Memory damage and disease

Dementia is an umbrella term for conditions
of memory loss caused by neuron damage

Frontotemporal
Frontotemporal dementia (FTD) occurs in the frontal and temporal lobes of the brain. When nerve cells here become damaged, connections can’t be made between these lobes and the rest of the brain. Damage to the frontal lobe causes behaviour and personality changes, while temporal lobe damage makes language more difficult to remember.

Alzheimer’s disease
This illness is the common cause of dementia. Memory loss worsens over time and is caused by a buildup of two proteins – amyloid and tau. Amyloids are abnormal proteins that build up along brain cells; tau causes tangles inside brain cells. This combination prevents the usual formation and retention of memories.

Vascular
This is the second most common form of dementia, caused by reduced blood supply to the brain. Vascular dementia can occur as a result of blood clots in the brain or a narrowing of blood vessels. As a result, oxygen levels in brain cells are reduced, causing damage and impairing memory circuits.

Lewy body
This form of dementia is a result of clumps of proteins called Lewy bodies forming inside brain cells. One in ten dementia sufferers has Lewy body dementia. These proteins prevent cells from communicating with each other to recall memories as they get in the way of the chemical messengers needed to do so.

Did you  know?
Temporarily forgetting something you know is called ‘blocking’

MRI scans show any changes in the
brain’s structure and function
following a severe injury

A hit to the memory

A knock to the head causing a traumatic brain injury (TBI) holds more risk than many other physical accidents, as the organ compromised is responsible for your mobility, personality and memory. A mild TBI can temporarily affect your brain cells, while a serious one has the potential to cause more long-lasting memory issues. Head trauma can cause tears or damage to the brain cell connections that send memory signals. This connection disruption can cause retrograde amnesia – the loss of long-term memories from before the accident – and makes it more challenging to form new memory connections.
A severe concussion, which results from a blow to the head that causes the brain to bounce against the inside of the skull, can result in brain tissue swelling. In these cases, the increased pressure in the head restricts blood flow and the lack of oxygen hinders memory. Finally, when cells are damaged during a head injury, the brain can’t regulate its release of chemical messengers like glutamate. Usually, glutamate helps send messages between nerve cells to aid memory. But too much can overstimulate the cells, damaging them and increasing forgetfulness.

“A mild traumatic brain injury can temporarily affect your brain cells”

How animal memories compare

Animals can remember key survival information
for a lifetime, but how long before they forget
trivial events in their working memory?

Chimpanzees

20 seconds

This suggests humans’ short-term memory developed after we evolved from our shared ancestors

25 years

Chimpanzees can retain memories of faces for
25 years

Bees

Two minutes

Bees’ short-term memory helps them navigate maze-like environments

Three days

Bees remember the location of a hive for days at a time

Crows

30 seconds

Most bird species forget short-term memories after half a minute has passed

17 years

Crows held a grudge against a human captor for nearly
two decades

27
seconds

The average short-term memory of 25 species  of birds, mammals  and bees

Elephants

Five minutes

Information is quickly dropped to keep their social and environmental memory strong

12 years

Elephants can remember  a relative’s scent for  over a decade

Humans

48 hours

Humans can recall random events for over two days

Indefinite

Our large brains can store some memories for a lifetime

Dogs

A dog will only remember the  last couple of throws in  a game of fetch

Ten years

Ingrained tricks stick with canines after a decade

Do plants have memory?

Plants don’t have brains, which means they can’t have memory in the same way humans have. However, most plants possess complex signalling systems that enable them to communicate with one another and learn from environmental triggers. One example of a plant deemed to have short-term ‘memory’ is the carnivorous Venus fly trap. The Venus fly trap has a jaw-like mouth made up of two sets of leaves that clamp shut when an insect enters.
To detect the presence of an object, the Venus fly trap has sensory hairs lining its leaves, which are bent when a fly lands on top of them. So that it can conserve energy, when a raindrop stimulates the plant’s hairs, the trap isn’t triggered, but the movement of a fly activates the snap. To achieve this, the plant has a memory of 30 seconds, during which it remembers the first point of contact with an object. A live insect will then crawl across the leaf, knocking another hair. The plant, knowing this is the second trigger by a potential meal, closes to secure its prey. In a sense, the plant is remembering a pattern corresponding to food.

When prey touches the hairs of a Venus fly trap, the plant releases calcium signals

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