Touch and Movement Neurons Shape the Brain’s Internal Image of the Body

The brain’s tactile and motor neurons, which perceive touch and control movement, may also respond to visual cues, according to researchers at Duke Medicine.

The study in monkeys, which appears online Aug. 26, 2013, in the journal Proceedings of the National Academy of Sciences, provides new information on how different areas of the brain may work together in continuously shaping the brain’s internal image of the body, also known as the body schema.

The findings have implications for paralyzed individuals using neuroprosthetic limbs, since they suggest that the brain may assimilate neuroprostheses as part of the patient’s own body image.

“The study shows for the first time that the somatosensory or touch cortex may be influenced by vision, which goes against everything written in neuroscience textbooks,” said senior author Miguel Nicolelis, M.D., PhD, professor of neurobiology at Duke University School of Medicine. “The findings support our theory that the cortex isn’t strictly segregated into areas dealing with one function alone, like touch or vision.”

Earlier research has shown that the brain has an internal spatial image of the body, which is continuously updated based on touch, pain, temperature and pressure – known as the somatosensory system – received from skin, joints and muscles, as well as from visual and auditory signals.

An example of this dynamic process is the “rubber hand illusion,” a phenomenon in which people develop a sense of ownership of a fake hand when they view it being touched at the same time that something touches their own hand.

In an effort to find a physiological explanation for the “rubber hand illusion,” Duke researchers focused on brain activity in the somatosensory and motor cortices of monkeys. These two areas of the brain do not directly receive visual input, but previous work in rats, conducted at the Edmond and Lily Safra International Institute of Neuroscience of Natal in Brazil, theorized that the somatosensory cortex could respond to visual cues.

In the Duke experiment, the two monkeys observed a realistic, computer-generated image of a monkey arm on a screen being touched by a virtual ball. At the same time, the monkeys’ arms were touched, triggering a response in their somatosensory and motor cortical areas.

The monkeys then observed the ball touching the virtual arm without anything physically touching their own arms. Within a matter of minutes, the researchers saw the neurons located in the somatosensory and motor cortical areas begin to respond to the virtual arm alone being touched.

The responses to virtual touch occurred 50 to 70 milliseconds later than physical touch, which is consistent with the timing involved in the pathways linking the areas of the brain responsible for processing visual input to the somatosensory and motor cortices. Demonstrating that somatosensory and motor cortical neurons can respond to visual stimuli suggests that cross-functional processing occurs throughout the primate cortex through a highly distributed and dynamic process.

“These findings support our notion that the brain works like a grid or network that is continuously interacting,” Nicolelis said. “The cortical areas of the brain are processing multiple streams of information at the same time instead of being segregated as we previously thought.”

The research has implications for the future design of neuroprosthetic devices controlled by brain-machine interfaces, which hold promise for restoring motor and somatosensory function to millions of people who suffer from severe levels of body paralysis. Creating neuroprostheses that become fully incorporated in the brain’s sensory and motor circuitry could allow the devices to be integrated into the brain’s internal image of the body. Nicolelis said he is incorporating the findings into the Walk Again Project, an international collaboration working to build a brain-controlled neuroprosthetic device. The Walk Again Project plans to demonstrate its first brain-controlled exoskeleton during the opening ceremony of the 2014 FIFA Football World Cup.

“As we become proficient in using tools – a violin, tennis racquet, computer mouse, or prosthetic limb – our brain is likely changing its internal image of our bodies to incorporate the tools as extensions of ourselves,” Nicolelis said.

(Image: Getty images)

Two left feet? Study looks to demystify why we lose our balance

It’s always in front of a million people and feels like eternity. You’re strolling along when suddenly you’ve stumbled—the brain realizes you’re falling, but your muscles aren’t doing anything to stop it.

For a young person, a fall is usually just embarrassing. However, for the elderly, falling can be life threatening. Among the elderly who break a hip, 80 percent die within a year.

University of Michigan researchers believe that the critical window of time between when the brain senses a fall and the muscles respond may help explain why so many older people suffer these serious falls. A better understanding of what happens in the brain and muscles during this lag could go a long way toward prevention.

To that end, researchers at the U-M School of Kinesiology developed a novel way of looking at the electrical response in the brain before and during a fall by using an electroencephalogram.

Findings showed that many areas of the brain sense and respond to a fall, but that happens well before the muscles react. Lead researcher Daniel Ferris likened the study method to recording an orchestra with many microphones and then teasing out the sounds of specific instruments. In the study, researchers measured electrical activity in different regions of the brain.

"We’re using an EEG in a way others don’t, to look at what’s going on inside the brain," said Ferris, a professor in kinesiology. "We were able to determine what parts of the brain first identify when you are losing your balance during walking."

During the study, healthy young subjects with electrodes attached to their scalps walked on a balance beam mounted to a treadmill. When participants lost their balance and went off the beam, they simply continued walking on the moving treadmill, thus avoiding injury.

Ferris and colleagues then used a method called independent components analysis to separate and visualize the electrical activity in different parts of the brain. They found that people sense the start of a fall much better with both feet on the ground. Two grounded feet make it easier to determine where the ground is relative to the body, but people aren’t as sure of their stability on one foot.

The researchers were surprised that so many different parts of the brain activate during a fall, and they didn’t expect the brain to recognize a loss of balance as early as it does.

Future studies comparing the elderly with younger subjects could determine if the elderly sense falls too late, in which case, pharmaceuticals might help them regain their balance. If it’s a simple motor problem such as muscles not responding properly, strengthening exercises could help.

Other experiments under the same grant in the Ferris lab look to separate sensory and motor contributions to brain activity during walking.

The study, “Loss of balance during balance beam walking elicits a broadly distributed theta band electrocortical response,” was published in advance online in the Journal of Neurophysiology.

Irreversible tissue loss seen within 40 days of spinal cord injury

The rate and extent of damage to the spinal cord and brain following spinal cord injury have long been a mystery. Now, a joint research effort between the University of Zurich, University Hospital Balgrist and colleagues from University College London have found evidence that patients already have irreversible tissue loss in the spinal cord within 40 days of injury. Using a new imaging measurement technique the impact of therapeutic treatments and rehabilitative interventions can be now determined more quickly and directly than before.

A spinal cord injury changes the functional state and structure of the spinal cord and the brain. For example, the patients’ ability to walk or move their hands can become restricted. How quickly such degenerative changes develop, however, has remained a mystery until now. The assumption was that it took years for patients with a spinal cord injury to also display anatomical changes in the spinal cord and brain above the injury site. For the first time, researchers from the University of Zurich and the Uniklinik Balgrist, along with English colleagues from University College London (UCL), now demonstrate that these changes already occur within 40 days of acute spinal cord injury.

Spinal cord depletes rapidly

The scientists studied 13 patients with acute spinal cord injuries every three months for a year using novel MRI (magnetic resonance imaging) protocols. They discovered that the diameter of the spinal cord had rapidly decreased and was already seven percent smaller after twelve months. A lesser volume decline was also evident in the corticospinal tract, a tract indispensable for motor control, and nerve cells in the sensorimotor cortex. The extent of the degenerative changes coincided with the clinical outcome. “Patients with a greater tissue loss above the injury site recovered less effectively than those with less changes,” explains Patrick Freund, the investigator responsible for the study at the Paraplegic Center Balgrist.

Gaining insights into effect of therapies

Treatments targeting the injured spinal cord have entered clinical trials. Gaining insights into mechanisms of repair and recovery within the first year are crucial. Thanks to the use of the new neuroimaging protocols, Freund says, we now have the possibility of displaying the effect of therapeutic treatments on the central nervous system and of rehabilitative measures more quickly. Consequently, the effect of new therapies can also be recorded more rapidly.

“This study is an excellent example of the value of combining the complementary expertise of the two universities,” says UCL’s Dean of Brain Sciences, Professor Alan Thompson, who is one of the senior authors of the study. “It provides exciting new insights into the complications of spinal cord trauma and gives us the possibility of identifying both imaging biomarkers and therapeutic targets.”

The findings are the result of a new three-year neuroscience partnership between the Neuroscience Centre Zurich (ZNZ) and UCL.

Literature:

Patrick Freund, Nikolaus Weiskopf, John Ashburner, Katharina Wolf, Reto Sutter, Daniel R Altmann, Karl Friston, Alan Thompson, Armin Curt. MRI investigation of the sensorimotor cortex and corticospinal tract after acute spinal cord injury: a prospective longitudinal study. The Lancet Neurology. July 2, 2013.

Secrets of Human Speech Uncovered

A team of researchers at UC San Francisco has uncovered the neurological basis of speech motor control, the complex coordinated activity of tiny brain regions that controls our lips, jaw, tongue and larynx as we speak.

Described this week in the journal Nature, the work has potential implications for developing computer-brain interfaces for artificial speech communication and for the treatment of speech disorders. It also sheds light on an ability that is unique to humans among living creatures but poorly understood.

“Speaking is so fundamental to who we are as humans – nearly all of us learn to speak,” said senior author Edward Chang, MD, a neurosurgeon at the UCSF Epilepsy Center and a faculty member in the UCSF Center for Integrative Neuroscience. “But it’s probably the most complex motor activity we do.”

The complexity comes from the fact that spoken words require the coordinated efforts of numerous “articulators” in the vocal tract – the lips, tongue, jaw and larynx – but scientists have not understood how the movements of these distinct articulators are precisely coordinated in the brain.

To understand how speech articulation works, Chang and his colleagues recorded electrical activity directly from the brains of three people undergoing brain surgery at UCSF, and used this information to determine the spatial organization of the “speech sensorimotor cortex,” which controls the lips, tongue, jaw, larynx as a person speaks. This gave them a map of which parts of the brain control which parts of the vocal tract.

They then applied a sophisticated new method called “state-space” analysis to observe the complex spatial and temporal patterns of neural activity in the speech sensorimotor cortex that play out as someone speaks. This revealed a surprising sophistication in how the brain’s speech sensorimotor cortex works.

They found that this cortical area has a hierarchical and cyclical structure that exerts a split-second, symphony-like control over the tongue, jaw, larynx and lips.

“These properties may reflect cortical strategies to greatly simplify the complex coordination of articulators in fluent speech,” said Kristofer Bouchard, PhD, a postdoctoral fellow in the Chang lab who was the first author on the paper.

In the same way that a symphony relies upon all the players to coordinate their plucks, beats or blows to make music, speaking demands well-timed action of several various brain regions within the speech sensorimotor cortex.

Brain Mapping in Epilepsy Surgery

The patients involved in the study were all at UCSF undergoing surgery for severe, untreatable epilepsy. Brain surgery is a powerful way to halt epilepsy in its tracks, potentially completely stopping seizures overnight, and its success is directly related to the accuracy with which a medical team can map the brain, identifying the exact pieces of tissue responsible for an individual’s seizures and removing them.

The UCSF Comprehensive Epilepsy Center is a leader in the use of advanced intracranial monitoring to map out elusive seizure-causing brain regions. The mapping is done by surgically implanting an electrode array under the skull on the brain’s outer surface or cortex and recording the brain’s activity in order to pinpoint the parts of the brain responsible for disabling seizures. In a second surgery a few weeks later, the electrodes are removed and the unhealthy brain tissue that causes the seizures is removed.

This setting also permits a rare opportunity to ask basic questions about how the human brain works, such as how it controls speaking. The neurological basis of speech motor control has remained unknown until now because scientists cannot study speech mechanisms in animals and because non-invasive imaging methods lack the ability to resolve the very rapid time course of articulator movements, which change in hundredths of seconds.

But surgical brain mapping can record neural activity directly and faster than other noninvasive methods, showing changes in electrical activity on the order of a few milliseconds.

Prior to this work, the majority of what scientists knew about this brain region was based on studies from the 1940’s, which used electrical stimulation of single spots on the brain, causing a twitch in muscles of the face or throat. This approach using focal stimulation, however, could never evoke a meaningful speech sound. 

Chang and colleagues used an entirely different approach to studying the brain activity during natural speaking brain using the implanted electrodes arrays. The patients read from a list of English syllables – like bah, dee, goo. The researchers recorded the electrical activity within their speech-motor cortex and showed how distinct brain patterning accounts for different vowels and consonants in our speech.

“Even though we used English, we found the key patterns observed were ones that linguists have observed in languages around the world – perhaps suggesting universal principles for speaking across all cultures,” said Chang.