Posts Tagged ‘Ventral striatum’

The Outlook Brain

March 19, 2020

The title of this post is identical to the title of a section in an important book by Richard J. Davidson, Ph.D. with Sharon Begley, “The Emotional Life of Your Brain.” The remainder of the title is How Its Unique Patterns Affect the Way You Think, Feel and LIve—And How You Can Change Them.

It was discovered in 1982 that greater activity in the left prefrontal cortex underlies positive emotions, while greater activity in the right prefrontal cortex is associated with negative emotions. Early research was spent trying to identify the specific aspects of positive emotion that are lacking in people suffering from depression. Depressed people have little drive to accomplish goals. Sometimes they do not even notice, let alone perk up, when they encounter something novel, the way other people notice a new batch of flowers in a neighbor’s yard or a new coffee bar that just opened down the street. They also lack persistence. Many depressed people are aware that they have plans and to-do lists, but they lack the tenacity required to carry them out.

Depressed people do respond positively to humorous film clips. They report as much positive emotion in response to these clips as non depressed participants, so they are able to experience joy. They key difference between depressed and healthy people is how well they can sustain positive emotion, as opposed to how much they feel. So they feel the positive emotion but do not sustain it.

Prof Richardson and his staff conducted a study with twenty-seven people suffering from clinical depression and nineteen healthy volunteers. The goal was to measure brain activity while people looked at emotionally evocative pictures projected onto the ceiling of an MRI tube. All the pictures depicted something joyous, or at least something designed to bring a faint smile to the lips—children playing and clearly enjoying themselves, adults dancing, people eating food that looked good enough to make a mere observer salivate.

For each image the volunteers got one of two instructions: either to simply view the pictures as they normally would, with no attempt to modify their emotional response, or to try to enhance and sustain the positive emotion the picture induced for as long as possible (or up to 20 seconds) after the image vanished from the screen.

A clear pattern emerged from the data on all volunteers, depressed and healthy. When the volunteers first saw the pictures depicting happy situations, activation in what we think of as the brain’s reward circuit shot up. This circuit is centered on a region in the ventral striatum, which is located below the cortical surface in the middle of the brain and has been shown in other studies to become active when people anticipate receiving rewarding or pleasurable stimuli. What becomes active during such experiences is a cluster of neurons within the ventral striatum called the nucleus accumbens, a region critical for motivation and generating a sense of reward. It also happens to be packed with neurons that either release or capture the neurotransmitter dopamine, which plays a role in positive emotion, motivation, and desire; and endogenous opiates, which provide the famous runner’s high. Levels of activity in the nucleus accumbens were similar in depressed and non depressed volunteers looking at the smile-inducing pictures. Everyone was able to feel an initial uptick of sympathetic joy, but this did not last. Although healthy people were able to maintain an emotional high for the entire session, in depressed patients the positive feeling evaporated within minutes.

Prof. Davidson concludes, “These findings indicate that activity in the nucleus accumbens and prefrontal cortex underly the ability to sustain positive emotion. The greater the activity in the nucleus accumbens—activity sustained by signals from the prefrontal cortex—the further toward the Positive end of the Outlook dimension on which someone falls. Lower activity in this region underlies a Negative outlook.

The Amygdala and the Problem of Reverse Inference

January 18, 2014

This blog post is based on the book Brainwashed: The Seductive Appeal of Mindless Neuroscience by Sally Satel and Scott O. Lillenfeld. Please bear with me as this is just the third post that I’ve written based on a source viewed on my Kindle.

The amygdala is a small region on each side of the brain. So we all should have two amygdalae. They are located in the temporal lobes, one in each hemisphere. In popular reports the amygdala has become almost synonymous with the emotional state of fearfulness. This is true. When you experience fear, the amygdala lights up. I have personal experience with research on the amygdala that I conducted when I was a graduate student. This was back in the days before brain imaging. I surgically implanted electrodes in rats placed under anesthesia so that they would electrically stimulate only their amygdalae. They were deprived of water and when placed in the operant chamber, they immediately started drinking. They received a shock after drinking. When they were placed back into the operant chamber they would not drink even if they were thirsty. However, if an electric current had been sent to the amygdalae when they were shocked the memory of the shock would never have been formed, so they would drink without fear when placed back in the operant chamber.

Although the amygdala is involved in fearfulness, it also responds to things that are unexpected, novel, unfamiliar or exciting. “This probably explains its increased activation when men look at pictures of a Ferrari 360 Modena. The amygdala reacts to photos of faces with menacing expressions, but also to photos of friendly, unfamiliar faces. If fearful faces are expected and happy faces unexpected, the amygdala will respond more strongly to the happy faces. The amygdala also helps register the personal relevance of a stimulus at a given moment. For example, one study revealed that hungry subjects manifested more robust amygdala responses to pictures of food than did their nonhungry counterparts.1

This amygdala example illustrates the problem of reverse inference, which is a problem that plagues the popular media. Reverse inference is the common practice of reasoning backward from the neural activation viewed in an image to subjective experience. The problem is that brain structures rarely perform single tasks, so one-to-one mapping between a given region and a particular mental states is highly prone to error. So “When Jeffrey Goldberg views a picture of Mahmoud Ahmadinejad and his ventral striatum lights up like a menorah, some investigators might think, ‘Well we know that the mental striatum is involved with processing reward, so this subject, with his activated mental striatum is experiencing positive feelings for the dictator’”2 This would be true only if the ventral striatum exclusively processed the experience of pleasure. But novelty can also stimulate the ventral striatum.

1ibid

2ibid

© Douglas Griffith and healthymemory.wordpress.com, 2013. 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.

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.