transcranial magnetic stimulation

Magnetic stimulation of the brain improved awareness of subject's own cognitive abilities

August 29, 2017

Science Daily/Aalto University

Researchers have succeeded for the first time ever in affecting metacognition of a tactile working memory task by combining neural pathway imaging and magnetic stimulation of the brain. Understanding brain function might help in the development of new treatments for neuropsychiatric illnesses in the future.

 

By combining different brain research methods in a versatile manner the researchers showed for the first time that transcranial magnetic stimulation of the brain targeting the prefrontal cortex can improve a test subject's ability to evaluate his or her performance in a tactile working memory task. The ability of human subjects to monitor and control their own cognitive processes is called metacognition.

 

Metacognition is important for people and in many neuropsychiatric illnesses, it is possible to recognize that it has weakened.

 

'The patient's reduced sense of being ill is familiar from conditions such as Alzheimer's disease, schizophrenia, and traumatic brain injury. Understanding the brain function of healthy test subjects could help in the development of new treatment methods for neuropsychiatric illnesses in the future,' says Doctoral Candidate Juha Gogulski.

 

Safe method

Transcranial magnetic stimulation refers to a method in which the nerve cells of the brain are activated from outside the skull with the help of a magnetic field. When used correctly the method is safe, and it is utilized in procedures such as pinpointing the location of the primary motor cortex or the speech area before brain surgery, and in the treatment of depression.

 

Taking part in the study as test subjects were 14 healthy volunteers. They first underwent structural magnetic resonance imaging (MRI) of the brain as well as a diffusion MRI that is sensitive to the movement of water molecules in the brain, making it possible to identify the direction of neural pathways. After the MRI, the neural pathway connections between the primary somatosensory cortex and the prefrontal cortex were determined for each individual.

 

In the last part of the study the test subjects completed working memory tasks in which they were asked to keep in mind the characteristics of touch sensations from the fingertip and to evaluate whether or not the touch stimulation that was just given was similar to or different from the previous stimulus. During the test they were given magnetic pulses to prefrontal cortex areas that had a neural pathway connection to the part of the somatosensory cortex representing the index finger. The test subjects also evaluated how certain they were about their answers, on which basis calculations were made on how well a person's own evaluation corresponded to the actual performance level.

 

Magnetic stimulation of the prefrontal cortex improved the test subjects' evaluation of their performance, as they were able to assess more accurately if their answers had been correct or incorrect.

 

The study was a collaboration between the Department of Neuroscience and Biomedical Engineering at Aalto University, and Department of Physiology in the Faculty of Medicine, University of Helsinki. The original article was published in the international science journal Cerebral Cortex.

https://www.sciencedaily.com/releases/2017/08/170829113800.htm

'Bursts' of beta waves, not sustained rhythms, filter sensory processing in brain

November 8, 2017

Science Daily/Brown University

Scientists have found that people and mice alike use brief bursts of beta brainwaves, rather than sustained rhythms, to control attention and perception.

 

To better understand the brain and to develop potential therapies, neuroscientists have been investigating how "beta" frequency brainwaves help the brain filter distractions to process sensations. A new Brown University study stands to substantially refine what they thought was going on: What really matters is not a sustained elevation in beta wave power, but instead the rate of specific bursts of beta wave activity, ideally with perfect timing.

 

The new insight, reported in the journal eLife, arose from the scientists looking beneath the covers of the typical practice of averaging beta brain wave data. With a closer examination, trial-by-trial for each subject, they saw that what really reflected attention and impacted perception were discrete, powerful bursts of beta waves at frequencies around 20 hertz.

 

"When people were trying to block distraction in a brain area, the probability of seeing these beta events went up," said senior author Stephanie R. Jones, an associate professor of neuroscience at Brown. "The brain seemed to be flexibly modulating the expression of these beta events for optimal perception."

 

The findings, made with consistency in humans and mice, can not only refine ongoing research into how beta waves arise and work in the brain, Jones said, but also provide guidance to clinicians as they develop therapies that seek to modulate beta waves.

 

Testing touch

 

The research team, led by graduate student Hyeyoung Shin, acquired the data through a series of experiments in which they measured beta waves in the somatosensory neocortex of humans and mice in the second leading up to inducing (or not inducing) varying amounts of a tactile sensation. Humans wore a cap of magnetoencephalography sensors, while mice had implanted electrodes. For people, the sensation was a tap on a finger tip or the foot. For mice, it was a wiggle of a whisker.

 

Subjects were merely required to report the sensations they felt -- people pushed a button, while mice were trained to lick a sensor in exchange for a reward. The researchers tracked the association of beta power with whether subjects accurately detected, or didn't detect, stimuli. What they found, as expected, is that the more beta activity there was in the corresponding region of cortex, the less likely subjects were to report feeling a sensation. Elevated beta activity is known to help suppress distractions.

 

A particularly good example, Shin said, was that in experiments where people were first instructed to focus on their foot, there was more beta power in the hand region of the neocortex. Correspondingly, more beta in the hand region resulted in less detection of a sensation in the hand.

 

"We think that beta acts a filter mechanism," Shin said.

 

Beta bursts

 

Consistently throughout various iterations of the experiments across both the human and mouse subjects, increases in beta activity did not manifest as a continuously elevated rhythm. Instead, when beta appeared, it quickly spiked in short, distinct bursts of power. Only if a subject's beta was averaged over many trials would it look like a smooth plateau of high-power activity.

 

After discovering this pattern, the researchers performed analyses to determine what features of the bursts best predicted whether subjects would report, or miss, a touch sensation. After all, it could be the number of bursts, their power, or maybe how long they lasted.

 

What Shin and the team found is that number of bursts and their timing both mattered independently. If there were two or more bursts any time in the second before a sensation, it was significantly more likely to go undetected. Alternatively, if just one burst hit within 200 milliseconds of the sensation, the stimulus would also be more likely to be overlooked.

 

"The ideal case was having large numbers and being close in timing to the stimulus," Shin said.

 

A better idea of beta

 

While the study helps to characterize the nature of beta in the somatosensory neocortex, it doesn't explain how it affects sensations, Jones acknowledged. But that's why it is important that the results were in lockstep in both mice and in people. Confirming that mice model the human experience means researchers can rely on mice in experiments that delve more deeply into how beta bursts arise and what their consequence are in neurons and circuits. Shin is already doing experiments to dissect how distinct neural subpopulations contribute to beta bursts and somatosensory detection, respectively. Co-author and postdoctoral researcher Robert Law is applying computational neural models that link the human and animal recordings for further discovery.

 

In the clinical realm, Jones said, an improved understanding of how beta works could translate directly into improving therapies such as transcranial magnetic stimulation or transcranial alternating current to treat neurological disorders, such as chronic pain, or depression. Rather than using those technologies to generate a consistent elevation in beta in a brain region, Jones said, it might be more effective to use them to induce (or suppress) shorter, more powerful bursts and to time those to be as close in time to a target brain activity as possible.

 

"Typically with non-invasive brain stimulation you are trying to entrain a rhythm," Jones said. "What our results suggest is that's not what the brain is doing. The brain is doing this intermittent pattern of activity."

https://www.sciencedaily.com/releases/2017/11/171108092409.htm

 

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