A Glossary of Key Brain Science Terms
GLOSSARY
A
adrenal glands: Located on top of each kidney, these two
glands are involved in the body’s response
to stress and help regulate growth, blood glucose levels,
and the body’s metabolic rate. They receive
signals from the brain and secrete several different
hormones in response, including cortisol and adrenaline.
adrenaline: Also called epinephrine, this hormone is
secreted by the adrenal glands in response to
stress and other challenges to the body. The release of
adrenaline causes a number of changes
throughout the body, including the metabolism of
carbohydrates to supply the body’s energy demands.
allele: One of the variant forms of a gene at a particular
location on a chromosome. Differing alleles
produce variation in inherited characteristics such as hair
color or blood type. A dominant allele is one
whose physiological function—such as making hair blonde—is
manifest even when only a single copy is
present (among the two copies of each gene that everyone inherits
from their parents). A recessive allele
is one that manifests only when two copies are present.
amino acid: A type of small organic molecule. Amino acids
have a variety of biological roles, but are
best known as the “building blocks” of proteins.
amino acid neurotransmitters: The most prevalent
neurotransmitters in the brain, these include glutamate
and aspartate, which have excitatory actions, and glycine
and gamma-amino butyric acid (GABA),
which have inhibitory actions.
amygdala: Part of the brain’s limbic system, this primitive
brain structure lies deep in the center of the
brain and is involved in emotional reactions, such as anger,
as well as emotionally charged memories. It
also influences behavior such as feeding, sexual interest,
and the immediate “fight or flight” stress reaction
that helps ensure that the body’s needs are met.
amyloid-beta (Aβ) protein: A naturally occurring protein in
brain cells. Large, abnormal clumps of this
protein form the amyloid plaques that are the hallmark of
Alzheimer’s disease. Smaller groupings (oligomers)
of Aβ seem more toxic to brain cells and are now thought by
many researchers to be important
initiators of the Alzheimer’s disease process.
amyloid plaque: The sticky, abnormal accumulations of
amyloid-beta protein aggregate around neurons
and synapses in the memory and intellectual centers of the brain,
in people with Alzheimer’s. These are
sometimes referred to as neuritic plaques or senile plaques.
While amyloid plaques have long been
considered markers of Alzheimer’s, they are also found to
some extent in many cognitively normal
elderly people. Plaques’ role in Alzheimer’s
neurodegeneration remains unclear.
animal model: A laboratory animal that—through changes in
its diet, exposure to toxins, genetic changes,
or other experimental manipulations—mimics specific signs or
symptoms of a human disease. Many
of the most promising advances in treating brain disorders
have come from research on animal models.
(Italicized terms are defined within this glossary.)
astrocyte: A star-shaped glial cell that delivers “fuel” to
the neurons from the blood, removes waste
from the neuron, and otherwise modulates the activity of the
neuron. Astrocytes also play critical roles
in brain development and the creation of synapses.
auditory cortex: Part of the brain’s temporal lobe, this
region is responsible for hearing. Nerve fibers
extending from the inner ear carry nerve impulses generated
by sounds into the auditory cortex for
interpretation.
autonomic nervous system: Part of the central nervous system
that controls functions of internal
organs (e.g., blood pressure, respiration, intestinal
function, urinary bladder control, perspiration,
body temperature). Its actions are mainly involuntary.
axon: A long, single nerve fiber that transmits messages,
via electrochemical impulses, from the
body of the neuron to dendrites of other neurons, or
directly to body tissues such as muscles.
basal ganglia: A group of structures below the cortex
involved in motor, cognitive, and emotional
functions.
basilar artery: Located at the base of the skull, the
basilar artery is one of the major vascular components
supplying oxygenated blood to the brain and nervous system.
B
biomarkers: A measurable physiological indicator of a
biological state or condition. For example,
amyloid plaques—as detected on amyloid PET scans, for
example—are a biomarker of Alzheimer’s
disease. Biomarkers can be used for both diagnostic and
therapeutic purposes.
brain-computer interface: A device or program that permits
direct or indirect collaboration between
the brain and a computer system. For example, a device that
harnesses brain signals to control a
screen cursor or prosthetic limb.
brain imaging: Refers to various techniques, such as
magnetic resonance imaging (MRI), diffusion
tensor imaging, and positron emission tomography (PET), that
enable scientists to capture images of
brain tissue and structure and to reveal what parts of the
brain are associated with various behaviors
or activities.
brain stem: A primitive part of the brain that connects the
brain to the spinal cord. The brain stem
controls functions basic to the survival in animal such as
heart rate, breathing, digestive processes,
and sleeping.
(continued)
C
central nervous system: The brain and spinal cord constitute
the central nervous system and
are part of the broader nervous system, which also includes
the peripheral nervous system.
central sulcus: The primary groove in the brain’s cerebrum,
which separates the frontal lobe in
the front of the brain from the parietal and occipital lobes
in the rear of the brain.
cerebellar artery: The major blood vessel providing
oxygenated blood to the cerebellum.
cerebellum: A brain structure located at the top of the
brain stem that coordinates the brain’s instructions
for skilled, repetitive movements and helps maintain balance
and posture. Recent research also
suggests the cerebellum may play a role, along with the
cerebrum, in some emotional and cognitive
processes.
cerebrum (also called cerebral cortex): The largest brain
structure in humans, accounting for about
two-thirds of the brain’s mass and positioned over and
around most other brain structures. The cerebrum
is divided into left and right hemispheres, as well as
specific areas called lobes that are associated
with specialized functions.
chronic traumatic encephalopathy (CTE): Once known as
dementia pugilistica and thought to be
confined largely to former boxers, this progressive
degenerative disease, with symptoms including
impulsivity, memory problems, and depression, affects the
brains of individuals who have suffered
repeated concussions and traumatic brain injuries.
cognition: A general term that includes thinking,
perceiving, recognizing, conceiving, judging, sensing,
reasoning, and imagining. Also used as an adjective
pertaining to cognition, as in “cognitive processes.”
cognitive neuroscience: The field of study that investigates
the biological mechanisms of cognition.
computational neuroscience: An interdisciplinary field of
study that uses information processing properties
and algorithms to further the study of brain function and
behavior.
computed tomography (CT or CAT): An X-ray technique
introduced in the early 1970s that enables
scientists to take cross-sectional images of the body and
brain. CT uses a series of X-ray beams passed
through the body to collect information about tissue
density, then applies sophisticated computer and
mathematical formulas to create an anatomical image from the
data.
connectome: A detailed map, or “wiring diagram,” of the
myriad neural connections that make up the
brain and nervous system.
consciousness: The state of being aware of one’s feelings
and what is happening around one;
the totality of one’s thoughts, feelings, and impressions.
corpus callosum: The collection of nerve fibers connecting
the two cerebral hemispheres.
cortex: The outer layer of the cerebrum. Sometimes referred
to as the cerebral cortex.
cortisol: A steroid hormone produced by the adrenal glands
that controls how the body uses fat,
protein, carbohydrates, and minerals, and helps reduce
inflammation. Cortisol is released in the body’s
stress response; scientists have found that prolonged
exposure to cortisol has damaging effects on the brain.
CRISPR (clustered regularly-interspaced short palindromic
repeats): A relatively precise and
reliable DNA editing technique, which is derived from a
primitive antiviral system found in bacteria.
There is hope that CRISPR technology can be adapted to help
treat brain disorders.
CT scan (also called CAT scan): See computed tomography.
D
deep brain stimulation: A method of treating various
neuropsychiatric and neurodegenerative disorders
through small, controlled electric shocks administered from
a special battery-operated neurostimulation
implant. The implant, sometimes called a brain pacemaker, is
placed within deep brain regions such as
the globus pallidus or subthalamus.
default-mode network: The network indicates that the brain
remains active even if not involved in a
specific task. So whether asleep or daydreaming, the brain
is in an active state.
delayed discounting: A common cognitive task used to measure
impulsivity in individuals. The task
measures an individual’s preference for the immediate delivery
of a small reward versus a larger reward
delivered later.
dementia: General mental deterioration from a previously
normal state of cognitive function due to
disease or psychological factors. Alzheimer’s disease is one
form of dementia.
dendrites: Short nerve fibers that project from a nerve
cell, generally receiving messages from the
axons of other neurons and relaying them to the cell’s
nucleus.
(continued)
depression: A mood or affective disorder characterized by
sadness and lack of motivation. Depression
has been linked to disruptions in one or more of the brain’s
neurotransmitter systems, including those
related to serotonin and dopamine. Clinical depression is a
serious condition that can often be effectively
treated with medications and/or behavioral therapy.
Diagnostic and Statistical Manual of Mental Disorders (DSM):
The standard classification manual
published by the American Psychiatric Association to be used
by mental health professionals to diagnose
and treat mental disorders.
diffusion tensor imaging: A brain imaging method that helps
visualize the brain’s white matter tracts.
DNA (deoxyribonucleic acid): The material from which the 46
chromosomes in each cell’s nucleus is
formed. DNA contains the codes for the body’s approximately
30,000 genes, governing all aspects of
cell growth and inheritance. DNA has a double-helix
structure—two intertwined strands resembling a
spiraling ladder.
dominant gene: A gene that almost always results in a
specific physical characteristic, for example a
disease, even though the patient’s genome possesses only one
copy. With a dominant gene, the chance
of passing on the gene (and therefore the trait or disease)
to children is 50-50 in each pregnancy.
dopamine: A neurotransmitter involved in motivation,
learning, pleasure, the control of body movement,
and other brain functions. Some addictive drugs greatly
increase brain levels of dopamine, leading to a
euphoric “high.” Virtually all addictive substances, from
nicotine to alcohol to heroin and crack cocaine,
affect the dopamine system in one way or another.
double helix: The structural arrangement of DNA, which looks
something like an immensely long ladder
twisted into a helix, or coil. The sides of the “ladder” are
formed by a backbone of sugar and phosphate
molecules, and the “rungs” consist of nucleotide bases
joined weakly in the middle by hydrogen bonds.
E
electroconvulsive therapy (ECT): A therapeutic treatment for
depression and other mental illnesses
that sends small electric currents over the scalp to trigger
a brief seizure. It is one of the fastest ways
known to reverse the symptoms of severely depressed
individuals.
endocrine system: A body system composed of several
different glands and organs that secrete
hormones.
endorphins: Hormones produced by the brain, in response to
pain or stress, to blunt the sensation of
pain. Narcotic drugs, such as morphine, imitate the actions
of the body’s natural endorphins.
enzyme: A protein that facilitates a biochemical reaction.
Organisms could not function if they had
no enzymes.
epigenetics: A subset of genetics that focuses on phenotypic
trait variations caused by specific
environmental factors that influence where, when, and how a
gene is expressed.
F
fissure: A groove or indentation observed in the brain.
Another word for sulcus.
frontal lobe: The front of the brain’s cerebrum, beneath the
forehead. This area of the brain is associated
with higher cognitive processes such as decision-making,
reasoning, social cognition, and planning,
as well as motor control.
frontal operculum: The part of the frontal lobe that sits
over the insula.
functional magnetic resonance imaging (fMRI): A brain
imaging technology, based on conventional
MRI, that gathers information relating to short-term changes
in oxygen uptake by neurons. It typically
uses this information to depict the brain areas that become
more active or less active—and presumably
more or less involved—while a subject in the fMRI scanner
performs a cognitive task.
G
gamma-aminobutyric acid (GABA): A neurotransmitter
implicated in brain development, muscle control,
and reduced stress response.
gene: The basic unit of inheritance. A gene is a distinct
section of DNA in a cell’s chromosome that
encodes a specific working molecule—usually protein or RNA—with
some role in brain or body function.
Gene defects (genetic mutations) are thought to cause many
disorders including brain disorders.
gene expression: The process by which a gene’s nucleotide
sequence is transcribed into the form of
RNA—often as a prelude to being translated into a protein.
gene mapping: Determining the relative positions of genes on
a chromosome and the distance
between them.
genome: The complete genetic map for an organism. In humans,
this includes about 30,000 genes,
more than 15,000 of which relate to functions of the brain.
glia (or glial cells): The supporting cells of the central
nervous system. Though probably not involved
directly in the transmission of nerve signals, glial cells
protect and nourish neurons.
glioma: A tumor that arises from the brain’s glial tissue.
glucose: A natural sugar that is carried in the blood and is
the principal source of energy for the cells of
the brain and body. PET imaging techniques measure brain
activity by detecting increases in the brain’s
metabolism of glucose during specific mental tasks.
gray matter: The parts of the brain and spinal cord made up
primarily of groups of neuron cell bodies
(as opposed to white matter, which is composed mainly of
myelinated nerve fibers).
gyrus: The ridges on the brain’s outer surface. Plural is
gyri.
H
hemisphere: In brain science, refers to either half of the
brain (left or right). The two hemispheres are
separated by a deep groove, or fissure, down the center.
Some major, specific brain functions are located
in one or the other hemisphere.
hippocampus: A primitive brain structure, located deep in
the brain, that is involved in memory and
learning.
hormone: A chemical released by the body’s endocrine glands
(including the adrenal glands), as well
as by some tissues. Hormones act on receptors in other parts
of the body to influence body functions or
behavior.
hypothalamus: A small structure located at the base of the
brain, where signals from the brain and the
body’s hormonal system interact.
I
induced pluripotent stem cell (iPSC): A cell that has been
taken from adult tissue and genetically
modified to behave like an embryonic stem cell, with the
ability to develop into any type of cell found
in the body, including nerve cells.
insula: Sometimes referred to as the insular cortex, this
small region of the cerebrum is found
deep within the lateral sulcus, and is believed to be
involved in consciousness, emotion, and body
homeostasis.
interneuronal: Between neurons, as in interneuronal communication.
ions: Atoms or small groups of atoms that carry a net
electric charge, either positive or negative. When a
nerve impulse is fired, ions flow through channels in the
membrane of a nerve cell, abruptly changing the
voltage across the membrane in that part of the cell. This
sets off a chain reaction of similar voltage changes
along the cell’s axon to the synapse, where it causes the
release of neurotransmitters into the synaptic cleft.
L
lesion: An injury, area of disease, or surgical incision to
body tissue. Much of what has been learned
about the functions of various brain structures or pathways
has resulted from lesion studies, in which
scientists observe the behavior of persons who have suffered
injury to a distinct area of the brain or
analyze the behavior resulting from a lesion made in the
brain of a laboratory animal.
limbic system: A group of evolutionarily older brain
structures that encircle the top of the brain stem.
The limbic structures play complex roles in emotions,
instincts, and behavioral drives.
M
magnetic resonance imaging (MRI): A non-invasive imaging
technology, often used for brain imaging.
An MRI scanner includes intensely powerful magnets,
typically 10,000 to 40,000 times as strong as the
Earth’s magnetic field. These magnets, combined with coils
that send electromagnetic pulses into the
scanned tissue, induce radio-frequency signals from
individual hydrogen atoms within the tissue. The
scanner records and processes these signals to build up an
image of the scanned tissue. MRI scans are
able to depict high resolution images of the entire brain,
allowing clinicians to determine if the brain
tissue that is visualized is normal, abnormal, or damaged
due to a neurological disorder or trauma. MRI
technology has also been adapted to measure brain activity
functional MRI.
melatonin: A hormone that is secreted by the pineal gland in
the brain in response to the daily light-dark
cycle, influencing the body’s sleep-wake cycle and possibly
affecting sexual development.
memory: The encoding and storage of information, in a way
that allows it to be retrieved later. In the
brain, memory involves integrated systems of neurons in
diverse brain areas, each of which handles
individual memory-related tasks. Memory can be categorized
into two distinct types, each with its own
corresponding brain areas. Memory about people, places, and
things—that one has experienced directly
or otherwise learned about—is referred to as explicit or
declarative memory and seems to be centered in
the hippocampus and temporal lobe. Memory about motor skills
and perceptual strategies is known as
implicit, or procedural memory and seems to involve the
cerebellum, the amygdala, and specific pathways
related to the particular skill (e.g., riding a bicycle
would involve the motor cortex).
metabolize: To break down or build up biochemical elements
in the body, effecting a change in body
tissue. Brain cells metabolize glucose, a blood sugar, to
derive energy for transmitting nerve impulses.
(continued)
microbiota: The community of various microorganisms found in
the digestive tract. Scientists are now
learning that microbes found in the microbiota can influence
brain development and behavior.
microglia: A small, specialized glial cell that operates as
the first line of immune defense in the central
nervous system.
minimally conscious state: A disorder of consciousness,
often caused by stroke, head injury, or loss of
blood flow to the brain, in which an individual maintains
partial conscious awareness.
molecular biology: The study of the structure and function
of cells at the molecular level and how these
molecules influence behavior and disease processes.
Molecular biology emerged as a scientific discipline
only in the 1970s, with advances in laboratory technologies
for isolating and characterizing DNA,
RNA, proteins, and other types of biological molecule.
motor cortex: The part of the brain’s cerebrum, just to the
front of the central sulcus in the frontal lobe,
that is involved in movement and muscle coordination.
Scientists have identified specific spots in the
motor cortex that control movement in specific parts of the
body, the so-called “motor map.”
MRI: See magnetic resonance imaging and/or functional
magnetic resonance imaging.
mutation: A permanent structural alteration to DNA that
alters its previous nucleotide sequence. In most
cases, DNA changes either have no effect or cause harm, but
occasionally a mutation improves an
organism’s chance of surviving and procreating.
myelin: The fatty substance that sheathes most nerve cell
axons, helping to insulate and protect the
nerve fiber and effectively speeding up the transmission of
nerve impulses.
N
narcotic: A synthetic chemical compound that mimics the
action of the body’s natural
endorphins—hormones secreted to counteract pain. Narcotic
drugs have a valid and useful role in the
management of pain but may lead to physical dependence in
susceptible individuals if used for long periods.
neuroeconomics: An interdisciplinary field of study that
uses neuroscientific research to help explain
human decision-making behavior.
neurodegenerative diseases: Diseases characterized by the
progressive deterioration and death of nerve
cells (neurodegeneration), typically originating in one area
of the brain and spreading to other connected
areas. Neurodegenerative diseases include amyotrophic
lateral sclerosis (also known as Lou Gehrig’s
disease), Huntington’s disease, Alzheimer’s disease,
frontotemporal degeneration, and Parkinson’s disease.
neuroeducation: Sometimes referred to as educational
neuroscience, this collaborative,
interdisciplinary field of study uses findings in cognitive
neuroscience to inform teaching and other
educational practices.
neuroethics: An interdisciplinary field of study that
addresses the ethical issues of our increased ability
to understand and change the brain. Privacy, life extension,
cloning, and many other issues are included
in this ongoing social-scientific debate.
neurogenesis: The production of new, maturing neurons by
neural stem and progenitor cells. Rapid
and widespread neurogenesis obviously occurs in the fetal
brain in humans and other animals. Neuroscientists
long believed that neurogenesis essentially does not occur
in the adult human brain. However,
over the past two decades, research has shown that it does
in fact occur in the dentate gyrus of the
hippocampus and possibly other brain regions. This “adult
neurogenesis” appears to be vital for
normal learning and memory, and may help protect the brain
against stress and depression. Neural
stem cells, which can produce new, “young” neurons and glial
cells, also may be used widely someday
to treat brain disorders, particularly neurodegenerative
diseases that otherwise deplete the neuronal
population.
neuroimmunology: A complex field in biomedical research,
which focuses on the brain, the immune
system, and their interactions. Neuroimmunology holds the
potential for conquering ills as diverse as
spinal cord injury, multiple sclerosis, and bodily reactions
to pathogens, both naturally occurring and
intentionally inflicted.
neuron: Nerve cell. The basic unit of the central nervous
system, the neuron is responsible for the
transmission of nerve impulses. Unlike any other cell in the
body, a neuron consists of a central cell
body as well as several threadlike “arms” called axons and
dendrites, which transmit nerve impulses.
Scientists estimate that there are approximately 100 billion
neurons in the brain.
neuroscience: The study of brains and nervous systems,
including their structure, function, and
disorders. Neuroscience as an organized discipline gained
great prominence in the latter part of the
last century.
neurotransmitter: A chemical that acts as a messenger
between neurons and is released into the synaptic
cleft when a nerve impulse reaches the end of an axon.
Several dozen neurotransmitters have been
identified in the brain so far, each with specific, often
complex roles in brain function and human behavior.
nurture: A popular term for the influence of environmental
factors on human development such as the
experiences one is exposed to in early life. The term is
often used in the context of “nature versus nurture,”
which relates to the interplay of “nature” (genetic or
inherited, predetermined influences) and environmental,
or experiential, forces.
O
occipital lobe: A part of the brain’s cerebrum, located at
the rear of the brain, above the cerebellum.
The occipital lobe is primarily concerned with vision and
encompasses the visual cortex.
olfactory: Pertaining to the sense of smell. When stimulated
by an odor, olfactory receptor cells in the
nose send nerve impulses to the brain’s olfactory bulbs,
which in turn transmit the impulses to olfactory
centers in the brain for interpretation.
opiate: A synthetic (e.g., Demerol, Fentanyl) or
plant-derived (e.g., opium, heroin, morphine) compound
that binds and activates opioid receptors on certain
neurons. Opiates typically but not always have pain-relieving,
anxiety-reducing, and even euphoria-inducing effects, and
are generally considered addictive.
opioid: An artificially derived drug or chemical that acts
on the nervous system in a similar manner to
opiates, influencing the “pleasure pathways” of the dopamine
system by locking on to specialized opioid
receptors in certain neurons.
opioid receptors (e.g., mu, delta, kappa): A class of
receptors found on neurons in the brain, spinal
cord, and digestive tract. Opioid receptors are involved in
numerous functions, including pain control,
mood, digestion, and breathing.
optogenetics: An innovative neuroscientific technique that
uses light to turn genetically modified
neurons on and off at will, in live animals.
oxytocin: Sometimes referred to as the “cuddle chemical,”
this hormone can work as a neurotransmitter
in the brain and has been linked to social attachment and
parental care.
P
pain receptors: Specialized nerve fibers in the skin and on
the surfaces of internal organs, which detect
painful stimuli and send signals to the brain.
parietal lobe: The area of the brain’s cerebrum located just
behind the central sulcus. It is concerned
primarily with the reception and processing of sensory
information from the body and is also involved in map
interpretation and spatial orientation (recognizing one’s
position in space vis-a-vis other objects or places).
peripheral nervous system: The nervous system outside the
brain and spinal cord.
persistent vegetative state: A disorder of consciousness,
often following severe brain trauma, in which an
individual has not even minimal conscious awareness. The
condition can be transient, marking a stage in
recovery, or permanent.
PET: See positron emission tomography.
pharmacotherapy: The use of pharmaceutical drugs for
therapeutic purposes.
pituitary gland: An endocrine organ at the base of the brain
that is closely linked with the hypothalamus.
The pituitary gland is composed of two lobes and secretes a
number of hormones that regulate the activity
of the other endocrine organs in the body.
plasticity: In neuroscience, refers to the brain’s capacity
to change and adapt in response to developmental
forces, learning processes, injury, or aging.
positron emission tomography (PET): An imaging technique,
often used in brain imaging. For a
PET scan of the brain, a radioactive “marker” that emits, or
releases, positrons (parts of an atom
that release gamma radiation) is injected into the
bloodstream. Detectors outside of the head can
sense these “positron emissions,” which are then
reconstructed using sophisticated computer programs
to create “tomographs,” or computer images. Since blood flow
and metabolism increase in
brain regions at work, those areas have higher
concentrations of the marker, and researchers are
able to see which brain regions are activated during certain
tasks or exposure to sensory stimuli.
Ligands can be added to a PET scan in order to detect
pathological entities such as amyloid or
tau deposits.
postsynaptic cell: The neuron on the receiving end of a
nerve impulse transmitted from another
neuron.
Post-traumatic stress disorder (PTSD): A mental disorder
that develops in response to a traumatic
event such as combat, sexual assault, terrorism, or abuse.
Symptoms can include mood disturbances,
hyperarousal, memory flashbacks, sleep problems, anxiety,
and depression.
prefrontal cortex: The area of the cerebrum located in the
forward part of the frontal lobe, which mediates
many of the higher cognitive processes such as planning,
reasoning, and “social cognition”—a
complex skill involving the ability to assess social
situations in light of previous experience and personal
knowledge, and interact appropriately with others. The
prefrontal cortex is thought to be the most recently
evolved area of the brain.
premotor cortex: The area of the cerebrum located between
the prefrontal cortex and the motor cortex, in
the frontal lobe. It is involved in the planning and
execution of movements.
presynaptic cell: In synaptic transmission, the neuron that
sends a nerve impulse across the synaptic
cleft to another neuron.
prion: A protein aggregate that can propagate itself,
inducing the formation of new aggregates
from individual copies of the protein it encounters. Prions
have the potential to spread within the
body and brain, and even from one organism to
another—“infectiously,” like a virus. The first prions
described were hardy aggregates of PrP, the prion protein.
They are responsible for a set of rapid,
fatal and potentially transmissible neurodegenerative
diseases including Creutzfeldt-Jakob disease
and bovine spongiform encepalopathy (“mad cow disease”).
Many researchers now argue that
protein aggregates in other neurodegenerative diseases, such
as the Aβ and tau aggregates of
Alzheimer’s, have such similar properties that they also
deserve to be called prions. In some
organisms, such as yeast, certain proteins apparently
evolved to function normally in a prion-like
form.
protein folding: The process by which the chain of amino
acids that make up a protein assumes its
functional shape. The protein aggregation that occurs in
some neurodegenerative disorders is thought
to be triggered when proteins “misfold.”
psychiatry: A medical specialty dealing with the diagnosis
and treatment of mental disorders. (Contrast
with psychology).
psychoactive drug: A broad term for any drug that acts on
the brain and noticeably alters one’s mental
state such as by elevating mood or alertness, or reducing
inhibitions. Psychoactive pharmaceuticals can
help control the symptoms of some neurological and
psychiatric disorders. Many “recreational drugs” are
also psychoactive drugs.
psychological dependence: In the science of addiction,
refers to the mood- and motivation-related
factors that sustain addiction (such as craving a cigarette
after a meal), as opposed to the “physical
dependence” that manifests when a person attempts to kick
the habit (e.g., tremors, racing pulse). Brain
scientists now understand that psychological factors are
central to addictive disorders and are often the
most difficult to treat. (Also see dependence.)
psychology: An academic or scientific field of study
concerned with the behavior of humans and
animals and related mental processes. (Contrast with
psychiatry.)
R
receptors: Molecules on the surfaces of neurons whose
structures precisely match those of chemical
messengers (such as neurotransmitters or hormones) released
during synaptic transmission. The chemicals
attach themselves to the receptors, in lock-and-key fashion,
to activate the receiving cell structure
(usually a dendrite or cell body).
recessive: A genetic trait or disease that appears only in
patients who have received two copies
of a mutant gene, one from each parent.
resting state: The state of the brain when it is not
consciously engaged in an explicit task. Brain
imaging techniques such as fMRI can be used to measure the
residual activity that occurs in this
state. Scientists are currently using resting state data to
help map the connectome, for example.
reward/reinforcement brain network: Also known as the
mesolimbic circuit, this important network of
brain regions is implicated in risk and reward processing,
as well as learning. It primarily uses dopamine
for signaling.
reuptake: A process by which released neurotransmitters are
absorbed for subsequent re-use.
ribonucleic acid (RNA): A chemical similar to a single
strand of DNA. The sugar is ribose, not deoxyribose,
hence RNA. In RNA, the letter U, which stands for uracil, is
substituted for T in the genetic code.
RNA delivers DNA’s genetic message to the cytoplasm of a
cell, where proteins are made.
S
senses: The physiological inputs that provide critical
information for perception and behavior from the
outside world. The five classic senses are: sight, hearing,
taste, touch, and smell.
serotonin: A neurotransmitter believed to play many roles,
including, but not limited to, temperature
regulation, sensory perception, and the onset of sleep.
Neurons using serotonin as a transmitter are
found in the brain and in the gut. A number of
antidepressant drugs are targeted to brain serotonin
systems.
social neuroscience: The field of study investigating the
biological systems underlying social processes
and behavior.
sonogenetics: A novel investigative approach that turns
genetically modified neurons on and off using
ultrasonic waves.
sono-stimulation: The activation of neural networks using
ultrasound.
spinal cord: The “other half” of the central nervous system
(with the brain). The spinal cord is a
cable that descends from the brain stem to the lower back.
It consists of an inner core of gray matter
surrounded by white matter.
stem cells: Undifferentiated cells that can grow into heart
cells, kidney cells, or other cells of the body.
Originally thought to be found only in embryos, stem cells
in the brain have unexpectedly been discovered
in adults. Researchers have shown on research animals that
stem cells can be transplanted into
various regions of the brain, where they develop into both
neurons and glia.
subgenual cortex: The region of the frontal lobes below the
genu of the corpus callosum implicated in
mood states.
sulcus: The shallower grooves on the brain’s cerebrum
(deeper grooves are called fissures). Plural is sulci.
synapse: The junction where an axon approaches another
neuron or its extension (a dendrite); the
point at which nerve-to-nerve communication occurs. Nerve
impulses traveling down the axon reach the
synapse and release neurotransmitters into the synaptic
cleft, the tiny gap between neurons.
synaptic transmission: The process of cell-to-cell
communication in the central nervous system,
whereby one neuron sends a chemical signal across the
synaptic cleft to another neuron.
T
tau protein: A type of protein abundantly found in neurons.
When this protein is not adequately cleared
from the brain, it can form tangles that are a key pathology
of several neurodegenerative disorders
including frontotemporal degeneration, CTE, and Alzheimer’s
disease.
telomere: The protective cap found at the end of a
chromosome. Research studies suggest that these
caps may be shortened in neurodegenerative disorders.
temporal lobes: The parts of the cerebrum that are located
on either side of the head, roughly
beneath the temples in humans. These areas are involved in
hearing, language, memory storage,
and emotion.
thalamus: A brain structure located at the top of the brain
stem, the thalamus acts as a two-way relay
station, sorting, processing, and directing signals from the
spinal cord and mid-brain structures to the
cerebrum, and from the cerebrum down.
transcranial electrical stimulation (tDCS and tACS): A
non-invasive procedure that applies electrical
stimulation to the scalp to increase or decrease neural
signaling.The two main types are direct current
stimulation (tDCS) and alternating current stimulation
(tACS). They are used for therapeutic purposes
as well as to study cognitive processing.
transcranial magnetic stimulation (TMS): A non-invasive
procedure that uses magnetic fields, applied
over the scalp, to stimulate changes in neural processing.
It is used as a treatment for depression as
well as a research method to investigate cognitive processes.
traumatic brain injury (TBI): An injury to the brain
acquired when the head is violently shook, struck, or
pierced by an object. Moderate to severe TBI causes
permanent impairments in brain function. Symptoms
of mild TBI may include headache, dizziness, attention
problems, or issues with behavior and
mood.
U
V
vagus nerve stimulation: A treatment for epilepsy that
involves a small implant that electrically stimulates
the vagus nerve, which runs from the brainstem to the
abdomen.
vertebral arteries: The major arteries of the neck, which
merge to form the basilar artery.
vestibular: Refers to the sense of balance. Many people with
hearing loss also have some degree of
balance difficulties, since the vestibular (or balance)
system and the auditory (or hearing) systems are
so closely related.
visual cortex: The area of the cerebrum that is specialized
for vision. It lies primarily in the occipital lobe
at the rear of the brain, and is connected to the eyes by
the optic nerves.
W
white matter: Brain or spinal cord tissue consisting
primarily of the myelin-covered axons that extend
from nerve cell bodies in the gray matter of the central
nervous system.
