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Neuroscience
Your Amygdala May House Both Positive and Negative Memories
Positive and negative memories are stored in different regions of the amygdala.
Posted October 17, 2016
A new study on mice from the RIKEN-MIT Center for Neural Circuit Genetics has pinpointed 'positive' neurons housed in the back of the amygdala and 'negative' neurons located in the front of the amygdala. This groundbreaking discovery was published today in the journal Nature Neuroscience.
The researchers also discovered that neurons towards the front (anterior region) of the amygdala play a role in regulating behaviors tied to negative emotional responses; neurons in the back (posterior region) of the amygdala respond to positive stimuli.
Pleasant experiences, tastes, and smells appear to be housed in specific neurons in the back of the basolateral nucleus (BLA), while unpleasant, traumatic, and fearful memories are stored in specific neurons at the front of the BLA. The researchers conclude that the basolateral amygdala plays an important role in associating negative and positive stimuli and appropriate response behaviors.
Although this study was on mice, it's likely that our amygdala works the same way. From a human perspective, memories that make you feel good—and lead to positive reward behaviors—may also be stored in a separate part of your amygdala than traumatic memories of pain and suffering that elicit a fear response.
Neurons of the Amygdala Have Different Shapes, Sizes, and Genetic Distinctions
Most interestingly, opposing positive and negative neurons in the amygdala were found to be both physically separated and genetically distinct. The positive and negative BLA neurons differ in shape, size, and electrical properties.
For this experiment, positive neurons were activated by exposing mice to pleasant smells, companionship, and water rewards. Negative neurons were activated by subjecting mice to unpleasant smells, isolation, or the pain of a foot shock. These positive or negative experiences left an imprint in the amygdala marked by a higher expression of the c-Fos gene.
The positive and negative neurons in anterior and posterior regions appear to engage in a tug-of-war which either leads to reward-seeking behavior or fear-based responses (such as freezing in place) depending on which neurons are emitting a stronger signal.
Through classical conditioning, the mice were trained to respond to footshocks by either freezing in place (the negative behavior) or to perform a nose poke to receive a dose of water (the positive behavior).
Then, using optogenetics—a method used to turn genetically tagged cells on and off with light—the researchers could weaken these positive and negative conditioned behaviors by targeting neurons in either the anterior or posterior BLA. For example, the expected freezing behavior was reduced by optogenetic light stimulation of positive neurons during the footshock training.
On the flip side, the activation of negative neurons impaired the mice from completing the water reward seeking task. Like a teeter-totter, optogenetic manipulation showed that the more robust positive or negative neurons could drown out their polar opposite within the amygdala and become dominant, as the polar signal became increasingly weaker.
The signal strength of the positive and negative neurons reflected how well mice learned a specific reward behavior associated with positive neurons or fear-based behavior associated with negative behaviors.
Based on these findings, it appears that anterior and posterior BLA neurons have the power to override a hardwired conditioned behavior such as the freezing response if they were turned on or off using optogenetic light stimulation in a laboratory.
Lastly, when the positive and negative neurons activated via optogenetics were genetically profiled by the RIKEN-MIT researchers, the team found two distinct genetic markers: Rpso2 for negative neurons and Ppp1r1b for positive neurons. Rspo2 was observed almost exclusively in the anterior BLA, whereas Ppp1r1b was concentrated in the posterior BLA.
My Life as a Human Lab Rat: Neuroscientific Hypotheses on Amygdala Neurons from an Athletic Perspective
My father was both a neuroscientist and my tennis coach. As a young adult, I began to approach sports—and practicing relentlessly to improve my athletic prowess—through the lens of neuroscience. For example, my father believed muscle memory was held in the cerebellum (Latin for "little brain"). He would constantly say to me, "Chris, think about hammering and forging the muscle memory of your Purkinje cells with every stroke."
As an ultra-endurance athlete, I subjected my body to extreme conditions and transversed unfathomable distances—such as running six marathons on a treadmill nonstop in 24 hours and completing the Triple Ironman in 38 hours and 46 minutes. I've always considered myself a human lab rat. Through trial and error, I learned how to apply neuroscientific research conducted in a laboratory to my daily athletic process.
Making the leap from empirical animal studies on mice to a human interpretation based on anecdotal life experience is always going to be speculative and riddled with conjecture. Please maintain a healthy skepticism while reading various ways I've used my imagination to apply neuroscience to sports and competition.
That said, when I read about this new study on mice getting footshocks—and how the RIKEN-MIT researchers used optogenetics to turn positive and negative neurons in the anterior and posterior amygdala on and off—the first thing that came to mind were some of the psychological tricks I used to reframe negative and painful experiences as an ultra-endurance athlete.
For example, I always visualized two bins that housed positive or negative emotions in my brain. One bin was for ‘warm fuzzy’ thoughts that made me feel good; the second bin was for ‘cold prickly’ feelings that made me feel bad. Deciding which bin something belonged in was very black and white, with zero shades of gray.
As an athlete, every physical sensation, thought, smell or emotion that I encountered while training and competing for ultra-endurance sports was tagged as either positive or negative and delegated to a specific bin. Everything that I tagged as being negative was immediately relegated to a big garbage disposal in my brain and obliterated.
The reason I always spray myself with copious amounts of Coppertone on cold and rainy days when I have to train outside is because the smell of sunscreen reminds me of bright sunshine and clear blue skies. This positive association puts me in a good mood and counters the negativity of bad weather on a neural level. This fortifies my reward-seeking behavior.
After reading this new study from RIKEN-MIT, I have a hunch that the Coppertone scent turns off the negative BLA neurons in my anterior amygdala and pumps up the volume of the positive neurons and Ppp1r1b in my posterior amygdala.
Although it's just an educated guess, I believe the smell of sunscreen boosts the positive neurons in my posterior amygdala (much like the researchers did with optogenetics) and allows these neurons to win the tug of war against the negative neurons in the anterior region of my amygdala. Again, to be clear, this is conjecture on my part.
Another way of letting go of negativity are various visualization techniques I used to flush away any pessimistic or cynical thinking that entered my mind while running, biking, and swimming extreme distances.
For example, during long-distance competitions, if I ever had a negative thought try to take hold in my brain, I would visualize the neurons associated with that mindset coated in Teflon and covered with Crisco. This visualization made the neurons associated with a neural circuit of negative loop-like thinking so slippery that it couldn’t stick to my consciousness. Once I let it go, I could literally feel the negativity slip sliding away. Conversely, I would imagine that positive emotions and joyful feelings were covered in Velcro and super glue, which made them stick.
Music is also a valuable tool for tuning out negativity. For example, every time I was near the end of the 7.2 mile nonstop swim during the Triple Ironman it felt as if my muscles and tendons were being ripped away from the bones in my upper body with every stroke. To counter this pain, I would start humming "Cherish" by Madonna, pretend I had a mermaid tail, and begin kicking to the rhythm of the song like a metronome. This always put me in a good mood, silenced the negative neurons in my brain, and made my legs feel turbocharged. It also took the strain off my upper body and allowed me to complete the 7.2-mile swim.
While reading about the painful footshocks the mice experienced in their cages during this experiment, I felt empathetic to their pain. I’ve been there myself. Every time I run the 135 mile nonstop Badwater Ultramarathon (often referred to as “the world’s toughest footrace”) through Death Valley in July—when temperatures reach 130° F and the pavement is hot enough to fry an egg upon—I get excruciatingly painful blisters that cover the soles of my feet.
One year at Badwater, the soles of my feet became two giant blisters filled with fluid that went from my heels to my toes. By mile 90, with 45 miles left to go, every step felt like I was walking on red hot burning coals.
In order to keep moving forward and reach the finish line, I had to come up with a psychological way to turn off the part of my brain that associated the footshock of my sneakers hitting the pavement with being a negative experience. I had to use my imagination and creativity to reframe the pain as something positive and drowned out the neurons that would lead to a 'freezing' response that would prevent me from finishing the race.
So, I decided that instead of stepping timidly or light footed I would do the opposite and pound my feet into the ground harder and harder. Instead of having an inner-dialogue of “OUCH! That hurts!!” I would stomp my feet into the blistering hot pavement and say, “YES! Bring it on!!” as I charged ahead.
While reciting this mantra, I would also imagine that the jolt of pain signified a source of energy coming up from the core of the earth and filling my body via the soles of my feet. I consciously flipped my thinking 180° to associate the negative pain as being a positive source of energy being transferred to my body that I welcomed and embraced.
Using this explanatory style, my burning feet became a conduit that allowed my body to tap into an infinite energy Source that propelled me forward to the finish line. I know it sounds masochistic and kind of woo-woo, but it worked. I used the same visualization to break a Guinness World Record by running 153.76 miles on a treadmill in 24 hours.
After reading this study from RIKEN-MIT, I realize now that these visualizations and explanatory styles I used to rid my brain of negativity were probably techniques that turned off the front of my BLA by activating Ppp1r1b concentrated in my posterior amygdala.
Of Mice and Men: Applying Animal Studies to Our Human Experience
Although it’s an educated guess, I suspect that from decades of ultra-distance training and competition I mastered the ability to turn BLA neurons in the anterior and posterior portion of my amygdala on and off much like the RIKEN-MIT researchers did using optogenetics.
Hopefully, my first person narrative and life experiences—combined with empirical evidence—will inspire you to pursue creative ways to boost your pragmatic optimism without becoming a Pollyanna. The latest research suggests that it's possible to avoid dwelling on the negative and overcome fear-based conditioning by pumping up the signals rooted in the positive BLA neurons seated in the back of your amygdala.
© 2016 Christopher Bergland. All rights reserved.
