2.0 measusing brain function1 electr

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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