- your own middle name
- the street you grew up on
- your best friend in elementary school
- the name of your first pet
- your second-grade teacher's name
Now, I'm presuming that none of you were actively thinking about any of those before I asked. So, here are a couple of questions:
Where was that information before I asked you about it? And how did you retrieve it from wherever that was?
The simple answer is, "we don't know." Well, we have a decent idea about where in the brain specific kinds of information are stored, mostly from looking at what gets lost when people have strokes or traumatic brain injury. (A technique my Anatomy and Physiology professor described as "figuring out how a car functions by smashing parts of it with a hammer, and then seeing what doesn't work anymore.")
But how exactly is that information is encoded? That's an ongoing area of research, and one we're only beginning to see results from. The prevailing idea for a long time has been that interactions between networks of neurons in the brain allow the storage and retrieval of memories -- for example, you have networks that encode memory of faces, ones that involve familiarity, ones that activate when you feel positive emotions, possibly ones that fire for particular stimuli like gray hair, glasses, being female, being elderly, or tone of voice -- and the intersection of these activate to retrieve the memory of your grandmother.
The problem is, all attempts to find a Venn-diagram-like cross-connected network in the brain have failed. Even so, the idea that there could be a much smaller and more specific neural cluster devoted to a particular memory was ridiculed as the "grandmother cell model" -- the term was coined by neuroscientist Jerome Lettvin in the 1960s -- it was thought to be nonsense that we could have anything like a one-to-one correlation between memories and neurons. As neuroscientist Charles Edward Connor put it, the grandmother cell model had "become a shorthand for invoking all of the overwhelming practical arguments against a one-to-one object coding scheme. No one wants to be accused of believing in grandmother cells."
[Image is in the Public Domain courtesy of photographer Michel Royon]
The problem came roaring back, though, when neurosurgeons Itzhak Fried and Rodrigo Quian Quiroga were working with an epileptic patient who had electrical brain-monitoring implants, and found that when he was shown a photograph of Jennifer Aniston, a specific neuron fired in his brain. Evidently, we do encode specific memories in only a tiny number of neurons -- but how it works is still unknown.
We have over eighty billion neurons in the brain -- so even discounting the ones involved in autonomic functioning, you'd still think there's plenty to encode specific memories. But... and this is a huge but... there's no evidence whatsoever that when you learn something new, somehow you're doing any kind of neural rewiring, much less growing new neurons.
The upshot is that we still don't know.
The reason this comes up is because of a study at Columbia University that was published last week in Nature Human Behavior, that looked at a newly-discovered type of brain wave, a traveling wave -- which sweeps across the cerebrum during certain activities. And what the researchers, led by biomedical engineer Joshua Jacobs, found is that when memories are formed, traveling waves tend to move from the back of the cerebrum toward the front, and in the opposite direction when memories are retrieved.
Of course, nothing in the brain is quite that simple. Some people's brain waves went the other direction; it seems like the change in direction is what was critical. "I implemented a method to label waves traveling in one direction as basically 'good for putting something into memory,'" said Uma Mohan, who co-authored the paper. "Then we could see how the direction switched over the course of the task. The waves tended to go in the participant’s encoding direction when that participant was putting something into memory and in the opposite direction right before they recalled the word. Overall, this new work links traveling waves to behavior by demonstrating that traveling waves propagate in different directions across the cortex for separate memory processes."
The other limitation of the study is that it doesn't discern whether the traveling waves, and the change in direction, are a cause or an effect -- if the change in direction causes recall, or if the shift in wave direction is caused by some other process that is the actual trigger for recall -- so the direction change is merely a byproduct. But it certainly is an intriguing start on a vexing question in neuroscience.
Me, I want to know what's going on with the "tip of the tongue" phenomenon. Just about everyone experiences it -- you know the memory is in there somewhere, you can almost get it, but... nope. Most puzzling (and frustrating), I find that giving up and going to The Google often triggers the memory to appear before I have the chance to look it up. This happened not long ago -- for some reason I was trying to come up with the name of the third Musketeer. Athos, Porthos, and... who? I pondered on it, and then finally went, "to hell with it," and did a search, but before I could even hit "return" my brain said, "Aramis."
What the fuck, brain? Do you do this just to taunt me?
At least I comfort myself in knowing that we don't really understand how any of this works. Which is slim consolation -- but at least it means that my own brain is no more baffling than anyone else's.
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