July 2019, ScientificAmerican.com 29strongly active at the same time, it would be as if all the orches-
tra members were playing as loudly as possible—and that sce-
nario would create chaos, not enable communication. The deaf-
ening sound would not convey the emotional overtones present
in a great musical piece. It is the pitch, rhythms, tempo and
strategic pauses that communicate information, both during a
symphony and inside your head.MODULARITY
Just as an orchestra can be divided into groups of instruments
from different families, the brain can be separated into collec-
tions of nodes called modules—a description of localized net-
works. All brains are modular. Even the 302-neuron network of
the nematode Caenorhabditis elegans has a modular structure.
Nodes within a module share stronger connections to one anoth-
er than to nodes in other modules.
Each module in the brain has a certain function, just as
every family of instruments plays a role in the symphony. We
recently performed an evaluation of a large number of indepen-
dent studies—a meta-analysis—that included more than 10,000
functional magnetic resonance imaging (fMRI) experiments of
subjects performing 83 different cognitive tasks and discovered
that separate tasks map to different brain-network modules.
There are modules occupied with attention, memory and intro-
spective thought. Other modules, we found, are dedicated to
hearing, motor movement and vision.
These sensory and motor cognitive processes involve single,
contiguous modules, most of which are confined to one lobe of
the brain. We also found that computations in modules do not
spur more activity in other modules—a critical aspect of modu-
lar processing. Imagine a scenario in which every musician in
an orchestra had to change the notes played every time another
musician changed his or her notes. The orchestra would spiral
out of control and would certainly not produce aesthetically
pleasing sounds. Processing in the brain is similar—each mod-
ule must be able to function mostly independently. Philoso-
phers as early as Plato and as recent as Jerry Fodor have noted
this necessity, and our research confirms it.
Even though brain modules are largely independent, a sym-
phony requires that families of instruments be played in unison.
Information generated by one module must eventually be inte-
grated with other modules. Watching a movie with only a brain
module for vision—without access to the one for emotions—
would detract greatly from the experience.
For that reason, to complete many cognitive tasks, modules
must often work together. A short-term memory task—holding
a new phone number in your head—requires the cooperation of
auditory, attention and memory-processing modules. To inte-
grate and control the activity of multiple modules, the brain
uses hubs—nodes where connections from the brain’s different
modules meet.
Some key modules that control and integrate brain activity
are less circumspect than others in their doings. Their connec-
tions extend globally to multiple brain lobes. The frontoparietal
control module spans the frontal, parietal and temporal lobes.
It developed relatively recently on the timescale of evolution.
The module is especially large in humans, relative to our closest
primate ancestors. It is analogous to an orchestra conductor
and becomes active across a large number of cognitive tasks.
The frontoparietal module ensures that the brain’s multiple
modules function in unison. It is heavily involved in what is
called executive function, which encompasses the separate pro-
cesses of decision-making, short-term memory and cognitive
control. The last is the ability to develop complex strategies and
inhibit inappropriate behavior.
Another highly interconnected module is the salience module,
which hooks up to the frontoparietal control module and contrib-
utes to a range of behaviors related to attention and responding to
novel stimuli. For example, take a look at two words: blue and red.
If you are asked to respond with the color of the word, you will
react much faster to the one set in red. The frontoparietal and
salience modules activate when responding to the color green
because you have to suppress a natural inclination to read the
word as “blue.”
Finally, the default mode module spans the same lobes as the
frontoparietal control network. It contains many hubs and is
linked to a variety of cognitive tasks, including introspective
thought, learning, memory retrieval, emotional processing,
inference of the mental state of others and even gambling. Criti-
cally, damage to these hub-rich modules disturbs functional
connections throughout the brain and causes widespread cogni-
tive difficulties, just as bad weather at a hub airport delays air
traffic all over the country.PERSONAL CONNECTIONS
although our brains have certain basic network components—
modules interconnected by hubs—each of us shows slight varia-
tions in the way our neural circuits are wired. Researchers have
recently devoted intense scrutiny to this diversity. In an initial
phase of what is called the Human Connectome Project, 1,200
young people have volunteered to participate in a study of brain-
network architecture, funded by the National Institutes of Health.
(The final goal of the project is to cover the entire life span.) Each
individual’s structural and functional connectivity networks were
probed using fMRI. These data were supplemented by a cognitive
battery of testing and questionnaires to analyze 280 behavioral
and cognitive traits. Participants provided information about how
well they slept, how often they drank alcohol, their language and
memory abilities, and their emotional states. Neuroscientists
from all over the world have begun to pore over this incredibly
rich data set to learn how our brain networks encode who we are.
Using data from hundreds of participants in the Human Con-
nectome Project, our lab and others have demonstrated that
brain-connectivity patterns establish a “fingerprint” that distin-
guishes each individual. People with strong functional connec-
tions among certain regions have an extensive vocabulary and
exhibit higher fluid intelligence—helpful for solving novel prob-
lems—and are able to delay gratification. They tend to have more
education and life satisfaction and better memory and attention.
Others with weaker functional connections among those same
brain areas have lower fluid intelligence, histories of substance
abuse, poor sleep and a decreased capacity for concentration.
Inspired by this research, we showed that the findings could be
described by particular patterns among the hub connections. If
your brain network has strong hubs with many connections across
modules, it tends to have modules that are clearly segregated from
one another, and you will perform better on a range of tasks, from
short-term memory to mathematics, language or social cognition.