Uncovering the brain's biggest secret - Melanie E. Peffer
In the late 1860s, scientists believed
they were on the verge
of uncovering the brain’s biggest secret.
They already knew the brain controlled
the body through electrical impulses.
The question was, how did these signals
travel through the body
without changing or degrading?
It seemed that perfectly transmitting
these impulses
would require them to travel uninterrupted
along some kind of tissue.
This idea, called reticular theory,
imagined the nervous system
as a massive web of tissue
that physically connected
every nerve cell in the body.
Reticular theory captivated the field
with its elegant simplicity.
But soon, a young artist would cut through
this conjecture,
and sketch a bold new vision
of how our brains work.
60 years before reticular theory was born,
developments in microscope technology
revealed cells to be the building blocks
of organic tissue.
This finding was revolutionary,
but early microscopes struggled
to provide additional details.
The technology was especially challenging
for researchers studying the brain.
Soft nervous tissue was
delicate and difficult to work with.
And even when researchers were able
to get it under the microscope,
the tissue was so densely packed
it was impossible to see much.
To improve their view,
scientists began experimenting
with special staining techniques
designed to provide clarity
through contrast.
The most effective came courtesy
of Camillo Golgi in 1873.
First, Golgi hardened the brain tissue
with potassium bichromate
to prevent cells from deforming
during handling.
Then he doused the tissue
in silver nitrate,
which visibly accumulated in nerve cells.
Known as the “black reaction,”
Golgi’s Method finally allowed researchers
to see the entire cell body
of what would later be named the neuron.
The stain even highlighted
the fibrous branches
that shot off from the cell
in different directions.
Images of these branches
became hazy at the ends,
making it difficult to determine exactly
how they fit into the larger network.
But Golgi concluded that these
branches connected,
forming a web of tissue comprising
the entire nervous system.
14 years later, a young scientist
and aspiring artist
named Santiago Ramón y Cajal
began to build on Golgi’s work.
While writing a book
about microscopic imaging,
he came across a picture of a cell
treated with Golgi’s stain.
Cajal was in awe of its exquisite detail—
both as a scientist and an artist.
He soon set out to improve
Golgi’s stain even further
and create more detailed references
for his artwork.
By staining the tissue twice
in a specific time frame,
Cajal found he could stain a greater
number of neurons with better resolution.
And what these new slides revealed
would upend reticular theory—
the branches reaching out
from each nerve cell
were not physically connected
to any other tissue.
So how were these individual cells
transmitting electrical signals?
By studying and sketching
them countless times,
Cajal developed a bold, new hypothesis.
Instead of electrical signals traveling
uninterrupted across a network of fibers,
he proposed that signals were somehow
jumping from cell to cell
in a linear chain of activation.
The idea that electrical signals could
travel this way was completely unheard of
when Cajal proposed it in 1889.
However his massive collection of drawings
supported his hypothesis from every angle.
And in the mid-1900s, electron microscopy
further supported this idea
by revealing a membrane
around each nerve cell
keeping it separate from its neighbors.
This formed the basis
of the “neuron doctrine,”
which proposed the brain’s tissue
was made up of many discrete cells,
instead of one connected tissue.
The neuron doctrine laid the foundation
for modern neuroscience,
and allowed later researchers to discover
that electrical impulses
are constantly converted between
chemical and electrical signals
as they travel from neuron to neuron.
Both Golgi and Cajal received
the Nobel Prize
for their separate,
but shared discoveries,
and researchers still apply
their theories and methods today.
In this way, their legacies remain
connected as discrete elements
in a vast network of knowledge.
