For a few days the research team in Hannah Monyer’s lab tracks a particular mouse’s movements and neural activity in its cage. And here’s a curious thing: when the mouse rests or sleeps, they notice the same neurons fire in the same sequences, or in curious reversed sequences, as they did when the mouse was moving around—but faster. Ten to twenty times faster. Monyer shows me printouts where these firing sequences have been expressed as graphs. You can compare the wakeful versions with the sleep versions. The patterns are not quite the same, but clearly similar, or symmetrically inverted. It’s as if, in sleep, the mouse were reliving its experience, in fast forward and fast rewind, and committing it to memory in some way. So that then when the experience is repeated—when, that is, the mouse finds itself in the same position in the cage (which must be rather often)—perception and memory are simultaneous as the familiar pattern fires off. At which point memory could be understood not exactly as something stored, but as a tendency for neural patterns to repeat. A kind of habit. Perhaps. Though why the repetition would come with a conscious recollection that it is a repetition is not clear. In any event, these are the stories one tells oneself in response to the read– outs produced after inserting electrodes into a mouse’s hippocampus.
After a few days, when enough data has been collected—that is, when nothing new is being observed—the mouse is decapitated and its brain instantly sliced into super-thin layers whose cells will live on for a few hours despite the animal’s death.
I suppose it’s pointless asking at this point whether the mouse suffers or whether it matters in any way at whatever level that a creature was alive one moment and dead the next. This is serious science of the kind that could one day bring benefits to human beings with distressing brain conditions. All the same, and ridiculous as it may seem, there’s a part of me that is not altogether on board with these decapitations, even if, as it turns out, the mouse is anesthetized first. Nor would I like this uneasiness to go away.
With the skull peeled off then and the brain sliced as thinly as anything can be sliced, and while the cells are still living, a powerful, interactive microscope is used to focus on single neurons and even open them up. By introducing an electrical stimulation, it is possible to trace their axons (long hair-like tendrils) and see where each cell connects, though only of course on the horizontal plane of the wafer of brain that has been cut. Certain neurons in the hippocampus have axons that reach far out into the cortex, where information is “processed and stored as long-term memory.”
“Stored? The information is actually in there?”
“Let’s just say neurons fire in that area when we are remembering things. What’s important is that we have established some neural correlates of consciousness. This neural activity takes place while this experience occurs. These are empirical facts.”
The hallmark, I suppose, of an empty notion is that you can set it aside without its making any difference. “Stored” and “information” are simply ditched.
Having prepared me for what I am about to see, Monyer now leads me into the lab proper, which is just the other side of the corridor from her office. What I remember of this interview and visit, writing almost a year after it took place, and with only scanty notes about the salient moments of our conversation, is the arrangement of the space and my position in it. Which means, above all, my position in relation to Monyer and the three young women working in there. So I recall that I was taken through a narrow entrance way with a screen to my left and a wall to my right, after which we turned left and walked between machines and workstations on every side to the far end of the lab where the mice brains were extracted from their skulls and prepared for slicing. No doubt it would have been an interesting exercise to record the neural firings in my hippocampus as I made that walk across the lab and again as I write about it now and then perhaps a third time when I reread what I have written, snipping a word here and adding another there, recalling that there were two young women seated at workstations to our left and one to our right as we crossed the lab. But even assuming this were done and the results showed satisfyingly similar patterns, I’m not sure this would mean that the memory was stored in the firing pattern. Might it not equally suggest that my finding my way back to the fact, leaning on one fact after another, in much the same way as one seeks out an old path in the fog, has caused those neurons to fire? They are one with the memory, perhaps I can’t have the memory without their firing, but they are not identical to the memory itself, which is more as though, from a great distance, uncertainly glimpsed and much distorted by the rarefied air between, the lab were still having an effect on me, still present to me.
“I’d like you to tell me,” I asked, when Monyer and I were back in our original waiting room for a chat about what we’d seen, “exactly what you understand by the word information.”
Read Part I of this post here
Tim Parks is the author of eighteen works of fiction, as well as a number of critical essays, works of nonfiction, and translations from the Italian. His series of considerations of consciousness began appearing in the NYR Daily in 2009. His visit to Hannah Monyer’s lab appears in his new book, Out of My Head: On the Trail of Consciousness, which will be published by NYRB Books in October.
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Image: Place firing rate maps of pyramidal cells in mice during open-field exploration and zigzag maze running. The filled and dotted lines represent the firing rate of the neurons as the mouse ran toward the two different ends of the track. From “Gap Junctions between Interneurons Are Required for Normal Spatial Coding in the Hippocampus and Short-Term Spatial Memory,” by Kevin Allen, Elke C. Fuchs, Hannah Jaschonek, David M. Bannerman and Hannah Monyer. The Journal of Neuroscience, 31(17)