58 THE SCIENTIST | the-scientist.com
F
or centuries, scientists have been
arguing about where memory
resides in the brain. I explore the
fascinating history of this quest to char-
acterize the machinery of memory in my
latest book, The Idea of the Brain.
Our modern understanding of the
nature of memory can be traced back to the
1940s. The Canadian psychologist Donald
Hebb argued that “memory must be struc-
tural,” and based on networks of cells. These
networks, Hebb claimed, became better con-
nected with repeated experience—the pre-
sentation of food after the sound of a bell, for
example. This idea is often summarized as
“cells that fire together wire together.”
At around the same time, McGill
University neurosurgeon Wilder Penfield
showed that it was possible to evoke very
precise, eerie memories by stimulating a
particular part of the human brain. Often
Penfield’s patients heard sounds—a piano
being played, someone singing a well-known
song, or a telephone conversation between
two family members. Memory, or at least
access to it, was clearly highly localized.
Another profound discovery was made
by Penfield’s colleague Brenda Milner. In
1953, a young man called Henry Molaison
underwent extensive psychosurgery to
relieve his debilitating epilepsy. As a result
of the operation, Molaison was unable to
form any new memories. He lived in a
perpetual present, with no knowledge of
anything that had happened after that
fateful surgery. Milner and her colleagues
suggested that the decisive damage had
been done to Henry’s hippocampuses, two
structures, one on either side of the base
of the brain.
But the hippocampuses are not the
site of memory storage. Rather, these
brain regions are the encoders and the
routes through which memory formationseems to pass. The memories that are
processed by the hippocampuses seem to
be distributed across distant regions of
the brain. As for how those complex net-
works of cells change their activity during
learning, this was shown in large part
through the work of a brilliant young
physician who was inspired in 1957 to
study memory by reading Brenda Mil-
ner’s first paper on Molaison.
This physician, Columbia University
neuroscientist Eric Kandel, investigated
the nature of memory in a simpler form—
in the neurons of a large sea slug known
as Aplysia. By studying changes in the
electrical and chemical activity of nerve
cells in this mollusc, Kandel was able to
provide support for Hebb’s suggestion
that the links between neurons, known as
synapses, become stronger with learning.
Once researchers tapped into the power
of molecular genetics in the late 1980s,
Kandel and his colleagues were able to
reveal the genes and chemicals involved
in learning, and to show that the same
processes that underlie learning in the
sea slug are also taking place, right now,
in your head.
Although the mechanisms underlying
memory have given up a few of their most
basic secrets, we are still far from under-
standing what is happening when we
learn and remember. Despite Penfield’s
unnerving findings, we do not appear to
be perpetually recording our whole lives,
and the link between normal memory
retrieval and experimentally-triggered
recall remains unclear.
The search for memory’s seat in the
human brain seems even more complex
today. Researchers now know that mem-
ories may not be found in a single place,
but precise cells and structures play a
key role in memory formation and recall.Memories are often multimodal, involv-
ing place, time, smell, light, and so on,
and they are distributed across the cortex
through intricate neural networks. Our
brains might be like computers in terms
of how they sometimes process informa-
tion, but the way we store and recall our
memories is completely different. We
are not machines, nor are we like any
machine we can currently envisage. gMatthew Cobb is a professor in the
School of Biological Sciences at the
University of Manchester in the UK,
where he studies olfaction, insect
behavior, and the history of science.
Read an excerpt of The Idea of
the Brain: The Past and Future of
Neuroscience at the-scientist.com.
Follow him on Twitter @matthewcobb.Basic Books, April 2020READING FRAMESA new book explores how research through the ages has tried to map the
intricacies of the human brain, including pinpointing the seat of memory.BY MATTHEW COBBFrom Whence Memories?