Lecture 2: Cognition & the Brain

1. Psyc 317: Cognitive Psychology Lecture 2: Cognition & the Brain

2. Nervous system functioning: Outline • Zoom out: Broad anatomy of the brain • Zoom in: Neurons • How one neuron works • How two neurons communicate • How groups of neurons process information and encode the world • Zoom out again: Localization of function and basic principles of brain functioning

3. Neuron signals • Neurons are both chemical and electrical! • To send a signal within a neuron: ELECTRICAL • Action potentials • To send a signal between neurons: CHEMICAL • Neurotransmitters

4. Excitation/inhibition • Neurotransmitters come in two types • Excitation: Increase rate of firing of the nerve • Inhibition: Decrease the rate of firing of the nerve

5. Excitation/inhibition

6. Individual neurons respond to basic things • Cell that respond to stimuli can be classified: • Simple cells: ex. Bar oriented 45 degrees • Complex cells: ex. Bar oriented 45 degrees and moving to the right

7. Increasing complexity… Individual cells get more and more complex…

8. Groups of neurons process more complex information • Neural circuits: Groups of interconnected neurons that interact to respond to stimuli • Often, many neurons connect to another • These neurons can be excitatory or inhibitory • Sum up activations together - exceed firing threshold?

9. + + + + + + + + + + + + How neural circuits work • Example: Visual system + + + + B B C C

10. Distributed coding • Complex things require multiple neurons and neuron groups to be activated in order to be identified • Recognizing objects requires more than just one neuron - network of cells that fire at different rates

11. How neurons encode objects • Grandmother cells? Not quite… distributed coding!

12. Distributed coding • It is through the distribution of firing rates ACROSS DIFFERENT NEURONS that an object is encoded

13. Nervous system functioning: Outline • Zoom out: Broad anatomy of the brain • Zoom in: Neurons • How one neuron works • How two neurons communicate • How groups of neurons process information and encode the world • Zoom out again: Localization of function and basic principles of brain functioning

14. Large groups of neurons are even more complex • Large groups of neurons form brain modules • Modules - Brains areas that are specialized for specific functions (memory, attention, etc.) • Localization of function - Different functions are found in different areas of the brain • Memory encoding is in the hippocampus • Attention is in the parietal lobe

15. Distributed activation • Big processes (like memory) require multiple functions - multiple groups of neurons • Emotions • Working memory • Long-term memory

16. How the brain encodes events Distributed: • Form/shape • Color • Motion • Depth • Location

17. The brain is a multitasker

18. How the brain works: Contralaterality • The receptor and control centers for one side of the body are in the opposite hemisphere of the brain • Left hemisphere controls right side of body • Right hemisphere controls left side of body

19. How the brain works: Hemispheric Specialization • Different brain functions tend to rely more heavily on one hemisphere or the other • Example: The left hemisphere controls language for most right-handed people

20. Outline • Basics of information processing • Nervous system functioning • Broad anatomy • How neurons work • Localization of function • Methods of cognitive neuroscience • Experience-dependent plasticity

21. Introduction to Neuroimaging • Localization by methods that look at brain • Damage: If the hippocampus supports long-term memory (LTM), then hippocampal damage will interfere with LTM • Activation: If the hippocampus supports LTM, then when LTM is used, the hippocampus will be active

22. Techniques of activation • Single cell recordings • Event related potentials • Position emission tomography • Functional magnetic resonance imaging

23. Single cell recordings • Record from just one neuron in the brain • See how it reacts to stimuli • Mostly used in animals • Distinguish what one person is saying within a crowd of people • Still important to record from as many neurons as possible

24. Event-related potentials • Electrical response of thousands of neurons to a single event • Average electrical signal over hundreds of trials • Recorded through scalp cap

25. ERPs are part of the EEG • EEG is a way of continually recording brain waves • Common in sleep studies

26. How to collect ERPs • Give subject hundreds of trials of doing the same thing while recording the EEG • Mark the time in the EEG when something happens (stimulus, response, etc.)

27. How to collect ERPs • Save the EEG for (for example) 600 ms after that time marker for each trial • Average those EEG parts together to create an ERP waveform

28. ERP Waveforms • Positive and negative components • Waves go up and down • Each peak is a different component that often reflects cognitive processes

29. ERP: Good and Bad • Good: Excellent temporal resolution • Can detect changes in the ERP waveform very quickly • Bad: Poor spatial resolution • Averaging over millions of neurons - where does the signal come from? Who knows!

30. Brain imaging techniques • When neurons fire, they require oxygen. • Blood brings oxygen to the neurons • Positron Emission Tomography (PET) • Measure blood flow to brain using radioactive tracer • Functional Magnetic Resonance Imaging (fMRI) • Measure blood flow to brain using magnetic properties of deoxygenated blood

31. Functional MRI Baseline blood oxygenation Baseline firing rate Increased blood oxygenation Increased firing rate

32. fMRI scanner & images

33. Simple Reaction Time experiment: Stimulus: The light Mind: Sees light Response: Press button Choice Reaction Time experiment: * Stimulus: The light Mind: Sees light Mind: Which button? Response: Press button Imaging & Subtraction • Subtraction technique • Like reaction time, but with brain imaging • (Experimental) - (Baseline)

34. Subtraction technique & imaging • How similar is seeing an object to visualizing it?

35. Imagery study: How would it work? • How similar is seeing an object to visualizing it? • Experiment with two conditions: • Actually seeing an object • Visualizing an object • Get brain scans for both conditions • What would you expect if there was no difference between visualizing and actually seeing?

36. fMRI: Good and Bad • Good: Excellent spatial resolution • Details of brain images can be accurate to several millimeters • Bad: Poor temporal resolution • Changes in blood flow take several seconds to occur - cannot pinpoint when something happened

37. Techniques of damage • Brain lesions that lead to dissociations • Transcranial magnetic stimulation (temporary “damage”)

38. Dissociations • Single Dissociation • A disruption in one cognitive process but no impairment of another • Just need one group with an impairment • Double Dissociation • Two patient populations with selective impairment to complimentary forms of a single task

39. Lesion studies • Problems with studying people with brain lesions?

40. Transcranial Magnetic Stimulation • High school physics… • Use moving magnet to create an electric field • A brief, changing magnetic pulse applied to the scalp of the participant • Creates an induced electrical field, which interferes with neuronal activity

41. Transcranial Magnetic Stimulation • This electrical field can either excite neurons or inhibit them • Excitation causes neurons to fire, making something happen • Inhibition causes neurons to decrease firing, making something stop happening

42. TMS procedure Performance drop! Prevent seeing the letter Letter onset