Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Stanford researchers observe the moment when a mind is changed

06.05.2015

A new algorithm enables a moment-by-moment analysis of brain activity each time a laboratory monkey reaches this way or that during an experiment. It's like reading the monkey's mind.

Researchers studying how the brain makes decisions have, for the first time, recorded the moment-by-moment fluctuations in brain signals that occur when a monkey making free choices has a change of mind.


This four-second time-lapse photo of a Los Angeles freeway illustrates the complexities of decision-making, as one driver appears to have made a late change of mind while most drivers decided in advance whether to stay on the main road or take an exit ramp.

(Photo: Susanica Tam)

The findings result from experiments led by electrical engineering Professor Krishna Shenoy, whose Stanford lab focuses on movement control and neural prostheses - such as artificial arms - controlled by the user's brain.

"This basic neuroscience discovery will help create neural prostheses that can withhold moving a prosthetic arm until the user is certain of their decision, thereby averting premature or inopportune movements," Shenoy said.

The experiments are described in the journal eLife. They were performed by neuroscientist Matthew Kaufman while he was a graduate student in Shenoy's lab.

Kaufman taught laboratory monkeys to perform a decision-making task. He then developed a technique to track the brain signals that occur during a single decision with split-second accuracy. This improvement on what's called the "single trial decoder" algorithm revealed the neural signals that occurred during a momentary hesitation or when the monkey changed his mind.

"We are seeing many cognitive phenomena in the brain for the first time," said Kaufman, who is now a postdoctoral scholar at Cold Spring Harbor Laboratory. "The most critical result of our work here is that we can track a single decision and see how the monkey arrived there: whether he decided quickly, slowly, or changed his mind halfway through."

The experiments

The experiments involved monkeys that were trained to reach for either of two targets on a computer screen. It was often possible to reach either target, inviting a free choice. Sometimes, one target was blocked, resulting in a forced choice. Other times, the researchers would switch between these configurations while the monkey was deciding, encouraging a change of mind.

The research focused on the time the monkey spent deliberating, before the actual movement began. The monkeys were trained to sit motionless while two jittering targets were positioned on either side of a computer screen.

Colored barriers on the screen created a simple maze. When the targets stopped jittering the monkeys were trained to move to one or the other target by sweeping his fingertip through the maze until he touched one of the targets.

During the experiments, 192 electrodes in each monkey's motor and premotor cortex began measuring brain activity the moment that the targets appeared on screen. The measurements continued until the targets stopped jittering and the monkey began to move. The interval between the targets' appearance and the beginning of movement marked the time of decision or, in some cases, hesitation.

The single-trial advantage

Using his single-trial decoder algorithm, Kaufman could analyze moment-by-moment brain activity during each individual decision. In a sense, he was able to read the monkey's mind during free choices, when each decision may be different.

In previous experiments on decision-making, researchers have had monkeys perform many trials and average the readings they obtain to get summary statistics. But these older approaches do not allow researchers to identify unique or idiosyncratic events during any individual decision.

"We can now track single decisions with unprecedented precision," Kaufman said. "We saw that the brain activity for a typical free choice looked just like it did for a forced choice. But a few of the free choices were different. Occasionally, he was indecisive for a moment before he made any plan at all. About one time in eight, he made a plan quickly but spontaneously changed his mind a moment later."

This deeper understanding of decision-making will help researchers to fine-tune the control algorithms of neural prostheses to enable people with paralysis to drive a brain-controlled prosthetic arm or guide a neurally-activated cursor on a computer screen.

Two former Stanford postdocs also contributed to this paper: Mark M. Churchland, now an assistant professor at Columbia University, and Stephen I. Ryu, now a consulting professor of electrical engineering at Stanford and a neurosurgeon at the Palo Alto Medical Foundation.

The philosophical implications

Kaufman said the team's findings also bear on a longstanding philosophical debate about human consciousness.

In the early 1980s, University of California, San Francisco neuroscientist Benjamin Libet conducted an experiment to assess the nature of free will. Subjects hooked up to an electroencephalogram (EEG) were asked to push a button whenever they liked. They were also asked to note the precise time that they first became aware of the wish or urge to move.

Libet's experiments showed that distinctive brain activity began, on average, several seconds before subjects became aware that they planned to move. Libet concluded that the desire to move arose unconsciously, and "free will" could only come in the form of a conscious veto: what he called "free won't."

Kaufman said that the brain activity Libet saw does not imply a demise of free will. Instead, his results show that you can plan to make a particular movement, but sometimes change your mind a second later. The moment of commitment to your choice might therefore happen late, just as Libet's subjects reported. "Being able to see how each choice unfolds on a millisecond timescale may help make it possible to better study these kinds of slippery issues," Kaufman said.

###

This work was supported in part by a Director's Pioneer Award from the National Institutes of Health and by a REPAIR grant from the Defense Advanced Research Projects Agency.

Media Contact

Tom Abate
tabate@stanford.edu
650-736-2245

 @stanfordeng

http://soe.stanford.edu 

Tom Abate | EurekAlert!

More articles from Health and Medicine:

nachricht Why might reading make myopic?
18.07.2018 | Universitätsklinikum Tübingen

nachricht Unique brain 'fingerprint' can predict drug effectiveness
11.07.2018 | McGill University

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Machine-learning predicted a superhard and high-energy-density tungsten nitride

18.07.2018 | Materials Sciences

NYSCF researchers develop novel bioengineering technique for personalized bone grafts

18.07.2018 | Life Sciences

Why might reading make myopic?

18.07.2018 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>