a new skill. The humans played the video game The Need for Speed 16 times in 2 hours and had their brains scanned before and after playing. The rats learned the location of a hidden platform in a pool of water over the course of one day, also being scanned before and after “playing”. These time frames are considered very short in the realm of brain imaging studies that aim to show structural differences that arise from experience. DTI measures diffusivity of water molecules in tissue. In nervous system white matter, the water molecules typically align themselves along the length of the axon, which is the part of the cell that extends from one brain area to another. A reduction in diffusivity is taken as a sign that the axons have increased their capacity to send information. Hofstetter and colleagues showed that learning in both humans and rats was associated with decreased diffusivity in the fornix, a band of fibers that connects the hippocampus to other brain structures. The researchers also demonstrated that the change in white matter was correlated with increased volume of the hippocampus gray matter. In addition, they examined in humans how much they learned about the race course, asking them to arrange scenes of the course in the order that they appear in the video. The more they learned about the course, the less diffusivity they had in the fornix.
Oogy and I have designated August as the month that we each sign up for a Craftsy class, with the hope of learning something new. She has decided on a class about shuttle tatting, while so far I have chosen a free mini class on short row techniques in knitting. Her tatting class is about 245 minutes long, while my “mini” class is 135 minutes. While we are learning how to tat and short row, perhaps the mean diffusivity of our fornix regions will decrease, indicating that the connections between the hippocampus and the memory regions that will eventually store our newfound knowledge have increased. While it would be impossible to show it directly, we might also assume that our ability to form these new memories will be due to cyclical CREB production in these brain areas.
Along with learning some new knitting skills, I also have exercised my hippocampus and fornix recently with a trip to New York City, with my buddy Selma Moss Ward. We traversed much of Manhattan, beginning in the financial district, where Selma took this great shot of One World Trade Center, I think from Fulton Street. We made our way uptown and found ourselves in a yarn store on the upper west side, The Yarn Company. I found one of Amy’s designs especially appealing and procured it and a few skeins of Lorna’s Laces sock yarn in NYC-inspired color ways unique to this shop. The design is for a hat in the tam o’shanter style called Triboro Tam. I’m making mine in the suggested Buildings and Sky colorway, and if I like it enough, I’ll make another in Newsprint.
It’s only recently that my trips to NYC have taken me outside the general area between the train stations, so exploring the upper west side and downtown has been very interesting. I’ve learned to navigate the grid of streets and avenues by foot and subway, and now I can even say I’ve ridden in a taxi. Lots of CREB cycling through my hippocampus!