Prof. Greg Francis 1/2/12 PSY 200: Intro. to Cognitive Psychology 1 Purdue University Brain scans PSY 200 Greg Francis Lecture 03 How to study the brain without killing someone. Purdue University Scanning  Technology provides insight into brain processes  EEG recordings  MRI  Functional MRI  Non-invasive  Maps of brain activity  The goal is to relate brain events to cognitive events Purdue University Resolution  For almost every technique we have to worry about its ability to discriminate differences in  Space: which place is active?  Time: when does something happen?  Finer resolution is usually better  But can be difficult to deal with so much data Purdue University Electroencephalogram  EEG  The brain produces electrical activity  Put electrodes on the head Purdue University EEG  Watch the electrical current change through time while reading sentences (averaged across many trials)  Good temporal resolution  Kutas & Hillyard (1980) Semantic anomaly Purdue University Brain maps  You can analyze the EEG signals in many different ways  Compare the signal strength for different situations  Ayahuasca is a Brazilian psychoactive teaProf. Greg Francis 1/2/12 PSY 200: Intro. to Cognitive Psychology 2 Purdue University Spatial resolution  Poor spatial resolution  You never really know which part of the brain is making the current  Lots of work to improve Purdue University Magnetic Resonance Imaging  Magnetic field forces protons in your body to line up  pulses of radio into field bounces protons around  as they return to normal position, they emit a signal that can be decoded into a map Purdue University Magnetic Resonance Imaging  MRI Scans: Like an x-ray machine, but can look at soft tissue (like lungs, heart,..)  Very good spatial resolution Purdue University Magnetic Resonance Imaging  MRI Scans: Like an x-ray machine, but can look at soft tissue (like ankles, my brain,..)  Very good spatial resolution  millimeters Purdue University MRI Scans  MRI provides a “slice” at a time  Take multiple slices to build up full image Nobel prize winning work! Purdue University MRI Scans  Can identify anatomical differences between brains  Alcoholic has larger ventricles and thinner corpus callosum  Note comparing across brains is a bit tricky!  Everyone’s brain is a bit differentProf. Greg Francis 1/2/12 PSY 200: Intro. to Cognitive Psychology 3 Purdue University MRI Scans  3-D maps  Normal  Ataxia:  loss of motor control Purdue University MRI Scans  Non-invasive, no side effects  Allows early detection of brain disease, tumors,…  Fantastic spatial resolution  But…  it only shows structure  no way to know what a brain area does Purdue University Functional MRI  Just like MRI, but with a new analysis  MRI differentiates between different types of tissue (cell types)  Functional MRI differentiates between active and inactive neurons: concentration of oxygen  The measurement is called the “blood oxygen level dependent” (BOLD) » It roughly tracks the flow of blood in the brain » More active neurons recruit more blood Purdue University Functional MRI  Color maps show strongest “responses”  E.g., fMRI scan of a woman after a stroke  Blue/green: normal blood flow  Red/black: abnormal blood flow Purdue University Functional MRI  Very good spatial resolution  millimeters  Pretty good temporal resolution  Seconds  (Silva, 2002) Purdue University Scanning  Consider this fMRI scan  It shows regional cerebral blood volume (rCBV)  You cannot tell how/if different regions are involved in different activities  Breathing  Digestion  Thinking about exams  …..Prof. Greg Francis 1/2/12 PSY 200: Intro. to Cognitive Psychology 4 Purdue University Differences  We have to look for differences in activity  Alzheimer’s patients have reduced brain activity Purdue University A simple experiment  Suppose you run an fMRI experiment where a person alternates between seeing a blank screen and a face  You take multiple fMRI scans with half recording brain activity during the blank and half recording brain activity during the face  Add them up pixel by pixel for each condition Viewing face Viewing blank Purdue University Subtraction method  Subtract the fMRI signals produced by one condition from the fMRI signals produced by another condition  The difference map indicates those brain regions that are involved in the different cognitive tasks  It requires a sophisticated statistical analysis to avoid false positives! Viewing face Viewing blank Difference map Purdue University Reporting  What is usually reported is just the difference map  Colors mark places in the brain that are statistically different between conditions  Czisch et al. (2009) for rare tones vs. frequent tones  The map would be different if it compared rare tones versus speech Purdue University Functional MRI  Color maps show strongest “responses”  e.g., during a task that requires covert spatial attention compared to one that does not require attention Purdue University Functional MRI  When moving a pointer to a target box compared to no movement  “activity” in areas involved in vision, planning, and motor controlProf. Greg Francis 1/2/12 PSY 200: Intro. to Cognitive Psychology 5 Purdue University Limitations  Brain scans do not really tell us how the brain works  the scans just tell us approximately where in the brain something occurs  sometimes it can tell approximately when  Even trying to find the place may be problematic  Lots of cognitive abilities involve many different areas of the brain  Most of the time theories of cognition are derived from experimental psychology  Brain studies explore how to implement the theories Purdue University Common misconception  Brain scans demonstrate a physiological basis to things that were thought to be emotionally or cognitively based  e.g., MRI scans of stutters  in fact, all behavioral traits are physiologically