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Bella edwards
Chapter2.pptChapter 2
Cognitive Neuroscience
Some Questions We Will Consider
- What is cognitive neuroscience, and why is it necessary?
- How is information transmitted from one place to another in the nervous system?
- How are things in the environment, such as faces and trees, represented in the brain?
- What does studying the brain tell us about cognition?
Cognitive Neuroscience
- The study of the physiological basis of cognition
- Involves an understanding of both the nervous system as well as the individual units that comprise that system
“The brain is the last and greatest biological frontier… the most complex thing we have yet discovered in the universe.”
James Watson,
co-discoverer of the structure of DNA
Cognitive Neuroscience
Levels of Analysis
- We do not examine topics of interest from a single perspective, but rather we look at them from multiple angles and different points of view
- Each “viewpoint” can add small amounts of information which, when considered together, leads to greater understanding
Building Blocks of the Nervous System
- Neurons: cells specialized to create, receive, and transmit information in the nervous system
- Each neuron has a cell body, an axon, and dendrites
Nerve Nets
- The interconnections of neurons create a nerve net, which is like a continuous network that is similar to a highway
- One street connects to another but without stop signs
- This allows for almost nonstop, continuous communication of signals throughout the network
- Contradicted by the neuron doctrine
- Ramon y Cajal
- Individual nerve cells transmit signals, and are not continuous with other cells
Nerve Nets
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Building Blocks of the Nervous System
- Cell body: contains mechanisms to keep cell alive
- Dendrites: multiple branches reaching from the cell body, which receives information from other neurons
- Axon: tube filled with fluid that transmits electrical signal to other neurons
Building Blocks of the Nervous System
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Building Blocks of the Nervous System
- Sensory Neurons
- Take info to the brain
- Motor Neurons
- Take info away from the brain
- Interneurons
- Take info between sensory and motor neurons
How Neurons Communicate
- Action potential
- Neuron receives signal from environment
- Information travels down the axon of that neuron to the dendrites of another neuron
- Measuring action potentials
- Microelectrodes pick up electrical signal
- Placed near axon
- Active for ~1 second
How Neurons Communicate
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How Neurons Communicate
- Measuring action potentials
- The size is not measured; size remains consistent
- The rate of firing is measured
- Low intensities: slow firing
- High intensities: fast firing
How Neurons Communicate
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How Neurons Communicate
- Synapse: space between axon of one neuron and dendrite or cell body of another
- Neuron makes chemicals.
- Neuron transports chemicals to the synaptic vesicles for storage.
- Action potential causes release of chemicals.
- Neurotransmitters attach to receptor sites on postsynaptic membrane.
- Neurotransmitters split and are destroyed or taken up by membrane.
How Neurons Communicate
Representation in the Brain
- Hubel & Wiesel (1960s)
- won a Nobel Prize in 1981 for their work on neuronal firing.
- Feature detectors: neurons that respond best to a specific stimulus
- In the video presented below, an anesthetized cat is shown features. The clicking sound you hear is the sound of a neuron firing.
- https://www.youtube.com/watch?v=jw6nBWo21Zk
- The simple neuron fires only when it sees a diagonal line in the exact space and orientation on the screen.
- The complex neuron fires to the vertical line only as right to left movement is detected, but not when it’s still.
- Some neurons are sensitive to which direction the line goes in.
- The hypercomplex cell responds only when the light moves a certain direction and only when it is a dot of light and not a line.
Representation in the Brain
Hierarchical Processing
- When we perceive different objects, we do so in a specific order that moves from lower to higher areas of the brain
- The ascension from lower to higher areas of the brain corresponds to perceiving objects that move from lower (simple) to higher levels of complexity
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Representation in the Brain
- Specificity coding: representation of a specific stimulus by firing of specifically tuned neurons specialized to just respond to a specific stimulus
- Some people call this the grandmother neuron; it responds when you look at your grandmother
- Population coding: representation of a particular object by the pattern of firing of a large number of neurons
- Sparse coding: when a particular object is represented by a pattern of firing of only a small group of neurons, with the majority of neurons remaining silent
Representation in the Brain
Representation in the Brain
Representation in the Brain
Localization of Function
- Specific functions are served by specific areas of the brain
- Cognitive functioning breaks down in specific ways when areas of the brain are damaged
- Cerebral cortex (3-mm thick layer that covers the brain) contains mechanisms responsible for most of our cognitive functions
Lobes of the Cerebral Cortex
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Localization of Function: Perception
- Primary receiving areas for the senses
- Occipital lobe: vision
- Parietal lobe: touch, temperature, pain
- Temporal lobe: hearing, taste, smell
- Coordination of information received from all senses
- Frontal lobe
Localization of Function: Language
- Language production is impaired by damage to Broca’s area
- Frontal lobe
- Language comprehension is impaired by damage to Wernicke’s area
- Temporal lobe
Localization of Function: Language
Double Dissociation
- When damage to one part of the brain causes function A to be absent while function B is present, and damage to another area causes function B to be absent while function A is present
- Allows us to identify functions that are controlled by different parts of the brain
Organization: Brain Imaging
- Magnetic Resonance Imaging
- Powerful magnet runs down the tube alongside of the body
- Hydrogen atoms are realigned on same axis in pulses
- As pulse turns off, atoms return to natural alignment and release energy which is recorded by machine
- Computer processes signal and produces an image
- Tissues low in water appear lighter in color and tissues higher in water appear darker in color
- Functional MRI (fMRI)
- Same as MRI but also tracks blood flow and oxygen levels
- Provides info over seconds rather than minutes
- http://screen.yahoo.com/new-york-times/mapping-highways-brain-113257410.html
Brain Imaging: Evidence for
Localization of Function
- Fusiform face area (FFA) responds specifically to faces
- Found in the temporal lobe
- Damage to this area causes prosopagnosia (inability to recognize faces)
- https://www.youtube.com/watch?v=kviA4w4i-VA
- Parahippocampal place area (PPA) responds specifically to places (indoor/outdoor scenes)
- Found in the temporal lobe
- Extrastriate body area (EBA) responds specifically to pictures of bodies and parts of bodies
Brain Imaging: Evidence for
Localization of Function
Distributed Representation in the Brain
In addition to localization of function, specific functions are processed by many different areas of the brain
Many different areas may contribute to a function
May appear to contradict the notion of localization of function, but the two concepts are actually complementary
Distributed Representation in the Brain
Neural Networks
Groups of neurons or structures that are connected together
- 100 billion neurons in the brain
- 10-100 trillion synapses
- In cerebral cortex
- 10-30 billion neurons
- Each has 10,000-15,000 connections
= 1 million billion connections in this area alone
Can be examined using diffusion tensor imaging (DTI)
