Research Hit: Exercise Helps in Forgetting Traumatic Memories - and Addiction
Exercise promotes growth of new neurons, rewires the brain, helps to forget traumatic memories, and improves generalised fear - in mice.
That’s a bunch of positive things you mention - but only in mice as you said!?
Yes, it is a bunch of positive things but all very promising - particularly for those who suffer from PTSD.
Yes, I report often on research into mice and animal models - it is the first step but often gives us very, very important insights into the precise functions of the brain in certain contexts.
Ok, and what was happening and how can this help those with PTSD or other fear disorders?
This paper just out by Fujikawa et al. was a collaboration between the University of Toronto, Canada, and Kyushu University of Japan. The title says it all:
“Neurogenesis-dependent remodeling of hippocampal circuits reduces PTSD-like behaviors in adult mice.”
You’ll have to explain that to me!
First of all, this research was specifically focused on PTSD symptoms. The standard treatments are therapy and anti-depressants. These researchers wanted to explore the impact of exercise.
It is well known that exercise is great for mind and body - and specifically that exercise induces changes in the brain and stimulates brain growth particularly in the hippocampus. The hippocampus, as you may know, is an area that is critical for memory formation.
Ok but that is help in forming new memories - how do you wipe out bad memories?
So, first let’s understand that neurogenesis is the formation of new brain cells - it is only relatively recently that it was discovered that we can indeed produce new neurons. But only in limited areas in the brain and in limited quantities - but still fantastic to know.
One of these areas is in a region of the aforementioned hippocampus. This is important for forming new memories but the current thinking is that integrations of new neurons into circuits can disrupt circuits and hence also enable or encourage forgetting.
And it is precisely this that Fujikawa et al. wanted to investigate. Can exercise induced neurogenesis disrupt previous traumatic memories?
Sounds fascinating - but how did they traumatise these poor mice?
Indeed poor mice - but remember lab mice generally have very good lives compared to their wild cousins.
First, they gave the mice a shock when entering from a light compartment into a specifically scented dark compartment (to make it unique). They repeated this in another dark compartment with a different scent.
This was to stimulate “trauma” to specific locations. They then started exhibiting PTSD like behaviours such as impaired sleep and lower sociality.
But didn’t they naturally recover from this?
Well, they could have but the design was to simulate trauma - and indeed a month later they still exhibited these behaviours, fear of entering the original locations of shock, but also of other dark locations suggesting that they were exhibiting generalised fear.
Ok, and what did exercise do then?
These traumatised mice were then split into two groups with one group having access to a running wheel. After four weeks the running wheel group had a higher number of new neurons, and critically, their PTSD-like behaviours improved.
What’s more in a group of mice who were given access to a running wheel between the two shock moments this seemed to inhibit PTSD-like symptoms appearing.
Sounds promising but is this due to the neurogenesis or something else?
Good question, exercises induces all sorts of metabolic changes so it could easily be something else such as elevated mood or generally reduced stress.
To investigate whether this was due to neurogenesis they then turned to optogenetics: activating neurons and networks with lasers, but also genetic engineering. They could therefore turn up the neurogenesis in shocked mice. What they found is interesting - the neurogenesis did shorten the time to forget the traumatic memory but it was not as effective as the exercise. Also general anxiety was not reduced.
This shows that some of the effect of this is directly due to neurogenesis but the reduction of PTSD symptoms was accelerated by exercise - probably due to its multiple other positive effects on the brain, mood, and body.
Oh, wow - good to know! What about addiction that you mentioned
Well, they also wanted to see if this could affect addiction - with the assumption that this is almost the opposite of PTSD i.e. a positive experience and positive memory encourages people to engage in repeating the same activity.
They repeated the experiment with different mice but instead of a shock they used cocaine in two different locations.
What drugged up mice! What happened?
See, I said lab mice could have it good (if you consider cocaine use positive that is!?).
But what was surprising is that they visited the cocaine location less often after exercise - also giving strength to the forgetting hypothesis. As already mentioned it could also be because of the other positive benefits of exercise reducing the need for that cocaine hit.
Wow, so exercise improves a lot of stuff
Well, I have reported on its positive benefits previously - and many others have noted that it should be mandated for many reasons. Exercise improves just about everything in life: brain growth, cognitive function, mood, general health, etc.
But for us it is another very useful reminder to get our daily, or regular, dose of exercise.
Indeed, here’s to growing more brain cells and reducing any traumatic memories!
Some other posts on the benefits of exercise:
Reference:
Risako Fujikawa, Adam I. Ramsaran, Axel Guskjolen, Juan de la Parra, Yi Zou, Andrew J. Mocle, Sheena A. Josselyn, Paul W. Frankland.
Neurogenesis-dependent remodeling of hippocampal circuits reduces PTSD-like behaviors in adult mice.
Molecular Psychiatry, 2024
DOI: 10.1038/s41380-024-02585-7