1. States of Brain Activity
Lec: Dr. Farah Nabil Abbas

2. Brain Waves
It is the electrical recording from the surface of the brain. Its intensity and patterns are determined to a great extent by the level of excitation of brain (sleep, wakefulness, diseases …etc). The entire recording is called EEG. Intensities range from micro-volts and frequency from once every few seconds to 50 or more per second.

3. Types of Brain Waves  
1.Alpha Waves: rhythmical waves of 8-13 /sec, frequency from an EEG of almost all normal adult people when they are awake in a quite, resting state of cerebration and closed eyes. When eyes are opened alpha waves change to beta waves. The voltage of alpha waves equals to 50 micro-volts and are easily recorded from occipital lobe, but also can be recorded from frontal and parietal regions of scalp.

4. Beta Waves: frequency from 14-25 /sec. It might reach to 80 /sec
Beta Waves: frequency from /sec. It might reach to 80 /sec. Always recorded from parietal and frontal regions during activation or tension of CNS.

5. Theta Waves: frequency from 4-7 /sec
Theta Waves: frequency from 4-7 /sec. occur mainly in parietal and temporal regions in children, can be recorded in some adults during emotional stress (disappointment and frustration). It also occurs in many brain disorders (degenerative brain disease).

6. Delta Waves: frequency below 3. 5 /sec. It reflects cortical activity
Delta Waves: frequency below 3.5 /sec. It reflects cortical activity. Can be recorded in deep sleep, in infancy and serious organic diseases.

8. Origin of Brain Waves
Thousands or even millions of neurons or fibers must fire synchronously, so that can be recorded from the scalp. Discharge of a single neuron or nerve fiber in brain can never be recorded. The intensity of brain waves are nullified when there is strong non-synchronously nerve signals (opposing polarities). Alpha waves result from spontaneous feedback oscillation in the thalamo-cortical system with the RAS (reticular activating system). While delta waves originate from cortical neurons alone independent from lower brain structure (RAS).

9. Sleep
Unconscious state from which the person can be aroused by sensory or other stimuli. Types of sleep: Slow wave sleep. Rapid eye movement sleep (REM). Slow Wave Sleep: deep, restful type of sleep. Experienced usually during the first hour of sleep after being kept awake for many hours, composed of 75% of total sleep period, interrupted by REM sleep, lasts for 90 minutes to recur after a period of REM of 5-30 minutes. It is associated with a decrease in blood pressure, respiratory rate and basal metabolic rate. Dreams do occur and even nightmares, however, they can not be remembered i.e. consolidation of the dreams in memory do not occur.

10. REM Sleep: occur periodically, not so restful type of sleep
REM Sleep: occur periodically, not so restful type of sleep. It occupies 20% of sleep time of young adults, lasts 5-30 minutes for every 90 minutes of slow wave sleep, it is associated with active dreaming that can be remembered in awakefulness, associated with decrease in all muscle tone except rapid movements of the eyes, heart rate and respiratory rate are irregular, it is difficult to arouse the person by sensory stimuli, however, people usually awaken in the morning during an episode of REM. In REM sleep the brain is active and the brain metabolism is increased, however, the brain activity is not channeled to let the person fully aware of his surrounding or to be awake. Drugs that mimic acetyl-choline increase the occurrence of REM sleep, this might indicate that RAS neurons are responsible for REM sleep (cholinergic fibers).

11. Basic Theories of Sleep
Passive Theory of Sleep: (old theory and not well accepted today) states that RAS gets fatigued during the periods of awaking day and become inactive leading to sleep.
Active Theory of Sleep: there are centers located below the mid-pons and responsible for inhibiting other parts of the brain. A

12. Sleep Centers
Raphi nucleus at lower pons and medulla secretes serotonin (a major neurotransmitter associated with sleep). This nucleus sends fibers to reticular formation, thalamus, hypothalamus, cortex and spinal cord (inhibit pain impulses). Drugs that block serotonin formation lead to insomnia (deprivation from sleep).
Nucleus of tractus-solitarius: in pons and medulla for visceral sensory signals by Vagus and Glossopharyngeal nerves, they act by exciting Raphi nucleus to release serotonin and cause sleep.
Hypothalamus (suprachiasmatic area) and the thalamus (diffuse nuclei) can promote sleep.
Sleeping factors e.x. muramyl peptide and nonapeptide that is collected from CSF of person or animal kept awake for several hours, when injected to other animal’s brain (in 3rd ventricle) will lead to natural sleep.
Lesions in sleep centers e.x. Raphi nucleus or hypothalamus (suprachiasmatic nucleus) lead to high state of awakefulness, animal might die of exhaustion.

13. EEG Changes in Wakefulness- Sleep
Alert wakefulness is characterized by high frequency Beta waves (opening eyes).
Quite wakefulness is associated with alpha waves (closing eyes).
Slow wave sleep which is divided into four stages, stage one characterized by low voltage waves broken by sleep spindles (alpha waves). In stage 2, 3, 4 the frequency becomes progressively slower (1-3 sec.) in stage 4 typical delta waves.
REM sleep: similar to alert awake person suggesting excessive and synchronized actively (beta wave).

16. Epilepsy (seizures): Uncontrolled excessive activity of either a part or all of the CNS, it is of 3 types:
1. Grand mal epilepsy: there is extreme neuronal discharge in all areas of brain (cortex, thalamus, brainstem, spinal cord) leading to tonic-clonic seizures, biting the tongue, difficulty in breathing, urination and defecation, then the person remains in stupor for a few minutes, then fatigued and sleeps for several hours.
On EEG, there are high-voltage synchronous discharges over the entire cortex on both sides of the brain.

17. 2. Petit-mal epilepsy: involves the basic thalamocortical activating system it is characterized by 3-30 seconds of unconsciousness or diminished consciousness during which muscles twitches may occur especially in the head e.x. blinking the eyes (the absence syndrome). On EEG, there is typically “The Spike & the Dome patterns” over most of the cortex. 3. Focal epilepsy: involves either localized regions of cortex or deeper structures, it results from localized organic disease (ex. Tumor) or scar tissue.