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Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press Chapter 4 The Tools: Imaging the Living Brain “I believe the study of neuroimaging has supported the localization of mental operations within the human brain.” -Michael I. Posner, 2003 Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press Chapter Outline 1.0 Introduction 2.0 A range of useful tools -- measuring electric and magnetic signals 3.0 fMRI and PET: indirect signals for neural activity 4.0 Conscious vs. unconscious brain events 5.0 Correlation and causation 6.0 Summary Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 1.0 Introduction Brain recording: more and less direct measurements How do brain recordings reflect human cognition? While they are indirect measures, each type of brain recording tells us part of the story of how the brain works. Here is an image of the brain using diffusion tensor imaging: this technique allows us to view white (myelinated) fiber tracts. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 1.0 Introduction The time-space tradeoff: some techniques provide high temporal resolution of brain activity (such as EEG) while others provide higher spatial resolution (such as fMRI). Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 A range of useful tools -measuring electric and magnetic signals Single-unit recording: Recording from individual neurons can tell us about spiking patterns in the brain. Here you see that the activity in this single unit is most active (shown in red) during the delay period. Such neurons are thought to be involved in the working memory system. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 A range of useful tools -measuring electric and magnetic signals Human Animal and human studies cast light on each other While humans and monkeys are very different, some monkeys, such as the macaque, are extensively studied because of the similarity between their brains and human brains. Macaque Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 A range of useful tools -measuring electric and magnetic signals Animal and human studies cast light on each other Some macaque behaviors are similar to humans as well, such as close infant-mother bonding. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 A range of useful tools -measuring electric and magnetic signals Electroencephalography (EEG) recordings reveal brain rhythms such as Gamma (40Hz). Gamma activity is thought to signal exchange of information between cortical and subcortical regions. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 A range of useful tools -measuring electric and magnetic signals Magnetoencephalography (MEG) MEG recordings reflect magnetic -- not electric -- cortical activity. MEG has higher source localization capabilities than EEG. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 2.0 A range of useful tools -measuring electric and magnetic signals Zapping the brain -- Transcranial Magnetic Stimulation (TMS) TMS uses brief magnetic pulses over the scalp to inhibit or excite a small region of cortex. TMS is used to test causal hypotheses about the contribution of specific brain regions to complex cognitive processes. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 3.0 fMRI and PET: indirect signals for neural activity PET was developed before fMRI and provides a measure of metabolic activity in the brain. It is very expensive to use and is invasive, requiring subjects to be injected with a radioactive tracer. PET is used less often in research studies today, but remains an important clinical and research tool. Both PET and fMRI rely on a subtraction method where brain scans for different experimental contrasts are subtracted from each other. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 3.0 fMRI and PET: indirect signals for neural activity fMRI provides a measure of hemodynamic (blood based) activity in the brain and is based on the premise that neuronal activation increases oxygen demand of neurons and related cells, leading to additional blood flow carrying oxygen molecules to the region. This can be measured using BOLD -- Blood Oxygen Level Dependent -- activity. fMRI is the dominant neuroimaging technique today in research. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 3.0 fMRI and PET: indirect signals for neural activity Regions of interest: The brain is a dynamic, complex entity. How do you know which brain activity corresponds to your research experiment? One technique is to define regions of interest (ROIs) before scanning to identify which areas you expect to see changes in activation. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 3.0 fMRI and PET: indirect signals for neural activity The resting brain is not silent … Many fMRI and PET research protocols subtract an experimental condition from a baseline -- frequently a ‘resting’ state where the subject does not have a task to perform. But, is the brain resting? While activity during a resting state may not be directly related to the tasks being performed in other states, we know that humans are constantly thinking, imagining, feeling, anticipating and remembering. Background activity in the left and right hemispheres during a resting state Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 4.0 Conscious and unconscious brain events A recent wave of brain studies are investigating conscious and unconscious phenomena in the brain. For example, a fMRI study compared brain activation for conscious and unconscious events: unconscious viewing of words activated visual areas only, while conscious viewing activated expanded regions in the cortex. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 5.0 Correlation and Causation Brain damage and causal inferences Brain injuries can provide evidence that areas are necessary for certain cognitive functions, however it is important to keep in mind that studies of brain-damaged individuals provide correlational, not causal, explanations about brain function. Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience Edited by Bernard J. Baars and Nicole M. Gage 2007 Academic Press 6.0 Summary The advent of brain imaging has transformed the study of human cognition. New and refined methods are constantly being produced. There is a wide array of methods and techniques for brain recording: brain imaging techniques allow us measure single neurons as well as large cortical activations, brain structures as well as dynamic brain activity. A powerful use of brain imaging is to provide converging evidence, across techniques and research populations, to better understand human cognition.