Normal brain function involves continuous electrical activity
Patterns of neuronal electrical activity recorded are called brain waves
Brain waves change with age, sensory stimuli, brain disease, and the chemical state of the body
An electroencephalogram (EEG) records this activity
EEGs can be used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epileptic lesions
A flat EEG (no electrical activity) is clinical evidence of death
The EEG be recorded with Scalp electrodes through the unopened skull or with electrodes on or in the brain. A normal EEG
Measures synaptic potentials produced at cell bodies and dendrites.
Create electrical currents.
Used clinically diagnose epilepsy and brain death.
Alpha: low-amplitude, slow, synchronous waves indicating an “idling” brain
Recorded from parietal and occipital regions.
Person is awake, relaxed, with eyes closed.
50 ~100 V .
Beta:high-amplitude waves seen in deep sleep and when reticular activating system is damped
Strongest from frontal lobes near precentral gyrus.
Produced by visual stimuli and mental activity.
Alpha Block: Replacement of the alpha rhythm by an asynchronous, low-voltage beta rhythm when opening the eyes.
Theta : more irregular than alpha waves
Emitted from temporal and occipital lobes.
Common in newborn some sleep in adult.
Adult indicates severe emotional stress.
Delta: high-amplitude waves;
Common during sleep and awake infant.
In awake adult indicate brain damage.
SPONTANEOUS CORTICAL ELECTRICAL POTENTIALS: THE EEG
Diagrammatic comparison of the electrical responses of the axon and the dendrites of a large cortical neuron. 2. Mechanism of EEG Current flow to and from active synaptic knobs on the dendrites produces wave activity, while AP are transmitted along the axon.
Mechanism of EEG
Continuous graph of changing voltage fields at scalp surface resulting from ongoing synaptic activity in underlying cortex
Inputs from subcortical structures
Brainstem reticular formation
EEG signals generated by cortex
Currents in extracellular space generated by summation of EPSPs and IPSPs
Evoked cortical potential
Electrical activities in cortex after stimulation of a sense organ
1. Primary evoked potential
2. Diffuse evoked potential
EEG Records During Epileptic Seizure Epilepsy is characterized by uncontrolled excessive activity of either a part or all of the central nervous system. Grand mal epilepsy: characterized by extreme neuronal discharges in all areas of the brain, last from a few seconds to 3 to 4 minutes. Petit mal epilepsy: Characterized by 3 to 30 seconds of unconsciousness or diminished consciousness during which the person has several twitch-like contractions of the muscle.
II Wakefulness and Sleep
Sleep is a behavior and an altered state of consciousness
Sleep is associated with an urge to lie down for several hours in a quiet environment
Few movement occur during sleep (eye movements)
The nature of consciousness is changed during sleep
We experience some dreaming during sleep
We may recall very little of the mental activity that occurred during sleep
We spend about a third of our lives in sleep
A basic issue is to understand the function of sleep
One passes through four stages of NREM during the first 30-45 minutes of sleep
REM sleep occurs after the fourth NREM stage has been achieved
Alpha, delta, theta activity are present in the EEG record
Stages 1 and 2: Alpha waves
Stages 3 and 4: delta activity (synchronized)
Termed slow-wave sleep (SWS)
Light, even respiration
Muscle control is present (toss and turn)
Dreaming (could but not vivid, rational)
Difficult to rouse from stage 4 SWS
Types and Stages of Sleep: NREM
Stage 1 – eyes are closed and relaxation begins; the EEG shows alpha waves; one can be easily aroused
Stage 2 – EEG pattern is irregular with sleep spindles (high-voltage wave bursts); arousal is more difficult
Stage 3 – sleep deepens; theta and delta waves appear; vital signs decline; dreaming is common
Stage 4 – EEG pattern is dominated by delta waves; skeletal muscles are relaxed; arousal is difficult
Presence of beta activity (desynchronized EEG pattern)
Physiological arousal threshold increases
Breathing more irregular and rapid
Brainwave activity resembles wakefulness
Pontine-Geniculate-Occipital (PGO) waves
Loss of muscle tone (paralysis)
Vivid, emotional dreams
May be involved in memory consolidation
Pontine-geniculate-occipital (PGO) wave – A synchronized burst of electrical activity that originates in the pons and like a wave it activates the lateral geniculate nucleus (first relay of visual information) and then the occipital lobe, specifically in the visual cortex (which receives and puts together the visual information that comes from the lat. geniculate nucleus). PGO waves appear seconds before and during REM sleep.
Sleep Stage Cycles
A typical sleep pattern alternates between REM and NREM sleep
SWS precedes REM sleep
REM sleep lengthens over the night
Basic sleep cycle = 90 minutes
The suprachiasmatic and preoptic nuclei of the hypothalamus regulate the sleep cycle
Importance of Sleep
Sleep is necessary for survival
Sleep appears necessary for our nervous systems to work properly.
During the SWS, growth hormone secretion increase and important for the infants growth and physical restorative process of adult
During REM, brain blood flow and protein synthesis increase, and it is important for the mental development of infants and long-term memory and mental restoration in adults.
Daily sleep requirements decline with age
What Happens if We are Deprived of Sleep?
Lack of alertness
Lack of motivation
Neural Regulation of Arousal
Electrical stimulation of the brain stem induces arousal
Dorsal path: RF--> to medial thalamus --> cortex
Ventral path: RF --> to lateral hypothalamus, basal ganglia, and the forebrain
Neurotransmitters involved in arousal:
NE neurons in locus coeruleus (LC) show high activity during wakefulness, low activity during sleep (zero during REM sleep)
LC neurons may play a role in vigilance
Activation of ACh neurons produces behavioral activation and cortical desynchrony
ACh agonists increase arousal, ACh antagonists decrease arousal
5-HT: stimulation of the raphe nuclei induces arousal whereas 5-HT antagonists reduce cortical arousal
Neural Control of SWS
The ventrolateral preoptic area (VLPA) is important for the control of sleep
Lesions of the preoptic area produce total insomnia, leading to death
Electrical stimulation of the preoptic area induces signs of drowsiness in cats
VLPA neurons promote sleep
possible causes: excessive noise, stress, drugs, medications, pain, uncomfortable temperature, sleep apnea, periodic limb movement disorder
Frequent, unexpected periods of sleepiness during the day