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2.0 Measuring Brain Function1
The Role of Electricity & Neurotransmitters in Brain Function
Carter pp. 1-13, 68-73, 122-123
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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
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Investigating the Brain
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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)
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Investigating the Brain
Galvani - electrical basis of nervous activity
Helmholtzspeed of
nerve conduction
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Discovery of Mirror Neurons
Berger
Discovery of Magnetic
Resonance Imaging (MRI)
EEG
Investigating The Brain
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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
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1791 - Galvani - first to discover nervous activity had an electrical basis
bioelectricity detected in sciatic nerve of frog
idea confined to muscles
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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
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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)
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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
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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
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Carter, p. 73
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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)
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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
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2NA +
K -_
NA +
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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
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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)
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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
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Example of Map of Electrodes In EEG CAP
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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?
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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
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Mirror Neurons One of the Landmarks in Recent
Neuroscience
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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
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