In the 2014 Sharp Lecture, May-Britt Moser of the Norwegian University of Science and Technology described her work on “grid cells,” which she co-discovered with husband Edvard Moser in 2005. The activity of these cells suggests that the brain maps 2D space onto a grid from which the animal’s location can be computed.
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Expanding our view of vision
Every time you open your eyes, visual information flows into your brain, which interprets what you’re seeing. Now, for the first time, MIT neuroscientists have noninvasively mapped this flow of information in the human brain with unique accuracy, using a novel brain-scanning technique.
This technique, which combines two existing technologies, allows researchers to identify precisely both the location and timing of human brain activity. Using this new approach, the MIT researchers scanned individuals’ brains as they looked at different images and were able to pinpoint, to the millisecond, when the brain recognizes and categorizes an object, and where these processes occur.
“This method gives you a visualization of ‘when’ and ‘where’ at the same time. It’s a window into processes happening at the millisecond and millimeter scale,” says Aude Oliva, a principal research scientist in MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL).
Oliva is the senior author of a paper describing the findings in the Jan. 26 issue of Nature Neuroscience. Lead author of the paper is CSAIL postdoc Radoslaw Cichy. Dimitrios Pantazis, a research scientist at MIT’s McGovern Institute for Brain Research, is also an author of the paper.
When and where
Until now, scientists have been able to observe the location or timing of human brain activity at high resolution, but not both, because different imaging techniques are not easily combined. The most commonly used type of brain scan, functional magnetic resonance imaging (fMRI), measures changes in blood flow, revealing which parts of the brain are involved in a particular task. However, it works too slowly to keep up with the brain’s millisecond-by-millisecond dynamics.
Another imaging technique, known as magnetoencephalography (MEG), uses an array of hundreds of sensors encircling the head to measure magnetic fields produced by neuronal activity in the brain. These sensors offer a dynamic portrait of brain activity over time, down to the millisecond, but do not tell the precise location of the signals.
To combine the time and location information generated by these two scanners, the researchers used a computational technique called representational similarity analysis, which relies on the fact that two similar objects (such as two human faces) that provoke similar signals in fMRI will also produce similar signals in MEG. This method has been used before to link fMRI with recordings of neuronal electrical activity in monkeys, but the MIT researchers are the first to use it to link fMRI and MEG data from human subjects.
In the study, the researchers scanned 16 human volunteers as they looked at a series of 92 images, including faces, animals, and natural and manmade objects. Each image was shown for half a second.
“We wanted to measure how visual information flows through the brain. It’s just pure automatic machinery that starts every time you open your eyes, and it’s incredibly fast,” Cichy says. “This is a very complex process, and we have not yet looked at higher cognitive processes that come later, such as recalling thoughts and memories when you are watching objects.”
Each subject underwent the test multiple times — twice in an fMRI scanner and twice in an MEG scanner — giving the researchers a huge set of data on the timing and location of brain activity. All of the scanning was done at the Athinoula A. Martinos Imaging Center at the McGovern Institute.
Millisecond by millisecond
By analyzing this data, the researchers produced a timeline of the brain’s object-recognition pathway that is very similar to results previously obtained by recording electrical signals in the visual cortex of monkeys, a technique that is extremely accurate but too invasive to use in humans.
About 50 milliseconds after subjects saw an image, visual information entered a part of the brain called the primary visual cortex, or V1, which recognizes basic elements of a shape, such as whether it is round or elongated. The information then flowed to the inferotemporal cortex, where the brain identified the object as early as 120 milliseconds. Within 160 milliseconds, all objects had been classified into categories such as plant or animal.
The MIT team’s strategy “provides a rich new source of evidence on this highly dynamic process,” says Nikolaus Kriegeskorte, a principal investigator in cognition and brain sciences at Cambridge University.
“The combination of MEG and fMRI in humans is no surrogate for invasive animal studies with techniques that simultaneously have high spatial and temporal precision, but Cichy et al. come closer to characterizing the dynamic emergence of representational geometries across stages of processing in humans than any previous work. The approach will be useful for future studies elucidating other perceptual and cognitive processes,” says Kriegeskorte, who was not part of the research team.
The MIT researchers are now using representational similarity analysis to study the accuracy of computer models of vision by comparing brain scan data with the models’ predictions of how vision works.
Using this approach, scientists should also be able to study how the human brain analyzes other types of information such as motor, verbal, or sensory signals, the researchers say. It could also shed light on processes that underlie conditions such as memory disorders or dyslexia, and could benefit patients suffering from paralysis or neurodegenerative diseases.
“This is the first time that MEG and fMRI have been connected in this way, giving us a unique perspective,” Pantazis says. “We now have the tools to precisely map brain function both in space and time, opening up tremendous possibilities to study the human brain.”
The research was funded by the National Eye Institute, the National Science Foundation, and a Feodor Lynen Research Fellowship from the Humboldt Foundation.
SAPAP-4
Neurons in the mouse cerebellum, expressing the synaptic protein SAPAP-4. Image: Louis Tee and Guoping Feng
2014 Phillip A. Sharp Lecture in Neural Circuits
SPEAKER: Dr. May-Britt Moser
ORGANIZATION: Kavli Institute for Systems Neuroscience
DATE + TIME: Wednesday February 5, 2014 at 4pm
LOCATION: MIT Bldg 46-3002 (Singleton Auditorium)
ABSTRACT: The medial entorhinal cortex (MEC) is part of the brain’s circuit for dynamic representation of self-location. The metric of this representation is provided by grid cells, cells with spatial firing fields that tile environments in a periodic hexagonal pattern. I will begin my lecture by discussing how grid cells are organized within the MEC. Based on recordings from large numbers of grid cells in individual rats, I will show that grid cells cluster into a small number of layer-spanning anatomically-overlapping functionally independent modules with distinct scale and orientation – a property that may be advantage to high-capacity memory in output areas such as the hippocampus. I will further discuss how inputs from grid cells and other functional cell types determine properties of place cells in the hippocampus. Using a combination of electrophysiological and optogenetic techniques, we find that the hippocampus receives input from a variety of sources, including border cells and head direction cells in the MEC, odour-responsive cells in the lateral entorhinal cortex, and, via the nucleus reuniens, decision-correlated cells in the medial prefrontal cortex. Collectively these inputs may be enable memory in ensembles of place cells in the hippocampus.
A Personal Message from Lore Harp McGovern
Charles M. Vest’s death came much too early. I miss this man terribly, his kindness, his intelligence, his fairness and most of all his simple humanity. Chuck was President of MIT when we started our discussion about the possibility of the McGovern Institute to be located at MIT. He was enthusiastic, if not ecstatic, but exercised reserve and a deep felt appreciation for what this would mean for neuroscience at MIT.
Our lengthy discussions and negotiations, some not so easy, were always fair with a win-win in mind, and his humorous use of narratives was a tactic to try and sway you without you noticing. I remember the time we met so I could listen to his rationale about postponing the start of building the MIBR. Of course we were opposed to that, and so I was invited by Chuck to a private lunch with the model of the building prominently displayed in view of our table. As in chess, where you try to corner the queen, Chuck suggested that we trade places, thereby putting the model in a less favorable light, all in the hope he could meet his objective. Oh Chuck! We started and finished pretty much on schedule. So many memories, bear hugs and laughter. I remember an MIT dinner where attendees were leaving, but you and I kept talking, the room cleared out, tables were folded up, the crew swept the floor around us sitting on our chairs, ignoring all. The topic of discussion still centered around the building. And then there always will be the story of French fries at Marché in Menlo Park! Chuck was passing the baton and visited many people across the country to say thank you. I had the pleasure to have dinner with him. Chuck was a runner and in great shape because he was mindful of what he ate; however, both of us ordered that occasional steak and unbeknown to us it was accompanied by two enormous pointed parchment bags in a gracious holder filled with (alas, delicious) French fries! We first looked at them in disdain, but one after the other they disappeared until they were gone. We laughed and tried to excuse away the consumption of all those French fries, and with a huge smile on your face “French fries” became your greeting to the bewilderment of those around us. You also shared private dreams post presidency about being interested in an ambassadorship, but that that would be not be feasible for different reasons. I wish we could have many more of our conversations, but instead I wish you goodbye with one last bear hug!
Be well in the place souls go to rest, my friend, and know that you were respected for all the right reasons, but loved by many and by me because you were very simply, Chuck!
Viral Core Image Gallery
To view the viral core image gallery, please click on one of the thumbnail images below.
McGovern Institute Holiday Greeting 2013
Wishing you a ball this holiday season — from your friends at the McGovern Institute for Brain Research at MIT!
Jisong Guan: McGovern Institute 2013 Fall Symposium
Jisong Guan, Tsinghua University
“Chasing the memory traces in mammalian cortex”
On November 4, the McGovern Institute for Brain Research at MIT hosted a joint symposium with the IDG/McGovern Institutes at Beijing Normal University, Peking University, and Tsinghua University. Guest speakers gave talks on subjects ranging from learning and memory to the neurobiology of disease. The symposium was sponsored by the McGovern Institutes and Hugo Shong.
Yichang Jia: McGovern Institute 2013 Fall Symposium
Yichang Jia, Tsinghua University
“Disease mechanisms underlying neurodegeneration caused by RNA metabolism abnormalities”
On November 4, the McGovern Institute for Brain Research at MIT hosted a joint symposium with the IDG/McGovern Institutes at Beijing Normal University, Peking University, and Tsinghua University. Guest speakers gave talks on subjects ranging from learning and memory to the neurobiology of disease. The symposium was sponsored by the McGovern Institutes and Hugo Shong.
Lihong Wang: McGovern Institute 2013 Fall Symposium
Lihong Wang, Tsingua University
“The neural correlates of trait rumination?”
On November 4, the McGovern Institute for Brain Research at MIT hosted a joint symposium with the IDG/McGovern Institutes at Beijing Normal University, Peking University, and Tsinghua University. Guest speakers gave talks on subjects ranging from learning and memory to the neurobiology of disease. The symposium was sponsored by the McGovern Institutes and Hugo Shong.