1. EE141 1 Brain Structures [Adapted from Neural Basis of Thought and Language Srini NarayananSrini Narayanan Comp Sci 182 / Cog Sci 110 / Ling 109 Broca’s area Pars opercularis Motor cortexSomatosensory cortex Sensory associative cortex Primary Auditory cortex Wernicke’s area Visual associative cortex Visual cortex

2. EE141 2 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.

3. EE141 3 Intelligence and Neural Computation Embodied Intelligence  What it means for the brain to compute and how that computation differs from the operation of a standard digital computer.  How intelligence can be implemented in the structure of the neural circuitry of the brain.

4. EE141 4 Brains ~ Computers  1000 operations/sec  100,000,000,000 units  10,000 connections/  graded, stochastic  embodied  fault tolerant  evolves, learns  1,000,000,000 ops/sec  1-100 processors  ~ 4 connections  binary, deterministic  abstract  crashes  designed, programmed

5. EE141 5 PET scan of blood flow for 4 word tasks

6. EE141 6 Neurons structures

7. EE141 7 Neurons cell body dendrites (input structure)  receive inputs from other neurons  perform spatio-temporal integration of inputs  relay them to the cell body axon (output structure)  a fiber that carries messages (spikes) from the cell to dendrites of other neurons

8. EE141 8 Neuron cells

9. EE141 9 Synapse  site of communication between two cells  formed when an axon of a presynaptic cell “connects” with the dendrites of a postsynaptic cell science-education.nih.gov

10. EE141 10 Synapse axon of presynaptic neuron dendrite of postsynaptic neuron bipolar.about.com/library

11. EE141 11 Synapse a synapse can be excitatory or inhibitory depolarizesarrival of activity at an excitatory synapse depolarizes the local membrane potential of the postsynaptic cell and makes the cell more prone to firing hyperpolarizes 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

12. EE141 12 Visual cortex of the rat

14. EE141 14 Somatotopy of Action Observation Foot Action Hand Action Mouth Action Buccino et al. Eur J Neurosci 2001

15. EE141 15 How does it all work?

16. EE141 16 Artist’s rendition of a typical cell membrane Amoeba eating

17. EE141 17 from Dr Rachel Swainson NEURAL COMMUNICATION 1: Transmission within a cell Neural Processing

18. EE141 18 Transmission of information Information must be transmitted  within each neuron  and between neurons

19. EE141 19 The Membrane  The membrane surrounds the neuron.  It is composed of lipid and protein.

20. EE141 20 The Resting Potential  There is an electrical charge across the membrane.  This is the membrane potential.  The resting potential (when the cell is not firing) is a 70mV difference between the inside and the outside. inside outside Resting potential of neuron = -70mV + - + - + - + - + -

21. EE141 21 Artist’s rendition of a typical cell membrane

22. EE141 22 Ions and the Resting Potential  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. inside outside Na + Cl - Na + K+K+ Cl - K+K+ Organic anions (-) Na + Organic anions (-)

23. EE141 23 Maintaining the Resting Potential  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. inside outside Na + K+ Na +

24. EE141 24 Neuronal firing: the action potential  The action potential is a rapid depolarization of the membrane.  It starts at the axon hillock and passes quickly along the axon.  The membrane is quickly repolarized to allow subsequent firing.

25. EE141 25 Course of the Action Potential  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]. Membrane potential (mV) [A] [B] [C] [D] excitation threshold Time (msec) -70 +40 0 0 1 2 3

26. EE141 26 Action potentials: Rapid depolarization  When partial depolarization reaches the activation threshold, voltage-gated sodium ion channels open.  Sodium ions rush in.  The membrane potential changes from -70mV to +40mV. Na + - + + -

27. EE141 27 Action potentials: Repolarization  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. K+K+ K+K+ K+K+ Na + + -

28. EE141 28 Action potentials: Resuming the Resting Potential  Potassium channels close.  Repolarization resets sodium ion channels.  Ions diffuse away from the area.  Sodium-potassium transporter maintains polarization.  The membrane is now ready to “fire” again. K+K+ K+K+ K+K+ K+K+ Na + K+ Na+ K+

29. EE141 29 The Action Potential  The action potential is “all-or-none”.  It is always the same size.  Either it is not triggered at all - e.g. too little depolarization, or the membrane is “refractory”;  Or it is triggered completely.

30. EE141 30 Conduction of the action potential.  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.

31. EE141 31 Membrane potential

32. EE141 32 Myelination  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.

33. EE141 33 Saltatory Conduction  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. Node of RanvierMyelin sheath

34. EE141 34 Synaptic transmission  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.

35. EE141 35 terminal dendritic spine synaptic cleft presynaptic membrane postsynaptic membrane extracellular fluid Structure of a synapse  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.

36. EE141 36 Neurotransmitter release  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+

37. EE141 37 Neurotransmitter release  Ca 2+ causes vesicle membrane to fuse with presynaptic membrane.  Vesicle contents empty into cleft: exocytosis.  Neurotransmitter diffuses across synaptic cleft. Ca 2+

38. EE141 38 Opening and closing of the channel in synaptic membrane

39. EE141 39 Ionotropic receptors  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

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41. EE141 41 Postsynaptic potentials  Depending on the type of ion channel which opens, the postsynaptic cell membrane becomes either depolarized or hyperpolarized.  Ions will tend to follow the concentration gradient from high to low concentration, and the electrostatic gradient towards the opposite charge.

42. EE141 42 Excitatory postsynaptic potentials (EPSPs)  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 (NB remember the action potential)  Ca 2+. (Also activates structural intracellular changes -> learning.) inside outside Na + Ca 2+ + -

43. EE141 43 Inhibitory postsynaptic potentials (IPSPs)  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 + (NB remember termination of the action potential)  Cl - (if already depolarized) K+K+ Cl - + - inside outside

44. EE141 44 Integration of information  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

45. EE141 45 Neuronal firing: the action potential  The action potential is a rapid depolarization of the membrane.  It starts at the axon hillock and passes quickly along the axon.  The membrane is quickly repolarized to allow subsequent firing.

46. EE141 46 Motor Control

47. EE141 47 Hierarchical Organization of Motor System  Primary Motor Cortex and Premotor Areas

48. EE141 48 Primary motor cortex (M1) Foot Hip Trunk Arm Hand Face Tongue Larynx

49. EE141 49 Leg motor control

50. EE141 50 Two major descending pathways Pyramidal vs. extrapyramidal Striated muscles Lower motor neurons (brain stem and spinal cord) Brain stem centers Motor cortex Pyramidal system Extrapyramidal system Pathway for voluntary movement Most fibers originate in motor cortex (BA 4&6) Most fibers cross to contralateral side at the medula Pathways for postural control/certain reflex mov’t Originates in brainstem Fibers do not cross Cortex can influence this system via inputs to brain stem

51. EE141 51 Somatotopy in M1

52. EE141 52 Cortical Motor System Pre-motor cortex Movement planning/sequencing Many projections to M1 But also many projections directly into pyramidal tract Damage => more complex motor coordination deficits Stimulation => more complex mov’t Two distinct somatotopically organized subregions SMA (dorso-medial) May be more involved in internally generated movement Lateral pre-motor May be more involved in externally guided movement

53. EE141 53 Cortical Motor System Posterior parietal cortex (PPC) Sensory guidance of movement Many projections to pre-motor cortex But also many projections directly into pyramidal tract Damage can cause deficits in visually guided reaching (Balint’s syndrom) and/or apraxia Likely part of the dorsal visual stream

54. EE141 54 Vision

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59. EE141 59 Vision and Action

60. EE141 60 Cortical Motor System Pre-motor cortex Movement planning/sequencing Many projections to M1 But also many projections directly into pyramidal tract Damage => more complex motor coordination deficits Stimulation => more complex mov’t Two distinct somatotopically organized subregions SMA (dorso-medial) May be more involved in internally generated movement Lateral pre-motor May be more involved in externally guided movement

61. EE141 61 Somatotopy of Action Observation Foot Action Hand Action Mouth Action Buccino et al. Eur J Neurosci 2001

62. EE141 62 Fly Brain Basic Atlas of the Drosophila Brain http://flybrain.neurobio.arizona.edu/Flybrain/html/index.html

63. EE141 63 This example shows the dendrites of two "uniglomerular" neurons, each invading a single olfactory glomerulus in the antennal lobe of the cockroach A stereopair taken with an "Edge microscope" (Edge Scientific Instrument Corporation, Santa Monica, CA 90404 Antennal Lobe Stereopair

64. EE141 64 The axons of projection neurons from the antennal lobes.

65. EE141 65  Sagittal section of the antennal nerve and lobe, showing olfactory receptor axons one of which is shown ending in a glomerulus that, is invaded by a local interneuron.

66. EE141 66  Mechanosensory endings from the right antennal nerve revealing three classes of terminals: small diameter axons, that distribute lateral to and around the back of the antennal lobe (ant lob); intermediate diameter axons that reside between these smaller fibers and a dense, bifurcating, tract of thicker varicose processes

67. EE141 67 two neurons that invade the ellipsoid body from dendrites within the lateral deutocerebrum

68. EE141 68  Optic array of inputs from the medulla to the lobula showing the layer relationship between the medulla afferents and lobula output dendrites

69. EE141 69  Optic lobes invading the lobula plate with branches that also extend to the inner layer of the medulla and the outermost layer of the lobula.

70. EE141 70 Type 1 and Type 5 T-cell  Horizontal section showing a Y-cell and a small-field Tm1 transmedullary cell in the medulla. The latter terminates in the outer layer of the lobula amongst dendrites of T5 neurons, several of which are shown here. Tm1 and T5 are essential components in the elementary motion detecting circuit

71. EE141 71  Drosphila optic lobes demonstrate the presence of orthogonally arranged dendrites of horizontal and vertical neurons in the lobula plate. Optical stacks show the vertical neurons and the three horizontal neurons. The axons of columnar neurons elements converge onto the giant fibre.

72. EE141 72  beneath the retina (ret) of the compound eye, the lamina neuropil is shown with the cross sections of the L1 and L2 monopolar cell axons denoting the mosaic of optic cartridges

73. EE141 73  The lobula (lo) is shown connected to the medulla (me) via the second optic chiasma (och 2)second optic chiasma

74. EE141 74 Lobula Complex The neural architecture of the lobula (lo) and the lobula plate (lo p), both connected to the inner layer of the medulla (me) by the second optic chiasma (och 2). The lobula plate shows three layers of tangential neurons (1-3). They receive inputs from chromatic motion-sensitive interneurons