-
2.0 Measuring Brain Function1
The Role of Electricity & Neurotransmitters in Brain
Function
Carter pp. 1-13, 68-73, 122-123
1
Outline
Early History Investigating The Brain Discovery of Brain
Electrical Function Discovery of Brain Neurotransmitters Anatomy of
Brain Cells and Nerve
Impulses
Measuring Action Potentials (AP) and Event Related Potentials
(ERP)
The Mirror Neuron System2
3
Investigating the Brain
1
2
3Sunday, September 21, 2014
-
Trephana(on 2500 BC to today -
Trephana(on
Hole bored in the brain - to alleviate pain, epilepsy, madness,
ba
-
Measuring Electrical & Neurotransmitter
Conductivity In the Brain(1791 til today)
7
8
Investigating the Brain
Galvani - electrical basis of nervous activity
Helmholtzspeed of
nerve conduction
9
Discovery of Mirror Neurons
Berger
Discovery of Magnetic
Resonance Imaging (MRI)
EEG
Investigating The Brain
7
8
9Sunday, September 21, 2014
-
Measuring Brain Function1Electricity - allows passage of
information between neurons
1791 - Galvani - first discovered nervous activity had an
electrical basis in muscle 1849 - Helmholtz - determined the speed
of electrical nerve conduction in muscle 1873 - Golgi - developed a
silver nitrate method that revealed the structure of
nerves in the brain
1906 - Ramon y Canal - discovered synapses in brain - networks
of nerves. But how they communicated was not known
Neurotransmitters - allow passage of electrical impulses across
synapses
1914 Henry Hallett Dale - discovers first neurotransmitter -
acetylcholine Basic anatomy and function of brain cells & nerve
Impulses 1924 - Berger - first EEG (electroencephalogram) -
patterns of electrical activity
from many locations on cerebral cortex
1940 - Single neuron recordings. 1996 - Major Discovery The
Mirror Neuron System
10
1791 - Galvani - first to discover nervous activity had an
electrical basis
bioelectricity detected in sciatic nerve of frog
idea confined to muscles
11
1849 - Helmholtz - determined the speed of electrical nerve
conduction
Widely assumed that electricity moved at an even lightening
speed through the muscles
measured the speed of electrical signals along the sciatic nerve
of a frog
12
10
11
12Sunday, September 21, 2014
-
1873 - Golgi - developed method that made neurons visible for
first time
Golgi stain - developed a silver staining method that showed
human neurons/worked at a hospital for the chronically ill
Proposed (wrongly)
13
HippocampusCerebellum
Ramon y Canal - 1906 - discovered neurons were connected by
intricate synapses
First to map the synapses of human brain - vision, audition,
olfactory, cerebellum, hippocampus
Argued (correctly) that electricity moved across synapses in a
non-continuous or variable way
Neural speed varied due to different sensory and mental
processes
14
Photomicrograph of human infant brain cells
1914 Henry Hallett Dale - discovered first neurotransmitter
BiochemistFirst to show that
neural transmission across synapses occurred as a result of
neurotransmitters
15
Carter, p. 73
13
14
15Sunday, September 21, 2014
-
Brain Cells and Nerve ImpulsesCarter pp 68-73
plus
DVD Nerve Cells and Impulse
Basic Anatomy of Neurons
Soma - body of neuron Axons - sends (efferent motor)
nerve signals forward; also called axonal process, neurite,
nerve fibre, motor neuron - by function
Dendrites - receives (afferent sensory) nerve signals
(feedback)
Synapse - Communication point between 2 neurons
Neurotransmitters released with excitatory or inhibitory
functions
Cell membrane - skin of soma (and dendrites/axons) creates
electrical impulses through inflow of sodium ions (NA, positive)
and outflow of potassium (K, negative) which generates action
potentials
Axon hillock - main source of electrical production
Basic Anatomy and Function of Neurons
Nucleus - Contains DNA which instructs how the neuron develops
and functions
Mitochondria - cellular power station; splits sugar and fat
molecules apart to release chemical energy; maintains the cell
membrane
Microtubules or Neurotubules - flexible rod structures (made of
protein) that provide scaffolding for the cell transport
neurotransmitters to the synapse
Breakdown of microtubules is source of tau in sports concussions
- CTE (chronic traumatic encephalopathy)
18
16
17
18Sunday, September 21, 2014
-
1) Nerve impulses are created by a traveling wave of chemical
particles (ions) which have electrical charges
Ion electrical charges are caused by the interaction of the
minerals sodium (NA+) and potassium (K-)
4 Steps in Neural Transmission
3
2NA +
K -_
NA +
20
2. Polarization - The axon is polarized at rest - More sodium
(NA+) ions are outside the membrane, and more negative potassium
(K-) ions are inside the membrane
3. Depolarization - Axon depolarizes as NA+ flows into
nerve/impulse passes Becomes positive. Depolarization is a change
in a cell's membrane potential making it more positive relative to
the outside
Repolarization - Ions pass out of nerve; inside of the cell
becomes negative relative to the outside.
4. Impulse Arrives At the Synapse 1.Neurotransmitters are
chemicals manufactured in the soma and
transported through microtubules to the synaptic
cleft2.Neurotransmitters are specific to various functions -
a) acetycholineb) dopaminec) serotonin
Neurotransmitter molecules
Neuotransmitters open Ion channelspermitting NA to pass and
create new electrical impulse (action
potential)
NA
19
20
21Sunday, September 21, 2014
-
Myelin Speeds Neural Transmission In Motor Neurons
Myelin Sheath - Spiral glia wrapping around axons speeds neural
transmissionNeural propagation - myelin allows rapid transmission
of electrical signals, esp during movementCurrent myelin controvery
- In multiple sclerosis (MS)
Action Potentials (AP)Event Related Potentials (ERP)
1924 - Berger - first EEG (electroencephalogram) - patterns of
electrical activity from locations on
cerebral cortex
EEG - Electroencephalogram: Many sensors on the scalp
(16-265)
22
23
24Sunday, September 21, 2014
-
Electroencephalograph (EEG) records electrical action potentials
or brain waves from cortical areas - 16-256 sensors
EEG waves during states of arousal
A) Alert awake state. Daily activities (beta)
B) REM (rapid eye movement) sleep - dreaming (alpha)
C) Drowsy - slower brain waves. Slowed frequency; higher
amplitude (delta)
D) Deep sleep -
E) Deeper Sleep -
F) Coma
Event-Related Potentials (ERPs) A Cognitive Task Is
Performed
Isolation of P3 wave which reflects greatest neural firing
during the task; direct neural measure of reaction time (RT)
P3 wave: - indicates
area of greatest activity
eg. right occipital cortex has
greatest activityV5 - motion detectors
25
26
27Sunday, September 21, 2014
-
Example of Map of Electrodes In EEG CAP
28
Occipital
Parietal
Temporal
Frontal
C Motor Cortex
Motor Planning
Mirror Neurons
Major Discovery by Rizzolati, Fogassi and Gallese (1996;
2001)
Technique: Single Cell Recordings Carter pp. 11, 122-123, 139
Locus of Motor Learning Within the
Brain?
29
Action Potential From A Single Cell
A micro-electrode (s) is inserted into the brain (of non-humans)
adjacent to the neurons to be studied
Electrical activity recorded - action potential (AP)
Many APs in a short period indicates higher brain activity
Single cell recordings - still a valuable method: used to
discover mirror neurons
Spikes
Hubel & Weissel (1954) - discovered properties of VI in
occipital cortex
28
29
30Sunday, September 21, 2014
-
Mirror Neurons One of the Landmarks in Recent
Neuroscience
31
Rizzolatti et al, 1996 In order to learn
motor skills we must be able to mimic the actions of others
Microelectrodes placed in area F5 of
Mirror Neuron System First discovered in
primates by: Rizzolati, Fogassi and Gallese (1996; 2001)
F5 - ventral pre-motor cortex
Now also located in the somatosensory/parietal lobe
First human in Motor skills: Calvo-Merino, Glaser, Grezes,
Passingham and Haggard (2004)
See also Vickers (2007) - pp. 24-25
Rizzolatti et al - Electrical Activity F5 Neurons - Accidental
Discovery
LeD - Electrode recorded brain trace as monkey watched
researcher pick up peanut; neural ac
-
Rizzolati et al (1995) Mirror NeuronEl
ectr
ical
act
ivity
Right: Researcher picked up peanut with a pair of pliers
Why was there no trace (on left above) from mirror system?
Monkey had no memories laid down that recognized pliers or knew
their function; mirror neurons silent
Electrodes recorded neuron activity (action potentials) as
monkey grasped objects
Left: watched researcher pick up peanut with hand - active
Right: actual grasp of monkey - activeEvidence of two memory
traces - one
that recognized hand function and another that moved the
hand
Mirror Neuron Area F5: Why is it so important? Microelectrodes
placed in F5 - Pre-Motor Area (PMA)
Involved in anticipation and planning of action
Activated during the reaction time period, before a movement is
performed
Also active when observing others perform goal-oriented
actions
Mirror neuron system helps us
F5
The Mirror System - Why Is It So Important?Main functions of
mirror neurons:
Frontal area activated before a movement is performed Active
when observing others perform goal-oriented
actions Mimicing movements of others fundamental to normal
growth and development Mirror neuron system helps us understand
the actions
and intentions of others
34
35
36Sunday, September 21, 2014