Neurociencia: The Study of the
Nervous System & Its Functions
Fred H. Gage
Any man could, if he were so inclined,
be the sculptor of his own brain.
–Santiago Ramón y Cajal,
Advice for a Young Investigator (1897)
Neuroscience is the scienti½c study of the nervous
sistema (the brain, spinal cord, and peripheral nerv-
ous system) and its functions. The belief that the
brain is the organ that controls behavior has an –
cient roots, dating to early civilizations that con-
nected loss of function to damage to parts of the
brain and spinal cord. But the modern era of neuro-
science began–and continues to progress–with the
development of tools, técnicas, and methods used
to measure in ever more detail and complexity the
structure and function of the nervous system. El
modern era of neuroscience can be traced to the
1890s, when the Spanish pathologist Santiago
Ramón y Cajal used a method developed by the
Italian physician Camillo Golgi to stain nerve tis-
sues to visualize the morphology and structure of
the neurons and their connections. The detailed de –
scription of the neurons and their connections by
Cajal, his students, and their followers led to the
“neuron doctrine,” which proposed that the neuron
is the functional unit of the nervous system.
We now know that the human brain contains ap –
proximately one hundred billion neurons and that
these neurons have some one hundred trillion con-
nections, forming functional and de½nable circuits.
These neural circuits can be organized into larger
© 2015 por la Academia Americana de las Artes & Ciencias
doi:10.1162/DAED_e_00313
FRED H. GAGE, a Fellow of the
Amer ican Academy since 2005, es
Professor in the Laboratory of Ge –
netics and the Vi and John Adler
Chair for Research on Age-Related
Neurodegenerative Disease at the
Salk Institute for Biological Stud-
es. He studies the unanticipated
plas ticity and complexity repre-
sented in the brain.
yo
D
oh
w
norte
oh
a
d
mi
d
F
r
oh
metro
h
t
t
pag
:
/
/
d
i
r
mi
C
t
.
metro
i
t
.
/
mi
d
tu
d
a
mi
d
a
r
t
i
C
mi
–
pag
d
/
yo
F
/
/
/
/
/
1
4
4
1
5
1
8
3
0
5
7
4
d
a
mi
d
_
mi
_
0
0
3
1
3
pag
d
.
F
b
y
gramo
tu
mi
s
t
t
oh
norte
0
8
S
mi
pag
mi
metro
b
mi
r
2
0
2
3
5
The Study
del
Nervous
Sistema
& Its
Functions
networks and anatomical structures that
integrate information across and between
all sensory modalities–including hearing,
seeing, touching, tasting, and smelling–
from all parts of the nervous system. Estos
networks process information derived
from the internal and external environ-
mento, and the consequence of processing
this sensory information is cognition, a con –
cept that includes learning and memory,
percepción, sleep, Toma de decisiones, emo-
ciones, and all forms of higher information
Procesando. In response to a simple or com –
plex sensory experience, an organism re –
sponds or behaves. The behavior can be
sim ple, like a motor reflex in response to
pain, or more complicated, like playing
squash, working a crossword puzzle, o
paint ing. Sin embargo, behavior is not just
what an organism does in response to a
stimulus or sensory input; it is most often
what an organism chooses to do from a va –
riety of available options in response to a
complex set of environmental conditions.
De este modo, except for rare responses, like simple
reflexes, a behavior is expressed in re –
sponse to a combination of the immediate
sensory stimuli integrated over time with
cognition.
Neuroscientists conduct experiments to
understand how sensory information is
processed to lead to behavior. Because of
the obvious complexity of the brain, neuro –
scientists conduct their studies at differ-
ent levels of depth. While neurons are con-
ceivably the smallest units in which be –
havior can be clearly described, the neu-
ron is itself made up of unique anatomi-
cal features, including a soma (cell body),
dendrites (the antennae branching from the
soma that receive signals from other neu –
ron), and axons (the processes extending
from the soma that send signals to other
neuronas).
These neuronal components in turn con –
tain subcellular specializations that rep-
resent the de½ning features of the neu-
ron. Key among these specializations is the
synapse: a structure shared by the dendrite
and the axon that represents the junction
point for the principal form of communi-
cation between two neurons. On the den-
dritic side of the synapse is a structure
called a spine, which responds to signals
from the axon. On the axonal side is the
bouton, which has vesicles containing neu –
ro transmitters–the signals to which the
spine responds. Each neuron can have mul –
tiple dendrites and thousands of spines
con nected to comparable numbers of bou –
tons, which together form the thousands
of synapses that make up the units of com –
munication between individual neurons.
In the soma, specialized proteins and
mi crostructures form the basis for the in –
tracellular communications and physio-
logical features of neurons; Por ejemplo,
specialized enzymes produce the neuro-
transmitters and vesicles that are used in
the bouton to signal the spine. Más-
más, specialized cytoskeletal proteins
form long and active extensions that allow
the dendrites and axons to act as a supply
train for the vesicles and neurotransmit-
ters that are made in the soma and trans-
ported to the boutons. Among the most
important proteins in the neuron are those
that form the ion channels. These are
multi-protein structures that span the neu –
ron’s membrane and allow neurons to
form electrochemical gradients, cuales son
the driving forces of activity in neurons.
These proteins–which are crucial for
the functioning of a neuron–are all the
products of genes that are the functional
unit of the genome, which is located in
the nucleus of the neuron. Each neuron’s
genome contains about twenty thousand
genes, but different genes are expressed in
different types of neurons, and it is this
unique expression pattern of genes in any
particular neuron that provides its unique
identity.
6
Dédalo, la Revista de la Academia Estadounidense de las Artes & Ciencias
yo
D
oh
w
norte
oh
a
d
mi
d
F
r
oh
metro
h
t
t
pag
:
/
/
d
i
r
mi
C
t
.
metro
i
t
.
/
mi
d
tu
d
a
mi
d
a
r
t
i
C
mi
–
pag
d
/
yo
F
/
/
/
/
/
1
4
4
1
5
1
8
3
0
5
7
4
d
a
mi
d
_
mi
_
0
0
3
1
3
pag
d
.
F
b
y
gramo
tu
mi
s
t
t
oh
norte
0
8
S
mi
pag
mi
metro
b
mi
r
2
0
2
3
Even from this brief survey of the dif-
ferent levels of brain connectivity it is clear
that it would be impossible to study the
total functioning of the brain–from be –
havior to gene expression–in one exper-
mento. So neuroscientists instead generally
choose some limited number of brain-
activity levels to probe as they address their
own speci½c questions. The many meth-
ods used to study the nervous system dif-
fer depending on the level of analysis, pero
they fall generally into one of two catego –
ries: descriptive, for generating hypotheses,
or manipulative, for testing hypotheses.
One type of descriptive study is a case
estudiar, in which an experimenter observes
the behavior of a person or group of peo-
ple before, durante, or after an event that
may demonstrate a role for the nervous
sistema. The circumstances surrounding
the event are usually non-repeatable and
cannot be precisely reconstructed in a
laboratory setting. One could argue that
these are not true experiments, but these
studies have revealed substantial informa –
tion about aspects of neural function that
was previously unknown. One remark-
able example is the case of H.M., a pa –
tient whose epilepsy was treated through
removal of a portion of his brain called
the hippocampus and parts of the tempo-
ral lobe on both sides of his brain. As a
result of the surgery, which did success-
fully control his epilepsy, he displayed a
unique form of memory loss, and his be –
havior was examined over a period of forty
years from the time of his operation until
he died, revealing through careful docu-
mentation and experimentation some of
the most important concepts about human
learning and memory. Another impor-
tant case study is that of Phineas Gage, a
railroad worker involved in an accident
en 1848 that resulted in an iron rod pass-
ing through his skull. The rod entered the
left side of his head, passing just behind
his left eye, exiting through the top of his
head and completely transecting his fron –
tal lobes. He lived for twelve years follow-
ing the accident and his behavior was re –
corded in some detail, informing scien-
tists about the unique function of the
front al lobes and their important role in
personality and decision-making. The in –
sights from such case studies have often
generated hypotheses to be tested in sub-
sequent manipulative experiments.
Descriptive studies can also consist of
the straightforward act of observing prop –
erties of the nervous system without ma –
nip ulations. This type of research is usually
the ½rst crucial step in acquiring knowl-
edge about a newly discovered gene, pro-
tein, neural subtype, or connection be –
tween neurons. Examples can be high-
lighted at every level of analysis. A novel
gene can be sequenced and its expression
pattern in the brain can be mapped, or the
peptide sequence of a protein can be de –
scribed and its distribution in the nervous
system can be shown in great detail. In ad –
condición, a speci½c neuron can be described
in terms of the genes and proteins it ex –
presses, as well as its unique morphologi-
cal characteristics and electrophysiological
propiedades. On a broader scale, the connec-
tions between groups of neurons can be
elucidated, describing both their input to
their respective dendrites and spines and
also their outputs, by way of the axons and
boutons. Once the anatomical properties
of a network are described, the electro-
chemical properties of their connections
and network can be revealed.
These descriptive studies are excellent
for generating hypotheses about the func –
tion of the brain at all levels of analysis.
Once there is enough basic information
to generate a coherent hypothesis about
the function of some level of the brain–
Por ejemplo, an anatomical pathway in
the brain that is responsible for our ability
to recognize a face–we then want to test
if the pathway is required for facial recog-
Fred H.
Gage
yo
D
oh
w
norte
oh
a
d
mi
d
F
r
oh
metro
h
t
t
pag
:
/
/
d
i
r
mi
C
t
.
metro
i
t
.
/
mi
d
tu
d
a
mi
d
a
r
t
i
C
mi
–
pag
d
/
yo
F
/
/
/
/
/
1
4
4
1
5
1
8
3
0
5
7
4
d
a
mi
d
_
mi
_
0
0
3
1
3
pag
d
.
F
b
y
gramo
tu
mi
s
t
t
oh
norte
0
8
S
mi
pag
mi
metro
b
mi
r
2
0
2
3
144 (1) Invierno 2015
7
The Study
del
Nervous
Sistema
& Its
Functions
nition. In all areas of biological sciences
and at all levels of analysis, testing a hy –
pothesis is achieved through gain- and loss-
of-function experiments. In a loss-of-func-
tion experiment, the experimenter silenc –
es, bloques, disrupts, or turns off speci½c
components of a proposed pathway in an
attempt to determine the required ele-
ments for appropriate function. En algunos
casos, the loss-of-function technique may
not be precise, so to further track down the
requirement for a component in the func-
tional path, a gain-of-function exper iment
can be conducted to replace each of the
com ponents of the pathway that were dis –
rupted in the loss-of-function experiment.
Loss-of-function experiments can be con-
ducted at all levels of function: to test the
importance of speci½c genes in cells with in
the inner ear for speci½c components of
hearing; to test the roles of speci½c re –
gions of the temporal lobe in learning; o
even to test the importance of sleep in the
consolidation of memory.
This volume of Dædalus dedicated to the
brain and nervous system cannot cover all
aspects of this very deep and broad ½eld
of study; but we are fortunate to have
recruited an outstanding group of active
scientists to help us examine select subdi-
visions in the ½eld of neuroscience. Estos
authors and scientists are not only major
contributors to their particular areas of fo –
cus, but are experienced communicators
with track records of explaining and trans-
lating complex concepts to intelligent
readers and listeners outside of their dis-
cipline.
Robert Wurtz, in “Brain Mechanisms for
Active Vision,” presents a clear and lucid
essay on the remarkable mechanisms be –
hind our ability to see the world around
a nosotros. In “Perceiving,” Thomas Albright re –
veals how we change the sensory experi-
ence of vision into a cognitive perception
and how this is regulated by other events
in the environment. A. j. Hudspeth’s es –
decir, “The Energetic Ear,” explains the dy –
namic inner workings of the ear and how
sound waves are translated in the brain to
allow us to hear. Larry Squire and John
Wixted offer a primer on memory enti-
tled “Remembering,” based on both crit-
ical case studies and the experimental stud –
ies that have led to our current under-
de pie. And in their essay “Sleep, Mem –
ory & Brain Rhythms,” Brendon Watson
and György Buzsáki provide a coherent
and provocative study of the importance
of sleep in our memory and how the rhyth –
mic activity in the circuits of the brain may
control the relationship between sleep and
memory.
Emilio Bizzi and Robert Ajemian have
contributed the essay “A Hard Scienti½c
Quest: Understanding Voluntary Move-
mentos,” which explains both the basics of
how we move through our environment
and how movement is regulated by sen-
sory experience. “Feelings: What Are They
& How Does the Brain Make Them?”–
Joseph LeDoux’s addition to the volume
–describes the fundamentals of emotional
behaviors both from the behavioral per-
spective and from the neurobiological ba –
sis of emotions. Earl Miller and Timothy
Buschman, in their essay “Working Mem –
ory Capacity: Limits on the Bandwidth of
Cognición,” discuss cognitive capacity,
with a special focus on processing limita-
tions rooted in oscillatory brain rhythms
(“brain waves”). Finalmente, in his essay “Con –
sciousness,” Terry Sejnowski tackles the
slippery concept of consciousness and
helps us understand the difference between
being aware and being consciously aware.
Although this volume cannot extend to
all sensory and motor systems and their
in tegration, we are hopeful that this sam-
pling of neuroscience will encourage you
to read more on these exciting topics, y
we hope we will be able to return to Dæ –
dalus with additional volumes on neuro-
8
Dédalo, la Revista de la Academia Estadounidense de las Artes & Ciencias
yo
D
oh
w
norte
oh
a
d
mi
d
F
r
oh
metro
h
t
t
pag
:
/
/
d
i
r
mi
C
t
.
metro
i
t
.
/
mi
d
tu
d
a
mi
d
a
r
t
i
C
mi
–
pag
d
/
yo
F
/
/
/
/
/
1
4
4
1
5
1
8
3
0
5
7
4
d
a
mi
d
_
mi
_
0
0
3
1
3
pag
d
.
F
b
y
gramo
tu
mi
s
t
t
oh
norte
0
8
S
mi
pag
mi
metro
b
mi
r
2
0
2
3
ciencia. More speci½c, we have not here
considered what happens when the brain
is damaged or aged, or when genetic er –
rors occur. A volume on “The Brain and
its Disorders” is currently in the planning
stages at the American Academy; in the
mean time, we hope this collection pro-
vides a foundation for you to learn about
the brain and whets your appetite for more.
Fred H.
Gage
yo
D
oh
w
norte
oh
a
d
mi
d
F
r
oh
metro
h
t
t
pag
:
/
/
d
i
r
mi
C
t
.
metro
i
t
.
/
mi
d
tu
d
a
mi
d
a
r
t
i
C
mi
–
pag
d
/
yo
F
/
/
/
/
/
1
4
4
1
5
1
8
3
0
5
7
4
d
a
mi
d
_
mi
_
0
0
3
1
3
pag
d
.
F
b
y
gramo
tu
mi
s
t
t
oh
norte
0
8
S
mi
pag
mi
metro
b
mi
r
2
0
2
3
144 (1) Invierno 2015