Lab 1 Flashcards
(51 cards)
EEG
Electroencephalogram;
Records electrical activity of neurons, or brain waves
EEG signals are affected by the state of arousal of cerebral cortex and show characteristic changes in different stages of sleep
EEG signals are affected by stimulation from the external environment
EEG is used in the diagnosis of epilepsy, sleep disorders, and the diagnosis of brain death
Brain waves
Patterns of neuronal electrical activity recorded
Generated by synaptic activity at the surface of the cortex, rather than by action potentials in the white matter
EEG made and recorded
EEG is made by placing electrodes on the scalp and then connecting the electrodes to an apparatus that measures electrical potential differences between various cortical areas
EEG is recorded by small voltage signals
Signals are small because recording electrodes are separated from the brain’s surface by the scalp, skull, and a layer of cerebrospinal fluid
Electrodes must be made of the right material and they must be connected properly
Might record artifacts
Artifacts
A range of unwanted interfering influences that may spoil Electroencephalogram (EEG) recordings
Origin of EEG
EEG results from slow changes in the membrane po-
tentials of cortical neurons, especially the excitatory and
inhibitory postsynaptic potentials (EPSPs and IPSPs)
Little contribution normally comes from action potentials propagated along nerve axon
EEG reflects the algebraic sum of the electrical potential changes occurring from large populations of cells; Therefore, large amplitude waves require
the synchronous activity of a large number of neurons
Components of EEG waveform
Amplitude
Frequency
Brain waves
Frequency
The number of peaks in one second; Expressed in hertz (Hz); A frequency of 1 Hz means that one peak occurs each second
Sleep induces lower amplitudes of brain waves
Amplitude
Amplitude or intensity of any wave is represented by how high the wave peaks rise and how low the troughs dip
Amplitude of brain waves reflects the synchronous activity of individual neurons
Usually, brain waves are complex and have low amplitude
Sleep induces higher amplitudes of brain waves
Alpha brain waves
8-13 Hz; amplitude 30-50uV
Relatively regular and rhythmic, low-amplitude, synchronous waves
Indicate a brain that is “idling” – a calm, relaxed state of wakeful-
ness; Alpha rhythm is seen when the eyes are closed and
the subject relaxed
It is abolished by eye opening and by mental effort such as doing calculations or concentrating on an idea
It is thus thought to indicate the degree of cortical activation where, the greater the cortical activation, the lower the alpha wave activity
Alpha waves are strongest over the occipital cortex (back of the head) and the frontal cortex
Beta brain waves
14-30 Hz; amplitude <20 uV
Beta waves are also rhythmic, but they are not as regular
as alpha waves and have a higher frequency
Beta waves occur when we are mentally alert, as when concentrating on some problem or visual stimulus
In awake, alert individuals with their eyes open, the dominant rhythm is beta
It may be absent or reduced in areas of cortical damage
and can be accentuated by sedative-hypnotic drugs such
as benzodiazepines and barbiturates
The greater the cortical activity, the higher the beta wave activity will be
Theta brain waves
4-7 Hz; amplitude <30 uV
Theta waves are still more irregular
Though common in awake children (up to adolescent age), theta waves are
uncommon in awake adults but may appear when concentrating
It is normal during sleep at all ages
(Note, however, that some researchers separate this frequency band into two components, low theta (4 - 5.45 Hz) activity that they correlate with decreased arousal and in-
creased drowsiness, and high theta (6 - 7.45 Hz) activity
claimed to be enhanced during tasks involving working
memory.)
Delta brain waves
4 or less Hz; amplitude up to 100-200 uV
Delta waves (4Hz or less) are high-amplitude waves
seen during deep sleep and when the reticular activating
system is damped, such as during anesthesia
In awake adults, they indicate brain damage
Delta rhythm is the dominant rhythm in sleep stages 3 and 4 but is not seen in the conscious adult. This rhythm tends to have the highest amplitude of any of the component EEG waves
Note that EEG artifacts caused by movements of jaw and neck
muscles can produce waves in the same frequency band
Gamma brain waves
30-50 Hz
Some people also recognize gamma waves but their
existence and importance is controversial
These waves may be associated with higher mental activity, including perception and consciousness and they disappear under general anesthesia
One suggestion is that the gamma rhythm reflects the mental activity involved in integrating various aspects of an object (color, shape, movement, etc) to form a coherent picture
Interestingly, recent research has shown that gamma waves are enhanced in Buddhist
monks during meditation and are absent in schizophrenic
Amplitude vs frequency relationship
In general, the more active the brain, the higher the frequency and the lower the amplitude of the EEG
Conversely, the more inactive the brain, the lower the frequency and the higher
the amplitude of the signal
Flat EEG
Spontaneous brain waves are always present, even during unconsciousness and coma
Their absence is clinical evidence of brain death
Consciousness
Encompasses conscious perception of sensations, voluntary initiation and control of movement, and capabilities associated with higher mental processing (memory, logic, judgment, perseverance, and so on)
Clinically, consciousness is defined on a continuum that
grades behavior in response to stimuli as: (1) alertness,
(2) drowsiness or lethargy (which proceeds to sleep), (3)
stupor, and (4) coma
Syncope
Fainting
A brief loss of consciousness and is usually caused by inadequate blood flow to the brain due to low blood pressure
Sleep
A state of partial unconsciousness from which a person can be aroused by stimulation
Cortical activity is depressed during sleep, but brain stem functions, such as control of respiration, heart rate, and blood pressure, continue
Even environmental monitoring continues to some extent, as illustrated by the fact that strong stimuli (i.e. things that go bump in the night) immediately arouse us
Coma
A state of unconscious-
ness for an extended period of time from which a person
cannot be aroused by even the most vigorous stimuli
Types of sleep
Two major types of sleep, which through most of the sleep cycle, are non-rapid movement (NREM) sleep and rapid eye movement (REM)
Sleep patterns
24-hour circadian rhythm
Hypothalamus is responsible for timing of sleep cycle
Suprachiasmatic nucleus (a biological clock) regulates its preoptic nucleus (a sleep-inducing center)
By inhibiting the brain stem’s reticular activating system (RAS), the preoptic nucleus puts the cerebral cortex to sleep
RAS centers maintain the awake state but also mediate some sleep stages, especially dreaming sleep
Orexins
Peptides released by hypothalamic neurons which act as “wake-up” chemicals
Certain neurons of brain stem reticular formation fire at maximal rates, arousing the sleepy cortex
Sleep stages
Stage 1: Associated with decreasing beta activity, alpha activity becomes less obvious, and the emergence of theta activity
Stage 2: Irregular theta activity, short bursts of sleep spindles, and sudden increases in wave amplitude
Stages 3 and 4: Delta activity predominates although there is delta activity for 50% of the time in Stage 3; Deep sleep
Stage 4: When bed-wetting, night terrors, and sleepwalking may occur
REM: Lasts from 20-60 minutes; Occurs about 90 minutes after sleep begins after NREM Stage 4; Brain change is coupled with increases in heart rate, respiratory rate, and blood pressure and a decrease in gastrointestinal motility; Eyes move rapidly under lids, but body’s skeletal muscles are actively inhibited
Sleep importance
NREM Stages 3 and 4: Presumed to be restorative; Deprivation of sleep leads to more time in slow-wave sleep
REM: Work through emotional problems and analyze day’s events; Reverse learning
