The brain is so highly interconnected that every part of it seems like it’s closely wired to every other part, opening up countless possible neural signaling pathways. But some very strong tendencies put reins on them.

“Not all of those paths are equally likely to be traveled,” Stanley said. “Some connections are much better wired than others due to genetic determination, or learning behavior.” Human behavior is partly genetically encoded and formed during development, like the capacity to speak, and partly learned, like mastering a language.

Some neural pathways are well paved, like signals for perception and motor movement traveling via the thalamus, a structure in the deep brain that acts as a neural super-turnstile. It is critical to coherent brain function, as it routes and modulates signals to and from the cortex, where some locations, like the visual cortex or the motor cortex, are assigned to specific functions.

Seahorse GPS

The hippocampus is aptly named. “Hippo” is ancient Greek for “horse,” “kampos” for “sea monster.” The deep brain region is curve-shaped like a sea horse, and it helps you get around from place to place by facilitating orientation.

It also slows down noticeably with age, and in Alzheimer’s disease, the hippocampus succumbs early on, leaving sufferers disoriented. That disease helps put the hippocampus in researchers’ focus.

Work on its encoding of location garnered scientists a Nobel Prize in 2014 for describing the brain’s GPS. They also found that the hippocampus, which is important for memory as well, lays down some consistent neural code, contrasting with neural networks’ often fluxing firing patterns.

“It was shown back in the 1970s that there are neuron groups in the hippocampus that fire in a particular location in space,” said neuroscientist and biomedical engineer Annabelle Singer, who studies hippocampal function in mice at the Wallace H. Coulter Department of Biomedical Engineering. “If the mouse is running around this room, for example, when it gets to this one spot, there’s a subset of cells that will fire.” Other subsets fire when the mouse arrives at other spots.

The existence of such neural activity has also been corroborated in humans.

Annabelle Singer, assistant professor in the Wallace H. Coulter Department of Biomedical Engineering, studies how the hippocampus’ neurons fire as the brain creates orientation in a video maze seen in the background. Photo: Christopher Moore.

Let’s label the cell groups that do this A, B, C and D. As you stroll to your local coffee shop (or as a mouse in a lab runs through a video maze toward a reward), neurons fire in sequence corresponding to recognized physical locations along the way. Sidewalk, fire A. Crosswalk, fire B. Supermarket entrance, fire C. Coffee shop counter, fire D.

Singer is researching how such cell groups collaborate to encode paths in the first place. And she has observed them firing in other instances. For example, when a mouse licks a delicious reward for running a maze, the pattern re-fires. “You get, really quickly, A-B-C-D. That’s called reactivation, or replay.”

What Singer does in mice, researcher Scott Moffat from the School of Psychology mirrors in his work with humans. He has human subjects navigate through video mazes inspired by video mazes rodents run, in part because, if mice and humans perform the same task, it makes comparing their brain activity easier.

But whereas Singer zeros in on finer neuron activities in a mouse’s brain, Moffat uses functional magnetic resonance imaging (fMRI) to measure broader patterns in humans’ brains. He focuses on diminishing navigational abilities in aging.

“There are very consistent areas of the human brain that are activated during navigation tasks,” said Scott Moffat, associate professor in the School of Psychology. He uses an fMRI machine, above, to record the patterns of brain activity in humans who are navigating a virtual landscape, right. Photo: Christopher Moore; graphic: courtesy Scott Moffat.

“There are very consistent areas of the human brain that are activated during navigation tasks,” Moffat said. The hippocampus taps into nearby brain regions like the parahippocampus, which has an area for computing place recognition. It even lights up when people just look at pictures of places.

“Younger people activate these areas when doing spatial tasks,” Moffat said. “When we run older people through these virtual navigation tasks, what we see pretty consistently is under-­activation in the same areas.”

In Alzheimer’s patients, as these areas break down, sufferers begin to lose their way and can even go missing.

I, Robot

Want to try an experiment that shows how your brain, without your even noticing, keeps you from tipping over?

Reach out your hand like you’re going to pick up a glass, and then pull your hand back. Repeat that motion and observe your torso. That back-and-forth sway is balance correction courtesy of your lower brain: the cerebellum and brainstem, which are adjusting multiple muscles to preserve your balance.

Now you have a small sampling of what mechanical engineer Lena Ting observes to study the nervous system’s control of balance. She looks at the body in motion to gain insights about the brain.

Lena Ting, professor in the Wallace H. Coulter Department of Biomedical Engineering, covers subjects in tracking markers and video records them while they are thrown off balance by a floorboard that shifts abruptly. Photo: Rob Felt.

“I can describe the mechanics, and if I have a good model of that, I should understand something about how the system is controlled, which gets me to what the brain and the nervous system are doing,” said Ting, a professor in the Wallace H. Coulter Department of Biomedical Engineering. She started out studying biological motion control to apply it to robots, but now also concentrates on evaluating rehabilitation techniques for people suffering from neurodegenerative diseases like Parkinson’s.

“We’re looking at how muscles are controlled in functional units we call motor modules,” she said. One motor module might be the combination of muscles that go to work when you extend your arm. Others would kick in when you hop on a bike.

Though motor modules work for the most part automatically, initially, they probably had to be learned, like when a child learns to stay balanced on a bike.

Also, our huge cognitive brain regions can override automatic balance to make us willfully walk upright when we otherwise couldn’t, perhaps due to a neurological ailment. But that overriding has limitations, because the brain regions that do it aren’t optimally wired for balance control.

“If you ride a bicycle, and you go through a narrow gap, if you think about it too much, you may wobble a lot,” Ting said, “whereas, normally, you could probably pass through that space.”

Elsewhere in the nervous system, your spinal cord is doing some things on its own, like triggering reflexes.

To watch these various functions interplay, in her lab at Emory University, Ting covers subjects in tracking markers and video records them while she purposely throws off their balance using a floorboard that shifts around abruptly. Cameras roll as the subjects strive to maintain posture — not an easy thing to do.

But watching them flail may help Ting assess the effectiveness of rehabilitation methods in treating neurological disabilities.

All Together Now

When cognitive neuroscientists say “cognition,” they’re not usually referring to how the brain ponders, but instead to how its networks learn facts, recall memories, or pay attention.

Though scientific understanding of “thought” and “psyche” may lie far down the research road, elements of “cognition” could be their building blocks, and the brick layer could be something called “cognitive control.” Cognitive psychologist Eric Schumacher studies how cognitive control employs functions like attention, memory, and learning to make very simple decisions or complete a nominal task.

“When you’re reading a book, you may want to understand the facts,” said Schumacher, an associate professor in Georgia Tech’s School of Psychology. “Your brain has to guide your eyes, encode the words, and link them up to knowledge you already have. There’s a way your brain recruits systems to achieve that, which is what we mean by control.”

Cognitive control constantly adjusts this coordination of senses, movements, knowledge, memory, and more. It’s an array of processes not yet completely understood, so to get a handle on some of them, Schumacher lets volunteers watch action movies and observes their brain activity in an fMRI.

“Things change as we go through the world, and movies, with their flow of actions, allow us to study that in a scanner,” he said. For example, there’s a marked contrast in the way the brain lights up during moments of high suspense and low suspense in the story line.

“With increasing suspense, you become more interested in the story, and regions of the brain’s visual systems that process the center of the screen, where the movie is, become more active, selecting more information from the film, and regions that process the visual periphery become less active.”

“That’s neural evidence for the focusing of attention,” Schumacher said.

Other brain regions — in the parietal and frontal lobes — are known for allocating that attention from one thing to the next. “There’s more activity in those regions in moments of high suspense,” Schumacher said.

And that cognitive control appears to link suspense with learning. “People are more likely to remember information presented at moments of high suspense than in moments of low suspense,” Schumacher said.

The Zone-Out Zone

Relax. Zone out. Welcome to the brain’s default mode network, where it may feel like the mind is just wandering. But a lot is still going on in the brain, which never shuts off.

Broad patterns of brain activity measured by functional Magnetic Resonance Imaging (fMRI). Graphic: courtesy Shella Keilholz.

Don’t believe it? Initially, Shella Keilholz didn’t quite either. The physicist, who researches in neuroscience as associate professor in the Wallace H. Coulter Department of Biomedical Engineering, thought that any activity in a brain in default mode would be extremely faint.

“When we started doing these studies, we thought resting state activity basically would fly under the radar of our detection possibilities,” she said. She’s glad that was wrong. “There’s more information in this resting state MRI than we’d ever hoped to find.”

“All these areas like visual cortex and auditory cortex that are ready for input from the outside world, their activity goes down, and the activity in this default mode network and the areas attached to it go up,” she said. The energy level, in sum, doesn’t change. It just kind of spreads around the brain.

Even though a volunteer subject may be lying flat and still, areas in the brain responsible for hand movement appear to be softly talking to each other. The default mode network stays on during most of sleep. It’s even on during a coma.

The brain transitions a lot between the default mode network and the task positive network, which becomes active when people do externally focused activities.

To research this, Keilholz has people gaze at a little blue dot and relax.

When the dot suddenly turns purple, the research subjects are supposed to punch a button, which requires the brain to quickly suppress the default mode network and jump into the task positive network.

Surprisingly, the more strongly a test subject went into default mode network, the more quickly they could bolt out of it and into the task positive network.

Keilholz has found an innovative way to address one of neuro­science’s great challenges. In rodents, she is taking measurements on a neuronal level and is correlating them with broader measurements of the fMRI. This may someday allow scientists to know what is going on between small bunches of neurons just by looking at an MRI image.

Ben Brumfield is a senior science writer with Georgia Tech’s Institute Communications. He is a former CNN.com editor.

Funding for McGrath, Lu, Streelman, Forest and Haider was provided by the National Institute of Neurological Disorders and Stroke, the National Institute of General Medical Sciences, the National Institute of Biomedical Imaging and Bioengineering, and the National Institute on Aging, all part of the National Institutes of Health. Funding was also provided by the BRAIN Initiative, the Single Cell Grant program, and the National Science Foundation. Funding for Singer, Moffat, and Ting was provided by the National Institute for Neurological Disorders and Stroke and the Eunice Kennedy Shriver National Institute of Child Health and Human Development, both part of the National Institutes of Health, and the National Science Foundation. Funding for Schumacher and Keilholz was provided by the National Institute for Neurological Disorders and Stroke and the National Institute of Mental Health, both part of the National Institutes of Health. Funding was also provided by the National Science Foundation and the Defense Advanced Research Projects Agency.