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Cognitive Neuroscience: How the Brain Works EDIT 600 Summer 2009 Instructor: Elise Christopher 1 Neuroscience: A New Phrenology? 1. Phrenologists: “everything about a person can be sussed out by feeling bumps on head” – Personality, Self-Esteem, Music Ability, etc 2. Neuroscience today is locating many functions in specific areas of the brain – Emotion, Memory, Face Processing 3. Integrationist: Neural Network Model of brain http://en.wikipedia.org/wiki/Phrenology 2 The Principle of Single Dissociation 1. Personality: Phineas Gage 2. Memory: HM 3. Emotion Recognition: SM http://www.ninds.nih.gov/health_and_medical/pubs/tbi.htm 3 The Neuron 1. Basic unit of the brain 2. Humans have 100 billion neurons 3. Computer model: • • • • Dendrites = transistors Neuron = microchip Brain regions = embedded systems Brain = supercomputer 4 The Neuron 1. Basic unit of the brain 2. Basic form of communication is electricity • • Intra-Neuron Communication: Action potentials Inter-Neuron Communication: Through the synapse 5 Intra-Cellular Communication: The Action Potential 1. Action potentials are electrical signals 2. Ever wonder why we crave salt? • Cell membranes 3. Sodium-Potassium (Na+-K+) pumps • Responsible for changing the brain’s electrical potential 1000s of times per second 6 Inter-Cellular Communication: Neurotransmitters 1. Neurotransmitters are chemical signals 2. Action potential triggers their release into synapse 3. Receptors on receiving neuron pick up neurotransmitters • Triggers action potential in receiving neuron 7 Neural Networks 1. Neuronal Communication 2. Early thought: • • On/Off Switches Binary Notation 8 Neural Networks 1. Neuronal Communication 2. Current thought: • Neural nets with weights 3. Neural weights change • Rescorla-Wagner Model 9 Across the Brain “It was looking at me! What should I do about it?” “What was that?” “I’ll go talk to her.” STS V1 pFC Amyg FG “That was a face. Was it emotional?” “Yes, it was happy. Where was it looking?” 10 Methods to Study the Brain 1. 2. 3. 4. 5. – Postmortem Studies Animal Studies Electrical Recordings: EEG/ERP Metabolic Imaging: PET Static Imaging Techniques: fMRI Stimulation Techniques: TMS 11 Neuroscience Methods 1. Observational vs. Correlational Methods 2. Observational: • • Postmortem Studies Lesion Studies • • • Electroencephalography (EEG) / Evoked-Response Potentials (ERP) Functional Magnetic Resonance Imaging (fMRI) Positron Emission Tomography (PET) • • Transcranial Magnetic Stimulation (TMS) Animal Studies 3. Correlational: 4. Experimental Methods 5. Time constraints, spatial constraints, subject comfort constraints 12 Postmortem Studies 1. Identify disorder and then examine after death • Alzheimer’s Disease brains 2. Pros: • Direct observation of brain 3. Cons: • Cannot run more studies of behavior on subject www.alzheimer.ca 13 Lesion Studies 1. Removal of area of brain results in single dissociation 2. Pros: • Very reliable measure of brain-to-behavior 3. Cons: • • Lesion sites often vary widely Subjects sometimes have other deficits that go along with brain injury Adolphs, Tranel & Buchanan (2005). 14 Nature Neuroscience 8, 512 - 518 Electroencephalography (EEG) / Evoked-Response Potentials (ERP) 1. Measures local field potentials of populations of neurons 2. Pros: +7V • Highly timesensitive 3. Cons: • Spatially insensitive 100m s -4V • Inverse problem 15 Functional Magnetic Resonance Imaging (fMRI) 1. Huge magnet sends pulses through brain • • Iron-rich hemoglobin in blood responds strongly De-oxygenated blood responds weakly 2. Assumption: Brain areas with more blood flow have been more active recently, so they must have been active in task You go here neurophilosophy.wordpress.com 16 Functional Magnetic Resonance Imaging (fMRI) 1. Pros: • High spatial sensitivity • Down to the mm! • Contrast ability • Negative vs. Positive Activity 2. Cons: • Poor time sensitivity • As much as several seconds www.sciencemuseum.org.uk 17 Positron Emission Tomography (PET) 1. Radioactive material is injected 2. Participant then scanned to produce an image of the brain’s activity 3. Pros: • High spatial sensitivity 4. Cons: • • Poor time sensitivity Subject must be injected health.howstuffworks.com 18 Transcranial Magnetic Stimulation (TMS) 1. Pulses of magnet to weaken or inhibit function in areas of brain 2. Pros: • • Non-correlational method Definitive measure of brain-to-behavior 3. Cons: • • Can be slightly unpleasant/painful to muscles Long-term repercussions unknown www.physpharm.fmd.uwo.ca 19 Animal Studies: In Vivo 1. Monitor activity of a single neuron 2. Pros: • Observing cell while firing is very reliable 3. Cons: • Limited sample size due to delicacy of equipment http://www.vis.caltech.edu/~zoltan/ 20 Cerebral Cortex Principles 1. Contralaterality • Right side of brain controls left side of body • Left side of brain controls right side of body 2. Corpus Callosum • Neural fibers connecting left and right lobes • Allows communication between right and left sides of the brain 21 Cerebral Cortex Principles 1. Localization of function • Specific mental processes are correlated with discrete regions of the brain 2. Hemispheric Specialization • Each lobe of the brain has specialized functions • Ex: Language on the left 22 Lobes of the Cerebral Cortex 1. Frontal • Reasoning & Planning 2. Parietal • Touch, Temperature, Pain, & Pressure 3. Temporal • Auditory & Perceptual processing 4. Occipital • Visual processing 23 Neuronal Communication • A really cool video of neuronal communication can be found on YouTube: • Neurons-HowTheyWork – Try to remember that the brain doesn’t actually have those sound effects! – Thought Question: Why does it make sense for the creators of this video (Discovery Channel) to use these sound effects when illustrating the brain? 24