Let's Explore our Memory: Some Memory Disorders

As I said in the ending part of yesterday's blog-isode, there are some lesions(damages of tissue) in the temporal cortex, particularly in the hippocampus and other structures near the base of the brain, which causes a memory disorder called anterograde amnesia.

Source

In this unfortunate situation, the patient most at times has very little trouble remembering what he had learned prior to the injury. The main challenge is in learning something new after.

Such lesions can occur in many ways. They are found in certain chronic alcoholic patients who suffer from what is called Korsakoff syndrome. The syndrome was named after the Russian physician who first described it.

In a famous case in neuroscience, there was a tragic side effect of a neurosurgery that was intended to minimize seizures in H.M(a particular patient with severe epilepsy). H.M.'s hippocampal lesion occurred when he was twenty - nine. After the surgery, he had a normal memory span. But he seemed to be incapable of adding any new information to his long - term storage .

He most of the times could not recognize any one he had not met before the surgery, no matter the number of times they met afterward. He was also not able to find his way to the new house his family moved into after his operation.

In a rather disturbing moment, when he was told that his uncle had died, he was deeply moved, but then forgot all about it and repeatedly asked when his uncle would come to visit. Every time he was told again about his uncle's death, his sadness was just as strong as the first time. Each time felt like it was the first time he heard the news.

H.M.'s ability to make new memories was almost completely gone after the operation. However, he could still remember things from before the surgery, especially events that occurred more than a year or so earlier.

He could still read, write, and have lively conversations. His ability to think and understand things intellectually was not affected in many ways.

This often happens to patients with damage to the hippocampus and related systems. For example, Korsakoff's first patient could still play chess well, even though he couldn't remember how the pieces got to their positions on the chessboard.

H.M.'s problem showed that his short-term memory was normal, but he couldn't move information from the short-term to the long-term store(memory).

But there are some patients with brain lesions whose problem is quite the exact opposite.

One such patient with this kind of issue showed some mild aphasic symptoms(language disorder), but no general intellectual impairment . His problems were with the short-term memory. He could remember only about two things, and in recall tests, he had a significantly reduced ability to remember recent information( diminished recency effect as we saw in yesterday's blog-isode).

However, his ability to remember things over the long term(long-term memory) was mostly normal, as demonstrated by different memorization tests. This appeared to confirm once again that there is a difference between the short-term and the long-term memory.

Now lets consider this:

Stage theory says that for things to go into the long-term memory, they first need to go through the short-term memory. But, as we know, short-term memory can only handle a few things at once. So, with this limit in capacity, how do we put a lot of information into long-term memory?

Stage theory suggests that the solution is to organize information. The loading platform can handle only a small number of packages, maybe around 7 plus or minus 2. However, what's inside these packages depends on how we organize them. If we can arrange the information more efficiently, we can fit more details into the same number of memory units.

For instance:

This is a very popular example: lets imagine someone trying to remember a series of numbers they heard once:

1 4 9 1 6 2 5 3 6 4 9 6 4 8 1

If they think of these as twelve separate, unrelated digits, remembering them is likely to be difficult. But if they notice a pattern

1 4 9 16 25 36 49 64 81

then now the task has become super easy. You see, in this instance, the only have to remember the relationship that exist between the figures.
"the squares of the digits from 1 to 9,"

and they can easily recall all fifteen numbers in the series.

Here's another example with letters:

C I A F B I I B M T W A

It's quite challenging if you see it as twelve unrelated letters. But, if you rearrange it into three-letter groups, like CIA FBI IBM TWA, remembering it becomes very easy. In both cases, the person has reorganized the material to be remembered. This is known as "chunking," where each chunk requires a similar amount of memory as the smaller units within it. However, when unpacked, each chunk provides much more information.

Break time guys:

A little memory Game for fun😊:

As kids, much of the process of grouping items into larger chunks (often called chunking) happened. As adults, we perceive a word as a complete and meaningful unit, not just a string of sounds. Memory for sentences involves even higher levels of organization. While the memory span for unrelated words is around six or seven items, we can easily recall a fairly long sentence after hearing it just once. This holds true even for sentences that might not make much sense, like "The enemy submarine dove into the coffee pot, took fright, and silently flew away." Despite consisting of fourteen words, it clearly contains fewer than fourteen memory packages; for example, "the enemy submarine" is essentially one unit, "took fright" is another, and so on.

The Bus Stops Here for today:

Thanks for joining me again in today's blog-isode. I hope you found it as interesting as yesterday's. I always appreciate hearing your thoughts on these blogs because I love doing this, and I want to ensure you enjoy reading. Until tomorrow, stay safe, friends.