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2. PSY270 Brain basic principles.docx

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University of Toronto St. George
Kristie Dukewich

PSY270 Ch.2 Cognition and the Brain: Basic Principles 10/8/2012 11:20:00 AM Outline: 1. Neurons & the nervous system 2. How neurons communicate 3. How neurons process info 4. How stimuli are represented by the firing of neurons 5. Cognitive processes & the brain 6. Interacting with the environment affects operation of the nervous system 1. Neurons & the nervous system  Camillo Golgi – developed a chemical technique that stained some neurons but left most unstained, which revealed the structure of single neurons in pictures  Neurons: cells that are specialized to receive and transmit information in the nervous system o Different neurons specialized for difference functions  Cell body (keeps the cell alive)  Dendrites (branch out from cell body, receive info from other neurons)  Axon/Nerve Fibre (transmitting structure of the neuron, tube filled with fluid to conduct electrical signals)  Sensory receptors (sometimes replace cell body + dendrites at receiving end. Receptors are specialized structures which respond to sensory info/changes in the environment) o Stimulus from environment  Sensory receptors  Electrical signal along nerve fiber  Synapse  Dendrites  Cell body  Axon o Transduction: the transformation of one form of energy into another form of energy (e.g. energy from environment into electrical energy)  Recording from Single Neurons o Detecting neuron‟s electrical signal and relating these signals to cognitive processes o Action potentials: signals recorded by using tiny wires called microelectrodes, which are places near an axon, and that pick up the electrical signals that travel down the axon  Axons electrical signals displayed on an oscilloscope show that the charge of the neurons change. o Action potential info about stimulus intensity is represented not by size of action potentials, but by their rate of firing. o Action potentials are propagated – they travel from one end of the axon to the other without decreasing in size  Signals can travel long distances as individual neurons are linked together 2. How neurons communicate  What happens once action potentials reach the end of the axon?  Communication between neurons occurs at the synapse: o Synapse: a space between the end of the axon and the next neuron which transmits signals to the next neuron  Chemical process that bridges the gap between the two neurons  When potentials reach the end of one neuron, they cause structures called synaptic vesicles to open and release chemicals called neurotransmitters onto the next neuron.  Excitation and inhibition interact at the synapse: o When neurotransmitters are released there are 2 scenarios that can occur  Release of an excitatory neurotransmitter from one of the neurons increases the chances that the next neuron will fire. Excitation = Increased nerve firing  Release of an inhibitory neurotransmitter decreases the chances that a neuron will fire. Inhibition = Decreases nerve firing 3. How neurons process information  Brain has 180 billion neurons, 80 billion involved in cognitive processes  Neurons process information by interacting with each other o Neural processing: occurs when a number of neurons synapse together to form a neural circuit – a group of interconnected neurons o Two basic properties of these circuits that contribute to neural processing are:  Convergence: a number of neurons sending signals to a single neuron  Interaction of excitation & inhibition  Neural processing creates neurons that respond to specific types of stimuli o Hubel & Wiesel (1965) research on visual system  Neurons that respond best to a bar of light with a particular orientation, called simple cells  Neurons that respond best to bars of light of a particular orientation that were moving across the retina in a specific direction, called complex cells  Neurons that respond best to an orientated bar of light with a specific length, or shaped like a corner, called end-stopped cells o Feature detectors: Neurons such as simple, complex and end- stopped cells which fire in response to specific features of the stimuli 4. How stimuli are represented by the firing of neurons  Neural code: firing of neurons in the cortex contains formation that stands for/represents external environmental stimuli. The information contained in the neural firing to specific stimuli is called the neural code for that object/experience.  Neural code for perceiving faces: o What is the nature of the info transmitted by the neural code? o E.g. how a particular face can be represented by the firing of neurons in the temporal cortex o Specificity coding: the representation of a specific stimulus by the firing of very specifically tuned neurons that are specialized to respond just to a specific thing (e.g. a persons face)  Specificity coding proposes that there are neurons that are tuned to respond just to one specific
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