Memory engram

Most animals do not learn as we do. Their behaviors are guided by powerful instincts. Some instincts are activated by hormones, others are dormant memories encoded on a genetic level. These memories are called engrams, and today I want to explore this subject. For more reading check out here.

Memories can be encoded into DNA!

We do not fully understand how, but some memory formation may change chromatin structure and allow access to DNA itself. This is how scientists report the epigenomic event: “The formation and preservation of memory is a very delicate and coordinated event that spreads over hours and days, and might be even months—we don’t know for sure. During this process, there are a few waves of gene expression and protein synthesis that make the connections between the neurons stronger and faster.”

The whole epigenome engineering field is very exciting. Scientists want to treat cancer and Alzheimer’s by editing the genome using specific agents. The understanding that our bodies do something similar is very strange. Passing memories from one generation to another through genes has been speculated for a century, but understanding the exact mechanism so far has been challenging.

Are memories physical?

Due to neuroplasticity and complexity of the human brain, we do not really understand the physical layer of memory storage. It is beyond the strength of synaptic connections.

I quote:

One of the first ventures on identifying the location of a memory in the brain was undertaken by Karl S. Lashley who removed portions of the brain in rodents. In Lashley’s experiments, rats were trained to run through a maze and then tissue was removed from their cerebral cortex. Increasing the amount of tissue removed increased the degradation of memory, but more remarkably, where the tissue was removed from made no difference.

Basically, there are many kinds of memory, and they are stored differently in cerebellum, striatum, cerebral cortex, hippocampus, and amygdala. Each part of the brain forms the memories slightly differently. Some parts of the brain store memories in a very distributed way, others are more selective.

The genetic memory of languages

The ability to generate and use languages is genetically encoded into us. However, there is no genetic predisposition towards the phonemic makeup of any single language. Children in a particular country are not genetically predisposed to speak the languages of that country. There is scientific evidence of a gene for the perfect pitch which is more common in Asian countries where the pitch is critical to the meaning of a spoken word.

Experimentation with humans is hard for very reasons. Experiments with mice are easier. The smell is a very strong and primal knowledge. In a very interesting experiment, mice running through maces were taught to fear a certain smell, which is usually neutral. This ability eventually was passed to their offsprings. Even without exposure to that unpleasant smell, the descendants of the mice taught to fear it expressed a visible fear of the smell.

There are theories of fear of snakes and infants crying being a genetic memory passed to us from our ancestors.

Instincts

By definition: a behavior that is performed without being based upon prior experience (that is, in the absence of learning), and is, therefore, an expression of innate biological factors. Examples include animal fighting, animal courtship behavior, internal escape functions, and the building of nests. 

Now, we can override our instincts in certain situations, but so can some animals after specific training. In a way, instincts are behaviors learned by ancestors, genetically passed to their offsprings, and often readily available for further modulation based on new environmental cues.

There is a strange text by the prophet Ezekiel in the Bible: “The fathers have eaten sour grapes and the children’s teeth are set on edge.” Somehow this assessment is now scientifically justified.

Three laws of genetics

Mendel’s Laws of Heredity are usually stated as:

1) The Law of Segregation: Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring, therefore, inherit one genetic allele from each parent when sex cells unite in fertilization.

2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.

3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.

Some of us learned these laws in school… While these laws used to serve scientists for more than a century, there is a growing body of examples when Mendel’s laws no longer apply. Mendel performed his experiments on pea plants, not even mice.

Memory formation is one of the “exceptions” to Mendel’s laws… As pea plants do not necessarily have a memory one can test. There is a whole field of study called non-mendelian genetics. For example, most real-world characteristics are determined not just by genotype, but also by environmental factors that influence how genotype is translated into phenotype.

This is very similar to the way we learn first classical physics with three laws expressed by Neuton, and then learn two more physics for relativity in large scales and for quantum phenomena in small scales.

How much data can we pass in DNA?

I quote:

In March 2017, Yaniv Erlich and Dina Zielinski of Columbia University and the New York Genome Center published a method known as DNA Fountain that stored data at a density of 215 petabytes per gram of DNA. In June 2019, scientists reported that all 16 GB of Wikipedia have been encoded into synthetic DNA.

So it is safe to assume that hundreds of gigabytes can be encoded into one chromosome, and we have 23 pairs of chromosomes. That would encode something similar to the capacity of your computer’s hard drive.

Babies know more than we think

Absolute pitch shows genetic overlap with music-related and non-music-related synesthesia. About 20% of people with perfect pitch are also synesthetes. Speakers of Sino-Tibetan languages have been reported to speak a word in the same absolute pitch (within a quarter-tone) on different days; it has therefore been suggested that absolute pitch may be acquired by infants when they learn to speak a tonal language. By the age of 10 months, an infant either keeps this ability or loses it! People of East Asian ancestry who are reared in North America are significantly less likely to develop absolute pitch than those raised in East Asia…

Now, language is not the only knowledge we may lose as we grow. Some infants have innate swimming ability. A reflex called the bradycardic response makes babies hold their breath and open their eyes when submerged in water.  Until around 6 months, babies placed in water tummy down reflexively move their arms and legs in a swimming motion, which makes them look like natural swimmers. A baby is not a natural swimmer and may drown though. After the age of a year, the risk of drowning actually grows, as some of the instincts switch off.

In Mongolia, babies learn to ride horses as soon as they walk. I did not find epigenetic research about it. I found various researches on “equine athletics”, showing that very young horses have an instinctive understanding of their disciplines. Racers control their breath and heart rate, jumpers do not fear obstacles and jump over them, quarters show sliding stop – before they were taught how to do the trick!

What is in it for me?

While this subject is very interesting, I do not believe you can practically benefit from it just yet. It’s not like Jews have an instinctive fear of trains: I used trains and it feels fine. If your child does not speak Cantonese it is probably not because you passed him a wrong set of genes. Maybe in the future babies will instinctively do the math  – I can only speculate about that. Currently, the relevant subjects are in the pure research stage. I do recommend you to keep an open mind regarding what people or animals can or cannot do…

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