Brain Rhythms

Question 1

What does the EEG measure?

Answer 1

• EEG measures AP excitation @ cerebrum
• Small EF by pyramidal cells detected by EEG
• Synchrony of PC’s detected
• Pmaker/ Inhibit or excited neurons

Question 2

Describe the International 10-20 system

Answer 2

• Standardised placement reproducible + symmetrical- electrode coverage over scalp
• Cap with electrodes embedded
• Frontal/Temporal/Parietal/ Occiptal/ Septal part
• Blink artifacts- frontal lobe area, ~ muscular activity interfering with EEG trace
• Need reference electrode in area with no AP, if you are going to use it partially. Normally @ earlobe where there is no muscular contraction. Active vs Reference electrode
• Electrode gel = no resistance and no air pockets
• AP is measured
• because has to pass skull so there is an amplifier to increase signal

Question 3

Explain the primary frequency bands recorded by an EEG

Answer 3

1. Delta <4= deep sleep, slowest thus less freq.
2. Theta 4-8 Hz= fatigue, slow but increased freq.
3. Alpha 8-13 Hz= awake

Beta >13= alert

Question 4

What is consciousness?

What are the grades of consciousness?

Answer 4

What is consciousness?

• Consciousness= AP @ large cortical surface area/ motor control/ connecting thoughts (memory)

What are the grades of consciousness?

• Grade of consciousness= alert, drowsy, stupor (between awake and coma), coma

Question 5

What is the difference between a seizure, convulsion and epilepsy?

Answer 5

• Seizure= abnormal AP @ cerebral cortex –> abnormal activity depending on where AP came from (sensory perception/ motor jerking/ autonomic changes or psychic phenomenon)
• Convulsion= motor seizure entire body
• Epilepsy= lots of seizures–> fit

Question 6

What is the cause of seizures?

Answer 6

• Ions distribution unbalanced due to altered membrane permeability
• Thalamus is pacemaker that can inhibit AP that would otherwise be needed for homeostasis
• Nt imbalance: low GABA = inhibitory neurons not working
• AP too excited/ inhibited (not homeostatic) due to strong interconnection

Question 7

What can be used to prevent seizures?

Answer 7

• Strong convulsants = meds that block inhibitory neurons (GABA neurons) making patient more prone in getting siezures
• Anticonvulsants do opposite, prolong inhibition of GABA

Question 8

Discuss the correlates of seizures, epilepsy and EEG

Answer 8

• General- disturbed consciousness:
  
  • Absence (AKA petitmal)/ Atonic (drop attack, poor muscle tone, droop),
  • Myoclonic (tonic= ongoing violent contraction/ clonic= repeat contraction and relax),
  • Tonic Clonic (grand mal- muscle contract and lose consciousness)
• Partial:
  
  • Simple (1 hemisphere)/
  • Complex (temporal -> 2 lobes)/ partial (2nd general seizure (one -> 2, involve thalamus or reticular formation)
• 2nd generalised
• convulsive STATUS EPILEPTICUS: 5/20min/ repeated seizure with no break (convulsive/non) -> death due to lung failure (1st Tx= BDZ increase inhibitory nt, 2nd Tx= anticonvulsants through IV, barbituate= coma inducing)
• Absence seizure- Large regular voltage, 3Hz rythm

Question 9

The human cerebral cortex is very large and folded. What do these foldings of the cortical surface do to the brain signals that are recorded by an EEG electrode at the sca

Answer 9

For the most part, an EEG measures voltages generated by the currents that flow during synaptic excitation of the dendrites of many pyramidal neurons in the cerebral cortex. The signal must penetrate several layers of non-neural tissue, including the meninges, fluid, bones of the skull, and skin to reach the electrodes. The population of cells deep within the folds of the cortical surface contributes very little to the recorded EEG, which measures activity only in the superficial layers of cortex close to the skull.

Question 10

The EEG rhythm that is associated with a quiet, waking state is the ________ rhythm.

a) alpha
b) beta
c) gamma
d) delta

Answer 10

a) alpha

Question 11

Seizures are usually accompanied by very large EEG patterns. a) true b) false

Answer 11

t

Question 12

In general, what part of the brain’s electrical activity is measured by an EEG?

a) brainstem
b) medulla
c) cerebellum
d) cerebral cortex

Answer 12

d) cerebral cortex

Question 13

Generalized seizures + tx:

Answer 13

consist of a tonic (muscles become stiff)- clonic (jerking) phase followed by a period of unconsciousness.

Treatment is based on modifying the balance between the inhibitory gammaaminobutyric acid (GABA) and glutamatergic network within the rain or the repetitive firing potential of neurons.

Question 14

The EEG recordings reveals what about epilepsy?

Answer 14

The EEG recordings reveals that epileptic fits (ictal events) are associated with either generalized synchronous or focal spike and wave discharges. These events can also be seen transiently at other times without a seizure (interictal activity)

Question 15

Model for the generation of an epileptic discharge

Answer 15

Interictal activity corresponds to a depolarizing shift with superimposed action potentials from an assembly of neurons. Hyperpolarization follows as local inhibitory interneurones are activated. Repeated interictal spikes leads to the period of hyperolarization shortening and this activates ion channels in the neurons and increases extracellular K+ concentrations, which further depolarizes the neurons. If sufficient neurons are activated then synchronous discharges are produced in many neurons which can lead to a seizure. Seizure (synchronous discharge) is then terminated by ion channel inhibition within the neurone and within neuronal network by GABA related interneuronal activity.

Question 16

1) Define epilepsy.

Answer 16

Epilepsy is a transitory disturbance of the functions of the brain and develops suddenly and can cease spontaneously. - Serious neurological condition prevalent mainly during early childhood and in the elderly

Question 17

2) What is the common non-invasive way to monitor epileptic fits?

Answer 17

Recording of the EEG reveals that epileptic fits (ictal events) are associated with either generalized synchronous or focal spike and wave discharges. - This abnormality can also be transient: interictal activity.

Question 18

3) Describe the cellular physiology model of epilepsy.

Answer 18

• Model for generation of epileptic discharge is that interictal activity corresponds to a depolarizing shift with superimposed action potentials from assembly of neurons -
• Followed by hyperpolarization as these neurons and activate local inhibitory interneurones - With repeated interictal spikes the period of hyperpolarization shortens and activates ion channels in the neurons and raises extracellular K+ concentration which further depolarize the neurons
• If sufficient neurons are activated then synchronous discharges are produced across populations of neurons which can lead to a seizure.
• Seizure or synchronous discharge is terminated by active processes of inhibition both within the neuron (via ion channels) and within the neuronal network by GABA associated interneuronal activity

Question 19

Seizures are usually accompanied by:

a) fast, small amplitude EEG patterns
b) very large amplitude EEG patterns of about 3 Hz
c) extensive beta activity
d) EEG activity >35 Hz
e) both a) and c) are correct

Answer 19

b) very large amplitude EEG patterns of about 3 Hz

Question 20

A generalized seizure involves the entire _______.

a) cerebellum
b) cerebral cortex
c) medulla
d) thalamus

Answer 20

b) cerebral cortex

Question 21

) Why do EEGs with relatively fast frequencies tend to have smaller amplitudes than EEGs with slower frequencies?

Answer 21

EEG signal amplitude depends on the synchronized activity of the underlying neurons. If a group of cells are excited simultaneously, the tiny signals sum to generate one large surface signal. However, when each cell receives the same amount of excitation, but spread out in time, the summed signals are small and irregular. That is, the number of activated cells and the total amount of excitation has not changed; however, the timing of the activity changes. Therefore, EEGs with relatively fast frequencies tend to have smaller amplitudes than EEGs with slower frequencies.

Question 22

2) List some common causes of seizures by age.

Answer 22

Question 23

3) Define simple partial seizures (focal).

Answer 23

• Simple partial seizures involve a limited region of the cortex. - The manifestation can be motor impairment (i.e., jacksonian seizure) or sensory impairment. - The seizures may be emotional or hallucinatory (visual, auditory, olfactory) phenomenon, epigastric rising or déjà vu. - Consciousness is maintained during a simple partial seizure as opposed to impairment consciousness during complex partial seizures. - May last seconds to many hours.

Question 24

Define complex partial seizures.

Answer 24

• Seizure may begin with or without warning or aura, or with stereotyped motor, sensory, autonomic, or psychic symptoms.
• Complex partial seizures alter consciousness due to bilateral spread of the seizure discharge, no recollection.
• Patient may sit, walk, mumble and exhibit autonomic acts such as lip smacking or other movements - Lasts 1-3 minutes and can be followed by period of confusion 5-20 minutes.

Question 25

5) Define generalized seizures.

Answer 25

- Involves **tonic-clonic activity.** - Muscle groups may be driven by tonic (ongoing) activity or clonic (rhythmic) patterns, or by both in sequence . - Behaviour is disrupted for many minutes. **- Consciousness is lost.**

Question 26

Define absence (petit mal) seizures.

Answer 26

* - Rapid onset of **unresponsiveness** that lasts aroun**d 10 seconds.** * - **Staring,** automatisms (eye blinking or lip movements), increase or decrease in muscle tone, mild jerks. * Recovery immediate but no recall * **Hyperventilation** often precipitates seizure. * Patients are 3-20 years

Question 27

7) List some anticonvulsants used to manage seizures.

Answer 27