9. A szinaptikus potenciálok típusai, mérésükre alkalmazott módszerek
A szinaptikus áramok abban különböznek az akciós poteciáloktól, hogy míg azok terjednek,
ezáltal mozgó extracelluláris mezőt hozva létre, előbbiek nem mozognak, amennyiben
ugyanazokat a szinapszisokat aktiváljuk: extracelluláris mezejük állónak tekithető. A kettő
közötti fő különbség a regeneratív természetükben és időbeli lefolyásukba rejlik. (Az akciós
potenciál ms-os vagy azon belüli, az EPSP 10-20 ms, az IPSP 100 ms is lehet.) (Karmos Gy.)
A szinaptikus poteciált a preszinaptikus sejtben kalcium beáramlása okozza (akciós potenciál,
ami az axodombtól végigfut az axonon a telodendria végéig), míg a posztszinaptikus sejtben
egy vagy egy pár különböző ion membránon keresztül-áramlása okozhatja. Forrás (source:
sejtből kifelé irányuló áram), nyelő (sink: sejtbe iráyuló áram). EPSP (excitatory post synaptic
potential): depolarizáló szinapszis, a nyelő aktív (pl. nátrium beáramlása), a forrás passzív, a
neuront a threshold irányába viszi; IPSP (inhibitory post synaptic potential): hiperpolarizáló
szinapszis, a forrás aktív, a nyelő passzív (pl. klór beáramlása), a neuront távolabb viszi a
threshold-tól.
A különálló EPSP-k és IPSP-knek nincs megfigyelhető hatása a membránpotenciálra. De
összeadódva meghatározzák, hogy geerálódik-e akciós potenciál (az „összeadási pont” az
axondomb (axon hillock)). Valószínűleg a neuronban az axondombnak van a legkisebb
threshold értéke (a feszültségfüggő nátrium és kálium csatornák nagy koncentrációja miatt).
It is thought that the axon hillock may have the lowest value for threshold potential in the neuron. This
is because there are a large number of voltage gated sodium and potassium channels concentrated in
this area.
During both EPSPs and IPSPs membrane resistance and conductance changes. Generally there is a
conduction increase and associated resistance decrease, caused by the opening of ion channels due to
stimulation by the neurotransmitter. Sometimes in IPSPs resistance actually increases, making it
harder for the membrane to polarize. The fact that membrane resistance changes however can be
experimentally verified. The experiment is a simple one based on the fact that neurons follow ohms
law. Ohms law states that voltage is equal to the resistance times the current. V=I(R). In the
experiment two micropippettes are inserted into the postsynaptic membrane during an EPSP. One is
used to measure voltage, while the other periodically sends out pulses of electrical current. During the
EPSP current is pulsed into the membrane and the resulting voltage is recorded. Before the EPSP
similar voltage tests were run to show that the voltage remained constant. During the EPSP, the
resulting voltage is shown to have decreased. Since the current was unaltered, a reduced voltage could
mean only one thing, a reduction in membrane resistance.
The next question one should be asking, is which ions exactly are experiencing this increase in
conductance. One way of testing this is to alter the membrane potential to the reversal potential. At
the reversal potential there is no net current flow across the membrane upon stimulation. Consequently
there is no change in the potential either. If the postsynaptic potential is caused by just one ion, the
reversal potential will be that ions equilibrium potential. If more than one ion is let into the cell upon
stimulation the reversal potential will be an intermediate of the equilibrium potentials for the ions in
question. For most EPSPs the reversal potential is approximately -10mV. Since that is not the
equilibrium potential for any one ion, the data suggest that more than one ion is responsible for this
reversal potential. In fact -10 mV is about midway between the equilibrium potentials for sodium and
potassium (potassium has an equilibrium potential around -90 mV and sodium?s is around +50mV).
Thus during an EPSP sodium and potassium conductance increases, causing sodium to flow in and
potassium out of the cell, eliciting a depolarization event. One should understand that ion channels are
more permeable to some ions than to others. Theoretically this means that the reversal potential could
be anywhere from -70mV to +50mV for an EPSP. Most EPSPs have a reversal potential between 0
and -20 mV. This shows that the ion channels are about equally permeable to both ions and gives a
good explanation for the potential difference in various EPSPs of neurons.
IPSPs are known to hyperpolarize the neuronal membrane. Thus the neuron will experience an efflux
of positive charge (K+) and/or an influx of negative charge(Cl-). This theory is readily acceptable since
both ions will flow the appropriate directions along their concentration gradient. IPSPs that have a
reversal potential near -70mV are known to be dependent only on chlorine conductance increase.
Those with more negative reversal potentials allow both chlorine and potassium to experience an
increase in conductance.
Synaptic currents do not move if the same synapses are activated: their extracellular field can
be regarded as standing. Action currents propagate, generating a moving field. The main
difference between action and synaptic currents are in their regenerative nature and time
course. (By George Karmos)
10. A biológiai előerősítők jellemző tulajdonságai
Experimetria's EEGM (EEG Monitor) is a low-noise, high
input impedance amplifier specifically designed for EEG
measurements. The coupler consists of a pre-amplifier and an
end-amplifier. The pre-amplifier substantially reduces input
noise, permitting the use of optimal length cords between the
electrode and the coupler. The output voltage is adjustable
+/-2.5 volts. Filtering is adjustable with five high-frequency
and four time-constant settings.
SPECIFICATIONS
Input impedance: >200 megaohm
Input offset: +/1 300 millivolts
Input: 10, 25, 50, 100, 250, 50 and 1000 µV at 1 volt output
Time constant, sec (Hz): 1 (0.16), 0.3 (0.53), 0.1 (1.6), 0.03 (5.3)
Filter cut slope: 6 dB/octave
Cut-off frequency attenuation: 3 dB, +1.5/-0.5 dB
High cut-off frequency: 15, 30, 70, 150 or 200 Hz
Noise (at 0.53-70 Hz): <=1.5 µV
CMMR: >86 dB
Output impedance: 100 ohms
Power supply: +/-20 volts, 100 mA
Dimensions: 40mm wide, 128.5mm high, 250mm deep
Mounting: standard R-01 type 19 inch rack
Weight: 0.5kg
Accessories: functional cables and operating instructions
BioAmp's main fields of applications:
-Microelectrode recording (Single-unit activity, Field Potential, Motor Units, etc.)
-Evoked Potentials (EVP)
-Multi-channel applications (EEG Brain Mapping, Cortical Depth Mapping, etc.)
-Body-surface potentials (ECG, EMG, EEG, ERG, etc.)
-Micropotentials (HIS-bundle, Late Potential, etc.)
Description of BioAmp
The most important difference (in comparison to other models) is that our BioAmp is a
programmable amplifier, but it has no sampling circuits at all. In other words, it is controlled
by a built-in microprocessor, but it has got only analogue amplifier circuits. This feature is
indispensable when you use averaging techniques for processing its output signal. The built-in
computer is optically isolated from the amplifier stages. In this way we could connect all the
advantages of high accuracy analogue amplifier circuits, and easy usage of digital control.
Although BioAmp is a programmable equipment, it does not need a separate computer to
work. According to this fact, it can be used as a stand-alone usual amplifier (while possessing
an optional RS-232 connector to communicate with a PC if it would be necessary). This
stand-alone feature is always useful, because the computer is usually given, but it should be
used to collect and processing experimental data. BioAmp's microprocessor-based control
panel supports high level of reliability and easy operation.
BioAmp family is powerful in multi-channel tasks, since such a level of reliability and
flexibility is unthinkable in a usual amplifier. And the top of all that, our amplifier system
offers the lowest cost as compared to the number of channels.
The amplifier has got a multi-purpose connector for external preamplifiers. This method gives
an opportunity for use of other type of input modules to meet all the future demands. Until
now we have developed six different
preamplifier versions for BioAmp. But if you
can not find the appropriate preamplifier for
your special task in our choice, we can develop
a model especially for you for NO charge (we
take all the expenses of development process).
The differential amplifier amplifies the
difference between two input signals (-) and
(+). This amplifier is also referred to as a
differential-input single-ended output amplifier.
The two input leads can be seen on the left-hand side of the triangular amplifier symbol, the output lead on the righthand side. As with the other example, all voltages are referenced to the circuit's ground point. Notice that one input
lead is marked with a (-) and the other is marked with a (+). Because a differential amplifier amplifies the difference in
voltage between the two inputs, each input influences the output voltage in opposite ways. Consider the following table
of input/output voltages for a differential amplifier with a voltage gain of 4:
An increasingly positive voltage on the (+) input tends to drive the output voltage more positive, and an increasingly
positive voltage on the (-) input tends to drive the output voltage more negative. Likewise, an increasingly negative
voltage on the (+) input tends to drive the output negative as well, and an increasingly negative voltage on the (-)
input does just the opposite. Because of this relationship between inputs and polarities, the (-) input is commonly
referred to as the inverting input and the (+) as the noninverting input.
This concept may at first be confusing to students new to amplifiers. With all these polarities and polarity markings (and +) around, it's easy to get confused and not know what the output of a differential amplifier will be. To address
this potential confusion, here's a simple rule to remember:
When the polarity of the
differential voltage
matches the markings for
inverting and
noninverting inputs, the
output will be positive.
When the polarity of the
differential voltage
clashes with the input
markings, the output will
be negative. This bears
some similarity to the
mathematical sign
displayed by digital
voltmeters based on
input voltage polarity.
The red test lead of the
voltmeter (often called
the "positive" lead
because of the color red's
popular association with the positive
side of a power supply in electronic
wiring) is more positive than the
black, the meter will display a
positive voltage figure, and visaversa.
Differential amplifiers are found
in any system that utilises
negative feedback where one
input is used for the input
signal, the other for the
feedback signal. A common
application is for the control of
motors or servos, as well as for signal amplification applications.
Negative feedback is a type of feedback, during which a system responds so as to reverse the
direction of change. Since this process tends to keep things constant, it is stabilizing and attempts to
maintain homeostasis. When a change of variable occurs within a stable negative feedback control
system, the system will attempt to establish equilibrium. Open systems (ecological, biological, social)
contain many types of regulatory circuits, among which are positive and negative feedback systems.
'Positive' and 'negative' do not refer to desirability, but rather to the sign of the multiplier in the
mathematical feedback equation. The negative feedback loop tends to slow down a process, while
the positive feedback loop tends to accelerate it.
EOG: http://www.adinstruments.com/research/rapps/eog.html
Amplifiers are a very important part of medical instruments due to the fact that many biological
signals produced are very low. This experiment serves to introduce the different designs for amplifiers
and to use amplifiers to build filters. The focus of this lab was on the voltage amplifier and its gain.
The gain can be calculated as Vout / Vin. The gain can be very large but the output voltage can never be
above the supply voltages. The differential amplifier that will be examined amplifiers the voltage
difference between two inputs, the gain is referred to as the differential gain. The common mode gain
is found when the two inputs are equal. Ideally, the common mode gain is 0 and the amplifier only
amplifiers the differential gain. The ratio of the two is called the common mode rejection ratio.
Most amplifiers will be connected to a load and the effects of that load will be investigated as well as
the effects of how a buffer corrects for that load. Using the amplifiers, a bandpass filter will be
constructed. Bandpass filters only allow signals of certain frequencies to be shown. Experimenting
with the bandpass filter, the differential gain and common mode gain will be found. It was found that a
buffer can be inserted into circuits to prevent voltage drops over the source resistance; this makes for a
better gain obtained by the amplifier. It was also found that differential amplifier could be constructed
to act like a band pass filter and that the cutoff frequency for such a filter is dependent on the
capacitors and resistors used. By altering the capacitor and resistor values, the cutoff frequency can be
set.
http://www.larryheadinstitute.com/eeg-training.html
Mire kellenek biológiai előerősítők? Vérnyomás, bioelektromos jelek (EKG, EEG), hőmérséklet,
lélegzés, tehát szinte mindenhez. EEG differenciálerősítő: magas bemeneti impedancia. Common
mode rejection (közös módusú zajelnyomás) (kb. 100 dB).
11. Az EEG elvezetés technikája
Alternative names
Return to top
Electroencephalogram; Brain wave test
Definition
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An electroencephalogram (EEG) is a test to detect abnormalities in the electrical activity of the brain.
How the test is performed
Return to top
Brain cells communicate by producing tiny electrical impulses. In an EEG, electrodes are placed on the scalp
over multiple areas of the brain to detect and record patterns of electrical activity and check for abnormalities.
The test is performed by an EEG technician in a specially designed room that may be in your health care
provider's office or at a hospital. You will be asked to lie on your back on a table or in a reclining chair.
The technician will apply between 16 and 25 flat metal discs (electrodes) in different positions on your scalp.
The discs are held in place with a sticky paste. The electrodes are connected by wires to an amplifier and a
recording machine.
The recording machine converts the electrical signals into a series of wavy lines that are drawn onto a moving
piece of graph paper. You will need to lie still with your eyes closed because any movement can alter the results.
You may be asked to do certain things during the recording, such as breathe deeply and rapidly for several
minutes or look at a bright flickering light.
How to prepare for the test
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You will need to wash your hair the night before the test. Do not use any oils, sprays, or conditioner on your hair
before this test.
Your health care provider may want you to discontinue some medications before the test. Do not change or stop
medications without first consulting your health care provider.
You should avoid all foods containing caffeine for 8 hours before the test.
Sometimes it is necessary to sleep during the test, so you may be asked to reduce your sleep time the night
before.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your
child's age, interests, previous experiences, and level of trust. For specific information regarding how you can
prepare your child, see the following topics as they correspond to your child's age:

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


Infant test/procedure preparation (birth to 1 year)
Toddler test/procedure preparation (1 to 3 years)
Preschooler test/procedure preparation (3 to 6 years)
Schoolage test/procedure preparation (6 to 12 years)
Adolescent test/procedure preparation (12 to 18 years)
How the test will feel
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This test causes no discomfort. Although having electrodes pasted onto your skin may feel strange, they only
record activity and do not produce any sensation.
Why the test is performed
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EEG is used to help diagnose the presence and type of seizure disorders, to look for causes of confusion, and to
evaluate head injuries, tumors, infections, degenerative diseases, and metabolic disturbances that affect the brain.
It is also used to evaluate sleep disorders and to investigate periods of unconsciousness. The EEG may be done
to confirm brain death in a comatose patient.
EEG cannot be used to "read the mind," measure intelligence, or diagnose mental illness.
Normal Values
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Brain waves have normal frequency and amplitude, and other characteristics are typical.
What abnormal results mean
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Abnormal findings may indicate the following:

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Seizure disorders (such as epilepsy or convulsions)
Structural brain abnormality (such as a brain tumor or brain abscess)
Head injury, encephalitis (inflammation of the brain)
Hemorrhage (abnormal bleeding caused by a ruptured blood vessel)
Cerebral infarct (tissue that is dead because of a blockage of the blood supply)
Sleep disorders (such as narcolepsy).
EEG may confirm brain death in someone who is in a coma.
12. EEG elvezetésnél jelentkező zavarok kivédése
Zavarok az EEG-ben (artefakt):
hálózati
- Szemmozgás (főleg a frontális lebenyben)
- izom
- elektromos jelek
- video monitor
- földhurok
- EKG
- Galván bőr válasz
- Digitális (DC offset, aliasing, multiplexing artefakt (A/D konverter okozza))
Szűrés: lowpass, highpass, lukszűrő (lásd a papírt). Differenciálerősítő.
Eye activity is one of the main sources of artefacts in EEG and MEG recordings. A new
approach to the correction of these disturbances is presented using the statistical technique of
independent component analysis. This technique separates components by the kurtosis of
their amplitude distribution over time, thereby distinguishing between strictly periodical
signals, regularly occurring signals and irregularly occurring signals. The latter category is
usually formed by artefacts. Through this approach, it is possible to isolate pure eye activity in
the EEG recordings (including EOG channels), and so reduce the amount of brain activity that
is subtracted from the measurements, when extracting portions of the EOG signals.
When monitoring the EEG, lead positioning is not as important as in a diagnostic EEG, during which the electrodes would have to be
exactly on the right spot over the skull. If a patient has a wound or a bandage placed so that the exact electrode placement cannot be
achieved, the nearest possible location should be used. However, it is essential that the electrodes should be placed symmetrically
toward the central line. This way, the EEG signal over the different hemispheres can be compared.
Montage means the placement of the electrodes. The EEG can be monitored with either a bipolar montage or a referential one. Bipolar
means that you have two electrodes per one channel, so you have a reference electrode for each channel. The referential montage
means that you have a common reference electrode for all the channels.
Different kinds of electrodes can be used for monitoring EEG. The stick-on electrodes are easy to use and attach on hairless areas. For
hairy areas, Ag/AgCl- or gold cups can be attached by using paste or colloidin. This takes time and is more difficult than using the stickon electrodes. Needle-electrodes are faster to attach on hairy areas, but the impedance may be quite high causing more artefacts to the
EEG signal. In a diagnostic EEG, electrode-caps are sometimes used for saving time.
The biggest challenge with monitoring EEG is artifact recognition and elimination. There are patient related artifacts (e.g. movement,
sweating, ECG, eye movements) and technical artifacts (50/60Hz artifact, cable movements, electrode paste related) which have to be
handled differently. There are some tools for finding the artifacts. For example, FEMG and impedance measurements can be used for
indicating contaminated signal. By looking at different parameters on a monitor, other interference may be found.
There are things that can be done for reducing the artefacts in the ICU:
1.
2.
3.
4.
5.
Make sure that the impedance values are as low as possible (< 5 kOhm). Prepping the skin properly and using the correct
amount of paste can do this. Also, all the electrodes used should be similar.
Remember to attach the ground electrode and follow the FEMG value (sometimes it is necessary to sedate and relax the
patient)
Use bipolar montage if you have an electrically controlled bed, because referential montage is more prone to artefacts
Keep the electrical device as far away from the patient's head as possible
Keep the pre-amplifier as close to the patient's head as possible and the cables as short as possible, or braid the cables
http://www.math.princeton.edu/~rbogacz/papers/Zakopane99.pdf
http://www.rgi.tut.fi/kurssit/71413/materials/71413%20Lecture7.pdf
ARTIFACTS
Artifacts are waves or groups of waves which are produced by
technical or other disturbances which are not due to brain activity.
The Massive amplification magnifies all manner of disturbances such as
EKG and Pulse artifacts, electrode and movement, and IV and 60 Hz artifacts and
Sweat artifacts
,
which represent salt solution between electrodes shorting them out.
EKG AND PULSE ARTIFACTS
Both artifacts are illustrated and are recognized by their periodicity.
The EKG shows periodic QRS complexes
as the EKG is a much larger electrical signal than EEG.
Pulse artifact is caused by a pulse under an electrode moving that electrode
periodically. Both are easily recognized usually but can be a problem.
ELECTRODE AND OTHER MOVEMENT ARTIFACTS
Patient movement artifacts are abrupt with a rapid upstroke in almost all instances.
They are large in amplitude and last a long time by EEG standards.
A 'POP' is a brief electrode shift which can be mistaken for a spike by the
naive but it is seen usually in only two adjascent channels and not three as.
occurs with epileptic spikes.
INTRAVENOUS ARTIFACT and 60 Hz ARTIFACTS
These artefacts are seen commonly in ICU recordings and both are electrical
interference. The 'drip' artifact is shown in red; it is periodic and small in
amplitude and easily recognized. Sixty Hz is seen where the electrode
contacts are poor, grounding is inadequate and electrical contrivances
are in use close by. This causes spikes at 60 per second - an inkblot at
at usual paper speeds.
13. Az EEG tevékenység jellemző összetevői
-4 Hz
delta
4-8 Hz
theta
8-13 Hz
alfa
- életkorral változik!
13-35 Hz
beta
35-80 Hz
gamma
szinkronizált aktivitás: ritmikus, nagy, szabályos, hullámok
deszinkronizált: kisebb, szabálytalan hullámok
alvási orsó (spindle): alfa és betában (ott miért???), kb. 14/sec.
Sharp waves
Spikes
Spike-and-wave
Polyspikes
Polyspike-and-wave
ALPHA
Alpha waves are those between 7.5 and thirteen(13) waves per second (Hz). Alpha is usually
best seen in the posterior regions of the head on each side, being higher in amplitude on the
dominant side. It is brought out by closing the eyes and by relaxation, and abolished by eye
opening or alerting by any mechanism (thinking, calculating). It is the major rhythm seen in
normal relaxed adults - it is present during most of life especially beyond the thirteenth year
when it dominates the resting tracing.
BETA
Beta activity is 'fast' activity. It has a frequency of 14 and greater Hz. It is usually seen on
both sides in symmetrical distribution and is most evident frontally. It is accentuated by
sedative-hypnotic drugs especially the benzodiazepines and the barbiturates. It may be absent
or reduced in areas of cortical damage. It is generally regarded as a normal rhythm. It is the
dominant rhythm in patients who are alert or anxious or who have their eyes open.
THETA
Theta activity has a frequency of 3.5 to 7.5 Hz and is classed as "slow" activity. It is abnormal
in awake adults but is perfectly normal in children upto 13 years and in sleep. It can be seen
as a focal disturbance in focal subcortical lesions; it can be seen in generalized distribution in
diffuse in diffuse disorder or metabolic encephalopathy or deep midline disorders or some
instances of hydrocephalus
DELTA
Delta activity is 3 Hz or below. It tends to be the highest in amplitude and the slowest waves.
It is quite normal and is the dominant rhythm in infants up to one year and in stages 3 and 4 of
sleep. It may occur focally with subcortical lesions and in general distribution with diffuse
lesions, metabolic encephalopathy hydrocephalus or deep midline lesions. It is usually most
prominent frontally in adults (e.g. FIRDA - Frontal Intermittent Rhythmic Delta) and
posteriorly in children e.g. OIRDA - Occipital Intermittent Rhythmic Delta).
WAVES IDENTIFIED BY MORPHOLOGY
Some waves are recognized by their shape and form. Included are:
spikes or slow waves. Spikes are narrow-based waves that have a
relatively high amplitude, giving them a narrow and high form and a sharp
top. A sharp wave is slightly broader than a spike, but has the same
significance - it is the common hallmark of seizure activity and implies
multiple synchronous firing or activity(of dendrites). Sharp waves are
thought to represent the discharge as seen from some distance away
while spikes are recorded from close to the focus.
COMPLEX WAVE PATTERNS:
Wave patterns that have some specificity because of their morphology include:
spike and wave,
polyspike and wave,
PLEDS,
Triphasic waves,
Burst supression,
Amongst other less common forms
SPIKE AND WAVE
Spike and wave format is seen at all ages but most often in children.
It consists of a spike, which is probable generated in the cortex, and
a large amplitude slow wave(usually delta), thought to originate from
thalamic structures, occuring recurrently. They may occur synchronously
and symmetrically in the generalized epilepsies or focally in the partial
ones. In the generalized types of spike and wave, true absense(petit mal)
is characterized by 3 Hz spike-wave, while slow spike-wave occurs more
usually with brain injury and the Lennox-Gastaut syndrome.
Faster than 3 Hz spike and wave will be dealt with in the section
on polyspike-wave below.
POLYSPIKE AND WAVE
Polyspike and wave is a form of spike wave in which each slow wave is
accompanied by two or more spikes. The usual pattern is that the spike
and wave is faster than 3 Hz - usually 3.5 to 4.5 Hz. It is often associated
with myoclonus or myoclonic seizures. It should not be confused with 6 Hz
spike and wave, otherwise known as phantom spike and wave - a normal variant.
PERIODIC LATERALISED EPILEPTIFORM DISCHARGES
PLEDS - Periodic Lateralized Epileptiform Discharges - are a form of
discharge associated with acute brain injury or damage. The pattern
is also said to be most evident when acute brain injury is coupled with
some metabolic derangement. It is an evolving pattern starting out with
sharp waves occuring at regular intervals over one whole area or side
with relative flattening between. It evolves to slow transients and then
slow waves occuring periodically with improving background activity
between. It finally clears completely. It is often associated with severe
focal signs andmuch illness early on with some improvement later.
TRIPHASIC WAVES
Triphasic waves are as illustrated the 3 waves are seen outlined in
white. They often occur as long runs causing an appearance of
pseudoparoxysmal activity. The waveform was originally found with
hepatic encephalopathy but has subsequently been found in association
with many other forms of metabolic encephalopathy.
BURST SUPRESSION
Burst-suppression is a pattern of burst of slow and mixed waves often
of high amplitude alternating with a flat baseline. The pattern is bilateral
but not always symmetrical. It is usually seen after severe brain injury
such as postischemia or postanoxia. It is also seen in temporary form
in deep anesthesia in a stage prior to total flattening of the EEG.
ATYPICAL BUT NORMAL WAVE FORMS
Atypical normal waves may include:
Lambda waves and POSTS
K Complexes
Vertex waves
Mu rhythm
Psychomotor variant
Fourteen and Six
Lambda and POSTS
Lambda and POSTS are similar morphologically, and have a triangular
shape.They occur posteriorly and symmetrically. POSTS stands for
'positive occipital transients of sleep' and occurs in stage 2 sleep.
Lambda occurs in the awake patient when the eyes stare at blank
surfaces. Both are normal wave forms and can occur singly or in
long or short runs.
K Complexes
K Complexes occur in sleep when arroused - thus K complexes are
seen with noises or other stimuli especially in stage 2 sleep. The
K complex is often followed by an arrousal response - namely a
run of theta waves of high amplitude. Following this the EEG
shows sleep again or the awake state.
V Waves
V waves occur in the parasaggital areas of the two sides and take the
form of sharp waves or even spikes which show in the biparietal
regions(vertex) withphase reversal at the midline in tranverse
montages or at the vertex in front-to-back ones. They are seen
in stage 2 sleep along with spindles, K complexes, POSTS, etc..
MU activity
Mu activity is a rhythm in which the waves have a shape
suggestive of a wicket fence with sharp tips and rounded bases.
It may show phase reversal between two channels. The frequency
is generally half of the fast activity present.
Psychomotor Variant
Psychomotor variant is a rare rhythm which appears to be an harmonic
of two or more basic rhythms causing a complex form. As can be seen
it is higher in amplitude than the surround and the waves have a notched
appearance. It is quite assymetrical and is often mistaken for paroxysmal
activity. It is benign. It is also known as
Fourteen and Six Rhythm
Fourteen and six activity is most often seen in children and adolescents.
As seen it takes the form of 6 Hz and 14 Hz waves sometimes going in
the same direction(up or down) and in others in opposite directions. It is
typically seen in sleep or drowsiness and is usually seen in monopolar
recordings.
Dr. Hans Berger
Az alfa-hullámok felfedezője.
They wanted to call the Alpha waves the Berger rhythm, but Hans
Berger was modest and rejected it.
Berger soon became world famous, except in Germany. There
Hitler's regime was oppressing his University of Jena. Thus he was
greatly surprised when in 1937 at an international congress in Paris he
found himself celebrated by researchers from around the world.
However on September 30, 1938 he was forced by Nazi officials to retire the next day. After a
series of further tragedies, Berger committed suicide in 1941. He was twice considered for
the Nobel Prize, but the Nazis prevented it from being awarded and accepted. By contrast, in
England two EEGs labs before the war had grown to 50 by the end because of the usefulness
in diagnosing brain injuries.
14. Eseményhez-kötött potenciálok típusai (exogén, endogén komponensek)
http://www.audiospeech.ubc.ca/haplab/aep.htm
The event-related potential (ERP) is a neural signal that reflects coordinated
neural network activity.
The traditional approach to the analysis of transient ERPs is to consider the ERP
as a characteristic waveform that occurs in relation to the behaviorally
significant discrete event. As a simplifying assumption, the ERP waveform is
usually treated as if it possesses the same amplitude and phase each time that the
event is repeated on multiple trials, although recent analysis shows that this
assumption may not always be valid (Truccolo et al., 2002). Nonetheless, as was
discussed above, the recorded single-trial field potential contains contributions
from network activity that are both associated (ERP signal) and not associated
(noise) with the event. Therefore, averaging of the single-trial field potential
time series, time-locked to the event, is commonly employed to extract the ERP
from the non-event-related noise. When the relevant event is a sensory
stimulus, such phase-locked ERPs are called ?evoked.? Averaged evoked
potentials (Figure 2) are most commonly described in terms of the succession of
waveform components that follow stimulus presentation. These components are
typically identified according to their polarity (positive or negative) and their
time latency following stimulus onset. (Note that the time latency is equivalent
to phase in this context.) Transient ERP waveform components having variable
phase may also reliably occur in relation to the repeated event. In this case, time
series averaging does not reveal the ERP but instead is destructive, since
components of opposite polarity on successive trials tend to be cancelled. Nonphase-locked ERPs are referred to as ?induced? when they occur following a
stimulus and ?spontaneous? in the period prior to a stimulus or motor response.
This type of ERP may be effectively analyzed by averaging the frequency
content of single-trial time series rather than the time series themselves.
http://www.ccs.fau.edu/~bressler/pdf/HBTNN.html
Event-Related Potentials
The electric response evoked in the central nervous system by stimulation of sensory
receptors or some point on the sensory pathway leading from the receptor to the cortex.
The evoked stimulus can be auditory (EVOKED POTENTIALS, AUDITORY),
somatosensory (EVOKED POTENTIALS, SOMATOSENSORY), or visual (EVOKED
POTENTIALS, VISUAL), although other modalities have been reported. Event-related
potentials is sometimes used synonymously with evoked potentials but is often associated
with the execution of a motor, cognitive, or psychophysiological task, as well as with the
response to a stimulus.
http://www.bnl.gov/neuropsychology/monetary_rewards_erp.asp
Within the ERP literature, it has become common practice to dissociate early
components of the ERP from late components in an attempt to identify neural behavior
associated with stimulus processing. ERP components (waveform peaks or troughs) that
occur within the first 200 ms of stimulus onset have been correlated with the physical
attributes of a stimulus (so-called exogenous components). By contrast, endogenous
components, occurring after 200 ms, have been correlated with conceptual behavior.
Early processing deficits could indicate sensory system impairments (e.g., inability to
detect features of a complex stimulus). Given such sensory deficits, a behavioral
intervention could target these impairments.
EEG and Event Related Potentials
There is a long history of attempts to correlate aspects of brain activity with psychometrically
measured IQ. In particular many studies have used the EEG, which is brain activity recorded
via electrodes glued on the scalp. There are various theories about the mechanisms of EEG,
however while it appears to reflect he activity of many brain cells its exact mechanism is
uncertain. EEG reflects a brain CORRELATE of behaviour - it does not provide a brain
MECHANISM. This is important - for showing that EEG relates to some cognitive activity
(e.g. intelligence) requires that the investigator rules out a great range of other possible
interpretations, such as motivation, movement, attention etc. before he or she can claim a
definitive relationship.
Event related potential (ERPs) are responses made by the brain for up to a second following
an eliciting stimulus. They can be reliably extracted from the ongoing EEG by a process of
averaging. The ERP is a waveform that is characterised a series of components that appear at
more or less fixed times for up to a second following the eliciting stimulus. Some researchers
distinguish between the earlier components of the ERP that they characterise as 'exogenous
(i.e. evoked by the stimulus) and the later or endogenous components. These latter are brain
processes that relate to cognitive processes generated by the subjects as a response to the
stimulus, rather than simply being sensory responses to the stimulus.
The ERP is responsive to changes both in stimulus parameters and also to changes in
cognitive state (e.g. attention) in subjects. It also varies according to where on the scalp
electrodes are placed - thus reflecting differing underlying brain structures.
ERPs and Intelligence - 'string length'
Hendrickson & Hendrickson 1980. These workers reported a correlation of 0.77 between full
scale WAIS IQ and a 'string' measure of the ERP to simple tones (overall length of wave
measured by a 'planimeter'). This was done on a sample of 254, 14 - 16 year olds. Obtained a
similar correlation subsequently using Raven's matrices.
There have subsequently been a variety of non-replications and in the main smaller
correlations, however many studies DO find a relationship between ERP and IQ. (See
Mackintosh 236 - 242 for a useful but unsympathetic review). For example Batt et al 1999
used both passive listening and active tasks taking recording at different brain sites. They
suggest that they had greater differences over frontal cortex, for later components and when
subjects were actively engaged in cognitive tasks.
While this may well show a correlation with IQ, the number of possible reasons becomes very
large - particularly since later components of the ERP may reflect a variety of possible
cogniti9ve processes. The problem then becomes one of interpreting the correlations - and it is
not clear that they reflect any simple notion of speed of processing. The fact that it is a brain
record does not make the logic of interpretation any different than say RT or IT.
----------------------------------------------------------------------------------------------------------------------ERPs and Intelligence N1- P2 slope
Deary and Caryl (1997) cite a series of studies claiming that a difference emerges between
140 and 200 msec between high and low intelligence groups when subjects are performing an
IT task. Higher intelligence is associated with a faster rising slope and correlations of up to
0.6 have been found.. Deary claims "This timing is consistent with the view that IT taps the
speed of stimulus intake".
This is an interesting finding and it is within the 'exogenous' range that might reflect stimulus
input more clearly. However this is also a component in the ERP that has historically has been
linked to correlates of attention. Showing a relation between IT and the N1-P2 rise time might
be regarded as verification of IT as reflecting processing speed - since the ERP rises faster
with quicker IT. But alternatively the same data might be used to argue that the ERP reflects
processing speed because faster rise time is associated wither quicker identification in IT.
Clearly a fuller analysis if the N1-P2 component as reflecting nothing but intake of stimulus
information would be needed in order to break out of such circularity.
When reading about brain research, one often comes across the abbreviations EP, ERP, and
AEP. These all refer basically to the same phenomenon. An evoked potential (EP) or an
event-related potential (ERP) is a brain wave response to auditory stimuli, such as a light
flash, a musical tone, a click, or a photograph. As recorded from the surface of the scalp, EPs
are exceedingly low level electrical signals. They have to be averaged before a reliable
waveform can be obtained. Among the many usages of the AEP is the investigation of
perceptual dysfunction in patients, such as those suspected of having schizophrenia.
The EP is a complex waveform. One way to label the ups and downs of the waves is to
designate positive deflections by the letter P and negative deflections by the letter N. Then the
ups and downs are labeled consecutively with numbers, the first up being P1, the next one
being P2, etc. The third upward wave is the P3 waveform. Because this component occurs
around 300 milliseconds after the presentation of the stimulus, it sometimes is referred to as
P300. P3 appears to reflect active cognitive processing of stimulus information by the subject.
Its latency and amplitude shows considerable variability from one person to another. The
presence of this variability has suggested that P3 might serve as a physiological index of an
individual's "cognitive style." The waveforms up to P3 are known as exogenous components,
and as endogenous components from P3 onward. The endogenous components are related to
the personality characteristics of the subjects.
In addition to EPs, there is a far-field potential, or brain stem auditory ERP. This occurs
within the initial 10 milliseconds following the presentation of an auditory stimulus such as a
click. There is evidence that the waveform of a typical brain stem auditory ERP consists of six
or seven distinctive, positive waves. Each of these waves signifies the arrival of the stimulus
at a particular anatomical location within the brain. Wave I signals the occurrence of activity
in the auditory nerve consequent to stimulation; wave II originates from the cochlear nucleus
in the medulla; wave II marks the arrival of the stimulus at the superior olivary complex in the
pons; wave IV denotes arrival at the lateral lemniscus, also in the pons; wave V signals arrival
at the inferior colliculus in the midbrain; and wave VI denotes arrival at the medial geniculate
body in the thalamus. These are helpful in diagnosing a variety of neurological disorders. For
instance, the far-field potential can help pinpoint a lesion in the brain.
Some important components:
Prestimulus:
CNV: contingent negative variation: attentional preparedness
Lateralized Readiness Potential: specific motor preparedness
Exogenous:
ABRs: sub-cortical, low-level auditory processing
N1 and P2: auditory processing in the auditory cortex (primary & secondary)
MMN: early, low-level detector of context inconsistent stimuli
Endogenous:
PN: attentional gating
P3: attentional deviance detector (P3a vs P3b)
Language related: N400, LP
FONTOS:
http://www.psych.ku.edu/psyc475/Electroencephalogram