WHAT IF YOU COULD REVERSE MEMORY LOSS by washing your brain in the liquid of someone younger? If this sounds like science fiction, you may be surprised that scientists reversed memory loss in mice by injecting them with a brain liquid from younger peers.

Today we learn how that substance — cerebrospinal fluid or CSF — washes in and out of our brain tissues in waves, helping to remove waste products. The cerebrospinal spinal fluid also bathes our brain with proteins or growth factors, facilitating normal development.

Decay theory of memory fading

When we learn something new, we create a neurochemical memory trace. The decay theory posits that our memory fades secondary to the passage of time, with information becoming less available for later retrieval as time goes by; the memory strength simply wears away.

Columbia University (USA) psychologist Edward Thorndike first coined the descriptor “decay theory” in The Psychology of Learning in 1914. Active rehearsal of the information can counteract the memory fading.

Memories fade like old photographs

Why do our memories, like old photographs, fade in quality over time? Not only do our recollections become less accurate over time, but we also experience decreases vibrancy and other visual qualities.

Are you like me? I sometimes have a memory that feels like I am reliving the moment. On other occasions, the details are remarkably fuzzy. An example of the former? After I had an emotionally significant event, getting engaged at New York’s Rainbow Room at Rockefeller Center, I have a good recall of the event, but everything has faded in my mind.

As events are forgotten or stored in memory, Boston College researchers wondered how their visual features evolve? Study participants reported changes in their memories akin to using a filter to edit a photograph on Instagram.

The researchers went a step further, inquiring if forgetting is similar to applying a filter to our experiences and whether the emotional significance of the event would change which filter we apply.

Here are the findings, as detailed by study author Rose Cooper:

“Memories seem to fade literally: people consistently remembered visual scenes as being less vibrant than originally experienced.” She continues, adding, “we had expected that memories would get less accurate after a delay, but we did not expect that there would be this qualitative shift in the way that they remembered them.”

Furthermore, negative emotions study participants experienced when viewing images raised the chances that they would accurately recall the images but did not influence memory fading.

In summary, the researchers discovered that the vibrancy of low-level details — colors and shapes, for example — fades in memory while we keep the general gist of the experience.

The fading appeared less for memories subjectively rated as more robust. Emotional memories did not influence the fading amount but did impact the likelihood with which the subjects remembered an exposure. My Rainbow is recalled, but not vividly.

What drives the memory fading? Do we forget over time, or is new material interfering with new information?

Cerebrospinal fluid basics

Researchers recently reversed memory loss in mice by injecting them with a brain fluid from younger peers. First, let’s take a quick look at that fluid, or cerebrospinal fluid (CSF).

The CSF is a body fluid surrounding the brain and cushion in the skull. Maiken Nedergaard and colleagues discovered that cerebrospinal fluid also acts as a lymph system in the brain.

Via a series of elegant experiments analyzing mice brains, the researchers visualized cerebrospinal fluid entering and flowing through the brain, ultimately draining into the same ducts used by the lymphatic system of the rest of the body.

The cerebrospinal fluid clears harmful amyloid-beta from the brain. The substance is associated with Alzheimer’s disease and other neurological conditions. While Nedergaard and co-investigators honed in on this protein, other leftover proteins are likely also removed.

In summary, cerebrospinal (spinal) fluid washes in and out of the crevices of our brains in waves. The process is central to waste removal.

Reversing memory loss in mice

Researchers reversed memory loss by injecting cerebrospinal fluid from younger mice peers.

Using a tiny tube and pump, the scientists infused cerebrospinal fluid from young adult mice into the brains of 18-month-old animals — the equivalent to about 60 years for humans — over seven days.

Imaging revealed higher levels of myelin, a fatty sheath that covers and protects nerve cells from damage. The injections led to practical changes, too: The elderly mice improved at a fear-conditioning task. The refreshed mice remembered a tone, and a flashing light meant a small electric shock was coming.

Growth factors and memory rejuvenation

Growth factors that can restore nerve cell function are the likely agents of memory improvement. Stimulated cells — oligodendrocytes — made more myelin, creating stronger connections between the nerve cells.

Genes normally expressed in oligodendrocytes appeared revved up or upregulated in the old mice who had received cerebrospinal fluid from young mice.

The researchers also found changes in gene expression in a structure important for memory, the hippocampus. The gene Fgf17 decreases activity with age; the CSF infusion restored function.

This research is stunning. With all of the troubles in the world, it is heartening to see brilliant scientists opening doors to a future where we may be able to improve memory. It is also disturbing. I hope we someday don’t go down this road; gene editing sounds much more appealing to me, especially for those with dementia.

Until we get a drug targeting memory in humans, I will continue to focus on a healthy diet, adequate sleep, regular physical activity, limiting alcohol consumption, and challenging my brain with activities such as my new Haydn Piano Sonatas.