Lab 1 Flashcards
Normal EEG tracing
A normal EEG tracing consists of waves of various frequencies. The dominant frequencies depend on several factors, including the state of wakefulness, the age of the subject, the location of the recording electrodes, and the absence or presence of drugs or disease. When a normal awake adult is relaxed with the eyes closed, the dominant frequencies of the EEG recorded over the parietal and occipital lobes are about 8 to 12 Hz, the alpha rhythm. If the subject is asked to open the eyes, the wave becomes less synchronized, and the dominant frequency increases to 13 to 30 Hz, which is called the beta rhythm. The delta (0.5 to 2 Hz) and theta (3 to 7 Hz) rhythms are observed during sleep
Alpha rhythm
When a normal awake adult is relaxed with the eyes closed, the dominant
frequencies of the EEG recorded over the parietal and occipital lobes are about 8 to 12 Hz, the alpha rhythm.
Beta rhythm
If the subject is asked to open the eyes, the wave becomes less synchronized, and the dominant frequency increases to 13 to 30 Hz, which is called the beta rhythm.
Amplitude and frequency of the oscillations when the eyes are closed?
8-12 Hz
Larger amplitudes than beta
Amplitude and frequency of the oscillations when the eyes are open?
13-30 Hz
Smaller amplitudes than alpha
What causes the rhythmic oscillation of the EEG when the eyes are closed?
Alpha occurs in the brains of healthy and awake adults who are resting with their eyes closed. Disappear during sleep and they also vanish when the individual begins to concentrate on a specific task
What causes the rhythmic oscillation of the EEG when the eyes are open?
Higher frequency waves that appear in people who are either concentrating on a task, under stress, or are in a state of psychological tension
Explain how the EEG exhibits larger amplitude oscillations when someone closes their eyes than when their eyes are open
In general, the amplitude of the EEG increases as the frequency decreases
When someone closes their eyes, the alpha rhythm with a frequency of 8-12Hz is prominent
When someone opens their eyes, the alpha rhythm is reduced and the beta rhythm with a frequency of 13-30Hz becomes more evident
Cortical evoked potential
is the specific activation of a particular population of cortical neurons in response to a defined stimulus
Alpha vs Beta rhythm
Alpha waves are seen in the EEG during resting with eyes closed and the beta EEG is present when a person is alert/attentive and thinking actively
Frequency of alpha rhythm
8-12 Hz
Frequency of beta rhythm
13-30 Hz
Visual evoked potential
The term visually evoked potential (VEP) refers to electrical potentials recorded from scalp overlying visual cortex that have been extracted from the electroencephalogram by signal averaging.Any abnormality that affects the visual pathways or visual cortex in the brain can affect the VEP.
Visual evoked potential
The term visually evoked potential (VEP) refers to electrical potentials recorded from scalp overlying visual cortex that have been extracted from the electroencephalogram by signal averaging.Any abnormality that affects the visual pathways or visual cortex in the brain can affect the VEP.
Biological data measurement
Input - amplification - filtering - sampling - display
Sampling is rate dependent and need a high enough rate to catch important events
The overall idea of digital biological recording
The biological events we record in physiology are continuous. Using digital technology, continuous data is sampled at some interval, and then turned into numbers that are stored in a digital device.This data can be optimised to display data that best represents real events by amplifying the signal, filtering out noise and selecting an appropriate sampling rate.
Scope mode
Used to record very rapid events over short periods
Chart mode
used for recording continuous events
Sampling rate
A correct sampling rate is essential to recording good quality data
Importance of the correct sampling rate for the finger transducer experiment
While the waveform you are recording looks like a continuous signal, digitised data is not continuous. The signal that enters the Powerlab from the finger pulse transducer is sampled at discrete and seperate intervals (determined by the sampling rate) and each data point is then connected by a series of lines to complete the waveform
High sampling rate
If the sampling rate is sufficiently high, then the sampled points are close together and there is very little data loss
Low sampling rate
If the sampling rate is too low, then data can be lost in-between each discrete sample
Out of 4/s and a 1k/s sample rate which one gives the most accurate recording of a pulse wave?
1k/s
The _____ pattern will affect the pulse wave amplitude over time (finger pulse transducer)
Breathing
What effect does breath holding have on the pulse wave form?
It decreases the amplitude therefore the pulse gets weaker
Overall idea of sample rate
If the sampling of data occurs more frequently then the trace will be more representative of the actual physiological phenomenon
Frequency
1/duration
Electrical waveform of the EEG depends on our …
State of consciousness
EEGs are recorded by
placing electrodes on the surface of the head - different recordings can be made from different parts of the brain, depending on where the electrodes are placed. Neurons closest to the electrodes will generate the largest signal
Noise artifacts in EEG
Large spike are noise artefacts dur to the signals caused by blinking and the eyes opening/closing
Why is important that the subject does not move during the EEG recording?
Movement will generate electrical noise from muscle activation
Synchronised activity in an EEG recording trace
- Firing of large numbers of EPSPs OR IPSPs at one time
- Similar signals occurring at the same time sum together
- Prominent alpha waves
- Occurs when ‘eyes closed’
Desynchronised activity in an EEG recording trace
• Firing of both EPSPs AND IPSPs at the same time. • The opposing signals will cancel each other out • No/neligible alpha waves • Occurs when ‘eyes open’
Most appropriate sampling rate for the EEG recording to capture alpha waves? (1, 10, 20 Hz or 1kHz)
1kHz
To ensure that 8-12 Hz alpha waves are recorded, need a sampling rate that is higher than the expected maximum value of the recording
Sampling rate needs to be high
enough to take many samples per event (each alpha wave) so that the trace will be representative of the actual physiological recording
Synchronised activity eyes open or closed
Eyes closed
Desynchronised activity eyes open or closed
Eyes open
Alpha waves for synchronised activity
Prominent peaks at 8-12Hz which is the alpha rhythm
Alpha waves for desynchronised activity
No prominent peaks
If EPSPs summate for synchronised activity then …
Will get a bigger alpha between 8-12 Hz
VEP
Visual evoked potential is a type of CEP evoked by a visual stimulus
VEP form
Is usually a triphasic form with a major peak (P100) flanked by 2 smaller peaks of opposite polarity
P100 VEP
P100 is where the waveform peaks at about 100ms and it is thought to be generated by activity in the optic radiations which project to the visual cortex, and in the visual cortex itself
Small early peak and small late peak VEP
The small early peak might result from activation of the lateral geniculate nucleus and the late peak from activity in the visual association cortex
What is responsible for the delay between the stimulus and the P100?
Phototransduction, signal transmission, synapses
CEP
cortical evoked potential is a stereotypical electrical response to a specific stimulus
Latency
The time delay between a stimulus and a response
Slow wave form peak than P100 would indicate…
Slower would means demyelination, slower reaction times etc
Sample mean
Which represents our best guess at the mean from the population
Sample standard deviation
Which gives an estimate of sampling precision/variance
measure of how spread out the numbers are
Sampling bias
Which are errors we make when taking a sample from a population that move us away from the correct conclusion about that population
T test
Statistical test that is used to compare the means from two samples. It does this by dividing the mean of the samples (the signal) by the sample standard deviation (variability). This means that if you have samples with low variability you can be surer that the difference between the sample means is real. The t-test assumes the populations from which the two samples were taken have symmetric bell shaped curves known as normal distribution that is entered around the sample mean and they also have equal variance.
Paired t test
Compares two data sets from the same population before and after a treatment/test
Unpaired t test
Compares two data sets form two different populations such as male vs females or young vs old
P<0.05
Statistically significant
P > 0.05
Not statistically significant
P100s different from male to female because….
due to endocrine (e.g. hormonal influence on myelin) or anatomical variance between sexes such as in head circumference
Are we unconscious when we are asleep?
No because we can be woken up
Coma vs vegetative state
The word coma usually refers to the state in which a person appears to be asleep but cannot be awakened. Persistent vegetative state refers to another form of altered consciousness in which the person appears to be awake but does not respond meaningfully to the outside world.
Vegetative state - patient exhibit the arousal component of consciousness but not awareness. which part of the brain is most likely malfunctioning in a patient in a vegetative state
if the patient has no awareness, this indicates that the cerebral cortex is malfunctioning
Amplitude of alpha rhythm is greater with the eyes…
closed (synchronised activity)
