I am shown into a small space that seems part office, part lab and is characterized above all by a very strong smell of mice. The sense of smell, we remember, from Galileo on, is reputedly generated entirely in the head, it doesn’t actually exist in the world, yet my head certainly hadn’t been producing this phenomenon just a few moments ago. Nor is it enjoying what it is producing now. The mouse odor is not quite a stench, but getting there, and along with it, instant and unbidden, comes a memory from perhaps fifty years ago of the time when I used to keep mice myself. A pet shop in North Finchley had sold me two innocent white mice in a small wooden cage. Originally, I had meant to keep them in my room, but very soon the smell began to bother me, so that after some negotiation with my parents I moved them into the outside boiler room of our sprawling Victorian vicarage. Here, in no more than a few months, the original pair had multiplied dramatically, gnawed their way out of the cage, and were scampering in their dozens in and under the synthetic lagging around the house’s ancient oil-fired boiler.
Hannah Monyer points to a single white mouse in a deep metal box on a low table and begins to describe what they are doing with it. But even as she does so I am aware that if I wanted to I could explore and expand this old memory of mine at will, building it up from the trigger of the mousey smell to include the wooden workbench to the left of the boiler-room door with its scatter of rusty tools, the roar when the boiler fired, the mouse droppings on every exposed surface, and so on. Memory, perhaps, it occurs to me in this lab where memory is being studied, is a routine you find yourself performing in response to a prompt, the way some music has you hazarding a dance step or two almost against your will. It’s something that both binds and enriches. But I must listen to what Professor Monyer is telling me. Because it’s complicated.
Unlike the mice I kept, this creature we’re looking at in Monyers’ lab, and indeed the four or five other similar animals in cages stacked against the wall, has a tiny black plastic box attached to the top of its head. A little less than a half an inch across and sitting slightly to the side of the head, this unexpected contrivance has the air of some incongruous military hat and bestows on the mouse an even more comic and pathetic look than little white mice ordinarily have. The creature looks vulnerable and ill at ease, crouched in his cage with his black box on his head. Or maybe her head.
“Protruding from under the box are four electrodes,” Monyer tells me, “much finer than needles, of course, that pass through the skull and the upper brain into the hippocampus.”
For a moment, staring at the mouse, I wonder at the practicalities of this. The animal’s head is so small. The hippocampus is not a large part of the brain, nor is it near the surface.
“Can you really be sure that the electrodes have gone where they’re supposed to?”
Monyer is breezy. Her lab technician is brilliant, she assures me. He has long experience. Above all, the hippocampus has a characteristic firing pattern, that is to say, its neurons send their electrical impulses at recognizable intervals. “So when the electrodes register that pattern, we know they’re in the right place.”
“But aren’t they painful? For the mouse?”
“Not at all.”
I’m reminded that while the brain may be “responsible” for the pain we feel in other parts of the body, it is apparently immune to pain itself. You don’t feel a scalpel cutting into it. So they say.
“As the mouse moves around the cage, the electrodes record the activity of the nearby neurons, or hopefully, if we’ve set things up correctly and we’re lucky, of a single nearby neuron.”
The cage is about a foot square and now I notice that there is a video camera placed directly above, presumably tracking the movements of the mouse.
“With the electrodes and the camera synchronized, we can associate the movement of the mouse around the cage with the firing of these neurons. For example, we’ve noticed that when the mouse has its left side against the near wall, leaving the rest of the cage empty to its right, then a particular neuron close by one of the electrodes always fires off, sends out an electrical signal.”
“Can you really be sure it’s the same neuron?”
One book I have read claims that about a million neurons could fit into a grain of rice.
“The signal is always received by the same electrode and is always the same strength. We’re confident it’s the same.”
“And this means?”
“The neuron is telling the mouse where it is in relation to the walls of the cage,” Monyer says. There are also neurons that fire when the mouse is at any part of the border of the cage, others again when it is at any one of four grid-related positions that form a rhomboid in relation to the square of the cage. So the creature would seem to have a kind of map in its head.
“Surely,” I object, “it is not telling the mouse anything. The mouse isn’t separate from its neurons, is it?”
“Of course it’s a metaphorical way of speaking,” Monyer acknowledges. “Let’s say the neuron is receiving input, processing it and passing it on.”
But where to? And why?
(Stay tuned for Part II!)
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: The imaged course of projections of a mouse neuron between brain areas from a 2012 paper by Hannah Monyer and colleagues on how the brain processes spacial orientation © DKFZ (Deutsches Krebsforschungszentrum)