Does human brain store duplicate data?

Question

There are several answers and articles about how the brain stores data, but none specifically cover whether a human's brain stores duplicate data.

I was reading in this article that a human brain can have a capacity of 1 terabyte to 2.5 petabytes. But for example, if you read a book a dozen of times, will it be stored as data several times?

Let me put it this way. When we read a book a couple of times, we remember it better. Is that because it's stored in several synapses and then retrieved better while trying to remember, or is it because reading it over and over makes the missing parts be stored?

We do recognize a familiar phrase when reading a book, which means the brain can differentiate the unknown from known. What matters is that does it decide to store it again or not? Just like a computer who refuses to save a file if the file already exists.

Answer 1

The way neuroscientists currently think about storage in the brain, it doesn't make any sense to think about "duplicate" data but rather about the "robustness" of a given memory to interference or confusion, which increases with consolidation and reconsolidation of memories or can degrade over time.

Repeated exposure can contribute to the robustness of a memory, but so can other factors such as the emotional content of a memory (which, depending on the emotional state, can increase or decrease memory robustness, and this can also vary with the "jist" versus "detail" of a memory).

Note that there are also very different types of memory, so that repetition is very important for motor plans and "muscle memory" whereas episodic memory can get lost in the repetition of daily recurrent events, such as parking your car or eating lunch: you might remember where you parked or ate today, but if you have a routine this can blur into all one memory, where you have a notion of eating at a particular restaurant many times, but you would struggle to remember specifically eating there on December 14th, 2011, unless there was some other special event on that day.

In your example of reading a book, there would likely be two types of memory: 1) memory for the episodic event of reading the book, which would be a separate memory because it is a separate event, though it could be confused with other similar episodic events. 2) Semantic memory for the content of the book: this would be a single memory, reinforced with subsequent readings of the book, and supplemented with all your other semantic experience with the content of a book: discussing the characters of a fiction book with your friends, learning about molecular genetics from a textbook and from a lecture course, etc.

Note also that talking about the "data capacity" of a human brain compared to a computer is a bit silly, because data isn't stored in the nervous system in bits, and a "fair" accounting of human memory needs to consider the vastly multidimensional interactions that are easily coded in a nervous system but not at all easily in a binary system. Note that other papers have come up with estimates that diverge greatly from the numbers you cite, for example Wang et al 2003 which gives a value of 10⁸⁴³² bits based on the number of synaptic connections. That number is truly inconceivable to our conscious experience even if it is within the capability of our brain. Clearly there are other limiting factors not involved in a simple binary system, for example confusion with similar memories, and there are types of memory that computers excel at (such as the pixel values of an image) whereas human memory deals in abstractions and hierarchical representations.

References

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LaBar, K. S., & Cabeza, R. (2006). Cognitive neuroscience of emotional memory. Nature Reviews Neuroscience, 7(1), 54-64.

Walker, M. P., Brakefield, T., Hobson, J. A., & Stickgold, R. (2003). Dissociable stages of human memory consolidation and reconsolidation. Nature, 425(6958), 616-620.

Wang, Y., Liu, D., & Wang, Y. (2003). Discovering the capacity of human memory. Brain and Mind, 4(2), 189-198.

Answer 2

Nature preserves redundancy by duplicating certain parts of living things - two lungs, two kidneys, two testes, two ovaries. I believe that as an instinct of self-preservation the brain does duplicate memory in some form. Otherwise a caveman who was clubbed on the head or fell and hit his head badly would (if he recovered) be bound to forget how to do some basic task - like remember where his cave is, or how to hunt, or how to eat.

This would explain why most Alzheimer's patients can remember the distant past, at least initially. It also explains why they have 'good' days (where they seem like their old selves - at least until the ravages of the disease take their toll) and 'bad' days, rather than 'bad' then immediately, 'much worse'.

Another example – you hear an old song from your childhood that's not played on the radio very often. You knew you used to know the title, song, and artist very well – but now you can't remember who the artist is anymore. You try to resist temptation to look it up immediately on the Internet because you know this can't be good for your memory recall, but curiosity eventually gets the better of you. When you do finally look it up you say, 'No way - it can't be HIM!". Reluctantly you accept this new memory but you realise that somewhere in the recesses of your mind this information is already stored (later you remember that you mixed this artist up with another artist at the time and performed some research and found it was this artist after all).

So what have you done? You have a piece of information already stored in your brain and you've now stored an exact duplicate - and, because of the emotional situation attached to each piece of information, these remain as backups of one another.