ChargeCurrent FluxVoltageCAPACITORRESISTORINDUCTORMEMRISTOR48 DISCOVERMAGAZINE.COM
ALISON MACKEY/DISCOVERindividual subunits. If they operated in a purely classical
fashion, as insulators — like wood, glass and other com-
mon materials that stop electrical current from flowing
freely — the amount of resistance across the microtubule
should increase. But Bandyopadhyay found something
very different when he applied specific charges of alter-
nating current. Resistance levels jumped by a factor of
1 billion. The microtubule was acting something like a
semiconductor, one of the most important developments
in electronics. He stood there in wonder at his own results.
“When you get results like this,” he says, “you are
scared. Am I wrong somehow?”
But he checked, even having colleagues outside
his lab at NIMS look over his results. In subsequent
experiments, he saw that this conducting activity in the
microtubule preceded neuronal, or membrane-level, fir-
ing. His microtubules research appeared in the journal
Biosensors and Bioelectronics. And he has another study
still under peer review.
The findings still need to be replicated by other scien-
tists. But those touting Bandyopadhyay’s findings are
philosophical about his standing.
“If you’re looking for frontier science, you have to drive
out to the edge of what’s known,” says David Sonntag, a
toxicologist who formerly worked in Tokyo for the U.S.
Air Force’s research and development wing and helped
fund some of Bandyopadhyay’s research.
“If you take a wrong turn,” he says, “you’ll run into
its crazy next-door neighbor, fringe science. The issue is
understanding when you’re at the bifurcation point. When
does the fringe become the frontier?”
For now, Bandyopadhyay remains clearly on the fringe.
But he has brought something new to the debate: an
experiment that can be replicated, or not, and a different
perspective on Hameroff.
He is careful to distance himself from Hameroff ’s
larger theory of consciousness. “This is not my concern,”
he says. Still, he describes Hameroff as a father to his ownresearch. “This man was talking about
microtubules back in 1982,” he says. “Just
thinking about them, unable to study them
as I have, he knew, and so far ahead of
everyone else. I wondered, ‘What kind of
brain has he got?’ ”A CIRCUIT’S MISSING ELEMENT
There is also another far more experi-
enced scientist working the same vein
of research and seeing dramatic results
regarding the microtubule.
Jack Tuszynski, a biophysicist at the
University of Alberta, is a longtime
Hameroff collaborator who creates
cancer drugs. His latest findings suggest
microtubules have interesting conductive
properties, but indicate they could also
be what are called “memristors.” The
memristor is the much sought-after fourth
element in an electrical circuit, first theo-
rized by Leon Chua, an electrical engineer
at the University of California, Berkeley.
Chua spotted something obvious. The
three existing circuit elements — resistor,
capacitor and inductor — depend on
relationships between pairs that control
how electricity flows, how it gets stored
and how it changes as it moves through
a circuit:- resistor (voltage + current)
- capacitor (voltage + charge)
- inductor (magnetic flux + current)
By studying the pairs, Chua theorized
there should be a fourth circuit element
governing the relationship between the
“missing” pair — charge and flux. Chua
coined the term memristor, playing off
the words memory and resistor, and from
there his work was strictly mathematical.
If such a circuit element existed, what
would it do? Chua’s equations suggested
that a memristor’s electrical resistance,
or conductivity, would not be constant,
like a lightbulb’s, but dynamic, and deter-
mined by the history of the current that
had flowed through the device.
What’s the big deal? In transistors,
any interruption in the flow of electrons
results in data loss. Memristors, however,
incorporate both electron flow and ions
— electrically charged atoms.
Because they remember the charge that
previously passed through the material,
information could be retained even when
turned off. In computers, the innovation
means no more rebooting. Computers
would turn on like lightbulbs, and hard
Memristor
Electrical circuits use four
fundamental variables —
current, voltage, charge
and magnetic flux-linkage.
Relationships between these
variables led to the classic
components of a circuit —
resistor, capacitor, inductor
— with the exception of one
pairing: charge + flux. The
memristor fills this hole, creating
a fourth circuit element that
would operate like a resistor
with memory.