Posts Tagged ‘Functional magnetic resonance imaging’

Tools of Cognitive Neuroscience

September 10, 2019

The title of this post is identical to a chapter title in an important book by Scott D. Slotnick titled “Cognitive Neuroscience of Memory.” The tools of cognitive neuroscience are highly technical. If the reader is interested in these techniques she should read Dr.Slotnick’s book, or look up the tools of interest in the Wikipedia.

One of the earliest techniques was positron emission tomography (PET). It required that a low level of radioactive material be injected into the participants bloodstream. This technique measured increased blood flow to the portions of the brain being activated. Fortunately a new technique that measured blood flow was found that did not require the injection of radioactive dye or any other type of material.

That technique was functional magnetic resonance imaging (fMRI), which also measured where in the brain the blood flow was increasing.

Event-related potentials (ERPs) can track brain activity in real time. ERPs directly measure neural activity and have a temporal resolution in milliseconds. Its spatial resolution is in centimeters, which is much lower than fMRI.

Electroencephalography (EEG) uses the identical data acquisition as ERPs, but refers to any measure of brain activity that corresponds to electric fields. This includes ERPs, but more commonly refers to brain activity that oscillates within a specific range of frequencies. EEG frequency analysis is a powerful alternative to the more commonly employed ERP analysis. Related to EEG, magnetoencephalography (MEG) refers to any measure of brain activity that corresponds to magnetic fields, and also typically refers to brain activity that oscillates within a specific frequency range. Like ERPs that are generated by averaging all the events of a given type from EEG data during a cognitive task, event-related fields (ERFs) are generated by averaging all the events of a given type from MEG data. The more general terms EEG and MEG also refer to ERPs and ERFs.

Dr. Slotnick writes, “fMRI is by far the most popular method in the field of cognitive neuroscience. However, brain activity is not a static set of blobs that represent a cognitive process. Rather, brain activity changes across different regions in milliseconds. Only techniques with excellent temporal resolution, such as ERPs, can track the functioning brain. This book highlights the temporal dimension of brain processing in addition to the spatial dimension of brain processing. One major advantage of temporal information is that one can use it to assess whether different brain regions are synchronously active, which indicates that these regions interact. This reflects how the brain is actually operating.”

Transcranial magnetic stimulation (TMS) can be used to temporarily disrupt processing in one region of the brain.

Transcranial direct current stimulation (tDCS) is similar to TMS in that it temp[orarily modulates processing in a target cortical region by stimulating with a weak direct current rather than a magnetic field.

A relatively new method called transcranial alternating current stimulation (tACS) uses the identical setup as tDCS, but the current alternatives at a specific frequency; this, tACS can stimulate the brain at a desired frequency.

Do not let yourself be discouraged or turned off by this technical stuff, but brief explanations are needed as these are the tools used in this research. The remainder of the posts will be on memory performance and on the portions of the brain contributing to this performance.

Outlook

April 11, 2012

Outlook is one of the dimensions of Davidson’s Six Dimensions of Emotional Style.1 Outlook refers to how one characteristically views life, typically along an optimism/pessimism dimension. There have already been a host of healthymemory blog posts on optimism (enter “optimism” into the search box). One can be too optimistic, or one can be too pessimistic. However, it is interesting to note that mental health tends toward the optimistic end. People who are clinically depressed tend to be more accurate making predictions where norms exist (for example, life expectation, or the likelihood of suffering from different diseases). This condition is known as depressive realism. Being more optimistic increases the likelihood of persevering and eventually achieving success. Optimism is a “Goldilocks” variable. You can have either too much or too little optimism. Somewhere in the middle is “just right.”

Davidson and his colleagues did a study2 in which the compared the brain activity of two groups: Healthy vs. Clinically Depressed. fMRI was used while they viewed pictures of people doing something joyous or, at least mildly pleasurable (children playing and enjoying themselves, adults dancing, people eating food that they were clearly enjoying. When the picture went off, they were asked to try to prolong the emotion (think of themselves in the same situation, imagine that the joy they felt would last and last). Seventy-two such images were projected to each participant over a forty-five minute session.

The brain imaging revealed activity in the reward circuit of the brain. This circuit involves the prefrontal cortex and the nucleus accumbens in the ventral striatum. Both groups showed activation in this reward circuit while the pictures were presented. However, it was only the Healthy participants who were able to maintain this activity once the pictures were turned off. The clinically depressed participants exhibited low activity in the ventral striatum due to decreased input from the prefrontal cortex.

I find these results to be both interesting and useful. It provides added context for interpreting my feelings. When my mood turns pessimistic, I can appreciate that my outlook, even though it might be more accurate, is less adaptive and less likely to lead to future success and happiness. I am also aware that my mood is likely due to decreased input from my prefrontal cortex to my ventral striatum, and if I can increase that input, via either internal or external means, I should become more optimistic.

1Davidson, R.J. & Begley, S. (2112). The Emotional Life of Your Brain. New York: Hudson Street Press.

2Ibid.

© Douglas Griffith and healthymemory.wordpress.com, 2012. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

Change Your Brain by Transforming Your Mind

June 12, 2011

“Change Your Brain by Transforming Your Mind” was the title of a presentation given by Richard J. Davidson at this year’s annual meeting of the American Psychological Society (APS). This was part of a Theme Program titled “Consciousness: From Neural Systems to Phenomenological Experience.” Davidson’s presentation is in the new arena of contemplative neuroscience or contemplative practice (see the Blog Post “Buddha’s Brain”). The goal here is to use contemplative practices to take advantage of the neuroplasticity of the brain and produce enduring changes in the habits of the mind. They are looking for neurally inspired behavioral interventions that put the brain back into biomedicine, a pathway back to the mind.

He described a study that assessed the effects of meditative expertise on the regulation of the neural circuitry of emotion.1 Both fMRI and subjective reports were collected. The specific neural structures and circuits involved in the circuitry of emotion were identified. The data indicated that the mental expertise to cultivate positive emotion alters the activation of circuits previously linked to empathy and theory of mind in response to emotional stimuli.

Readers of the Healthymemory Blog should be well aware of the importance of attention and the ability to selectively attend to desired information. The famous psychologist, William James, noted that the facility of voluntarily bringing back wandering attention over and over is extremely important. Research indicates that meditation develops this facility. Meditation in Sanskrit means familiarization. So meditation is a matter of becoming familiar with our own minds. There is a positive correlation between gamma activity in our brains and clarity ratings.

There are a variety of Healthymemory Blog Posts on meditation such as “Does Meditation Promote a Healthy Memory,” “Is Daydreaming Bad for You,” “Costly Gadgets or Software are Not Required for a Healthy Memory,” “Continuing to Be Positive After Thanksgiving,” “Intensive Meditation Training Increases the Ability of to Sustain Attention,” “Restoring Attentional Resources,” “More on Restoring Attentional Resources, “The Relaxation Response,”, and “How to Avoid Temptation.”

1Lutz, A. Brefczynski-Lewis, J., Johnstone, T., & Davidson, R.J. (2008). Regulation of the Neural Circuitry of Emotion by Compassion Meditation> Effects of Meditative Experience., PloS one, www.plosone.org, March, Volume 3, Issue 3, e1897.

© Douglas Griffith and healthymemory.wordpress.com, 2011. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

Two Brains, One MRI Scanner

May 18, 2011

The New Scientist reported that Ray Lee of Princeton has developed the first dual-headed fMRI scanner.1 Up until now these machines had been unable to handle more than one brain at a time. And for reasons that I don’t understand (because I don’t understand the technology), they cannot synchronize two or more scanners to scan different individuals at the same time. Although they can scan people in different machines and link them by video. But Lee has designed his scanner that scans two brains at the same time in the same scanner.

In one of the first tests, Lee asked couples to face each other and to blink in unison. The fusiform gyrus, which is involved in facial recognition, was tightly correlated in the two brains. He also had couples embrace, which revealed similar synchronous brain activity.

James Coan of the University of Virginia has some interesting ideas on how to use this device. He notes that “People distribute neural processing across multiple brains when solving problems. …You essential contract out part of a given problem to someone else’s mind. Lee’s work would give us the opportunity to see two brains reacting to a problem simultaneously.” Using the terminology of the Healthymemory Blog, this activity involves transactive memory, memories that are stored in someone else’s brain.

Many of our activities involve, either implicitly or explicitly, transactive memory. When you are trying to communicate with somebody or some group, successful communication requires that the material be pitched at the appropriate level. This entails knowing something about what the other party(ies) knows. When you are trying to persuade somebody, it is extremely helpful to know what that person knows and believes. And it games, you are constantly trying to decipher what the other person is thinking. Transactive memory is a big player in many activities.

1Ferris jabr (2011). At last, an MRI scanner for the man with two brains. New Scientist, 29 January, 12. 

© Douglas Griffith and healthymemory.wordpress.com, 2011. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

Hope for an Aging Population: STAC

November 21, 2010

By 2050 in wealthy, developed countries it is estimated that there will be many more older adults (26%) than children under 15 (about 16%). Today adults aged 85 and older have a dementia rate of nearly 50%. Projecting this into the future yields a frightening prospect. It portends a large percentage of underproductive older people. Beyond that, there would be a large percentage of older people living unfulfilling lives.

Looking at both the neurological and behavioral changes that occur in the aging brain can also be discouraging. There are decreases of volume in the caudate nucleus, the lateral prefrontal cortex, both cerebral hemispheres, and the hippocampus. There are also decreases in processing speed and in the ability to focus and screen out extraneous information. Fortunately, not everything declines. The primary visual cortex and the entorhinal cortex suffer minimal or no loss in volume. Similarly our vocabularies and expertise typically do not decline. Although sometimes it might be difficult finding a word, it usually comes to mind eventually.

Fortunately there is evidence that there are compensatory mechanisms to counter or ward off this decline (see the Healthymemory Blog Post “HAROLD”). And it is clear that these mechanisms work. Many people function quite well even in to advanced old age. What is even more remarkable that some people show little or no evidence for cognitive decline in spite of a great deal of pathology discovered during autopsies.

What is needed is a theory to understand the mechanisms that ward off this decline. The Scaffolding Theory of Aging and Cognition (STAC)1 provides such a theory. Some of the basis of this theory comes from brain imaging, fMRI especially. This imaging has revealed differences in the pattern of neural activation between young and older adults. Whereas young adults show focal left prefrontal activity when engaged in certain cognitive tasks, older adults show activity in both the left and right prefrontal areas.

It should be understood that scaffolding is a process that occurs across the lifespan. It is not just the brain’s response to normal aging; it is the brain’s response to challenge. For anyone acquiring a new skill an initial set of neural circuits must be engaged and developed to provide the structure for task performance in the early stages of skill acquisition. With practice, performance becomes less effortful and the neural circuitry becomes more specific to the task.

The basic idea underlying STAC is that this same mechanism can compensate for losses in brain structure and function as we age. So what can be done to activate this mechanism? The answer is to challenge the brain and then address this challenge. As we age it becomes easier to rely upon old habits and ways of thinking and to avoid new challenging activities. But it is these challenging activities that activate the STAC process that can ward off cognitive decline.

One can regard the Healthymemory Blog as a means of providing this cognitive challenge. First of all, it provides information and data about human cognition. This can be new learning that can provide challenge in itself if not insight into the working and malfunctions of human cognition. It also presents mnemonic techniques that not only can improve cognitive performance, but offer cognitive exercise and challenge in trying to implement them. Finally, there is transactive memory, where there is knowledge from fellow humans and from the internet (and more traditional sources of knowledge) to challenge the mind.

1Park, D.C. & Reuter-Lorenz, P. (2009). The Adaptive Brain: Aging and Neurocognitive Scaffolding. Annual Review of Psychology,60, 173-196.

© Douglas Griffith and healthymemory.wordpress.com, 2010. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.