«The future belongs to the one with the longest memory. »
Friedrich Nietzsche
We will first study the emergence of memory during evolution, then in humans, from the embryo to adulthood.
Then we will look at the memory capacities of plants,
impressive for living beings deprived of strict nervous system.
3.1 Animals
All animals are endowed with memory, from the first
unicellular organisms, then worms, cephalopods or insects to vertebrates, to culminate in man.
Invertebrates
Physarum polycephalum
The blob, a unicellular with a complex genome, preserves its learnings for more than a year and transmits its acquired knowledge by merging with its congeners.
Dugesia japonica
The flat worm with many stem cells survives beheading.
Amputated, it forms a new head finding back its previous memory intact.
Apis mellifera
The bee also has developed learning and memory skills,
allowing it to orient itself in-flight, associate colors and even recognize faces.
Octopus vulgaris
The octopus, with its central brain, has remarkable learning and memory skills.
He may observe and copy his congeners or adopt the
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appearance of other animals to camouflage himself.
Vertebrate
Amatitlania siquia
The cichlid is a fish living as a couple. It has an emotional memory, the females experiencing grief to the loss of the spouse.
Parus majors
The great tit is endowed with a procedural memory and capable of learning by mimicry.
In England in the 19th century, many of them attacked the milk bottles placed on the door sill, imitating each others.
Psittacus erithacus
The parrot Alex learned during his life to distinguish 50
objects, counting up to 6 and had a vocabulary of 150 words.
Sciurus vulgaris
Squirrels hide their food in the ground in different places to feed in winter and can collect it even after the deodorization of its caches.
Pan troglodytes
The chimpanzee has an amazing immediate memory. At the
Primate Institute in Kyoto, Ayumu can render a series of 19
digits before the human eye can see them all.
Summary
The simplest animals yet devoid of neurons, already possess some form of memory.
Memory is therefore neither the prerogative of man, nor of vertebrates, nor even of animals endowed with a primitive brain.
The more animals evolve, the more their memory develops, 31
becomes more complex and effective in short and long term.
3.2 Humans
We receive thousands of information daily, corresponding to hundreds of events, the most striking ones are recorded.
Memory development in children
At the end of the pregnancy, the child memorizes the auditory experiences. The newborn remembers smells inhaled in utero.
At 5 months, the infant recognizes images that were presented to him a few weeks before.
At 1 year the long-term memory appears, at 16 months the child remembers the facts dating from 6 months and even from one year to 20 months.
At 7 years the child can memorize alternating sequences of numbers and letters.
Remembrance formation
The creation of a memory can be divided into 6 stages, 2 years being necessary for its definitive consolidation.
Attention
Either the brain targets its attention on a single event, recording a multitude of information or it captures simultaneously several but superficially.
The frontal lobe targets the object of attention and the thalamus supports neuronal activity at a high level.
Emotion
Emotion increases attention, therefore emotionally rich
experiences are memorized in priority.
First unconscious, the stimulus arrives at the amygdala*
inducing an emotional response long before we react.
Then the amygdala keeps the emotions active, contributing to a 32
Sensation
The majority of memories come from sensory experiences,
with olfactory, gustative and visual perception forming the substrate of remembrance.
The conscious perceptions form in the associative cortical aeras, the more intense the sensations, the more likely they are to be recorded.
Working and short-term memory
Working memory manages temporarily visual or sound
information, allowing its processing.
Short-term memory allows you to retain and reuse a limited amount of information for up to one minute.
It is a gateway to long-term memory.
Role of the hippocampus
The hippocampus encodes the most striking experiences by sustainably strengthening the synaptic efficiency of its neurons.
The essential data is then sent back to the initial brain regions, as an echo of the initial event.
Consolidation
During consolidation, the neural patterns established between the hippocampus and the cortex are reactivated repeatedly until the information is transferred to the latter.
This period is spread over 2 years, takes place during slow sleep and frees up space in the hippocampus.
Child amnesia
With the exception of a few unconscious memories, we have no conscious remembrance of our first 2 years.
For neurobiologists, the childhood amnesia is due to the 33
progressive hippocampus maturation between 2 and 7 years.
In childhood, every second more than a million neurons are generated and hundreds of thousands of synapses are replaced.
The appearance of new neurons allows new learning but at the expense of the older ones erased.
Autobiographical memories require self-awareness and remain fragile as long as the child does not master his mother tongue.
At the cellular level
Using fluorescent RNA* in mice, A.R.Buxbaum showed that
the hippocampus stimulation induced the synthesis of β-Actin*.
In stimulated neurons, mRNA induces the production of this dendrite protein, thus participating in the creation of memory.
Summary
Before birth, the child memorized certain experiences and at one year, his long-term memory appears.
Attention, emotions and sensations are the driving forces behind the formation of remembrance.The β-Actine
participates by strengthening the synapses of the hippocampus.
The appearance of new neurons allows new learnings but at the expense of the older ones erased.
2 years are necessary for the definitive consolidation of memory, transferring information from the hippocampus to the cortex during sleep.
The slow maturation of the hippocampus would explain the child amnesia disappearing around the 7th year.
Awareness of own existence is a prerequisite for
autobiographical memories.
3.3 Plants
Plants are able to record facts or acquired knowledge.
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The flytrap closes its jaws when two hairs are touched less than 20 seconds apart, meaning that it remembers the first contact.
In the medium term
Throughout the day, the flowers of the sunflower follow the course of the sun, repositioning itself at night to the East, anticipating its position at the next sunrise.
Long-term
After a few learning sessions, the sensitive remembers the absence of risk when falling on a dampening mat.
She remembers this information for a month, during which time she does not fold her leaves while falling.
Summary
Memory capacity is an integral part of plant intelligence.
Without a complex nervous system, plants nevertheless have short-, medium- and long-term memory.
3.4 Conclusion
The simplest animals yet devoid of neurons, already possess some form of memory.
Attention, emotions and sensations are the driving forces behind the formation of remembrance.
Before birth, the child memorized certain experiences and at one year, his long-term memory appears.
The progressive maturation of the hippocampus explains the childhood amnesia observed in early childhood.
During sleep, neural patterns are transferred from the
hippocampus to the cortex, consolidating memories.
Without a complex nervous system, plants nevertheless have short-, medium- and long-term memory.
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