What are the advantages of forgetting?

Question

How forgetting things is helpful for the brain or the human body biologically? This web page

After some moment of being rude, selfish, or weak, either we are able to put it behind us, or the person who suffered at the result of our imperfection moves on. The reason for this is our ability to forget about it. We forget not because we have an imperfect hippocampus (our brain’s memory organ); it's actually an evolved solution. The ability to lose information allows new information to come in that is more relevant, more pertinent to an ongoing reality. Forgetting allows us to update.

and this Huffington post article

According to a study in Nature, our awareness is limited to only three or four objects at any given time. To be able to think at your highest level, you therefore must be very efficient at filtering out all of the background noise: Your racing thoughts, the ringing phone, your neighbor’s barking dog, and the list goes on.

The Nature study found that when participants were asked to “hold in mind” certain objects while ignoring others, there are significant variations in how well each of us can keep irrelevant objects out of our awareness.

The researchers concluded that our memory capacity is therefore not simply about storage space, but rather “how efficiently irrelevant information is excluded from using up vital storage capacity.”

provide some backgrounds.

Answer 1

Short answer
It has been shown that loss of long-term memories may enhance the retrieval of others. Short-term working memory is explicitly designed to be volatile and non-lasting. However, there are many other types of memories where memory loss may not be explicitly beneficial, or even outright debilitating such as in the case of Alzheimer's or stroke.

Background
First off all, there are many types of memories, including sensory memory, motor memory, short-term (working) memory, long-term memory, explicit & implicit memory, declarative & procedural memory and so on. Hence, because the question is quite broad, I will focus on long-term memory, short term-memory and sensory memory to discuss that memory loss can be beneficial, neutral, or detrimental.

• Beneficial effects of loosing memories
  Long-term memory is probably what you are after and there are studies in that field that have linked the loss of memories to enhanced processing of other memories. More specifically, there are adaptive benefits of forgetting, namely a reduced demand on cognitive controls during future acts of remembering of other stored information. Even more specific: retrieval of memories after forgetting others are thought to reduce the necessary engagement of functionally coupled cognitive control mechanisms that detect (anterior cingulate cortex) and resolve (dorsolateral and ventrolateral prefrontal cortex) mnemonic competition (Kuhl et al., 2007). The improvement of particular memory processes by forgetting others may be linked to them being closely related. Indeed, motor tasks more remote do not benefit much from forgetting unrelated ones (Shea & Right, 1991).
• Inherently volatile memory
  Short-term working memory is explicitly designed to aid in on-demand task performance. Short term memory is for example used to remember a set of components (e.g., colors) and use that information to deal with a certain task at hand (which objects depicted here match the colors you just saw?). If all these memories would be retained, tasks dependent on working memory would not be possible. Sensory memory an ultra-short term memory that is kept only for very short amounts of time, allowing people to, e.g., track a light and make a symbol or letter out of it before the information is funneled to the short term-memory.
• Neutral effects of loss of neural function: a side track off memory lane
  However, forgetting may be simply another example of the use it or lose it principle that applies to pretty much everything in the human body; when you don't walk, the bones in the legs will weaken along with the musculature used for locomotion. Similarly, when the inner ear or the retina becomes dysfunctional and degenerate, the deafferented auditory nerve and optic nerve start to degenerate, respectively. The associated deafferented sensory cortices will slowly be taken over by other adjacent cortical areas due to the plasticity of the cortex. In blind folks, for example, the tactile and auditory cortices have been shown to take over the primary visual cortex. Given that the visual cortex is huge compared to the tactile and auditory cortex, one would expect substantial increase in performance on tactile and acoustic tasks in blind folks. Yet, this is debated (Stronks et al, 2015). In fact, normally sighted folks can learn braille as well as their blind peers, suffice they get an equal amount of practice. In other words, practice is the key, not enhanced areas of cortex being available per se. Hence, 'forgetting' to see or 'forgetting' to hear is, as far as my knowledge goes, not associated with any benefits whatsoever, barred a minority of studies that showed a slight benefit of being blind in auditory tasks (Stronks et al., 2015).
• Pathological memory loss - not so good:
  However, forgetting of memories may also be pathological; think of the impaired short-term memory of Alzheimer's patients, or amnesia due to stroke. Forgetting is not always beneficial.

<sub>References
- Kuhl et al., Nature Neurosci (2007); 10: 908-14
- Shea & Right, Res Quarterly Exercise Sport (1991); 62(3)
- Stronks et al., Brain Res (2015); 1624: 140–52</sub>

Answer 2

Memory is formed by building connections between nerve cells (i.e. neurons). These connections are called synapses. The synapses form a network between several (or tens or hundreds) of neurons, therefore giving us the ability to retrieve something we had memorized before.

Learning something new requires building new connections, but the older connections might interfere with the new ones and thereby interrupt our memory or what we have learnt. So sometimes older connections must be broken in favor to new connections and new abilities. For instance, you might remember crawling on both hands and knees as a child, but slowly you practiced walking and at one point you stood up and never crawled again. Children crawl like it's no big deal, but grown-ups have to think and struggle and in the end it's not gonna be very good. That's because older connections regarding crawling have been broken in favor to new connections for walking.

Check out: Izquierdo, Ivan. "The art of forgetting." Springer International Publishing, 2015.

Answer 3

One famous person, Solomon Shereshevsky, had an unusual ability to remember everything he encountered: sights, numbers, words in foreign languages, events from infancy, and more.

Unfortunately, S’s gift was a serious handicap. He was unable to block unwanted memories. Also, he had a terrible memory for faces because he memorized them so exactly. People’s faces change with time, lighting, mood, and expression. S had difficulty recognizing faces because they looked so different to him from the ones he had completely memorized in the past.

Extrapolating from that, one could conclude that the inability to block unwanted memories could easily lead to the development of PTSD — especially if, as in Shereshevsky's case, the total recall is combined with synaesthesia.

Answer 4

Who says it has to be good? We cannot assume that every trait that evolves is beneficial to the species. A lot of people assume that the species of an ecosystem will evolve optimally; that is, they assume each species evolves to have the best possible genes for its environment. My understanding is this is not the case. Species have to adapt or face extinction, but they only have to adapt to be good enough. Perhaps it's not that forgetting is good, but rather it just doesn't impede survival or reproduction. (Well, except when you forget your spouse's anniversary!) Which leads us to the next point...

It's a side effect of how human memory works. First off, storing a memory in the brain is not like running a tape recorder or camera. The brain actually stores very little of the information coming into it, just enough so that it can later fill in the blanks and make a decent reproduction. In computer terms, the data is filtered through a very lossy compression algorithm before being stored. It's just good enough that we usually don't notice, but sometimes things go wrong and we get phenomena like confabulation.

Now about how that data is stored. As you know, the data is stored by the synapses in the neurons. But here's the thing: those synapses aren't dedicated to that specific memory! Storing a new memory affects synapses that are part of other memories. One synapse might be storing a piece of information for any number of memories, because those memories all have some tiny thing in common. I wish I could explain this better and in more detail, but this became pretty obvious to me when I read up on artificial neural networks, which are crude models of brains.

Sometimes, neurons just die. Obviously this is going to affect the brain's ability to recall the information the dead synapses contained. There's enough redundancy built into the brain that this is rarely a problem, except in cases like Alzheimer's, where the brain just suffers too much damage.

To me, the question isn't why we forget. The question is how we can remember stuff at all!

Answer 5

What are the advantages of forgetting?

Perhaps the question asked should be what is the disadvantage of remembering every little detail?

The answer is cost. It cost energy/neuron to remember everything. Neural tissue are expensive to maintain and feed. At rest, the human brain consume 20% of all calories. And that is alot of energy when the human brain is only 1% of all tissue in the body.(http://www.nature.com/neuro/journal/v1/n1/full/nn0598_36.html)

It is also inefficient. If you remember everything, it will take time to reach the appropriate memory. When time is life, it is inefficient to have a large store of unimportant memories to search through for the one important memory.

Also, this being biology... is there a selective drive for perfect memory? Without a section pressure for perfect memory, it won't evolve. Memory that is good enough to survive is what we will get. We do not get cheetahs which are as fast as biologically possible. We get the cheetah that can catch the slowest gazelle.