General Question

inunsure's avatar

How are sequences of memories stored in the brain?

Asked by inunsure (423 points ) February 2nd, 2012

I can clearly visualise and understand how a hard drive stores lets say a song, but how does our brains do it? How does our brains store a sequences of memories and retrieve that memories and play it in sequence?

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18 Answers

dabbler's avatar

I don’t think the current state of our science of the brain/mind can explain that yet…

JaneraSolomon's avatar

Different types of memories are stored in different ways, and they are mostly encoded in the areas of the brain in which they enter. Thus visual memories are stored spatially in the areas of the brain that process visual information (occipital cortex) while auditory information is stored in the auditory cortex. This is known largely through studies of brain damaged individuals, where damage to the left side of the occipital cortex causes a loss of ability not only to perceive objects in the right field, but also to recall objects on the right side. For instance asking a person what was on the right side of the hall as they entered their childhood home. This and more can be explored by reading about cognitive neuroscience. One of the foremost experts on the neuroscience of memory is Stephen Kosslyn, director of the Center for Advanced Study in the Behavioral Sciences at Stanford University, and former chair of Psychology at Harvard. His books “Wet Mind” and “The Case for Mental Imagery” introduce this subject. Fully explaining the process of encoding these memories is more than can be covered here.

RealEyesRealizeRealLies's avatar

The terminologies used to describe this phenomenon may be completely inadequate. They may be completely wrong. Not everyone agrees that memory, or song, is stored.

Not everyone believes that memory (thought) can be compared to storage, like water in a bucket.

Some, like me, noting that memory and song are thoughts, believe that thought is a non physical agent. It cannot be stored by a physical object. But it can be represented and accessed by physical objects.

“Hey Joe” is a song by Jimmy Hendrix. It is the physical representation of a non physical thought of Jimmy’s mind. Your computer represents Jimmy’s thought with an MP3. Mine does too. I also have an old vinyl record that represents it. My neighbor has a CD, and Youtube has a video flash player. All these different mediums are physical objects that represent the same thought. It’s not many different thoughts in many different places. It’s one thought being pointed to and accessed in many different ways. We can access Jimmy’s thought with a sheet of music. That’s just ink and paper. But ink and paper do not equal the thought. But ink and paper can point to the thought.

Right now, your computer, mine, and @JaneraSolomon‘s computer have the exact same words on our screens. Those words represent individual thoughts. But they are not three sets of thoughts.

So consider that losing part of the occipital cortex may not be equal to losing the memory. It may only affect the ability to access that memory. The memory itself… the thought… may still exist regardless if we can access it or not.

JaneraSolomon's avatar

@RealEyesRealizeRealLies that reminds me of an old joke from the computer science crowd about “WOM… write-only memory” Debating whether there is any meaning to memories that can be stored but never read is the stuff of late night beer parties but doesn’t tend to yield much useful insight in my experience.

CaptainHarley's avatar

As best we can tell at this point, memories are stored holographically in the brain and not confined to any particular physical location. This goes a long way toward explaining why we can access memories in a wide variety of ways: chronologically, spatially, memories related to one individual irrespective of time, etc.

thorninmud's avatar

My understanding of the question is that you want to know not how memories in general are encoded, but how the sequence of events related to a certain episode is recorded, so that the memory “plays back” like a movie, instead of being a bunch of snapshots.

One theory is that episodes are recorded as assemblies of activated neurons (a single neuron that represents a particular feature may participate in many different assemblies that share that feature). The hippocampus, which acts as the gatekeeper of memory, encodes the sequence in which the neurons were activated at the time of the episode. The memory then exists as both a particular assembly of neurons, and the sequence in which they were activated. Reactivating them in that sequence reconstructs the episode.

philosopher's avatar

@inunsure
You can find studies about this at sciencedaily.com and a lot of information on bigthink.com.
Scientist do not understand exactly how the brain works.
The brain is a complex organ.
They are doing research and learning more all the time.

RealEyesRealizeRealLies's avatar

@JaneraSolomon “Debating whether there is any meaning to memories that can be stored but never read…”

You may have missed my point. I don’t know. Point being, that memory may not be “stored” at all, but rather referred to or accessed from another agent separate from the brain altogether.

Tell me, if memory (thought) is stored, then where is the thought that your last comment represents? Is it in your brain, mine, your computer, mine, or perhaps on fluther servers? And if it is stored in all of these physical places, then does that mean there are now at least 5 memories? One for each medium that expresses it?

Or could it be that the memory isn’t stored at all. Could it be there are 5 mediums which all refer to the one memory which isn’t physical? These mediums are encoded. And this encoding is a key which provides access to the memory. Those without the key code can’t access the memory.

See, I don’t believe that you and I have two separate copies of Adobe Photoshop. I believe we have two separate key codes that access the single thought structure which actually is Adobe Photoshop.

JaneraSolomon's avatar

Memories do indeed exist in partial and complete form in a variety of media simultaneously. When an audience watches a movie, a partial memory forms in each person’s brain, whereas the movie film itself comprises a complete memory. Perhaps bits and pieces (memories) of the film are recorded on a couple cell phones as well. In practice we don’t merely find and recall memories, but reconstruct them. This is necessary in part because different parts of them are stored in different places, for instance the auditory and visual cortex, and also the frontal lobe and amygdala, recalling the narrative structure, and emotional cues. In most social settings memory is socially reconstructed: “Hey Joe, remember that time we snuck into Yankee Stadium? Oh yeah, Ted, it was so foggy that day!”

RealEyesRealizeRealLies's avatar

@JaneraSolomon

So you believe that memory has a “form” and it is stored within a physical medium? Am I reading you correctly? I’m confused if you’re suggesting that one memory is exists in many medias, or if each media represents an individual memory.

Do you accept or reject that memory is a type of thought?

RealEyesRealizeRealLies's avatar

This symbol ”Ω”...

Is it an actual thought/memory? Or does it represent a thought/memory?

JaneraSolomon's avatar

A monkey was restrained and forced to stare at a target-like pattern after being injected with a radioactive marker. The monkey was then killed and its brain was pressed against a photographic emulsion and it produced an image where the original target was visible embedded in the tissues of the brain.
http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/V1/LGN-V1-slides/v1-retinotopy.gif
Spatial information such as the target pattern does indeed have a form and is indeed store-able within a physical medium such as the brain’s occipital cortex. The monkey however presumably has no idea of what the word “target” means. When humans look at the target, they record not only the image but also the name, associations they have with targets, such as “William Tell,” and other such information. This is true whether we are talking about a target form or a Greek letter. Looking at the Greek letter, we have “associative memory” triggered such as “that reminds me of a horseshoe that my grandfather nailed above the door to his barn.” The physical analog of a memory is a recording. So yes, many people can have their own memories of an event such as 9/11 and every one will be different because people bring to it different associations, different experiences, perception from different angles, cultural norms, and so forth.

phoebusg's avatar

Memory, language and higher functions in the brain are highly generalized and co-dependent on many neural substrates. As per @JaneraSolomon first response – memory is a multi-modal system. You have the specific memory systems of the senses. Then you have a registry and modulator (hippocampus) – that links and makes sense of the implicit fragments (of each system).

Now to add to this complexity, and since you brought up the computer. To store any kind of information on any system you need a mode of representation so that the information holds some sort of relevant integrity – and can be utilized by the system. That is, the information remains non-noise, and is usable and relevant to the original ‘entry’. The computer uses a binary system that is error-free (99.99%) – which allows it to operate – when there is an error, functions break down and you get a BSOD or segfault or other cute error with its warning. The brain is somewhat like that, but not really. The representation ‘format’ is so dynamic that it’s continually reconstructed. So long your brain is ‘on’ it keeps on changing. And unlike the computer, BOTH the hardware AND the software is undergoing a change.

In the brain the hardware is the neural pathways – cell bodies and neurotransmitters. Information flows via electric waves, AND chemical messengers inter and intra-cellularly. That is, each neuronal cell changes itself – that changes how it reacts to stimuli. The reason I bring this up is because memory is local to the single neuron – how it potentiates and changes its reaction to stimulation. But memory is ALSO the co-firing/activation of sets of neurons.

Without going into disgusting detail and breaking out reaction chains and funny acronyms. Memory in the brain is part of the ongoing processing – as in as neurons keep on firing, they both maintain their state and simultaneously change it a little. Every time you remember something, unlike the copying that occurs in the so far binary computer systems (not the quantum computers / models) – you are copying one for one. In the brain, you’re reconstructing a memory at each recall, by piecing together with the help of the hippo-mammilary bodies etc. Changing it a little (depending on current mood/suggestion/co-activations).

Now, sequences… there’s some evidence that sequences may be more in implicit memory. For explicit memory is narrative-driven (as in relevancy… what is relevant to the ‘fetch’ for information you’re executing in your brain).

That’s all for now… I should get to bed. I may add more later per request.

RealEyesRealizeRealLies's avatar

That’s interesting research @JaneraSolomon. Thanks for posting that slide. I’d like to read more about the data if you have a link. It raises the question of what constitutes an actual memory. A physical impression, a retina burn, isn’t much different than putting that same pattern on my arm and allowing the sunlight to form a tan around it, thereby making an impression. But is that what memory is?

A past conversation about this subject was fraught with confusion about the word memory. Some equate the metaphor of memory as akin to a metallic spring, or a dent in a car that pops back to original position, or a bi-metallic coil in a thermostat. We apply the term memory to those items in a metaphorical way. As humans, we often mistakenly personify objects and/or objectify people in attempt to communicate more effectively.

I’m not convinced this is the same type of memory that we refer to when discussing properties of brain and mind. There is no thought involved with the memory of a bi-metallic thermostat. Likewise, I don’t believe there was any thought involved with the monkey experiment either. No meaning is attributed by the monkey to the impression of the pattern.

I was just dropping my son off to his Aikido class. Driving home I thought about the monkey experiment. It left me trying to imagine a brain impression of every observation I saw on the way home. The stop signs, the road, other cars… Am I reading this monkey experiment correctly in that it suggests a smaller microscopic version of everything I saw on the way home is sitting in my brain somewhere? That’s a tough swallow.

JaneraSolomon's avatar

See Kosslyn’s book “Image and Brain” for more details on that, the experiment was by Tootell et al. The mechanics of memory storage within brains involves training neural networks. When you learn something it physically alters the structure of your brain. A simplified explanation of recalling is that the process works in reverse. Recalling a mental image effectively reconstructs that image within the visual cortex. Again, more details on this in Kosslyn and Koenig’s “Wet Mind”

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