The Brain and Sleep Flashcards
What is an electrocephalogram?
• The EEG is the classical method of recording brain rhythms and is essential for studying sleep, epileptic seizures.
• It is a measurement of electrical activity from the surface of the scalp that enables us to glimpse the generalized activity of the cerebral cortex
• Can be recorded by applying electrodes on the scalp in patients or by placing them on the surface of the brain in experimental animals
• The electrical activity appears on a multichannel recorder as waves of variable intensity (0-200 uV) and frequency (1-50 Hz)
How does an electroencephalogram work?
• The electrodes are wires taped to the scalp, along with conductive paste to ensure a low-resistance connection
• Small voltage fluctuations, usually a few tens of microvolts in amplitude, are measured between selected pairs of electrodes.
• Different regions of the brain-anterior and posterior, left and right-can be examined by selecting the appropriate electrode pairs.
• The typical EEG record is a set of many simultaneous squiggles, indicating voltage changes between pairs of electrodes
Describe the standard positions for placement of EEF electrodes?
A, auricle (or ear)
C, central
Cz, vertex
F, frontal;
Fp, frontal pole
O, occipital
P, parietal
T, temporal.
What does an EEG record?
An EEG measures voltages generated by the currents that flow during synaptic
excitation of the dendrites of many pyramidal neurons in the cerebral cortex
- Therefore, it takes many thousands of underlying neurons, activated together, to generate an EEG signal big enough to be measured at all
- electrical contribution of any single cortical neuron is exceedingly small, and the signal must penetrate several layers of non-neural tissue to reach the electrodes
Describe the generation of large EEG signals by synchronous activity?
• In a population of pyramidal cells located under an EEG electrode, each neuron receives many synaptic inputs.
• If the inputs fire at irregular intervals, the pyramidal cell responses are not synchronized, and the summed activity detected by the electrode has a small amplitude.
• If the same number of inputs fire within a narrow time window so the pyramidal cell responses are synchronized, the resulting EEG is much larger
Name the 4 types of normal EEG waves?
Alpha - awake and resting
Beta - awake with mental activity
Theta - sleeping
Delta - deep sleep
Describe alpha waves of an EEG?
• These are rhythmic waves occurring at a frequency of 8-13/s (8-13 Hz) with an amplitude of about 50 uV.
• These are most marked in the parieto-occipital region but they are sometimes observed in other locations.
• Alpha waves are recorded in mentally & physically relaxed person who is awake but with the eyes closed
Describe beta waves of an EEG?
When the awake person’s attention is directed to some specific type of mental activity, the alpha waves are replaced by asynchronous, higher-frequency (8-30 Hz) but lower-voltage beta waves.
Seen in the parietal and frontal regions.
Describe theta waves of an EEG?
• These are large 100 V waves with frequencies between 4 and 7 Hz
•They an occur during both sleeping and waking states
• They occur normally in the parietal and temporal regions in children
• They also occur during emotional stress in some adults, particularly during disappointment and frustration.
• They also occur in many brain disorders, often in degenerative brain states
Describe delta waves of an EEG?
Include all the waves of the EEG with
frequencies less than
3.5 Hz, and they often have voltages two to four times greater than most other types of brain waves.
• They occur in very deep sleep, in infancy, and in serious organic brain disease
• When theta & delta waves occur in an adult during the waking state, it always indicates abnormality
• Hyperventilation induce theta and delta waves bilaterally
How do you localize brain tumors with an EEG?
• Large tumours block electrical activity
• Voltage of the brain waves in the region of the tumour is considerably reduced
• On the other hand the presence of a tumour can lead to very high-voltage waves in the EEG
Describe the Clinical uses of the EEG?
- Diagnosis of psychopathic disturbances
• This needs an experienced electroencephalographer and is useful in only certain types of psychopathic disturbances - Diagnosis of different types of epilepsy
• Seizures, the most extreme form of synchronous brain activity, are always a sign of pathology.
• Epilepsy is characterized by recurrent and unprovoked seizures
Describe the different types of seizures in epilepsy?
- A generalized seizure involves the entire cerebral cortex of both hemispheres
- A partial seizure involves only a circumscribed area of the cortex
- If it begins in a sensory area, it can trigger an abnormal sensation (an aura) such as an odd smell or sparkling lights
- If it begins in a small area of motor cortex, it can cause clonic movement of part of a limb
What is REM sleep?
Several times during a night, you enter a state called rapid eye movement (REM) sleep when your EEG looks more awake than asleep, your body (except for your eye and respiratory muscles) is immobilized, and you conjure up the vivid, detailed illusions we call dreams.
- The rest of the time, you spend in a state called non-REM sleep in which the brain does not usually generate complex dreams
Describe the functional state of the brain when you’re awake?
EEG: Low voltage, fast
Sensation: Vivid, externally generated
Thought: Logical, progressive
Movement: Continuous, voluntary
REM: Often
