Lecture 3: Imaging the Brain Flashcards
Electroencephalograms (EEGs)
a graph that records electrical activity through the skull or from the brain and represents graded potential of many neurons
Polygraph
an apparatus for simultaneously recording blood pressure, pulse, and respiration, as well as variations in electrical resistance of the skin
popularly known as a lie detector
Generator
the part of a neuron that produces a signal in response to changing inputs
also called a signal generator
Volume Conducted
a descriptor for electrical potential recorded in tissue at some distance from its source
Beta Rhythm
a fast brain-wave activity pattern associated with an alert state, or waking, EEG
Delta Waves
a slow brain-wave activity pattern associated with deep sleep
Parietal Seizure
abnormal electrical discharges restricted to only one or a few brain regions
also called a focal seizure
Generalized Seizures
a bilaterally symmetrical seizure without focal onset that can be characterized by loss of consciousness and by stereotyped motor activity
typified by three stages; tonic, clonic, and postictal depression
Electrocorticography
a procedure for transcranial EEG recording during surgery, in which electrodes are placed directly onto the brain surface, providing a more direct way of identifying the source of epileptic seizure
Coherence Theory
the proposal that, rather than brain activity consisting of a number of conscious “states”, a continuum of states exists, from high coherence (the brain is idling) to low coherence (the brain is actively processing information)
Event-Related Potentials
a complex electroencephalographic waveform related in time to a specific sensory event
Readiness Potentials
an event-related potential that occurs just before a movement
Magnetoencephalogram (MEG)
magnetic potentials recorded from detectors placed outside the skull
Deep Brain Stimulation
neurosurgery in which electrodes implanted in the brain stimulate a targeted area with a low-voltage electrical current to facilitate behavior
Akinesia
absence or poverty of movement
Transcranial Magnetic Stimulation (TMS)
a noninvasive procedure in which a magnetic coil is placed over the skull to stimulate the underlying brain
can be used either to induce behavior or to disrupt ongoing behavior
Conventional Radiography
an X-ray procedure
Pneumoencephalography
an invasive X-ray technique in which cerebrospinal fluid is replaced by air introduced through a lumbar procedure
Angiography
radiographic imaging of blood vessels filled with a contrast medium
Computed Tomography (CT Scan)
an X-ray technique that produces a static, three-dimensional image of the brain in cross section
Voxel
an area from which a measurement is taken, thus defining the resolution of brain-imaging method
Positron Emission Tomography (PET)
an imaging technique that detects changes in blood flow by measuring changes in the uptake of compounds such as oxygen or glucose
used to analyze the metabolic activity of neurons
Magnetic Resonance Imaging (MRI)
a technique that produces a static, three-dimensional brain image by passing a strong magnetic field through the brain, followed by a radio wave, an then measuring the radiation emitted from hydrogen atoms
Precession
a comparatively slow gyration of the rotation axis of a spinning body about another line intersecting it, describing a cone shape
Teslas
a unit for measuring the strength of a magnetic field
Magnetic Resonance Spectroscopy (MRS)
a modification of MRI to identify changes in specific markers of neuronal function, including all macromolecules (DNA, RNA, most proteins, and phospholipids); cell membranes; organelles (such as mitochondria); and glial cells, not imaged by magnetic resonance imaging
Diffusion Tenor Imaging (DTI)
a magnetic resonance imaging method that, by detecting the directional movements of water molecules, can image fiber pathways in the brain, DTI tractography maps the brain’s pathways and connectivity
Functional Magnetic Resonance Imaging (fMRI)
magnetic resonance imaging in which changes in elements such as iron or oxygen are measured during the performance of a specific behavior
used to measure cerebral blood flow during rest or behavior
BOLD Contrast
an acronym for blood oxygen level-dependent contrast, a measure used in fMRI that provides an index of the brain’s relative activity level
Resting State fMRI (rs-fMRI)
a functional magnetic resonance imaging method that measures changes in elements such as iron or oxygen when the individual is resting (not engaged in a specific task)
Motifs
recurring elements formed in waves of cortical activity, indicating functional connectivity (inherent functional relationships) among cortical systems
Optical Tomography
a noninvasive, dynamic imaging technique (such as functional near-infrared spectrography [fNIRS]) in which the image of an object is constructed by measuring the intensity of light transmitted through it
Default Mode Network (DMN)
linked brain regions active in participants who are resting rather than engaged in specific cognitive tasks and also active during such directed tasks as thinking about one’s past (autobiographical memory), thinking about the future, or when the mind is wandering
What is an electroencephalography (EEG)?
electrical potential: scalp recorded (summation), first described by Berger (1929)
quantified in two domains:
time: measured by frequency (Hz) and voltage
frequency: frequency and power (Fourier transform)
event-related potentials: time locked activity, neurotransmitter binding
components:
exogenous: outside the body (loud noise, bright light)
endogenous: inside the body (thinking about dinner, having anxiety)
What is the electrode placement for EEG?
10-20 system (size of people’s head varies)
measure distance from nose to back of the head, electrodes are placed within 10/20% of that distance
10 or 20% of midline distance from nasion to inion
Pz = parietal zero
O1 = occipital left
T4 = temporal right
What do the letters and numbers on an EEG mean?
large first letter: where on the head it is
odd #: left
even #: right
magnitude of #: how far away it is from the midline
What is the comparison between EEG and behavior?
ERP can elucidate specific cognitive processes underlying overt behavior
online measure in absence of overt behavior
e.g., automatic processes; below awareness threshold
also correct responses versus errors
small amplitude of ERP necessitate greater number of trials than RT experiments
What are some advantages of EEG?
non-invasive
temporal resolution
cost (very cheap)
What are Computerized Axial Tomography (CAT) Scans?
taking X-rays at different points on the brain
What are the different ways of image acquisition for a CAT scan?
no one slice gets you a whole image of the brain (need many slices)
resolution is only as good as the slices you have
ascending: start at 1
descending: start at 11
interleaved: collect slice 1, 3, 5, 9, 11 then 2, 4, 6… (reduces imaging time)
What is the static field in an MRI?
constant magnetic field (e.g. 0.5 Tesla - 7 Tesla)
alignment (all hydrogen atoms/tissue line up perfectly)
What is the radio frequency field pulse sequence in an MRI?
transmitter coil: perturbation of static field - hydrogen atoms - excitation -resonance
receiver coil - reception (realignment) - image acquisition
What is the gradient field in an MRI?
spatial information
What is the difference between anatomical versus functional imaging?
CAT & MRI study what the brain looks like
functional imaging studies how the brain works
What is the Positron Emission Tomography (PET)?
radioactive tracers (isotope): oxygen, glucose
positron (charged particle): released, collides with electron
annihilation: releases energy
photo cells
reverse triangulate where the photon was released
What are the differences between MRI vs. fMRI?
MRI: high resolution, one image
fMRI: low resolution, many images (every 2 seconds for 5 minutes)
