Neuro Electro Physiology

Neuro electrophysiology is the study of the electrical properties of biological cells and tissues in the nervous system. The electroencephalogram (EEG) is the recording of electrical activity of brain.

1. NEURO ELECTRO PHYSIOLOGY Dr. Subhendu Sekhar Dhar

2. INTRODUCTION Neuro electrophysiology is the study of the electrical properties of biological cells and tissues in the nervous system. Changes in these properties allow the nervous system to perform its functions.

3. RESTING MEMBRANE POTENTIAL Resting Membrane Potential (RMP) is the voltage (charge) difference across the cell membrane when the cell is at rest. In neurons, the resting membrane potential is usually about –70 mV, which is close to the equilibrium potential for K+. Because there are more open K+ channels than Na + channels at rest, the membrane permeability to K+ is greater.

4. ACTION POTENTIAL

5. ACTION POTENTIAL Action potentials are usually generated in the initial segment of the axon (called the axon hillock ) within about 50 μm of the neuronal cell body.

6. ACTION POTENTIAL Once generated, action potentials propagate rapidly, and the wave of depolarization jumps from node to node in a form that transmits the signal faithfully to nerve terminals. This process of action potential spread through myelinated axons is called saltatory conduction (Latin word saltare meaning “to jump”).

7. Neurons pass signals via action potential created by exchange between sodium and potassium ions in and out of the cell. When the wave of ions reaches the electrodes on the scalp, they can push or pull electrons on the metal on the electrodes, the difference in push, or voltage, between any two electrodes can be measured by a voltmeter. Recording these voltages over time gives us the EEG. Scalp EEG activity shows oscillations at a variety of frequencies. Several of these oscillations have characteristic frequency ranges, spatial distributions and are associated with different states of brain functioning.

8. ELECTROENCEPHALOGRAM The electroencephalogram (EEG) is the recording of electrical activity of brain (superficial layer i.e. the dendrites of pyramidal cells) by placing the electrodes on the scalp.

9. HISTORY In 1875, Richard Caton , a physician practicing in Liverpool, presented his findings about electrical phenomena of the exposed cerebral hemispheres of rabbits and monkeys. EEG were first done on human by German Psychiatrist Hans Berger in 1929.

10. BASIC ELEMENT NEEDED FOR EEG ELECTRODES AMPLIFIERS FILTERS WRITER UNITS

11. TECHNICAL STANDARDS Electrodes - 21(25) (silver or gold) – collodion, electrode paste, Impedance < 5 kohm .(10- 20 system) Channels - 8-16 , standard montages(5). Sensitivity - 5-10 micro volts/mm ( avg 7)* Filters - Low 1 Hz, High – 50 Hz ( upto 500 Hz) Paper speed – 30 mm/ sec ( adjustable) Length of recording – 2 min each montage - 30 min awake record ( 10 min sleep)

12. ELECTRODE PLACEMENT 10 – 20 INTERNATIONAL SYSTEM OF ELECTRODE PLACEMENT. Each electrode is 10 or 20 % away from neighbouring electrode. Electrodes have identifying names - Odd numbers on Left side Even numbers on Right side Midline – smaller number and more lateral larger number. The names include first letter of the general area where the electrode is placed.

13. 10- 20 % SYSTEM OF ELECTRODE PLACEMENT

14. STANDARD ELECTRODE PLACEMENT Fp 1, 2 – prefrontal F 3,4 – Frontal C 3,4 – Central T 3,4 – Mid Temporal T 5,6 – Posterior temporal A 1,2 – Ear ( for Mastoid ) P 3,4 – Parietal O 1,2 – Occipital F 7,8 – Anterior Temporal FZ- Frontal Midline CZ – Central Vertex PZ – Parietal Midline

15. STANDARD ELECTRODE PLACEMENT

16. LEAD ORIENTATION

17. EEG MONTAGES An electrode capturing brainwave activity is called an EEG channel. Typical EEG systems can have as few as a single channel to as many as 256 channels. Each EEG channel records the difference in electrical potential between two recording electrodes. System of arranging these channels to get optimum representation of selected brain areas- Montages .

18. EEG MONTAGES Channels record voltage differences between adjacent electrode sites (bipolar recording) or between various electrode sites and a common reference electrode (referential recording ). An upward pen deflection means a negative potential difference between the two electrodes; a downward pen deflection means a positive potential difference between the two electrodes. 

19. TYPES OF MONTAGES REFERENTIAL (MONOPOLAR): Referential recording involves the difference between an active electrode on the scalp, and an inactive electrode away from the scalp ( ear, nose, chin ) – indifferent or reference electrode BIPOLAR: Involves the difference between 2 active scalp electrodes. AVERAGE REFERENCE: The outputs of all of the amplifiers are summed and averaged, and this averaged signal is used as the common reference for each channel. LAPLACIAN: Each channel represents the difference between an electrode and a weighted average of the surrounding electrodes.

20. MAJOR FREQUENCY RANGES OF RHYTHMS The frequencies of brain waves range from 0.5-500 Hz. The most clinically relevant waves: Alpha waves – 8 - 13 Hz Beta waves - Greater than 13 Hz (13-35) Theta waves – 4 - 8 Hz Delta waves – less than 4 Hz.

21. ALPHA WAVES Frequency- 8-13 Hz Seen in all age groups but are most common in adults.  Most marked in the parieto-occipital area. Occur rhythmically on both sides of the head but are often slightly higher in amplitude on the nondominant side, especially in right-handed individuals Occur with closed eyes , relaxation, wondering mind. Disappear normally with attention ( eg , mental arithmetic, stress, opening eyes, any form of sensory stimulation) & during deep sleep.

22. ABNORMAL OCCURRENCE OF ALPHA WAVES Frontally prominent & persistent Alpha may indicate hypometabolism (reduced blood flow) & may relate to depression and attention problems. Alpha that fails to attenuate (diminish) with eye opening may be due to drowsiness or other pathology, including abnormalities in the visual system. Decreased Alpha peak frequency may reflect disease or brain injury such as TBI, dementia, medication effects, and age-related cognitive decline. Slowed Alpha rhythms may reflect neurological diseases such as dementia, Alzheimer’s, head injuries. Excessively fast Alpha can be associated with anxiety and OCD symptoms.

23. BETA WAVES Frequency- 13-35 Hz/sec. Seen in all age groups. They are recorded mainly from the parietal and frontal regions during states of concentration and problem solving. Beta waves are common in the EEG’s of most waking adults but may also be present during drowsiness. When the awake person's attention is directed to some specific type of mental activity, the alpha waves are replaced by asynchronous, higher-frequency but lower-voltage beta waves. Drugs such as barbiturates and benzodiazepines, augment beta waves.

24. ABNORMAL OCCURRENCE OF BETA WAVES Bi-laterally increased Beta can be due to previous craniotomy (Breech Rhythm). Spindling Beta generally reflects increased cortical irritability and is most likely seen in clinical conditions such as ADHD Epilepsy Psychosis including during hallucinations Anxiety disorders Excessive Beta activity can relate to symptoms of brain over arousal such as anxiety, obsessiveness, sleep difficulties, hyperactivity, etc. Deficient Beta activity can relate to symptoms of brain under aroused such as difficulty concentrating, problem solving, etc.

25. THETA WAVES Theta waves oscillate about 4 – 8 times per second (Hz) Normally seen during sleep at any age. They occur normally in the parietal and temporal regions in children, but they also occur during emotional stress in some adults, particularly during disappointment and frustration. Theta may occur in some individuals who are day dreaming. Theta and delta waves are known collectively as slow waves.

26. ABNORMAL OCCURRENCE OF THETA WAVES Excessive Theta activity in the waking EEG of adults is considered abnormal. It can represent reduced metabolism cortical grey matter (too little oxygen uptake). Excessive Theta is often seen in conditions such as ADHD Learning disabilities Head injuries or brain lesions

27. DELTA WAVES Slow waves, have a frequency of less than 4 Hz. Often, have the largest amplitude of all waves. Delta waves are rarely seen in the healthy waking adult EEG but are prominent and normal during sleep, especially of infants, children, and young adults. Delta waves are common in stage 3 & 4 sleep in adolescents and teenagers. Delta waves begin to disappear from the sleep records of adults after age 45 and tend to be almost entirely absent from those older than age 75.

28. ABNORMAL OCCURRENCE OF DELTA WAVES Delta should generally be absent from the waking EEG records of adults. If Delta appears in the waking EEG record, it may indicate the presence of Head trauma such as might occur in a car accident or bad fall. Exposure to toxins such as heavy metals, pesticides, etc. Cognitive impairment that might be the result of liver disease or degenerative brain diseases like dementia or Alzheimer’s disease. Focal Delta may be the result of a lesion or tumor or may indicate damage from a stroke.

29. SLEEP SPINDLES Groups of waves that occur during many sleep stages but especially in stage 2. Have frequencies in the upper levels of alpha or lower levels of beta. (11-16 Hz) Lasting for a second or less, they increase in amplitude initially and then decrease slowly. The waveform resembles a spindle. They usually are symmetric and are most obvious in the parasagittal regions.

30. NORMAL AWAKE EEG

31. ABNORMAL PATTERNS SLOW WAVES are rhythms , appearing during wakefulness and that are slower than in normal. Adults should not have theta and delta waves in the waking record, and if they appear they are called slow waves abnormalities. Slower the frequency and more often it occurs – greater degree of abnormalities. Abnormal Slow Wave appears when the brain cell are damaged

32. SLOW WAVES 1.5 Hz

33. ABNORMAL PATTERNS SPIKES / SHARP WAVE - a sudden appearing electrical explosion Spikes - 70 milliseconds. Sharp wave lasts 70 – 200 milliseconds. Spikes / sharp wave signify an epileptogenic region of the brain Spike and wave form – these complexes usually repeat at frequency of 3 times/ sec and at times 6 times/ sec when bilateral.

34. SPIKE-WAVE COMPLEX

35. ACTIVATION PROCEDURES HYPERVENTILATION SLEEP DEPRIVATION PHOTIC STIMULATION HYPERVENTILATION Patients are asked to breathe deeply and quickly for 3 mins to induce hyperventilation. Hyperventilation is used to induce 3 Hz spike and wave activity which is associated with the diagnosis of absence seizures. SLEEP DEPRIVATION It is the best activation for patients with complex partial seizures.

36. ACTIVATION PROCEDURES PHOTIC STIMULATION The patient sits in a chair and the strobe light is placed 12 inches directly front and center of the patient’s eyes. The flashing lights escalates in intervals of slow to fast, between 1 to 35 flashes per second . The entire procedure takes about two minutes. Photic stimulation can induce 2 forms of abnormal responses A photomyogenic response is characterized by repetitive muscle movements or jerking, and stops when the lights are turned off. A photoparoxysmal response can be observed by generalized repetitive spike and wave bursts.

37. EEG ARTIFACTS

38. EEG CHANGES IN PSYCHIATRIC MEDICATIONS Benzodiazepines always generate significant amount of beta activity . The highest proportion of abnormal EEGs occurred with Clozapine followed by Lithium. Lithium is capable of causing abnormal generalized slowing, paroxysmal activity or both. The highest incidence of EEG abnormalities was associated with Clozapine >Olanzapine >Aripiprazole >Risperidone >Quetiapine. (Manuel Dias Alves et al. Electroencephalogram Modifications Associated With Atypical Strict Antipsychotic Monotherapies; Journal of Clinical Psychopharmacology, 2018) Among typical antipsychotics Fluphenazine >Haloperidol cause abnormal EEGs .

39. EEG CHANGES IN PSYCHIATRIC DISORDERS Currently there is no accepted indication of EEG in diagnosing either axis I or II disorders.

40. EEG IN SCHIZOPHRENIA EEG abnormalities have overall frequency of 20-60%. May predict conversion of subjects at risk into psychosis. Their presence indicate worse outcome. It helps to identify those with comorbid epileptic condition. EEG abnormalities in schizophrenia Dysrhythmia Spike waves Generalized slowing

41. THE P300 WAVE The P300 (P3) wave is an event related potential (ERP) component elicited in the process of decision making. Its occurrence links not to the physical attributes of a stimulus, but to a person's reaction to it. When recorded by EEG, it surfaces as a positive deflection (spike) in voltage with a latency (delay between stimulus and response) of roughly 250 to 500 ms . The signal is typically measured most strongly by the electrodes covering the parietal lobe. Reduction in P300 amplitude and increased latency is noted in people with schizophrenia .

42. EEG IN MOOD DISORDERS Abnormal EEG found in 20-40% of patients. In bipolar patients increase in beta activity and decrease in alpha activity noted. Acute mania has increased posterior slow rhythms. An asymmetric alpha activity in left frontal region has been reported in depression. Unipolar and bipolar depression have sleeping EEG recording abnormality i.e., short REM latency, increased REM density and reduction in stage 3 and 4 of sleep. Frequent increase sharp spikes in patients with suicidal ideation.

43. EEG IN OCD & ANXIETY DISORDERS Fast Alpha wave is associated with anxiety and OCD symptoms. 25-30% of panic attack patients have EEG abnormalities. Helps in differentiating panic attack from epilepsy. Spindles are seen in pts. with Anxiety disorders.

44. EEG in DEMENTIA Increased slow activity and decreased mean frequency are correlated with cognitive impairment and measures clinical severity of Alzheimer's dementia. The amount of theta activity shows the best correlation with cognitive deterioration. Increased delta appears to be correlate of severe advanced dementia, occurring subsequent to increased theta.

45. EEG in DELIRIUM Hallmark of delirium usually is the slowing of the background EEG rhythm. This is positively correlated with the degree of severity of the condition. Exception is in delirium tremens (DT), which usually shows a normal EEG record with fast rhythms. Delirium accompanying the neuroleptic malignant syndrome shows only a mild diffuse slow wave. Delirium can be differentiated from dementia, and the significant factors are an increased theta activity

46. EEG IN ALCOHOL AND SUBSTANCE ABUSE Acute Alcoholic intoxication shows slowing in the EEG, seen as decreased alpha frequency and abundance & increased amount of theta , and even some generalized delta rhythm . These slow waves have a relationship with the degree of intoxication. The extent of the disturbance of consciousness is related to the amount of slow activity. Increased beta waves seen in alcohol dependence. Increased alpha waves , especially in anterior regions, has been reported in withdrawal, as well as after acute exposure to cannabis .

47. LIMITATIONS OF EEG IN PSYCHIATRY Nonspecificity of findings. Problem with placing electrodes in psychiatric patients. Limitations of scalp EEG i.e., Only 1/3 rd of brain can be covered, EEG activity of sub-cortical area can’t be recorded. Currently there is no accepted indication of EEG in diagnosing either axis I or II disorders.

48. REFERENCES Kaplan & Sadock’s Comprehensive Textbook of Psychiatry 10 th Edition. http://scottsdaleneurofeedback.com/services/qeeg-brain-mapping/eeg-brainwaves Baldin et al. Utility of EEG Activation Procedures in Epilepsy: A Population-Based Study. Journal of Clinical Neurophysiology: November 2017 - Volume 34 - Issue 6 - p 512–519. Standard Electroencephalography in Clinical Psychiatry, A practical handbook. Psychiatric Electroencephalography, Gerald Ulrich, Updated and revised edition (2002) of the original textbook. Psychiatrische Elektroenzephalographie (in German); Gustav Fischer Verlag, Jena-Stuttgart-New York, 1994 (ISBN 3-334-60841-1) Manuel Dias Alves et al. Electroencephalogram Modifications Associated With Atypical Strict Antipsychotic Monotherapies; Journal of Clinical Psychopharmacology, 2018. Google images.

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