How we create Memories ?

I was recently invited to a screening of the film Upstream Colour, and lead a discussion of the scientific elements of the film afterwards. It's an excellent film, but challenging. Spoiler warnings are irrelevant; I could describe in detail the exact sequence of events in the film and you'd still be none the wiser as to what happens. During the discussion I used the phrase 'the corresponding pig' numerous times, and it made sense in context. Suffice to say, this is not a Michael Bay film.

One scientific element of the film (I think) concerns the workings of human memory. Memory and disruptions to it have provided a surprising amount of fodder for science fiction and other pop culture, but it's often distorted or portrayed in ways which don't match what the science tells us. In an attempt to rectify this, and as someone who did his PhD in memory processing, what follows is a brief guide to the workings of human memory. And please be aware that there are probably other neuroscientists and psychologists out there who would take issue with parts/all of this. This is just how I learned things.

At the basic level, most seem to know about long-term and short-term (or "working") memory. The latter lasts a few seconds and has restricted information capacity. The former potentially lasts forever and we don't know the upper limit on how much information it can hold. It'll be a while before we can fit the average human memory on a USB stick, at least.

Although short-term memory is undeniably important, it's rarely focussed on in pop culture. It's hard to imagine a gripping drama about someone can only remember three things at once, rather than four.
Long term memory is also subdivided into "explicit" and "implicit" memory. Implicit memories are things like knowing how to ride a bike, play an instrument (assuming we've learned how to do so at some point) and other types of "muscle memory", as are emotional responses we experience to familiar stimuli; we do them without thinking, they are experienced with no conscious awareness.

Again, pop culture doesn't really dwell much on implicit memory; a film about someone repeatedly having to learn to ride a bike would prove a tricky sell.

Explicit memory can also be subdivided into episodic and semantic memory. Episodic is memories for episodes from your life (e.g. the time you went to Paris), semantic memory is for information, which isn't attached to a specific context or experience (e.g. the fact that Paris is the capital of France). There is a lot of overlap between the two, but it's a handy system anyway.

Many people seemingly think of memory as a precise and objective record of what happened, like the memory card in a digital camera (NOTE: I originally wrote "film in a camera" there like some sort of caveman). But our memory is far more flexible, and the list of things that can alter it is worryingly long. My personal favourite is the egocentric bias, which is when people remember things in a way which makes them look better, emphasising their own role in an event, performance at a sport etc. meaning our brains are lying to use to make us feel good about ourselves.

This is how confusing and complex memory gets when it's working normally. When things go wrong, as they do often in science fiction and the like, it gets even worse.
There are three stages of memory formation where things can go wrong; encoding (formation of the memories from perceptual inputs), storage (storing the encoded memories) and retrieval (accessing/using stored memories).

Encoding of long-term explicit memories typically involves the hippocampus. Memories are believed to stored across the neocortex, not in one specific location per se. Retrieval involves several areas. Retrieval appears to have several forms. For example, there's a difference between recognition and recall. Recognition is when someone's face is maddeningly familiar but you can't work out how you know them. Recall is when you suddenly remember that this is a former co-worker who you'd rather avoid after the Christmas party incident.

Retrieval can also be affected be context; you're more likely to remember something when in the context where the memory was encoded. This can be an external context, like being underwater, or internal context, like alcohol intoxication level; yes, as counterintuitive as it may seem, in certain scenarios, alcohol intoxication can enhance memory retrieval.

Given the localised and fragile nature of the hippocampus, disruptions to memory encoding leading to anterograde amnesia (i.e. the one in Memento) are more likely than disruptions to retrieval, leading to retrograde amnesia (i.e. the one in soap operas).

The diffuse storage of memories, coupled with a lack of any way to recognise what they actually represent, means the technology for adjusting/erasing specific memories is still way off. It does seem worryingly easy to implant false memories though, at least on the small scale, so maybe that sort of technology is more likely.
(That previous link references Total Recall, the original. Everyone seems to have totally forgotten about the 2012 remake, which is ironic given the title)

So that's a brief guide to human memory. A lot of this information is gleaned from study of cerebral trauma or neurodegenerative diseases that affect memory so may be somewhat different to what occurs in the average, healthy brain. But still, it's worth keeping in mind.

So next time you see a work of fiction that focuses on human memory, try and remember this article. Although even if you forget it entirely, that's still sort of appropriate.

Dean Burnett is a largely forgettable presence on Twitter, @garwboy

Upstream Colour is released in the UK on Friday the 30th of August.