Category: Neuroscience Page 10 of 15

Imagine catching a ball thrown at you out of mid-air. Your response seems almost instinctive, like a reflex. However, this seemingly simple movement contains complex components: one must judge the ball’s arc to decide where it will intersect a particular height, and how fast one must move his hand to catch the accelerating ball.

This calculation requires an entire concert of neural signals, firing in a manner so precise that it produces an accurate estimate of the speed and direction of the ball’s trajectory. Add to this complicated model the fact that each individual neuron produces a certain amount of noise — that is, across various trials, the same neurons produce different firing responses to the same stimuli. These multiple layers of convolution would frustrate most, but Dr. Stephen Lisberger thrives upon it.

Lisberger, the Chair of Neurobiology at Duke School of Medicine, emphasizes that while a single noisy neuron cannot produce an accurate estimate of speed and direction, the key lies in populations of neurons. On January 25, Lisberger presented his research to a diverse crowd of Duke scientists.

Lisberger and his team have performed multiple trials in which a monkey tracked a visual stimulus with his eye, thus activating certain neurons. They found that the noise persisted even in neural populations.

Lisberger, rather than being discouraged, turns this noise into an asset. He reasons that variation is something which the brain must handle; therefore, he can use variation to learn about the brain.

When a monkey follows a visual stimulus with his eye, he integrates the sensory system with a motor region of the brain called MT. Lisberger isolated the source of the noise to the sensory system, rather than MT. He found that other movements originating from MT did not display the same noise; thus, the noise in eye tracking must have come from the sensory system.

The noise from the sensory system propagates down to MT, and Lisberger follows in his analysis.

One of his colleagues proposed that the random noise over a large population of neurons should cancel itself out. Lisberger contradicts this idea, noting that the variation is correlated among neurons in MT. Variations in pairs of neurons fluctuate up and down together. Thus, some of the “noise” is actually signal. This shared noise is transmitted through the circuit, while independent noise averages itself away.

Ultimately, Lisberger models neural responses over multiple trials to statistically estimate the direction and speed indicated by a particular response. The brain though, has not the luxury of simultaneously integrating and analyzing such large pools of data in its fraction-of-a-second estimate. Instead, the brain makes do with what it has, which, as Lisberger points out, is enough.

By Olivia Zhu  

By Karl Leif Bates

From the top side, it looks like a miniature of the landmark Apple store on Fifth Ave. in Manhattan — a simple glass cube.

The entrance to the new DIBS space is just a glass box on the plaza next to LSRC.

But descending the stairs or the glass elevator brings one into the newest, hippest space on campus, the new headquarters of the Duke Institute for Brain Sciences (DIBS). DIBS opened the new underground space at the Levine Science Research Center (LSRC) this week with a reception and lecture.

(The inaugural lecture by Sarah-Jayne Blakemore of University College London, was about her work on the adolescent brain. The peak volume of gray matter in the human brain comes around age 14 and then declines, Blakemore says, but that’s not all a bad thing. It’s the pruning and streamlining of connections that turns a socially obsessed, impulsive teenager into a confident, somewhat-rational adult.)

The atrium of the new center feels spacious, despite being underground.

The 11,000-square-foot space stretches south from the cube and  beneath the Blue Front dining hall in a big bay that used to house utilities equipment for LSRC. The ceilings still boast giant pipes marked CHILLED WATER and such, but the rest of it is comfortable, ultra-modern space for brain scientists to communicate, collaborate and learn, with space-saving sliding doors on the offices, and glass garage doors to section off or open up the meeting rooms.

There are actually two levels in the new lair. The mezzanine, ringed by a groovy steel-cable balustrade, provides offices,  a conference room, and even a sort of balcony overlooking the main events space where Blakemore spoke.

The lecture hall is a flexible space with a ‘balcony’ of sorts.

The main level below is larger and has more staff offices, two teaching labs, and an airy atrium topped with big ring-shaped light fixtures. A divisible “team room” can be used for Bass Connections meetings or other gatherings, and an even larger multi-function space is set up for lectures, but has a flat floor and stackable chairs, so it could do lots of other things too.

There’s even a little room between the teaching labs that might come in handy for storing brains, DIBS Director Michael Platt points out on an introductory tour.

“We haven’t come up with a name yet,” Platt says. “It’s been called the DIBS underground, the Cube…” Standing nearby, psych and neuroscience professor Scott Huettel offers, “We could call it the voxel,” a cubic measure often used in MRI studies.

DIBS Director Michael Platt and Associate Director Zab Johnson designed the new space.

The orange walls on the lower level offices don’t go all the way to the ceiling, which helps it feel less underground but may require some new telephone and meeting etiquette, says communication director Julie Rhodes.

“We’re thrilled with it,” said DIBS Associate Director Elizabeth “Zab” Johnson, who co-designed the space with Platt and has already relocated her office from LSRC to the still-unnamed new space.