The document discusses electrophysiology techniques used to study the electrical activity of neurons and other excitable cells. It begins by explaining that electrophysiology allows measurement of ionic currents across cell membranes and helps understand how cells and tissues function. Different techniques are then described, including intracellular recordings, patch clamp recordings, and extracellular recordings. The document outlines the historical development of the field and covers topics like resting membrane potentials, action potentials, ion channels, and how neurons encode and transmit information.

1. Presenter: Dr Ravikant Kumar ( PG , Final Year)

2.  Exploring electrical activity of cells and investigates the molecular and cellular processes
that govern their signaling
 permit measurement of ionic currents across the cell membrane
 helps to understand pathophysiological functions of excitable cells and tissue

3. Emil du Bois- Reymond

4.  Sir John Carew Eccles, Andrew
Fielding Huxley and Alan Lloyd
Hodgkin won the 1963 Nobel Prize in
Physiology or Medicine
 ‘for ionic mechanisms involved in
excitation and inhibition in the
peripheral and central portions of the
nerve cell membrane’

5.  Electrical activity is based on:
 relative concentration gradients and electrostatic gradients of ions within the cell and in
the extracellular fluid
 types of ion channels present within the neuron
 Difference in charge between the intracellular and extracellular sides of the
membrane creates an electrical potential, measured in units of Voltage(V)
 Ions moving across the membrane generate current (I), the movement of charge
over time
 Movement of ions across the membrane is limited by membrane resistance (R)
 Ohm’s law: V = I × R

6.  Resting potential is about −70 mV
 differences in the permeability of
inorganic ions, particularly sodium
(Na+), potassium (K+), and chloride (Cl−)
 active contributions of a sodium–
potassium pump

7. • The intracellular portion of the α
subunit has
• Na+-binding site (1)
• Phosphorylation site (4)
• ATP-binding site (5).
• The extracellular portion has
• K+-binding site (2)
• Ouabain-binding site (3)

8.  Neurons communicate by causing changes in membrane potential
 Membrane potential becomes more positive-depolarization
 Membrane potential becomes more negative-hyperpolarization
 Local voltage change-graded potential or localized potential
 Action potential- all-or-none, rapid, transient depolarization of the neuron’s
membrane when a local depolarization reaches to the threshold potential

10.  Categorized into three types based on the placement of the electrode :
(1) extracellular recordings
(2) intracellular recordings
(3) patch clamp techniques
Electrophysiology Chapter | 4 97
Extracellular
Recording
Patch Clamp
Recording
Intracellular
Recording
FIGURE 4.4 The three categories of electrophysiological recordings. Each type of recording

11.  How does a neuron encode information in action potentials?
 How does the activity (or inactivity) of one neuron affect the activity of another
neuron?
 How do pharmacological agents, neurotransmitters, and neuromodulators affect
the firing of a neuron?
 How is the spiking activity of a group of neurons coordinated?

12.  How does the activity (or inactivity) of one neuron affect the local potentials and
action potentials of another neuron?
 How do pharmacological agents, neurotransmitters, and neuromodulators affect
the local potentials and action potentials of a neuron?

13.  How do an ion channel’s open and closed times depend on the membrane
potential?
 How do the concentrations of ions, pharmacological agents, neurotransmitters,
and neuromodulators affect the current owing into an ion channel or cell?
 How much current does a single ion channel carry?
 What contributions does a single channel provide to an entire neuron?

16. Electrophysiology Chapter | 4 93
Ground electrode
Amplifier
Oscilloscope (can be digitized
and displayed on the computer)
Computer
10x Microscope
Microelectrode
Headstage/
Micromanipulator/
Microdrive
Microelectrode
detects signal
Through amplifier
Into an oscilloscope:
display of the
membrane potential
over time

17.  Electrophysiological techniques can be used for:
 Diagnostics
 Therapeutics
 Research and investigational purposes

18.  EEG
 ERP
 ECG
 EMG
 EOG
 ERG

19.  Experimental evidence of brain derived electrical potentials first established in
1874 by Richard Caton
 Coined by Hans Berger
 First recording of a human EEG in 1929 by Hans Berger

20.  Summed electrical potentials generated by large number of neurons recorded from
the scalp
 Transduction from cortex to scalp occurs when large number of neurons are
synchronized which occur
 Spontaneously
 In response to a stimulating event
 Unsynchronized activity cancels out

21. • 10-20 system by Herbert Jasper
• Standard 10-20 system contains 21 electrodes
• Electrode pairs known as Montage
• Two main types Referential and Bipolar
• Reference independent montages:
- Average reference
- Current source density

22.  Normal intrinsic frequencies
 Delta- <=3 Hz, not present in normal waking, generated by thalamocortical circuits
 Theta- 4-7 Hz, limited in the waking EEG, prominent in Stage 1 sleep
 Alpha- 8-12 Hz, Closed- eye waking EEG, by Posterior Cortex
 Beta- 13 -29 Hz, adult waking EEG and REM sleep
 Gamma- 30 -80 Hz, Transient gamma rhythms in:
 integration of neural networks to generate coherent cortical repreesentation
 role in sensation, perception and cognition
 Artifacts
 Physiological
 Extraphysiological

24.  EEG data is dimensional and complex
 Abundant data that cannot be ascertained through visual inspection alone
 Highly detailed EEG analysis possible
 Measurement of magnitude and differentiation of features rather than qualitative
decisions
 Still requires human judgments

25.  Segmentation- divides into epochs
 Averaging- Consistencies in signal average while noise cancels out
 Artifact rejection-based on threshold of accepted amplitude or change in
amplitude over time

26.  Fourier transform
 Fast Fourier transform
 Short time Fourier transform/wavelet transform
 Oscillatory activity measured by time frequency decomposition are:
 Transient evoked
 Steady state evoked
 Induced

27.  Appreciation of EEG as an ensemble of neurophysiology generated oscillatory
components with unique functional properties
 More precise characterization of neural activity and function

28. • When applied to stationary and time-series measures
• relationship of spectral power between two regions (spatial coherence)
• dependence of one frequency on another (cross-spectrum coherence)
• consistency in the phasic cycle of oscillatory activity over repeated trials (intertrial
coherence)
• Combination of spectral power and coherence measures
• enhances the ascertainment of neural dynamics comprising the human EEG
• increases capability to understand the functional interactions of brain areas on a large
spatial scale

29.  Computerized EEG tomography developed for multichannel Q-EEG data
 Bi or three dimensional matrix for topographic representation of Q-EEG data
 Matrix points not corresponding to recording electrodes are calculated interpolating
the values of nearest 2 or 3 electrodes

30. Current source density- Method of analysis of extracellular electric
potentials
 The EEG does not represent the specific activity of local brain due to
“volume conducted” loss
 To reducing the volume conduction
 Computerized method used to calculate local Field Potential is the
current source density (CSD)

32.  Electrophysiological responses to external stimuli administered over several
repetitions with change in stimulus properties across presentations
 Time locked to the delivery of a stimulus
 Visual Evoked Potentials(VEPs) and Brain Auditory Evoked Potentials(BAEPS)
measured by EEG
 Somatosensory evoked potentials(SSEPs) measured by EMG

33.  Conceptually similar to EP but are not necessarily time locked
 Contingent Negative Variation (CNV) and Lateralized readiness potential (LRP)
are examples which are not time locked
 To study:
 Bottom up sensory evoked responses
 Changes in neural activity associated with higher order cognitive processes

34.  Potentials are of smaller magnitude compared to ongoing EEG activity
 Components of EEG consistent across repeated trials of stimulus
 Extracted by averaging, resulting in a signal which reflects change in neural activity
 BAEPs are labelled I, II, III, IV, V
 ERPs, SSEPs, VEPs labelled according to their polarity and latency
 P or N indicate positive or negative direction of stimulation
 E.g: P300 meaning positive deflection peaking at 300 ms

35.  Early latency potentials- before 10ms like BAEP and reflect processing dependent
on exogenous factors
 Mid- latency potentials- upto 200ms
 Long latency potentials- after 200ms
 P50 – registration of salient stimuli
 N100 –perceptual processing
 P200 -sensation-seeking behavior
Reflect Endogenous potentials

36.  N200 or N2 wave
 There are 3 components of the N200 waveform —
 N2a/ Mismatch negativity (MMN)
 MMN is a negative component which is elicited by any discriminable change in a
repetitive background of auditory stimulation
 MMN represents the brain’s automatic process involved in encoding of the stimulus
difference or change.
 N2b.
 N2c

37.  P300- postattentional ERP component related to
 directed attention
 contextual updating of working memory
 attribution of salience to deviant stimuli
 N400
 semantic incongruity
 inversely related to the expectancy of a given word to end a sentence
(Kutas and
Hillyard, 1980)
 P600- language processing, a P600 effect occurs to sentences that
 contain a syntactic violation
 have a nonpreferred syntactic structure
 have a complex syntactic structure (Osterhout and Holcomb,
1992)

39.  Measurement of the magnetic field generated by the electrical activity of neurons
 Combined with a magnetic resonance imaging to get what is called magnetic source
imaging
 MEG fields pass through the head without any distortion. This is a significant
advantage of MEG over electroencephalography
 High spatial and temporal resolution
 MEG currently indicated for pre-operative brain mapping and for use in epilepsy
surgery

41.  Record of fluctuations in potential during the cardiac cycle is the ECG
 Triangle with the heart at its center (Einthoven triangle) can be approximated by
placing electrodes on both arms and on the leg
 Depolarization moving toward an active electrode- positive deflection
 Depolarization moving in the opposite direction- negative deflection

43. Fridericia formula ( QTc = QT/⎷3 RR )
Bazett’s formula ( QTc = QT/ ⎷RR ) or
linear adjustment for RR interval)
Bazett’s formula is most often used

44. • QT interval prolongation by Antipsychotics
• TCAs lead to prolonged PR, QRS and QT intervals and T-wave flattening or inversion
• SSRIs leading to QRS lengthening or prolonged QT interval
• Lithium intoxication- QTc prolongation, T wave inversion

46. BIOFEEDBACK
 Clinical technique providing feedback of physiological changes to the patient, so
that the patient can learn to modify the physiological response
(Williamson , 1985)
 Wide variety of ongoing intrinsic natural functions of organism occur at level of
awareness generally called the “unconscious”
(Brown et.al., 1975)
Psychological benefits:
 Depression Drug abuse
 Phobias Anxiety
 Sexual dysfunctions

47. BIOFEEDBACK
 Principle - Any measurable physiological behavior respond in some
way to voluntary control
 Involuntary physiological responses could actually be brought under
voluntary control through - instrumental conditioning
Measures -
Temperature, Heart rate, GSR level, Vasodilation, Brain waves,
Muscle tension, Blood pressure
(Williamson , 1985)

48. BIOFEEDBACK
 Feedback - visual or auditory
1. Binary feedback – provides yes/no information
 whether physiological response changed sufficiently to meet a pre-established
criterion
2. Analogue –provides information about changes in the
physiological response
 Changes of the feedback signals are made directly proportional to changes of
physiological response .

49. NEUROFEEDBACK 1. Neuroelectrical
activity is detected via
surface electrodes
Activity is then amplified
Processed by software
programs
auditory or visual feedback to
the pt.
Brain activity is monitored and desired changes are rewarded, computer
program gives a reinforcement each time

51.  Electric current or changing magnetic field to induce current within the brain to alter neuronal
firing
 Mechanism of action
- Electrical stimulation:
- Direct via application of electricity
- Indirect via magnetic stimulation
- Comparison of brain stimulation with psychopharmacology

52.  Acute effects:
 Phasic activation of neural circuits
 Observable motor responses
 Temporary disruption or facilitation of ongoing processing
 Prolonged effects:
 Changes in synaptic efficacy
 Alteration in neurotropic factors
 Modulation of cortical excitability
 Modulation of functional connectivity

53.  Persistent activation of neural circuits induce prolonged changes
Dynamic alterations
in synaptic efficacy
High electrical
frequency
Increase efficacy of
the circuit,
Long term
potentiation
Low electrical
frequency
Depress efficacy of
the circuit,
Long term
depression

54.  The first use of convulsive
therapy for the treatment
of a psychiatric disorder in
modern times dates to
Ladislaus von Meduna in
1934

55.  Goal of an ECT treatment session is to induce a generalized seizure of "adequate"
duration in the CNS.
 Treatments are ineffective if:
 seizures are terminated immediately following stimulation
 Subconvulsive electrical stimuli
 inducing only partial (focal) seizures

56. ECT
 A brief-pulse stimuli -repeated brief pulses (0.5 to 2.0 milliseconds) of
current to trigger action potential firing at rates similar to the intrinsic
firing patterns of neurons in critical regions of the CNS is preferred.
 pulses less than 0.5 millisecond in duration - "ultrabrief" pulses
 Seizure threshold-Minimum amount of electrical charge that induces a
generalized CNS seizure.
 Factors which influence seizure threshold include age, sex, and electrode
placement.

57.  Mechanisms for the therapeutic and adverse effects are not well understood
 Proposed mechanisms involve
 Structural including neuroplasticity
 Biochemical including neurochemistry and neuroendocrine
 Molecular including genetic and epigenetic
 Psychological
 Psychiatric Indications include Major Depression, Mania, Schizophrenia
 Clinically for Rapid response, risk of alternative treatments, past history of good
response, failure or intolerance to pharmacotherapy
 Neurologic indications include Parkinson’s, intractable epilepsy and delirium

58.  Application of rapidly changing magnetic field to the superficial layers of the cortex
 Focal stimulation possible as magnetic fields are unaffected by impedance
 Noninvasive
 Single pulse TMS- one pulse at a time at low rates of delivery
 Low frequency TMS - <=1 Hz
 High frequency TMS – 5 to 20 Hz
(Di Lazzaro et
al., 2011)
 Theta burst stimulation- High frequency bursts(e.g., 5 bursts per second of 3 pulses at
50 Hz)

60. KEY TMS THERAPY TERMS
time
Pulse
Train
(10 pulses/sec)
1 sec
Treatment
Session
4 sec 26 sec
~ 40 min
Single
Magnetic
Pulse
time
.2 msec
•Pulse Train: group of
electromagnetic pulses
followed by non-pulse
interval
•Stimulation Time:
duration of pulse train,
measured in seconds
•Interval: time period
between pulse trains,
measured in seconds
60

61.  Mechanism:  Technical parameters:
Induced EMF directly proportional to time rate of change of
magnetic flux
Induction of small circular electric currents called ‘eddy or
Foucault currents’ in a plane perpendicular to the plane of the
magnetic field
Local neuronal depolarization leads to propagated action
potential
Stimulation intensity
Pulse frequency
Intertrain interval
Total number of pulses
Coil shape and position
Waveform shape and
polarity

63.  In 2010 APA recommended TMS for acute phase of depression
 FDA approved indication is treatment of depressive episodes in adult patients
suffering from MDD without satisfactory improvement from previous
antidepressant medication
 Controllable pulse shape TMS(cTMS)- Generate rapid rate trains of near
rectangular electrical pulses varying in width, direction and amplitude

64.  Noninvasive and nonconvulsive
 Very weak direct electrical current
applied with at least two scalp
electrodes
 Elicits polarity dependent alterations
in RMP
Weak direct current shift of the RMP
Affects firing and conductance of neurons
Anodal currents excite and cathodal currents inhibit
the neurons

65.  Experimental research technology
 Much work needed to demonstrate efficacy
 Could be an inexpensive and relatively safe alternative
 Recent development of HD-tDCS
 Small arrays of HD-electrodes
 Increased focality

67. CONCLUSION
 Advantages & Disadvantages
 Can be used as an aid to-
 Differential diagnosis
 Endophenotying
 Severity of disorder
 Prognostication of disease
 To understand the pathophysiology of disorder
 Assess treatment non-responders
 Most methods are still used as a research tools
 Decreased specificity contributes to their unpopularity
 Inconsistent findings - Further research needed

68. FUTURE DIRECTION
 Diagnostic
 EEG changes during and after treatment needed to be correlated to
psychopharmacological furthermore
 predictive markers for cognitive & motivational factors that underlie successful
neurofeedback training
 Therapeutic
 EP to refine the treatment procedures
 Evaluate need for high or low frequency stimulation/ area specificity
 Optimization of electrical stimulus in ECT