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SONGDO HIGH SCHOOL · READING MATERIALS

The Art of Manipulating Neural Circuits

By Cheon Ki-beom

There are about 100 billion nerve cells in the
human brain. Each neuron is linked to a number
of other neurons and generates more than 100
trillion neurological connections. Our sensory ex-
perience is an ‘electrical event’ that occurs in this
enormous neural circuits. In the neural circuits in
our brain, electricity flows constantly and creates
a sensory world. The technique of manipulating
neural circuits was discovered a long time ago,
and continues to be developed. At first, Luigi Gal-
vani found that the nerves and muscles respond
to electrical stimulation in the middle of the 18th
century. Since the early 19th century, neurophysi-
ologists have started research on brain functions
by inserting electrodes into the brain and flowing
micro electric currents.

But it is difficult to manipulate delicately the neu-
ral circuits of the brain by this way. It is because
there are microscopic nerve cells at an incredibly
high density in the human brain. It is technically
difficult to stimulate only the desired neural circuit
because it contains tens of millions of neurons in the 1㎤ brain. If the electrode is inserted incorrectly, it can stimulate the wrong
neural circuit and cause unexpected reaction. Surprisingly, it was not the neuroscience research team, but the microbiology re-
search team that solved the problem. They focused on a green algae which have a phototaxis that makes creatures move toward the
light if they are lit up. The researchers guessed that there would be something in the green algae that mediates between ‘sensing’
the light and ‘acting’ toward it. The researchers found that a molecule called ‘Channelrhodopsin’ senses light and generates electric
current through various experiments. Then neuroscientists tried to plant the gene of Channelrhodopsin in the green algae into
nerve cells. Finally, in 2005, a research team from the United States primally announced the first result of controlling neural circuits
by using light and Channelrhodopsin in mammalian neurons. This technology, which combines light and channelrhodopsin genes,
is called ‘optogenetics’.

Scientists are now manipulating neurons and behaviors in alive animals as well as nerv-
ous tissues. Even recently, research in mice to create fake memories by using optoge-
netics has been published. Based on these experimental results, the idea of treating
various mental diseases such as anorexia, Parkinson’s disease, and depression by us-
ing optogenetics is actively proposed and studied. If we unearth the human neural
circuits in the future, manipulation of the neural circuits will greatly contribute to the
welfare of humanity. Although there is still a long way, there is an enough possibility.
In the near future, the world will not suffer from mental diseases through the tech-
nique of manipulating neural circuits.

November 2018 No.10 21