What is a memory?

Today I want to talk about memory, and what’s wrong with some of our standard conceptions of how memory works, and even fundamentally what memory is. After decades of research in the cognitive sciences we seem to know more about memory than ancient philosophers thought imaginable, and we’re learning new things every day (see my post on the role of theta waves in memory formation). A quick visit to the Wikipedia page on memory will provide ample information on encoding, storage, and retrieval of memory. It discusses the difference between long term memory and short term memory, and talks about working memory. It elucidates the difference between implicit and explicit memory, and it even gets into the different brain regions involved in memory. Finally, it discusses cellular biology, the real underpinnings and root of our memory formation. We’ve decided that memories are “encoded” by synaptic change, that these cellular changes “store” our memories. All we need is some sort of cue, the correct neurons proceed to fire, and bam, we’ve retrieved our memory from storage! But not a single sentence in this wikipeida page is devoted to considering just how the heck changes in the strength of connections between cells causes memory formation! Where exactly is this memory? If you open up a brain and look inside you won’t see any memories. You don’t open up a neuron like a storage container and memories come spilling out. What about a network of them makes this story any different?

Let’s consider this idea that a pattern of neurons encode for a memory. What does that mean exactly? Let’s use a computer analogy for a second. A computer encodes let’s say an image as a pattern of 0s and 1s on a hard drive. But those 0s and 1s are completely meaningless to the computer (take a look at my chinese room post if you want to explore this idea further). It doesn’t *see* an image or *know* that some pattern of 0s and 1s is a picture of a dog and another is a picture of a cat. It’s just bits, a meaningless stream of information. The central processor passes that pattern to a program, and that program will cause a specific array of pixels on a computer screen to light up. And only then, when observed by someone, does that “encoding” gain any meaning…it never means anything to the computer. An encoding needs to be interpreted by a knower for it to represent something. So how is it that a pattern of neurons that encodes a memory can become meaningful to you?

You’re not aware of the pattern of neuronal firing, in fact, you’re not aware of any of the physical processes in your brain. You are just aware of a memory. But there’s also no little man inside the brain that takes that pattern of neuronal firing and understands what it is. A little guy that sees the neuronal pattern and goes, “ahhhh…that’s the time I went skiing in Vermont” or who, like a computer, takes that pattern and projects it on a screen in some sort of internal theater in your mind. It’s not like there’s a “you”  who experiences this memory. There’s not a YOU and a MEMORY. There’s just you in the state of experiencing what we call a memory. Your conscious experience, your sense of self, emerges from the same neuronal firing, the same physical processes that “encodes” for a memory. How any amount of neuronal firing, any physical process can cause conscious experience is a mystery.

You experience all sorts of different things. And whether it’s the experience of remembering, or perceptual experiences (seeing, hearing), or the feeling of pain or anger or love or excitement, for all these aspects of consciousness, there is a brain state that underlies them. ‘Encodings’ as the standard literature would put it. But brain states are just physical processes. It’s just a big web of interconnected cells passing signals electrochemically. Why should any amount of physical process lead to conscious experience? Atoms are processes that aren’t conscious. Stars aren’t conscious. Cells aren’t conscious. What is? Algae? Trees? Worms? Mice? Cats? Apes? Humans? Why are some physical processes conscious, and others not? There’s nothing in our laws of physics that would predict it, neurons or no neurons. And all of science so far seems ill equipped to address this question. Neuroscience can point out all sorts of important correlations between certain aspects of cognition and consciousness, but it has no tools for even trying to address the phenomenal (subject experience) aspects of those processes. Psychology can illuminate and describe all sorts of aspects of human behavior and thought, but itself already starts from a level above the physical processes. These sciences together can tell us about which brain states are conscious and which aren’t, but this just begs the question even more, why are some types of neuronal firing unconscious, and other types conscious? It’s all the same neurons right?

I was talking about memory though, and so you might be thinking, how does all this explicitly relate to memory? Well, once we realize that the encoding framework has serious theoretical issues for consciousness, we can think about how this affects our conception of memory. How exactly does a pattern of neuronal firing relate to the experience of a memory? What is the necessary relationship between that pattern and the memory? For instance, let’s say neuroscience can determine the exact pattern of connections that constitute a memory by using the most advanced neuroimaging techniques, and subtracting out everything that is deemed to be not “necessary” to the memory. Some set of neurons IS your memory.

On the left is the web of possible neuronal connections. On the right is the exact pattern of firing determined to "encode" for a memory.

So if that same exact pattern of firing is later stimulated will you have the same “exact” memory experience? What if you had artificially stimulated that same pattern *before* that memory was ever formed, what would you subjectively experience? We know we can insert memories through psychological means (through interactions with words and pictures), but can we insert memories through neuroscientific insertion? Is that even a coherent concept? If we artificially strengthen certain synapses, and create new connections on other neurons, what would be the mental change that occurs? If you find yourself skeptical that creating some random neuronal connections in the brain could cause someone to have specific memories they never experienced, you’re probably right to (though until the experiment is run we can’t be sure). But this has to tell us something about the incoherence of neurons actually ‘storing’ memories.

What about when you have a lot of very similar experiences? Are the various experiences literally very similar neural patterns? Where a few neurons veer right instead of left?  Or can similar experiences be underlied by completely different patterns of firing?

On the left is a pattern that encodes for a memory. On the right is slightly different one. What would be the difference in experience of the two patterns?

Psychologists often talk about multiple memories merging to stabilize a memory. But is that really what is going on? How does an encoding for a “general” memory come about, if each new experience is explicitly encoded as its own memory? Meaning, if one experience encodes pattern A, and another pattern B, and a third pattern C. And you then later have a general memory that is neither A nor B nor C, what is it exactly that makes that pattern a general memory if it itself was never encoded? If memories are encoded by patterns of neuronal firing, how can a memory arise from a new and different pattern? What is the difference between thinking about your ski trip last week, your skiing experiences in the last few years, and the idea of skiing in general? Are they different encodings? Or is there something else fundamentally going on here?

I don’t have the answers; I barely even know how to pose the questions, though some of the things I bring up could conceivably be researched.  What I’m arguing is that we might need an entirely new conception of how memory works if we ever want to make real breakthroughs in understanding ourselves. We have long known that memories are not faithful replicas of past events. Memories are reconstructed at the time of recall. And that act of recall at the same time necessarily changes them. That general memory I described above may not be a memory at all, but an entirely new mental experience constructed in the moment, a story I’m creating, which we label “memory”.  Even your specific memory of a party last weekend is itself an entirely new mental experience every time you go through the act of “remembering” it. And even though scientists for the most part have long ago left behind the naïve concepts of memory as a filing cabinet, we are still stuck in a paradigm that may prove insurmountable because figuring out how to even ask the right questions is perplexing.

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