Post on 19-Jan-2016
transcript
How the brain perceives the outside
world
Saturday Morning PhysicsDecember 4, 2004
Presenter: Rhonda Dzakpasu
Brain blunders
Kanizsa’s Triangle
“Peripheral drift” by Akiyoshi Kitaoka Taken from Nationalgeographic.com
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W.E. Hill
Central Nervous System:Brain and spinal cord
• The Brain– Three pound
wrinkled mass– Fits into cranial
cavity surrounded by cerebrospinal fluid cushioning
– Consists of multiple areas
– Localized regions are task specific
Courtesy of Morphonix LLC, Sausalito, CA
Central Nervous System:Brain and spinal cord
• Spinal cord– Carries fibers that
relay information from brain to rest of body and from the body to the brain
– Encased in bone fortress known as the vertebrae
– Surrounded by cerebrospinal fluid
Courtesy of Morphonix LLC, Sausalito, CA
Peripheral Nervous System:nerves to rest of body
• Somatic nerves– Fibers that relay commands from
brain to all muscle groups below the neck and controls somatosensory function such as touch, pain, temperature and joint position
Courtesy of Morphonix LLC, Sausalito, CA
Peripheral Nervous System:nerves to rest of body
• Autonomic nerves– Fiber carrying
information from brain to all organs in the body
– And all this is done automatically
• Cranial nerves– 12 nerves connecting
the brain to the organs in the head; also have sensory and motor functions Courtesy of Morphonix LLC,
Sausalito, CA
The “Sense”ational Organs
Receives “raw” data from around us
Each organ handles single function
Converts external stimuli to language of the brain
Seeing is believing: The Eye
Courtesy of Morphonix LLC, Sausalito, CA
Retina is initial visual processing centerHas three basic layers of cells:
Light sensitive photoreceptorsBipolar cellsGanglion cells
Seeing is believing: The Retina
Courtesy of Morphonix LLC, Sausalito, CA
Color is coded by photoreceptor rods and cones
Intensity is coded by frequency of firing of ganglion cells
Can you hear me now?
Courtesy of Morphonix LLC, Sausalito, CA
The ear: Wide dynamic range: 20 Hz – 20000 Hz
Three major components:Outer earMiddle earInner ear
Can you hear me now?
Courtesy of Morphonix LLC, Sausalito, CA
Cochlea: neurosensory component for hearing
Hair cells convert sound pressure to “brain language”
Outermost end – high frequencies
Innermost end – low frequencies
Olfaction and Taste
Smell and taste are related (artificially separated?)
Both are chemical senses
Odors bind to receptors which send electrical signals to olfactory bulb
Tastes are dissolved in mucous fluid in oral cavity to be carried to taste receptors
Courtesy of Morphonix LLC, Sausalito, CA
Like minded ordering
Cells of similar type group according to their function
Located in well defined layers
Advantage: facilitates ease of communicaton
Disadvantage: disease or injury can wipe out entire function
Brain Structure
whyfiles.org
The Cerebral Cortex
Purves et al., Life: The Science of Biology, 4th Edition
Cortical Parallel Processing Visual system
Must decode shape,color, position and movement
Auditory system Must decode many aspects of sound,
e.g., loudness, pitch, harmonics, timing and location of multiple sounds
Olfactory System Odors are composed of different
chemical groups that bind to different receptors
The Father of Modern Neuroscience
Courtesy: The Nobel Foundation
Outlined fundamental architecture of CNS
Demonstrated basic changes neurons undergo as they function in the CNS First to isolate neurons near surface of the brain
Santiago Ramon y Cajal, 1852-1934
The Father of Modern Neuroscience
Courtesy: The Nobel Foundation
Santiago Ramon y Cajal, 1852-1934
Who are the main players?
Neuron– Generate and propagate electrical
activity– Responsible for our thinking, feeling,
hearing, seeing, moving, loving and hating!
Glial cells– Supporting cells
The Neuron
There are ~ 100 billion
Small enough for 30000 to fit on head of a pin
Connects with thousands of other neurons
Generally do not reproduce
Courtesy of Morphonix LLC, Sausalito, CA
The Neuron
Three major components:
Dendrites:
Receives information from other neurons
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The Neuron
Soma:
Cell body containing the nucleus, the brain of the neuron
Courtesy of Morphonix LLC, Sausalito, CA
The Neuron
Axon:
Connects with other cells to transmit informationCan be up to several feet long!Covered in myelin allowing for fast information transfer
Courtesy of Morphonix LLC, Sausalito, CA
The Neuron
Always active!
Constantly integrating and generating information
Hotbed of activity! Neurons don’t hibernate!
Courtesy of Morphonix LLC, Sausalito, CA
How is information transmitted?!
The Resting Potential
Primarily due to concentration of K+ions inside and outside cell membrane
Typically between -80 mV to –55 mV
Action Potential:Generation
Excitatory input from synapses to dendrites depolarizes cell
Voltage activated Na+ channels open
Inside of cell becomes positive, ~20mV
Change in voltage creates current that depolarized adjacent region in axon
Impulse travels down axon Lasts ~2 ms
Action Potential: Propagation
Neuronal Communications
Neurons are like islands: no physical contacts
Chemical signals are converted to electrical ones
The supporting cells
Glial cellsOutnumber neurons by 10:1 margin
Two types:Astrocytes
Oligodendrites and Schwann cells
The supporting cells
Astrocytes:Provide physical supportby forming a mesh around neuronsFormation of blood-brain barrierRemove dead cellsTransport of nutrientsDestroyneurotransmitters in extra cellular space
The supporting cells
Oligodendrites (CNS) and Schwann cells (PNS):
Prevents abnormalcommunication between neuronsContain myelin and wraps around neuronal axons to boost communications, up to 200 mph!
Where’s the Physics?!
The “big” questions?
How do high-level psychological processes come about from basic neurophysiological effects?
How does the complex organization of brain cells, give rise to behavior?
Where’s the Physics?!
Computational models of neuronal behavior How can neural activity be defined? What types of coding mechanisms are
involved? Models from single ion channel and
synaptic models to “black-box” models describing psychological phenomena
The “Standard” Model
• Hodgkin-Huxley (1950’s)– First model of action potential
propagation
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Hodgkin-Huxley Model
• Simulates action potential from giant axon of squid
Hodgkin, A. L. and Huxley, A. F. (1952) Journal of Physiology 117: 500-544
Where’s the Physics?!
Study of spatio-temporal patterns
What new types of behaviors occur in large-scale models?
Synchronization Oscillations Are they important to brain function?
Patterns of Emergence
Large scale behavior of networks of neurons
Makeig, S., et. al., Science, 295, 690, 2002
Patterns of Emergence
Temporal and spatial changes in networks
Seidemann, E., et. al., Science, 295, 862, 2002
Where’s the Physics?!
Imaging techniques
How can we “see” inside the brain? Structural methods Functional methods
Imaging Techniques
Clinical application– PET scans– CT scans– MRI
Research applications– Fluorescence based imaging– Nuclear magnetic resonance (NMR)
imaging
What can we do when the brain fails?
Why should you care that we want to understand how the brain works???
Hybrid Brain Machine Interfaces*
Real-time direct interfaces between brain, electronics and mechanical devices
Can be used to restore lost or impaired sensory and motor function
* Nicolelis, M., Nature, 409, 403,2001
Prosthetic Ear: Cochlear Implants
Converts acoustic signal to electrical stimuli
Couples to array of implanted electrodes to auditory nerves
Stimulates cochlea:High frequencies – basalLow frequencies – apical
Mimics normal auditory processing Reprinted with permission from Rauschecker,
J.P., and Shannon, R.V., Science, 295, 1025-1029, (2002) Copyright 2002, AAAS
A Bionic Eye? Retinal Prostheses
Reprinted with permission from Zrenner, E., Science, 295, 1022-1025, (2002) Copyright 2002, AAAS
A Bionic Eye? Retinal Prostheses
Type 1: subretinal implantReplaces photoreceptors with microphotodiodes and electrodes
Type 2: epiretinal implantNo light-sensitive areasUses camera and processor outside of bodyImplanted electrodes stimulate axons of ganglion cells
It’s all Monkey Business!
Reprinted with permission, Nicolelis, M., Nature Reviews, 4, 417, 2003
It’s all Monkey Business!
Monkeys learn to produce complex hand movementsImplanted microwire arrays record activity of hundreds of neurons
Linear and non-linear models are used to extract motor control signals
Outputs used to control movement of the robot arm
Reprinted with permission, Nicolelis, M., Nature Reviews, 4, 417, 2003
Stay tuned!Next week’s lecture
• Imaging techniques
– Clinical methods– Research methods