Neuroscientist Christof Koch of Caltech and Itzhak Fried, who is both a
neuroscientist and a practicing neurosurgeon at UCLA Medical School, recently
uncovered evidence for a neural coding scheme long ago discarded as
implausible. This scheme had been disparaged as the "grandmother cell"
hypothesis, because in its reductio ad absurdum version it implies that
our memory banks dedicate a single neuron to each person, place, or thing that
inhabits our thoughts -- such as Grandma. Most theorists assume that such a
complex concept must be supported by large populations of cells, each of which
corresponds to one component of the object -- like the bun, the bifocals, and
the woolen sweater of Grandma.
Yet Fried and Koch have found neurons that act very much like grandmother
cells. Their subjects were epileptics who had electrodes temporarily inserted
into their brains to provide information that could guide surgical treatment.
The researchers monitored the output of the electrodes while showing the
patients images of animals, people, and other things. A neuron in the amygdala
of one patient spiked only in response to three quite different images of Bill
Clinton -- a line drawing, a presidential portrait, and a group photograph. A
cortical cell in another patient responded in a similar way to images of
characters from The Simpsons. In future experiments, Koch and Fried
plan to show patients photographs of their grandmothers to see if they can
locate actual grandmother cells.
It makes intuitive sense, Koch says, that our brains should dedicate some
cells to people and things frequently in our thoughts. He adds that his
findings might seem less surprising if one realizes that neurons are much more
than simple "threshold" switches that fire whenever incoming pulses from other
neurons exceed a certain level. A typical neuron receives input from thousands
of other cells, some of which inhibit rather than encourage the neuron's
firing. The neuron may in turn encourage or suppress firing by some of those
same cells in complex positive or negative feedback loops.
In other words, a single neuron may resemble less a simple switch than a
customized minicomputer, sophisticated enough to distinguish your grandmother
from Grandma Moses. If this view is correct, meaningful messages might be
conveyed not just by hordes of neurons screaming in unison but by a small
group of cells whispering, perhaps in a terse temporal code.
If true, I wonder if you could zap that single Grandma neuron -- and as a
consequence not recognize your Grandma the next time you saw her.
Surely, there must be other neural cells that also recognize her features in
as efficient a way as the cell you zapped. But....maybe not? These
studies have been done with small electrodes implanted within the human
cortex. You could easily induce a few volts running the opposite way,
down the electrode, to kill a particular neural cell (and possibly a few
others in the neighborhood -- too bad). They do these electrode implants
on patients suffering from epilepsy to identify where exactly in the cortex
the epileptic seizures emanate from, so they can excise them later through
If you ran into a neuron that was associated with an unreasonable fear or
phobia, or a really bad memory, you might indeed want to zap it away.
Personally, I'd like to zap the cell that remembers "Sparks", a particularly
nasty bully boy who inhabited my neighborhood when I was a small child -- a
guy who gave me a lot of grief growing up. It would do me no good to
kill Sparks physically now, 50+ years later, since his legacy would remain in
my brain. But if I could kill the legacy itself -- that is truly an
Unlike Jim Carey in Eternal
Sunshine of the Spotless Mind, I'd not want to expunge the memories of my
ex-girlfriends, ex-wife or other lovers. In the fullness of time, I've
managed to survive and overcome the hurt & pain of lost love. It was not
a particularly easy thing to do -- and it would have been unbearable except
for the knowledge that almost everyone has to do it at some point in their
lives. Love hurts, but the memory of its burning pain is one thing I'd
rather not lose. It measures off the dues paid to be a human being.
There would probably be a number of other things I'd want to expunge from
my brain, but for the fact that my nature doesn't include a large proportion
of vengeance. Sure, I've had a few asshole bosses and colleagues over
the years that gave me some grief, but I can't say that I harbor any ill-will
towards them. Perhaps that's because they ultimately self-destructed, in
the fullness of time -- and I watched it happen, while I myself survived.
At any rate, they don't plague my ongoing thoughts, nor my dreams.
I could wish to expunge the burned-in images of Nazi atrocities, or the
killing fields of Pol Pot, or the starvation occurring in Africa due to
current political unrest. To what end? These images will repeat
forever, given mankind's propensity for mayhem. There is no keeping up
with them. Call me callous, but I don't internalize them to the point
that I lose any sleep over it.
I have no images of child abuse that I can throw in the burning barrel, nor
any memories of such a powerful negative nature that I would want them gone
forever. I barely even remember my childhood, and so I would not
want to lose any significant part of it -- other than that Sparks guy!
"How happy is the blameless vestal's lot! The world
forgetting, by the world forgot. Eternal sunshine of the spotless mind!
Each pray'r accepted, and each wish resign'd." -- Alexander Pope
Much of this material extracted from:
Back to Essays...