Lecture 4 Neuroimaging PDF

Lecture 4 Neuroimaging Introduction to Cognitive Neuroscience PSYCH 375 A1 James Farley, Fall 2024 Method: Brain Imaging Functional Magnetic Resonance Imaging (fMRI) Magnetic Resonance Imaging (MRI) uses magnetic elds and radio waves to generate anatomical images of body tissue Functional...

Lecture 4 Neuroimaging Introduction to Cognitive Neuroscience PSYCH 375 A1 James Farley, Fall 2024 Method: Brain Imaging Functional Magnetic Resonance Imaging (fMRI) Magnetic Resonance Imaging (MRI) uses magnetic elds and radio waves to generate anatomical images of body tissue Functional Magnetic Resonance Imaging (fMRI) is an MRI application that measures changes in the BOLD signal (blood-oxygen-level-dependent signal), which is correlated with cognitive activity As neurons become more active they require/use oxygen, which changes the magnetic properties of the surrounding blood This change can be detected in the BOLD signal, and can therefore be used to make inferences about changes in neural activity Remember that the BOLD signal is simply a correlate of neural activity, it is not a direct measurement of it! fi  Method: Brain Imaging Functional Magnetic Resonance Imaging (fMRI) fMRI analyses ‘draw’ what we can think of as imaginary boundaries based on three-dimensional pixels (voxels) that are superimposed onto the brain The BOLD signal does not tell us anything about the activity of individual neurons but can provides estimates for changes in the average/overall activity within speci c voxels (e.g. those that overlap with a brain region of interest, such as the amygdala) https://medium.com/swlh/classical-conditioning-brain-state-classi cation-a ective-bcis-for-ad-patients-8478cd271ef0 fi fi ff http://gureckislab.org/courses/fall19/labincp/labs/images/brain_basics.svg Method: Brain Imaging Functional Magnetic Resonance Imaging (fMRI) fMRI - How it Works and What it's Good For: https://www.youtube.com/watch?v=Rb_mdzgw-Jc Note that how an fMRI works is pretty complicated but this video is just included in case you’re interested, you don’t need to understand the physics behind this for our course!  High Spatial Resolution Imaging Positron Emission Tomography (PET) Positron Emission Tomography (PET) was an early functional brain imaging method in use by the 1970’s Typical PET protocol involves the injection of radioactive 2-DG (structurally similar to glucose) that is rapidly taken up by active cells until gradually breaking down This allows a map to be produced showing where the radioactive dye goes, which correlates with neural activity https://radiology.ucsf.edu/patient-care/services/specialty-imaging/alzheimer Spatial vs. Temporal Resolution Trade-o s This fundamental distinction between imaging methods with high spatial resolution and high temporal resolution has lots of implications, and a major one is that there are trade-o s when choosing one method over another Both approaches can be important for more fully understanding cognitive and neurological phenomena (e.g. they o er di erent perspectives) Some methods allow for source localization using EEG (providing limited spatial resolution), and ERP’s can also be combined with fMRI for more balanced spatial and temporal resolution ff ff ff ff  Spatial vs. Temporal Resolution Trade-o s https://slideplayer.com/slide/12835414/ ff Assessing Functional Connectivity Functional Magnetic Resonance Imaging (fMRI) Given some of the limits of understanding brain and behaviour based just on localization of function, how else can researchers use neuroimaging techniques to develop more complete theories? Various alternative methods can contribute to this pursuit… Can asses functional connectivity Can asses structural connectivity Can manipulate neural function etc. Assessing Functional Connectivity Functional Magnetic Resonance Imaging (fMRI) fMRI can be used to assess functional connectivity 1. Can use task-related fMRI to determine brain location associated with a speci c task (these data are referred to as the seed location) 2. Measure the resting-state fMRI at the seed location 3. Measure the resting-state fMRI at another location (referred to as the test location) 4. Calculate the correlation between the seed and test location responses to assess the degree of functional connectivity fi  Assessing Structural Connectivity Diffusion Tensor Imaging (DTI) Di usion tensor imaging (DTI) uses MRI technology to map out major pathways (tracts: bundles of axons) in the brain Can also be referred to as track- weighted imaging (TWI) This is useful for understanding how di erences in the structural connectivity between di erent regions of the brain are related to various factors ff ff ff  Making Causal Inferences Transcranial Magnetic Stimulation (TMS) Transcranial Magnetic Stimulation (TMS) uses a magnetic eld and an electrical current to modulate brain activity at speci c sites (generally decreasing or increasing ring) Can create what is referred to as a ‘virtual lesion’, producing a temporary impairment and thus providing a means for ethical manipulation of neural function in humans (allowing causal inferences to be drawn!) Repetitive TMS (rTMS) can produce longer lasting changes in neuronal activity, though there is still some debate about the safety and e cacy of this method https://www.eugeneweekly.com/2019/01/03/tms-clinic-open-in-eugene/ https://psychscenehub.com/psychinsights/transcranial-magnetic-stimulation-for-depression/ fi fi ffi fi  Optogenetics Manipulating Neuronal Firing The use of optogenetics in cognitive neuroscience involves genetically engineering neurons that are light- sensitive (e.g. ion channels that open when exposed to a particular wavelength) This allows neurons to be e ective controlled, or turned on/o , by exposing them to light https://www.post-gazette.com/news/health/2015/02/01/Pittsburgh-researchers-use-light-on-animal-brains-to-study-mental-disorders/stories/201502010006 ff ff Optogenetics Implanting False Memories This video describes an experiment in which a classically conditioned association is rst created using fear conditioning, then the neurons associated with that fear-based memory can be ‘turned on’ in safe environments to produce freezing behaviour: The Memory Mirage (THE NATURE OF THINGS): https://gem.cbc.ca/media/the-nature-of-things/ season-58/episode-6/38e815a-00fb9922920 (20:33-23:30) fi  Magnetic Resonance Spectroscopy (MRS) Measuring Chemical Compositions Magnetic Resonance Spectroscopy (MRS), also sometimes called nuclear magnetic resonance (NMR), is a technique that uses an MRI machine to produce estimates related to metabolic changes in the brain This allows estimates related to the chemical composition in particular brain regions, and has applications for both basic research and clinically relevant purposes One major advantage is that it can be used to produce in vivo (i.e. within a living organism) estimates related to some simple neurotransmitters (e.g. GABA and glutamate) One major disadvantage is that, at present, it is not capable of measuring more (chemically) complex neurotransmitters that are of interest of cognitive neuroscientists (e.g. serotonin, dopamine) https://link.springer.com/article/10.1007/s00429-021-02273-0  Functional Near-Infrared Spectroscopy (fNIRS) Measuring Neuronal Activation Functional Near-Infrared Spectroscopy (fNIRS) is a relatively cheap, non- invasive method for estimating changes in neural activation Hemoglobin absorbs a signi cant amount of infrared light, more so than most of the other substances/tissue in our brain Changes in the relative proportion of light that is re ected back can therefore be used to estimate changes in hemoglobin concentration (which can, in turn, be used to infer changes in neural activation) https://www.frontiersin.org/articles/10.3389/fnins.2020.00724/full fl fi  Case Studies Observing the Unusual Case studies undertaken in cognitive neuroscience involve in-depth investigations into individuals presenting with atypical neurology (e.g. what e ects does not having a hippocampus have on our various memory systems?) One major advantage of case studies is that they provide unique research opportunities that would not otherwise be possible with conventional experimental methods Major disadvantages relate to generalizing the results (which can be particularly complicated given the heterogeneity of di erences associated with case studies), as well as disentangling cause and e ect https://www.psychologywizard.net/scoville--milner-ao1-ao3.html ff ff ff Lesion Studies Manipulating the Brain Lesion studies typically involve training a non-human animal to perform a task, damaging a part of the brain, then observing how that damage a ects the organism’s ability to perform the previously learned task One major advantage is that they allow relatively straightforward causal inferences to be made about the contribution of various brain regions One major disadvantage relates to the di culty in generalizing observations from non-human animals to humans (since this method cannot be used with humans) ff ffi