Author Archives: Kenzo Le Vaillant

Everybody forgets. But how?

Accessible Science

Everyone forgets and for many different reasons.

This is the first part of a study of the article

The Seven Sins of Memory by Daniel L. Schacter

There are seven problems our memory has. The seven can be divided into 3 groups. The first group, includes the different types of forgetting.

Forgetting

The first way we forget is called transience.

This is simply about how a memory becomes harder to retrieve over time.

This effect is stronger if the information is less frequently used.

This shows the importance of rehearsal as it prevents the synapses from becoming weaker which is the cause of transience.

The mechanisms of short term and long term memory are not the same.

For example, people who cannot create long term memories due to injuries or illness have been able to perform well on tasks requiring short term memory.

However, transience happens in both short term memories and long term memories.

The likeliness of the happening of transience may also be simply due to the brain area used.

For example, it has been shown that verbal information is better remembered when the left parahippocampal gyrus is being used, while it is less remembered when the left inferior frontal gyrus is activated.

Parahippocampal gyrus

a grey matter region that surrounds the hippocampus, an important area for the creation of memory

Left inferior frontal gyrus

a region, in the inner left front of the brain, important in language comprehension and production

Other examples are a better remembering of images by activation of the right prefrontal and parahippocampal areas

Prefrontal cortex

The part of our brain right behind our eyes. It regulates actions, thoughts and behaviour.

and impairments in functions such as language and working memory from injuries in the left parietal lobe.

Left parietal lobe

The part of the brain on the top left of our heads. It is important in the receiving of sensory information and assembling it together. It also helps us in knowing where our body parts are for smoother movements.

This means it may be possible to improve our memory by changing the way we see things into a way that uses the stronger areas.

It is said that the left parietal lobe stores information based on sound and the left inferior prefrontal cortex ( aka the Broca’s area ) participates in the rehearsal of this information.

Broca’s area

An area important in the production of speech. When damaged, the individual will have a harder time creating proper sentences and expressing what they want to.

Also, the left hemisphere ( side of the brain ) is said to be more involved in encoding of verbal information whilst the right does the same for non verbal information.

Absent-mindedness

The second way we forget is by absent mindedness.

When we don’t pay much attention to something, our brain will not be able to process it very deeply, making it a weak memory that lacks detail and is hard to output.

This often happens when we are doing things we don’t have to think much of like habits.

That is why we sometimes can’t remember what we ate minutes earlier or if we locked the door.

However, this can happen even when we pay enough attention if we don’t process it deeply enough.

This can happen if the information is less related to you or uninteresting which explains the difficulty most of us face at school in subjects we don’t like.

This can also be seen in what is called change blindness where people are not able to recognise changes that happen around them.

An experiment has shown that less than half of the participants were able to notice that the person they were talking to changed when people holding a door passed between them.

When the information is processed deeply, a stronger activation of the lower regions of the left frontal cortex was seen.

The activation of this area in addition to the left parahippocampal areas have been associated with semantic processing.

Semantic processing

Processing that enables us to understand the meaning of sounds, movements, images and more.

=Deep processing.

Absent mindedness is also when we forget to do something.

This is called absent mindedness in prosepective memories.

Prosepective memories

Memories of things to do in the future

Thay have been associated with activity in the right frontal lobe, the front part of the left frontal lobe and the center parts of the frontal lobe.

The frontal lobe playing an important role in mental time travel may make it easier to understand it’s participation in this kind of memory.

Frontal lobe

The front part of the brain, has important roles in many high level executive functions ( thoughts, attention… )

Mental time travel

The activity of imagining yourself or something in a different time.

They can be divided into 2 types.

Event based and time based. The first goes as, do X when Y happens, while the second is, do X at Y o’clock.

Event based prospective memories are externally cued ( triggered by something outside of the individual ). In this case, the forgetting is usually caused by a failure to recognise the cue.

However the time based memory depends on being able to generate appropriate cues at the right time meaning forgetting is caused by failure to generate the cues.

Older adults have been found to be better at event based prospective memories than time based ones.

Blocking

The last kind of forgetting is called blocking.

This is when we aren’t able to access the information for a certain time. This occurs in both semantic an episodic memory and we are aware of the blocking when we experience it.

One famous example of this is the TOT ( tip of the tongue ) phenomenon.

TOT phenomenon

When having difficulties remembering a known word

This phenomenon is usually resolved quickly with studies showing more than half of the cases being solved in less than 1 minute. It is said to be caused by words or names that are “ugly sisters”.

Ugly sisters

Items that are incorrectly related and keep popping up into our awareness when trying to recall the proper one.

However, it is said to become more frequent with age and to happen more with names. The brain regions associated to this phenomenon are the anterior regions of the left temporal lobe.

Temporal lobe

The part of the brain in the side of our heads, involved in encoding of memory and processing of sound.

The regions depend on what kind of information is trying to be recalled.

The research on blocking has led to the discovery or confirmation of a feature of the brain called emsemble inhibition which happens during recall.

Ensemble inhibition

The blocking of the activation of brain regions that aren’t related or used by parts that are activated during recall.

It is thought to be a necessary process of human recall.

Part 2

Part 3

Does memory storage really need plasticity or do cells remember?

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This is the third part of a study of the article:

Is plasticity of synapses the mechanism of long-term memory storage? By Wickliffe C. Abraham, Owen D. Jones and David L. Glanzman

The SPM hypothesis states the potentiation of the synapses and their changes to be where information is stored.

Potentiation

the increase in strength of the electrical signal caused by the transmission in the synapse

However, it may be possible that instead of this, the information is stored in the connection between cells in a memory circuit that are created from a learning experience.

In this case, LTP would only be needed for the retrieval of the information and not the storage.

Another argument against plasticity for storage is that proteins aren’t stable and have a half like of 2 to 5 days in the adult brain.

Also, it has been found that spines change frequently.

Spine

part of a neuron, in the shape of thorns coming from branches of the neuron, that is involved in a synapse

Though the fact that proteins don’t need to last the full life of the memory is a valid counter argument for the first.

This leads to the cell intrinsic hypothesis of memory storage. In this hypothesis, information is stored inside a cell by stable molecules instead of in a synapse.

Cell intrinsic hypothesis of memory storage

A hypothesis stating that memories are stored on the inside of a cell.

There are several potential mechanisms for it and currently, the most likely is epigenetic storage and particularly DNA methylation.

The arguments for DNA methylation are that it is relatively stable, compact and energy efficient in addition to the possibility of a large storage amount due to the high number of methylation sites on the genome.

It is believed that memory signals modify the DNA of the neuron which will change the neuron’s phenotype. This will then cause the neuron to send certain signals when receiving particular information related to the memory.

Epigenetic

Related to DNA changes that turn genes on and off

DNA methylation

The binding of a methyl group to a part of the DNA to block the transcription of the gene.

Phenotype

Observable traits.

Another suggested mechanism is that of histone modification.

Histone

a protein that creates the structure for DNA to stick to and be shaped into chromosomes ( the figure 8 )

When they bind to acetyl groups, they ease the transcription of the gene to create proteins and do the opposite when they are disconnected.

However, this is less stable than methylation making the first the more likely one.

It is also possible that the mechanism behind storage depends on the type of information and many other factors.

Part 1

Part 2