mized for richness; in the other, for
speed and reliability.
In the brain, this same type of
balance is usually thought to be
an effect of the division of labor.
Certain regions—for example, the
cingulate cortex—are involved in
processing higher-level emotional
and motivational information. Other
regions, like the amygdala, work to
keep you safe from more immediate
dangers. In other words, one helps
you at the dinner party and the
other at the sea. These specialized
functions have often been attributed
to anatomy: one region might have
greater or fewer neurons than the
other, and those neurons might wire
into different circuits. In either case,
it has been assumed, the neurons
present are using neural codes with
the same basic design.
Neurons can either fire or remain
silent, and the combination of the two
over time gives rise to a neural code,
like dots and dashes in Morse code.
As with Morse code, there are
theoretical limits on the richness and
speed of information transfer. A new
Morse code with 1,000 characters
could exchange richer information, but
the speed and reliability of its SOS
signal would suffer. Neural codes
accommodate this trade-off in their
design, and it has been presumed that
from neuron to neuron and region to
region the balance between richness
and speed is the same.
But a closer look at what exactly
the neurons in the human cingulate
cortex and amygdala are saying has
revealed that they employ strikingly
different neural codes. One is op -
timized for richness and one for
speed—just such a trade-off as might
be expected given the function of
these brain regions. Moreover, a
comparison of human and monkey
brains has revealed that in both of
the studied brain regions, the code
used by human neurons is more rich.
In effect, different regions—and the
brains of different animals—use
different neural codes.
These discoveries, published
earlier this year in Cell, have
wide-ranging and potentially stun-
ning implications. The function of a
neural circuit—whether it underliesecholocation, feeding, or any other
behavior—is often understood by its
wiring diagrams. As with an electrical
diagram, many pieces are considered
to be interchangeable—a resistor is a
resistor, and a switch is a switch.
Thus, a circuit diagram made up of
mouse, monkey or human neurons
might be expected to perform the
same computation. These new
findings challenge that idea, showing
that even the basic building blocks in
two regions of the same brain can
behave very differently.
It is as though some regions of the
brain employ an English vocabulary;
others employ that of Newspeak.
Given the interregion and interspe-
cies nature of this study, its results
will require plenty of additional
corroboration and support before
they can be fully adopted and
generalized. But at a minimum, the
authors have shown the following: in
both humans and rhesus monkeys,
neurons in the cingulate cortexemploy a richer neural code than
neurons in the amygdala. Not only is
the code simpler in the amygdala,
but multiple amygdala neurons were
often observed to use the same code
in concert. As in the example of the
shark at the beach, this is thought to
aid in the robust and rapid transmis-
sion of information about immediate
threats. Finally, neural codes are
more rich in human brains than in
macaque brains, regardless of the
region. In total, these findings
suggest that there is a trade-off
between regions and species in the
neural code. This trade-off likely
helps to shape the cognitive or
computational capacities of different
brains and different brain regions.
More broadly, this study highlights
a number of routes for additional
work. For starters, whereas many
diseases and disorders of the brain
have obvious physical manifestations
that can be detected with an x-ray or
an MRI, some do not. Changes toNEWS
Neurons can either fire or remain silent, and the
combination of the two over time gives rise to a neural code,
like dots and dashes in Morse code.