Amazing Memory

1. Memory Mysteries

Remember Ghajini, the Amir Khan starrer Hindi film released in 2008?

In the film, Sanjay Singhania (the character played by Amir Khan), suffers from anterograde amnesia after a violent attack on him. After this incident, he was unable to remember anything new and used sticky notes, whiteboards, even his own body to note down information and have it easily accessible.

In neurology, anterograde amnesia is the inability to create new memories after an event that caused amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact.

Generally, in movies/serials the character is shown to lose memories (???????? ??? ??) before an event. This is called retrograde amnesia, where memories created prior to the event are lost while new memories can still be created.

Human memory is truly amazing. In this article, we’ll try to understand what neuroscience says about our memory – types of memories, how are they formed, where are they stored, how are they accessed, and many more. We’ll also try to understand if what happened to Amir in Ghajini was pure fiction. And then we’ll talk about some interesting topics related to memory.

2. Memory defines us

Memory is what makes us who we are. Some memories are the ones we are aware of – the seminar you attended, that time as a child when you were publicly honored, knowing that peacock is our national bird, and the fact that the LinkedIn is a great place to connect!

These are known as explicit memories – ones we can consciously recall.

But there are also implicit memories, which may be even more important. For example, when you talk, you’re using motor memories to move your lips and tongue in a way that reproduces sounds you’ve learnt. When you play cricket, you’re using motor memories to coordinate movement of your body parts.

If we didn’t have memories we’d just be a body. We’ll remain unaware of how to survive in the world around us.

In short, memory is crucial in transforming us from helpless newborns into capable adults.

As an analogy, memory is as integral to our brain as memory in a computer. Our brain cannot function without memory like a computer cannot work without memory.

3. Types of memories

There are several different types of memories, some of which are fleeting, and others that last a lifetime.

The fastest kind of memory is sensory memory. It is the brief hold perception of sensory inputs. For example, when you hear something or see something, you can recall that perception for a moment. It sort of stays around in your head for a little bit. You might not even think of that as memory.

The other short-term memory is known as working memory, which can last just few seconds. This is like a temporary storage of computer, which we use to hold information in our head while we engage in other cognitive processes. For example, you briefly remember the mobile number as a friend recites it and you add it to your mobile’s contact list.

The other categories of memory are long-term.

What we typically think of as memory is explicit memory. This can be divided into

• Episodic memories, which are events that have happened in your life
• Semantic memories, which are retained facts or general knowledge.

The other type of long-term memory is unconscious, or implicit. These are memories you can’t consciously bring to mind, but which shape your behavior. The most common types are:

• Procedural - this is concerned with how actions are performed, like how to ride a bike or play guitar.
• Priming - refers to the influence one stimulus has on how people respond to a subsequent stimulus. For example: if people are asked to fill the gap in the group – BREAD, JUICE, MILK, SO_P, the answer would be SOUP. But if the group was – TOWEL, SHOWER, SHAMPOO, SO_P – the answer would be SOAP.

4. How memories are formed?

A memory isn’t something that we can find in any given neuron (brain cell). Rather memory is a result of neurons making new connections among them called Neural Pathways. The connection between neurons involves crossing over the synapse, the small gap between two neurons.

The more a neural pathway is activated, the stronger the synaptic connections along the way become. Whereas those that aren’t used get weaker and can eventually disappear entirely. This concept is known as Synaptic Plasticity.

An analogy for memory formation is the way foot traffic creates a path along a stretch of grass. The more a patch of grass is trampled as people pass along it, the clearer the path becomes and the easier it is to follow – it’s as if a ‘memory’ of all the walking has been created. The same thing happens in the brain.

5. Where are memories formed and stored?

In 1953, while treating Henry Molaison for his epilepsy, his hippocampus (a tiny organ in the brain) was surgically removed. His epilepsy was cured, and he lived a further 55 healthy years. However, after the surgery he was not able to form new episodic memories. As a result, his memory became mostly limited to events that occurred years before his surgery. Does it remind you Ghajini?

However, Henry Molaison was still able to learn new motor tasks and improve his performance on them. This indicated that although the hippocampus is crucial for laying down long-term memories, it is not the site of permanent memory storage and isn’t needed for motor memories. The study of Henry Molaison was revolutionary because it showed that multiple types of memory existed.

Neuroscience studies so far have shown that memories aren’t stored in just one part of the brain. Different types of memories are stored across different, interconnected brain regions:

EXPLICIT MEMORY

o Hippocampus – episodic memories (specific events of life)

o Neocortex – semantic memories (acquired knowledge)

o Amygdala - attaches emotional significance to memories making strong emotional memories (e.g. those associated with shame, joy, love or grief) are difficult to forget.

IMPLICIT MEMORY

o Basal ganglia and cerebellum – procedural memories (motor activities)

o The cerebellum - fine motor control

WORKING MEMORY

o Prefrontal cortex – short term memory

6. The Need for Sleep

The memories of our experiences during the day are stored in hippocampus. While we sleep, a process of systems consolidation takes place. During this, brain determines what is worth retaining and such memories are transferred to neocortex where they reside long-term. And the trivial ones are discarded. This happens during deep sleep, so if you aren’t getting enough sleep, you aren’t letting your brain consolidate memories.

7. Once A memory has been stored, how is it accessed?

According to one popular theory, the hippocampus serves as a memory index. As an analogy, it is like the catalog of a library of books where books are stored in different shelfs. We search for a book by first checking the catalog of the library which tells the location of the book and we go to that shelf to pick that book.

This idea of memory indexing and recollection is still only a theory.

9. Exceptional Memory

Some individuals have awe-inspiring abilities to remember particular kinds of information—personal experiences, historical facts, musical compositions, or others. Exceptional memory is this ability to have accurate and detailed recall in a variety of ways. These powers of memory can also appear in people who are otherwise intellectually ordinary, or who show deficits in other areas of cognitive functioning. Hyperthymesia and Eidetic Memory are examples of such exceptional memory.

Hyperthymesia

Hyperthymesia, also known as Highly Superior Autobiographical Memory (HSAM), is an ability that allows people to remember nearly every event of their life with great precision. It includes details of personal experiences, when they occurred, what he personally did, what the weather was like, or what the top news was on a randomly chosen date many years ago. The person may also be able to recall the exact dates on which various events occurred.

HSAM is rare, with only less than 100 people in the world diagnosed with it. Jill Price, a California based author, was the first person in the world to be diagnosed with it. In her late 50s, Price still remembers every detail of every day she lived since 1980. She remembers every conversation she ever had and every person she ever met in her life.

However, rather than feeling like a person with superior mind, such a person is found to feel that he is cursed. Remembering every mistake he’s ever made and unable to forget negative experiences rather than having to relive them in full pain again and again. Also, people with HSAM do not show such unusual memory for all kinds of information and they may not stand out on other cognitive characteristics.

Eidetic Memory

An eidetic memory is a mind which can recall large bits of information quickly – like remembering Pi to 10,000 digits, an entire play of Shakespeare after just one viewing, or an entire skyline of a city after just one short helicopter ride. British artist Stephen Wiltshire uses his eidetic memory for a living. He takes helicopter rides over cities, and then re-creates the cityscape from memory in incredible detail. Even going so far as to remember the exact number of windows on skyscrapers.

List of some famous people claimed to possess an eidetic memory:

• Bill Clinton, 42nd President of the United States
• Chaitanya Mahaprabhu, an Indian saint
• Nikola Tesla
• Leonardo da Vinci
• Swami Vivekananda
• The mathematician John von Neumann

Photographic memory is considered to be a visual information imprinted on the brain. Unlike eidetic memory, it is considered to be recallable over long-term. It is still considered to be an unproven phenomenon due to insufficient research.

10. Some Interesting Facts about Memory:

• The brain has an astounding storage capacity. It is estimated that it can store about 2.5 petabytes of data. That’s 2,500,000 gigabytes of data or about 300 years of television.
• Dolphins have the longest memories in the animal kingdom, next to humans. Bottlenose dolphins can remember whistles of other dolphins, even after 20 years of separation.
• Memories start forming in the womb – as early as 4 months into a pregnancy!
• Children don’t remember consistently until about the age of 4, when language skills and the hippocampus are more mature.
• People tend be able to hold only 7 +/- 2 chunks of information in the short-term memory before needing to further process them for longer storage. For instance, most people would be able to remember a 7-digit phone number but would struggle to remember a 10-digit number. This led to Miller describing the number 7 +/- 2 as a “magical” number. Some studies have even indicated a higher Miller number for a person is reflective of Higher IQ!

The concept of Miller’s number is used in design of user interface. For example, presenting large numbers as chunks of four – as in Aadhar or Credit Card. Another example is OTP – which is kept between 4 to 6 digits. And password is mandated to be more than 8 characters.

With 86 billion neurons, 400 miles of capillaries, 100 thousand miles of axons (enough to circle the earth 4 times), more than 10 trillion synapses, the human brain is truly a fascinating organ. And every day, scientists discover a new wonder hidden within the wrinkles of our brain!

Hope your brain found something more about itself today!!