Download Single-unit recording

ELECTROPHYSIOLOGY
Single Neuron Recording
Patch Clamp Recording
ECG
EEG- Brain activity Recording
PET, MRI, fMRI ,CAT
Single-unit recording
•It is the use of an electrode to
record the electrophysiological
activity (action potentials)
from a single neuron.
• An electrode introduced into the
brain of a living animal will detect
electrical activity that is generated
by the neurons adjacent to the
electrode tip. If the electrode is a
microelectrode, with a tip size of 3
to 10 micrometers, the electrode
will often isolate the activity of a
single neuron.
• The activity consists of the
voltages generated in the extra
cellular matrix by the current
fields outside the cell when it
generates an action potential.
Recording in this way is generally
called "single-unit" recording.
• The recorded action potentials
look very much like the action
potentials that are recorded
intracellularly, but the signals are
very much smaller (typically about
0.1 mV).
• Recordings of single neurons in living
animals have provided important insights
into how the brain processes information,
following the hypothesis put forth by
Edgar Adrian that unitary action potential
events are the fundamental means of
communication in the brain.
• Microelectrodes used for extra cellular
single-unit recordings are usually very fine
wires made from tungsten or platinumiridium alloys that are insulated except at
their extreme tip and are less often glass
micropipettes filled with a weak electrolyte
solution similar in composition to extra
cellular fluid.
• Hubel and Wiesel were awarded the
Nobel Prize in Physiology or Medicine
in 1981.
The patch clamp technique
• It is a laboratory technique in
electrophysiology that allows the
study of single or multiple ion
channels in cells.
• The technique can be applied to a wide
variety of cells, but is especially useful in
the study of excitable cells such as
neurons, cardiomyocytes, muscle fibers
and pancreatic beta cells. It can also be
applied to the study of bacterial ion
channels in specially prepared giant
spheroplasts.
• It is a laboratory technique in
electrophysiology that allows the study of
single or multiple ion channels in cells
• Erwin Neher and Bert Sakmann
developed the patch clamp in the late
1970s and early 1980s.
• This discovery made it possible to record
the currents of single ion channels for the
first time, proving their involvement in
fundamental cell processes such as action
potential conduction.
• Neher and Sakmann received the Nobel
Prize in Physiology or Medicine in 1991
for this work.
• Patch clamp recording uses, as an
electrode, a glass micropipette that has an
open tip diameter of about one
micrometer, a size enclosing a membrane
surface area or "patch" that often contains
just one or a few ion channel molecules
• In some experiments, the micropipette tip
is heated in a microforge to produce a
smooth surface that assists in forming a
high resistance seal with the cell
membrane.
• The interior of the pipette is filled with a
solution matching the ionic composition of
the bath solution, as in the case of cellattached recording, or the cytoplasm for
whole-cell recording
• Unlike traditional two-electrode voltage
clamp recordings, patch clamp recording
uses a single electrode to record
currents.
• ELECTROCARDIOGRAPH
• As cardiac impulses pass through the
heart, electrical currents spread into the
tissues surrounding the heart, and a small
portion of these currents spread
throughout the surface of the body.
• If electrodes are placed on the skin on
opposite sides of the heart, electrical
potential generated by these currents can
be recorded.
• Electrocardiograph is an instrument which
records the electrical activity of the heart
during a cardiac cycle.
• A record of the minute electrical pulses
generated by the heart used to determine
the condition of the patient’s heart is the
ElectroCardioGram.
• Electrodes are placed on the chest and
limbs, and the impulses which they detect
are amplified by the electrograph to which
the electrodes are connected.
• The ECG was developed by William
Einthoven of Leiden University, England
between 1903 and 1910
• Electrical impulses in the heart originate in
the sinoatrial node and travel through the
heart muscle where they impart electrical
initiation of systole or contraction of the
heart.
• The electrical waves can be measured at
selectively placed electrodes (electrical
contacts) on the skin.
• Electrodes on different sides of the heart
measure the activity of different parts of
the heart muscle.
• An ECG displays the voltage between
pairs of these electrodes, and the muscle
activity that they measure, from different
directions, also understood as vectors.
• This display indicates the overall rhythm of the
heart and weaknesses in different parts of the
heart muscle.
• It is the best way to measure and diagnose
abnormal rhythms of the heart, particularly
abnormal rhythms caused by damage to the
conductive tissue that carries electrical signals,
or abnormal rhythms caused by levels of
dissolved salts (electrolytes), such as potassium,
that are too high or low. In myocardial infarction
(MI), the ECG can identify damaged heart
muscle
• The ECG cannot reliably measure the
pumping ability of the heart; for which
ultrasound-based (echocardiography) or
nuclear medicine tests are used.
• A typical electrocardiograph runs at a
paper speed of 25 mm/s, although faster
paper speeds are occasionally used. Each
small block of ECG paper is 1 mm².
• At a paper speed of 25 mm/s, one small
block of ECG paper translates into 0.04 s
(or 40 ms).
• Five small blocks make up 1 large block,
which translates into 0.20 s (or 200 ms).
• Hence, there are 5 large blocks per
second.
• A standard signal of 1 mV must move the
stylus vertically 1 cm, that is two large
squares on ECG paper.
Leads used in ECG
• Limb Leads
• Leads I, II and III are the so-called limb leads
• Lead I is a dipole with the negative (white)
electrode on the right arm and the positive
(black) electrode on the left arm.
• Lead II is a dipole with the negative (white)
electrode on the right arm and the positive (red)
electrode on the left leg.
• Lead III is a dipole with the negative (black)
electrode on the left arm and the positive (red)
electrode on the left leg.
Augmented limb
• Leads aVR, aVL, and aVF are 'augmented limb
leads'. They are derived from the same three
electrodes as leads I, II, and III. However, they
view the heart from different angles
• Lead aVR or "augmented vector right" has the
positive electrode (white) on the right arm. The
negative electrode is a combination of the left
arm (black) electrode and the left leg (red)
electrode, which "augments" the signal strength
of the positive electrode on the right arm.
• Lead aVL or "augmented vector left" has the
positive (black) electrode on the left arm. The
negative electrode is a combination of the right
arm (white) electrode and the left leg (red)
electrode, which "augments" the signal strength
of the positive electrode on the left arm.
• Lead aVF or "augmented vector foot" has the
positive (red) electrode on the left leg. The
negative electrode is a combination of the right
arm (white) electrode and the left arm (black)
electrode, which "augments" the signal of the
positive electrode on the left leg
Precordial
• The precordial leads V1, V2, V3, V4, V5,
and V6 are placed directly on the chest.
Because of their close proximity to the
heart, they do not require augmentation
Waves and intervals
• A typical ECG tracing of a normal
heartbeat (or cardiac cycle) consists of a P
wave, a QRS complex and a T wave.
• A small U wave is normally visible in 50 to
75% of ECGs. The baseline voltage of the
electrocardiogram is known as the
isoelectric line.
• Typically the isoelectric line is measured
as the portion of the tracing following the T
wave and preceding the next P wave.
Schematic representation of
normal ECG
P wave
• During normal atrial depolarization, the main
electrical vector is directed from the SA node
towards the AV node, and spreads from the right
atrium to the left atrium.
• This turns into the P wave on the ECG, which is
upright in II, III, and aVF and inverted in aVR . A
P wave must be upright in leads II and aVF and
inverted in lead aVR to designate a cardiac
rhythm as Sinus Rhythm.
• The relationship between P waves and
QRS complexes helps distinguish various
cardiac arrhythmias.
• The shape and duration of the P waves
may indicate atrial enlargement
QRS complex
• The QRS complex is a structure on the
ECG that corresponds to the
depolarization of the ventricles.
• Because the ventricles contain more
muscle mass than the atria, the QRS
complex is larger than the P wave.
• In addition, because the His/Purkinje
system coordinates the depolarization of
the ventricles, the QRS complex tends to
look "spiked" rather than rounded due to
the increase in conduction velocity.
• A normal QRS complex is 0.08 to 0.12 sec
(80 to 120 ms) in duration represented by
three small squares or less, but any
abnormality of conduction takes longer,
and causes widened QRS complexes
PR/PQ interval
• The PR interval is measured from the
beginning of the P wave to the beginning
of the QRS complex.
• It is usually 120 to 200 ms long. On an
ECG tracing, this corresponds to 3 to 5
small boxes. In case a Q wave was
measured with a ECG the PR interval is
also commonly named PQ interval
instead.
• A PR interval of over 200 ms may indicate
a first degree heart block.
• A short PR interval may indicate a preexcitation syndrome via an accessory
pathway that leads to early activation of
the ventricles, such as seen in WolffParkinson-White syndrome.
• A variable PR interval may indicate other
types of heart block.
• The duration, amplitude, and morphology
of the QRS complex is useful in
diagnosing cardiac arrhythmias,
conduction abnormalities, ventricular
hypertrophy, myocardial infarction,
electrolyte derangements, and other
disease states.
• "Buried" inside the QRS wave is the atrial
repolarization wave, which resembles an
inverse P wave.
• It is far smaller in magnitude than the QRS
and is therefore obscured by it.
ST segment
• The ST segment connects the QRS
complex and the T wave and has a
duration of 0.08 to 0.12 sec (80 to 120
ms).
• It starts at the J point (junction between
the QRS complex and ST segment) and
ends at the beginning of the T wave.
• The typical ST segment duration is usually
around 0.08 sec (80 ms).
• The normal ST segment has a slight
upward concavity.
T wave
• The T wave represents the repolarization
(or recovery) of the ventricles.
• The interval from the beginning of the
QRS complex to the apex of the T wave is
referred to as the absolute refractory
period.
• The last half of the T wave is referred to as
the relative refractory period (or vulnerable
period). Tall or "tented" symmetrical T
waves may indicate hyperkalemia.
• Flat T waves may indicate coronary
ischemia or hypokalemia.
QT interval
• The QT interval is measured from the
beginning of the QRS complex to the end
of the T wave.
• Normal values for the QT interval are
between 0.30 and 0.44 seconds.
• The QT interval as well as the corrected
QT interval are important in the diagnosis
of long QT syndrome and short QT
syndrome.
• The QT interval varies based on the heart
rate, and various correction factors have
been developed to correct the QT interval
for the heart rate.
• The QT interval represents on an ECG the
total time needed for the ventricles to
depolarize and repolarize
U wave
• The U wave is not always seen. It is
typically small, and, by definition, follows
the T wave. U waves are thought to
represent repolarization of the papillary
muscles or Purkinje fibers. Prominent
• An inverted U wave may represent
myocardial ischemia or left ventricular
volume overload
Computed Axial Tomography
(CAT)
• Computed tomography (CT) is a medical
imaging method employing tomography.
• Digital geometry processing is used to
generate a three-dimensional image of the
inside of an object from a large series of
two-dimensional X-ray images taken
around a single axis of rotation.
• CT scan was invented by Sir Godfrey
Hounsfield
• He got Nobel prize in 1979 for the
discovery
CT Scanner
CT Image of Brain
Brain Images
• The word "tomography" is derived from the
Greek tomos (slice) and graphein (to
write).
• Computed tomography was originally
known as the "EMI scan" as it was
developed at a research branch of EMI, a
company best known today for its music
and recording business.
• It was later known as computed axial
tomography (CAT or CT scan) and body
section röntgenography.
Positron emission tomography
(PET)
• Positron emission tomography
(PET) is a nuclear medicine imaging
technique which produces a threedimensional image or picture of
functional processes in the body
• The system detects pairs of gamma rays
emitted indirectly by a positron-emitting
radionuclide (tracer), which is introduced
into the body on a biologically active
molecule.
• Images of tracer concentration in 3dimensional space within the body are
then reconstructed by computer analysis.
• In modern scanners, this reconstruction is
often accomplished with the aid of a CT Xray scan performed on the patient during
the same session, in the same machine.
• If the biologically active molecule chosen
for PET is FDG, an analogue of glucose,
the concentrations of tracer imaged then
give tissue metabolic activity, in terms of
regional glucose uptake.
• To conduct the scan, a short-lived
radioactive tracer isotope, is injected into
the living subject (usually into blood
circulation).
• The tracer is chemically incorporated into
a biologically active molecule
• The molecule most commonly used for
this purpose is fluorodeoxyglucose (FDG),
a sugar, for which the waiting period is
typically an hour.
• As the radioisotope undergoes positron
emission decay (also known as positive
beta decay), it emits a positron, a particle
with the opposite charge of an electron.
• After traveling up to a few millimeters the
positron encounters and annihilates with
an electron, producing a pair of
annihilation (gamma) photons moving in
opposite directions.
• These are detected when they reach a
scintillator in the scanning device, creating
a burst of light which is detected by
photomultiplier tubes or silicon avalanche
photodiodes
PET
PET IMAGE
PET Image of Brain
PET Acquisition Process
Radioisotopes
• Radionuclides used in PET scanning are
typically isotopes with short half lives such
as carbon-11 (~20 min), nitrogen-13 (~10
min), oxygen-15 (~2 min), and fluorine-18
(~110 min).
• These radionuclides are incorporated
either into compounds normally used by
the body such as glucose (or glucose
analogues), water or ammonia, or into
molecules that bind to receptors or other
sites of drug action. Such labelled
compounds are known as radiotracers.
Applications
• PET is both a medical and research tool
• It is used heavily in clinical oncology
(medical imaging of tumors and the search
for metastases), and for clinical diagnosis
of certain diffuse brain diseases such as
those causing various types of dementias
• PET is also an important research tool to
map normal human brain and heart
function.
Magnetic resonance imaging
(MRI)
• Magnetic resonance imaging (MRI), or
nuclear magnetic resonance imaging
(NMRI), is primarily a medical imaging
technique most commonly used in
radiology to visualize the structure and
function of the body. It provides detailed
images of the body in any plane.
MRI
• NMR was discovered by Bloch and Purcell
in 1952
MRI Image of Brain
• MRI provides much greater contrast
between the different soft tissues of the
body than computed tomography (CT)
does, making it especially useful in
neurological (brain), musculoskeletal,
cardiovascular, and oncological (cancer)
imaging
• Unlike CT, it uses no ionizing radiation,
but uses a powerful magnetic field to align
the nuclear magnetization of (usually)
hydrogen atoms in water in the body.
• Radiofrequency fields are used to
systematically alter the alignment of this
magnetization, causing the hydrogen
nuclei to produce a rotating magnetic field
detectable by the scanner.
• This signal can be manipulated by
additional magnetic fields to build up
enough information to construct an image
of the body.
• The body is mainly composed of water
molecules which each contain two
hydrogen nuclei or protons.
• When a person goes inside the powerful
magnetic field of the scanner these
protons align with the direction of the field.
• A second radiofrequency electromagnetic
field is then briefly turned on causing the
protons to absorb some of its energy.
• When this field is turned off the protons
release this energy at a radiofrequency
which can be detected by the scanner.
• The position of protons in the body can be
determined by applying additional
magnetic fields during the scan which
allows an image of the body to be built up.
These are created by turning gradients
coils on and off which creates the
knocking sounds heard during an MR
scan.
• Diseased tissue, such as tumors, can be
detected because the protons in different
tissues return to their equilibrium state at
different rates.
Applications
• In clinical practice, MRI is used to distinguish
pathologic tissue (such as a brain tumor) from
normal tissue.
• One advantage of an MRI scan is that it is
harmless to the patient. It uses strong magnetic
fields and non-ionizing radiation in the radio
frequency range
• Compare this to CT scans and traditional X-rays
which involve doses of ionizing radiation and
may increase the risk of malignancy, especially
in a fetus.
MRI Signs
Safe
Conditional
Unsafe
Functional MRI (fMRI)
• It is a type of specialized MRI scan. It
measures the haemodynamic response
related to neural activity in the brain or
spinal cord of humans or other animals
• It is one of the most recently developed
forms of neuroimaging.
• Since the early 1990s, fMRI has come to
dominate the brain mapping field due to its
low invasiveness, lack of radiation
exposure, and relatively wide availability.
f MRI Image
Electroencephalography (EEG)
• EEG is the recording of electrical activity
along the scalp produced by the firing of
neurons within the brain.
• In clinical contexts, EEG refers to the
recording of the brain's spontaneous
electrical activity over a short period of
time, usually 20-40 minutes, as recorded
from multiple electrodes placed on the
scalp
• EEG used to be a first-line method for the
diagnosis of tumors, stroke and other focal
brain disorders, but this use has
decreased with the advent of anatomical
imaging techniques such as MRI and CT.
• EEG was discovered in 1929 by a German
psychiatrist Hans Berger
• In 1932 by a British electrophysiologist,
Edgar Adrian won Nobel prize for the
demonstration of electrical impulses from
brain
EEG
1 Second EEG
• It is generally accepted that the activity
measured by EEG is electrical potentials
created by the post-synaptic currents,
rather than by action potentials.
• More specifically, the scalp electrical
potentials that produce EEG are due to the
extracellular ionic currents caused by
dendritic electrical activity (whereas the
fields producing
magnetoencephalographic signals are
associated with intracellular ionic
currents).
Wave patterns
• delta waves.
• Delta is the frequency range up to 3 Hz. It
tends to be the highest in amplitude and
the slowest waves. It is seen normally in
adults in slow wave sleep. It is also seen
normally in babies
Delta Wave
• Theta is the frequency range from 4 Hz to
7 Hz. Theta is seen normally in young
children. It may be seen in drowsiness or
arousal in older children and adults; it can
also be seen in meditation
Theta Wave
• Alpha is the frequency range from 8 Hz to
12 Hz. Hans Berger named the first
rhythmic EEG activity he saw, the "alpha
wave." This is activity in the 8-12 Hz range
seen in the posterior regions of the head
on both sides, being higher in amplitude
on the dominant side. It is brought out by
closing the eyes and by relaxation.
Alpha Wave
• Beta is the frequency range from 12 Hz to about
30 Hz.
• It is seen usually on both sides in symmetrical
distribution and is most evident frontally.
• Low amplitude beta with multiple and varying
frequencies is often associated with active, busy
or anxious thinking and active concentration.
Rhythmic beta with a dominant set of
frequencies is associated with various
pathologies and drug effects, especially
benzodiazepines.
Beta Wave
• Gamma is the frequency range
approximately 26–100 Hz.
• Gamma rhythms are thought to represent
binding of different populations of neurons
together into a network for the purpose of
carrying out a certain cognitive or motor
function.
Gamma Wave
Medical Imaging Instruments
•
•
•
•
•
•
•
Barium X ray
CT Scan
Bronchography
Endoscopy
PET
MET
Echocardiograph
X ray
X ray
Optical
Optical
Nuclear
Nuclear
Ultrasound
• ECG
• Electromyograph EMG
• EEG
Bioelectricity
Bioelectricity
Bioelectricity