Motor cortex Somatosensory cortex Sensory associative cortex Pars

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Motor cortex Somatosensory cortex Sensory associative cortex Pars opercularis Visual associative cortex Broca’s area

Motor cortex Somatosensory cortex Sensory associative cortex Pars opercularis Visual associative cortex Broca’s area Visual cortex Primary Auditory cortex Wernicke’s area Brain Structures [Adapted from Neural Basis of Thought and Language Jerome EE 141 Feldman, Spring 2007, feldman@icsi. berkeley. edu 1

Intelligence Learning and Understanding • I hear and I forget • I see and

Intelligence Learning and Understanding • I hear and I forget • I see and I remember • I do and I understand attributed to Confucius 551 -479 B. C. There is no erasing in the brain 2 EE 141

Intelligence and Neural Computation q What it means for the brain to compute and

Intelligence and Neural Computation q What it means for the brain to compute and how that computation differs from the operation of a standard digital computer. q How intelligence can be implemented in the structure of the neural circuitry of the brain. q How is thought related to perception, motor control, and our other neural systems, including social cognition? q How do the computational properties of neural systems and the specific neural structures of the human brain shape the nature of thought? q What are the applications of neural computing? 3 EE 141

Nervous System Divisions q Central nervous system (CNS) § brain § spinal cord 4

Nervous System Divisions q Central nervous system (CNS) § brain § spinal cord 4 EE 141

Nervous System Divisions q Peripheral nervous system (PNS) consists of: § Cranial and spinal

Nervous System Divisions q Peripheral nervous system (PNS) consists of: § Cranial and spinal nerves § Ganglia § Sensory receptors q Subdivided into: § Somatic § Autonomic – Motor component subdivided into: l l sympathetic parasympathetic § Enteric 5 EE 141

Brains ~ Computers q q q q 1000 operations/sec 100, 000, 000 units 10,

Brains ~ Computers q q q q 1000 operations/sec 100, 000, 000 units 10, 000 connections/ graded, stochastic embodied fault tolerant evolves learns q q q q 1, 000, 000 ops/sec 1 -100 processors ~ 4 connections binary, deterministic abstract crashes designed programmed 6 EE 141

PET scan of blood flow for 4 word tasks EE 141 7

PET scan of blood flow for 4 word tasks EE 141 7

Neurons structures 8 EE 141

Neurons structures 8 EE 141

Neurons cell body dendrites (input structure) v receive inputs from other neurons v perform

Neurons cell body dendrites (input structure) v receive inputs from other neurons v perform spatio-temporal integration of inputs v relay them to the cell body axon (output structure) v a fiber that carries messages (spikes) from the cell to dendrites of other neurons 9 EE 141

Neuron cells Øunipolar Øbipolar Ømultipolar 10 EE 141

Neuron cells Øunipolar Øbipolar Ømultipolar 10 EE 141

Synapse Ø site of communication between two cells Ø formed when an axon of

Synapse Ø site of communication between two cells Ø formed when an axon of a presynaptic cell “connects” with the dendrites of a postsynaptic cell science-education. nih. gov 11 EE 141

Synapse axon of presynaptic neuron dendrite of postsynaptic neuron bipolar. about. com/library 12 EE

Synapse axon of presynaptic neuron dendrite of postsynaptic neuron bipolar. about. com/library 12 EE 141

Synapse • • a synapse can be excitatory or inhibitory arrival of activity at

Synapse • • a synapse can be excitatory or inhibitory arrival of activity at an excitatory synapse depolarizes the local membrane potential of the postsynaptic cell and makes the cell more prone to firing arrival of activity at an inhibitory synapse hyperpolarizes the local membrane potential of the postsynaptic cell and makes it less prone to firing the greater the synaptic strength, the greater the depolarization or hyperpolarization 13 EE 141

Visual cortex of the rat 14 EE 141

Visual cortex of the rat 14 EE 141

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Somatotopy of Action Observation Foot Action Hand Action Mouth Action Buccino et al. Eur

Somatotopy of Action Observation Foot Action Hand Action Mouth Action Buccino et al. Eur J Neurosci 16 2001 EE 141

EE 141 How does it all work? 17

EE 141 How does it all work? 17

Amoeba eating Artist’s rendition of a typical cell membrane 18 EE 141

Amoeba eating Artist’s rendition of a typical cell membrane 18 EE 141

Neural Processing From lecture notes by Dr Rachel Swainson NEURAL COMMUNICATION 1: Transmission within

Neural Processing From lecture notes by Dr Rachel Swainson NEURAL COMMUNICATION 1: Transmission within a cell and from a lecture notes based on www. unisanet. unisa. edu. au/Information/12924 info/Lecture Presentation - Nervous tissue. ppt 19 EE 141

Transmission of information Information must be transmitted q within each neuron q and between

Transmission of information Information must be transmitted q within each neuron q and between neurons 20 EE 141

The Membrane q The membrane surrounds the neuron. q It is composed of lipid

The Membrane q The membrane surrounds the neuron. q It is composed of lipid and protein. 21 EE 141

EE 141 Artist’s rendition of a typical cell membrane 22

EE 141 Artist’s rendition of a typical cell membrane 22

Cell Electrical Potential Every neuron is covered by a membrane The membrane is selectively

Cell Electrical Potential Every neuron is covered by a membrane The membrane is selectively permeable to the passage of chemical molecules (ions) The membrane maintains a separation of electrical charge across the cell membrane. The cell membrane has an electrical potential Electrical potentials Electrical charge of the membrane is related to charged ion that cross the membrane through lipids, ion channels and protein ion-transporters. Electrical currents (ionic flux) The flow of electrical charge between the cell’s interior and exterior cellular fluids 23 EE 141

Forces determine flux of ions – Electrostatic forces • Particles with opposite charges attract,

Forces determine flux of ions – Electrostatic forces • Particles with opposite charges attract, Identical charges repel – Concentration forces • Diffusion – molecules distribute themselves evenly – – Protein – ion channels • Selective Non – gated ion channels • Selective Voltage-dependent gated ion channels – Protein – ion transporters – K+ Na + pump • Cl - pump 24 EE 141

The Resting Potential outside - - + - - q + q There is

The Resting Potential outside - - + - - q + q There is an electrical charge across the membrane. This is the membrane potential. The resting potential (when the cell is not firing) is a 70 m. V difference between the inside and the outside. + q inside + + - Resting potential of neuron = -70 m. V 25 EE 141

Ions and the Resting Potential q q Ions are electrically-charged molecules e. g. sodium

Ions and the Resting Potential q q Ions are electrically-charged molecules e. g. sodium (Na+), potassium (K+), chloride (Cl-). The resting potential exists because ions are concentrated on different sides of the membrane. § Na+ and Cl- outside the cell. § K+ and organic anions inside the cell. Na + Na Organic anions (-) K+ EE 141 Cl- + Na+ K Organic anions (-) + Cl- outside inside Organic anions (-) 26

Maintaining the Resting Potential q q Na+ ions are actively transported (this uses energy)

Maintaining the Resting Potential q q Na+ ions are actively transported (this uses energy) to maintain the resting potential. The sodium-potassium pump (a membrane protein) exchanges three Na+ ions for two K+ ions. Na EE 141 + Na+ outside K+ K+ inside 27

Neuronal firing: the action potential The action potential is a rapid depolarization of the

Neuronal firing: the action potential The action potential is a rapid depolarization of the membrane. q It starts at the axon hillock and passes quickly along the axon. q The membrane is quickly repolarized to allow subsequent firing. q 28 EE 141

Course of the Action Potential q q q The action potential begins with a

Course of the Action Potential q q q The action potential begins with a partial depolarization (e. g. from firing of another neuron ) [A]. When the excitation threshold is reached there is a sudden large depolarization [B]. This is followed rapidly by repolarization [C] and a brief hyperpolarization [D]. 29 EE 141

The Action Potential q The action potential is “all-or-none”. q It is always the

The Action Potential q The action potential is “all-or-none”. q It is always the same size. q Either it is not triggered at all - e. g. too little depolarization, or the membrane is “refractory”; q Or it is triggered completely. 30 EE 141

Action potential 2 phases: § Depolarisation – graded potentials move toward firing threshold –

Action potential 2 phases: § Depolarisation – graded potentials move toward firing threshold – if reach threshold voltage regulated sodium channels open – reversal of membrane permeability § Repolarisation – sodium channels close – potassium channels open 31 EE 141

Before Depolarization 32 EE 141

Before Depolarization 32 EE 141

Action potentials: Rapid depolarization q q q When partial depolarization reaches the activation threshold,

Action potentials: Rapid depolarization q q q When partial depolarization reaches the activation threshold, voltage-gated sodium ion channels open. Sodium ions rush in. The membrane potential changes from -70 m. V to +40 m. V. + EE 141 - - Na+ Na+ + 33

Depolarization 35 EE 141

Depolarization 35 EE 141

Action potentials: Repolarization q q q Sodium ion channels close and become refractory. Depolarization

Action potentials: Repolarization q q q Sodium ion channels close and become refractory. Depolarization triggers opening of voltage-gated potassium ion channels. K+ ions rush out of the cell, repolarizing and then hyperpolarizing the membrane. Na+ Na EE 141 + K Na+ + K+ K + + - 36

Repolarization 37 EE 141

Repolarization 37 EE 141

Conduction of the action potential q q Passive conduction will ensure that adjacent membrane

Conduction of the action potential q q Passive conduction will ensure that adjacent membrane depolarizes, so the action potential “travels” down the axon. But transmission by continuous action potentials is relatively slow and energy-consuming (Na+/K+ pump). A faster, more efficient mechanism has evolved: saltatory conduction. Myelination provides saltatory conduction. 39 EE 141

Action Potential 40 EE 141

Action Potential 40 EE 141

Propagation of the Action Potential • Action Potential spreads down the axon in a

Propagation of the Action Potential • Action Potential spreads down the axon in a chain reaction • Unidirectional – it does not spread into the cell body and dendrite due to absence of voltage-gated channels there – Refraction prevents spread back across axon 41 EE 141

Myelination q q q Most mammalian axons are myelinated. The myelin sheath is provided

Myelination q q q Most mammalian axons are myelinated. The myelin sheath is provided by oligodendrocytes and Schwann cells. Myelin is insulating, preventing passage of ions over the membrane. 42 EE 141

Saltatory Conduction q q q Myelinated regions of axon are electrically insulated. Electrical charge

Saltatory Conduction q q q Myelinated regions of axon are electrically insulated. Electrical charge moves along the axon rather than across the membrane. Action potentials occur only at unmyelinated regions: nodes of Ranvier. Myelin sheath EE 141 Node of Ranvier 43

Summary of axonal conduction q Unmyelinated fibres § continuous conduction q Myelinated fibres §

Summary of axonal conduction q Unmyelinated fibres § continuous conduction q Myelinated fibres § saltatory conduction – High density of voltage gated channels at Nodes of Ranvier q Larger diameter axons propagate impulses faster q Stimulus intensity encoded by: § frequency of impulse generation § number of sensory neurons activated EE 141 44

Synaptic transmission q q q Information is transmitted from the presynaptic neuron to the

Synaptic transmission q q q Information is transmitted from the presynaptic neuron to the postsynaptic cell. Chemical neurotransmitters cross the synapse, from the terminal to the dendrite or soma. The synapse is very narrow, so transmission is fast. 45 EE 141

Structure of a synapse q q q An action potential causes neurotransmitter release from

Structure of a synapse q q q An action potential causes neurotransmitter release from the presynaptic membrane. Neurotransmitters diffuse across the synaptic cleft. They bind to receptors within the postsynaptic membrane, altering the membrane potential. terminal extracellular fluid synaptic cleft presynaptic membrane postsynaptic membrane dendritic spine 46 EE 141

Neurotransmitter release q q Synaptic vesicles, containing neurotransmitter, congregate at the presynaptic membrane. The

Neurotransmitter release q q Synaptic vesicles, containing neurotransmitter, congregate at the presynaptic membrane. The action potential causes voltage-gated calcium (Ca 2+) channels to open; Ca 2+ ions flood in. vesicles Ca 2+ 2+ Ca Ca 2+ 47 EE 141

Neurotransmitter release q q q Ca 2+ causes vesicle membrane to fuse with presynaptic

Neurotransmitter release q q q Ca 2+ causes vesicle membrane to fuse with presynaptic membrane. Vesicle contents empty into cleft: exocytosis. Neurotransmitter diffuses across synaptic cleft. Ca 2+ 48 EE 141

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49 EE 141

Opening and closing of the channel in synaptic membrane EE 141 50

Opening and closing of the channel in synaptic membrane EE 141 50

Ionotropic receptors q q q Synaptic activity at ionotropic receptors is fast and brief

Ionotropic receptors q q q Synaptic activity at ionotropic receptors is fast and brief (milliseconds). Acetyl choline (Ach) works in this way at nicotinic receptors. Neurotransmitter binding changes the receptor’s shape to open an ion channel directly. ACh 51 EE 141

Ionotropic Receptors 4 nm 52 EE 141

Ionotropic Receptors 4 nm 52 EE 141

Metabotropic Receptors (GProtein) 53 EE 141

Metabotropic Receptors (GProtein) 53 EE 141

Postsynaptic Ion motion 54 EE 141

Postsynaptic Ion motion 54 EE 141

Excitatory postsynaptic potentials (EPSPs) q Opening of ion channels which leads to depolarization makes

Excitatory postsynaptic potentials (EPSPs) q Opening of ion channels which leads to depolarization makes an action potential more likely, hence “excitatory PSPs”: EPSPs. § Inside of post-synaptic cell becomes less negative. § Na+ channels (remember the action potential) § Ca 2+. (Also activates structural intracellular changes -> learning. ) outside - Ca 2+ + Na+ inside 56 EE 141

Inhibitory postsynaptic potentials (IPSPs) q Opening of ion channels which leads to hyperpolarization makes

Inhibitory postsynaptic potentials (IPSPs) q Opening of ion channels which leads to hyperpolarization makes an action potential less likely, hence “inhibitory PSPs”: IPSPs. § Inside of post-synaptic cell becomes more negative. § K+ (remember termination of the action potential) § Cl- (if already depolarized) outside - K+ + Cl- inside 57 EE 141

Integration of information q q PSPs are small. An individual EPSP will not produce

Integration of information q q PSPs are small. An individual EPSP will not produce enough depolarization to trigger an action potential. IPSPs will counteract the effect of EPSPs at the same neuron. Summation means the effect of many coincident IPSPs and EPSPs at one neuron. If there is sufficient depolarization at the axon hillock, an action potential will be triggered. axon hillock 58 EE 141

Requirements at the synapse For the synapse to work properly, six basic events need

Requirements at the synapse For the synapse to work properly, six basic events need to happen: 1. 2. 3. 4. 5. 6. Production of the Neurotransmitters Storage of Neurotransmitters Release of Neurotransmitters Binding of Neurotransmitters Generation of a New Action Potential Removal of Neurotransmitters from the Synapse 59 EE 141

Three Nobel Prize Winners on Synaptic Transmission Arvid Carlsson discovered dopamine is a neurotransmitter.

Three Nobel Prize Winners on Synaptic Transmission Arvid Carlsson discovered dopamine is a neurotransmitter. Carlsson also found lack of dopamine in the brain of Parkinson patients. Paul Greengard studied in detail how neurotransmitters carry out their work in the neurons. Dopamine activated a certain protein (DARPP-32), which could change the function of many other proteins. Eric Kandel proved that learning and memory processes involve a change of form and function of the synapse, increasing its efficiency. This research was on a certain kind of snail, the Sea Slug (Aplysia) that has relatively low number of neurons (20, 000 ). 60 EE 141

Neural circuits q Divergence § Single presynaptic neuron synapses with several postsynaptic neurons –

Neural circuits q Divergence § Single presynaptic neuron synapses with several postsynaptic neurons – Example: sensory signals spread in diverging circuits to several regions of the brain q Convergence § Several presynaptic neurons synpase with single postsynaptic neuron – Example: single motor neuron synapsing with skeletal muscle fibre receives input from several pathways originating in different brain regions 61 EE 141

Neural circuits q Pulsing circuit § Once presynaptic cell stimulated causes postsynaptic cell to

Neural circuits q Pulsing circuit § Once presynaptic cell stimulated causes postsynaptic cell to transmit a series of impulses – Example: coordinated muscular activity q Parallel after-discharge circuit § Single presynaptic neuron synapses with multiple neurons which synapse with single postsynaptic cell – results in final neuron exhibiting multiple postsynaptic potentials l Example: may be involved in precise activities (eg mathematical calculations) 62 EE 141

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63 EE 141