Chapter 3: Methods of Cognitive Neuroscience

What are the limitations of the fMRI?

• *Correlation does NOT imply Causation*: Excel. Control ○ Area may be active during task but not critical for task ○ Reverse Inference: Activation may not be related to putative mental process but something else • Delayed, indirect measure of *synaptic activity* ○ Local field potentials; NOT action potentials at size ○ Reflect *input* & intracortical processing; Not Output • Signal very small; Must avg. across many subjects • Brains diff shapes, sizes, activation (can be diff for same tasks for diff people); Must morph brains to find average • 1000s of voxels; Heavy duty statistics • Diff pre- and post-processing method > diff results

How do we see neurological dysfunction?

• Alzheimer's Disease (medial-temporal lobe-> parietal, cortex, white matter) ○ Neurons/white matter themselves are degenerating and brain is contracting and CSF fills up the spaces, no shunting needed • Stroke • Used for ages to elucidate brain function (how they work, diff functions involved in) ○ Broca's area ○ Phineas Gage (iron through prefrontal cortex) ○ HM (bilateral medial temporal lobe to control seizures)

What does the Functional Magnetic Resonance Imaging (fMRI) measure?

• Blood Oxygenation Level Dependent (BOLD) Signal Measures increase in blood flow: initial decrease in oxygenated blood (using up that oxygen as neural activity occurs), then big ^ • ^ in BF to delayed by seconds (after event) • High spatial resolution imaging of ENTIRE BRAIN = huge advantage of single cell recording • Wildly popular technique

What are the consequences of combining methods?

• Combined use of fMRI and TMS to demonstrate the role of the visual cortex in tactile perception a. Increased basal forebrain in visual areas during tactile exploration b. Accuracy of judging orientation of tactile stimulus impaired with TMS subjects generated visual images of tactile stimuli

What does traumatic brain injury look like?

• Coup (=occurs on the brain directly under the point of impact), Countrecoup, Damage to orbitofrontal cortex (OFC) • Shearing of dendrites & axons • Sports-related injuries (Boxing, football, etc.) ○ Chronic Traumatic • Encephalopathy (CTE) Improvised explosive devices (IEDs)

How are event-related potentials related to EEG?

• ERP: EEG averaged over many trials • Avg. EEG time-locked to specific events • Electrocorticogram (Ecog): On cortical surface • You are recording EEG from the scalp; POOR SOURCE LOCALIZATION for EEG

What is the advantage of using Electroencephalography (EEG)?

• Electroencephalography (EEG); Scalp electrodes • Summed activity of MANY neurons • Good temporal resolution; very poor spatial resolution

What are the pitfalls/limitations of using brain dysfunction (e.g., neurologic diseases, strokes, brain damage, tumors or lesions) to elucidate the function of given brain area?

• Fibers of passage • Downstream effects= lesion in one part of cortex, this part of cortex may have projections of other cortex so other areas of brain may be dysfunctional as a result • Mass effects= slowly growing tumor in brain, it will start pressing against parts adjacent to it and it push the brain stem => you could die! • Diff lesions locations in diff patients • Multiple regions affected (e.g. Huntington's Disease)

What are the advantages and disadvantages of using Single-Cell Recordings?

• Imp advance: Extensively used in wide variety of tasks • Advantages? You can record activity of single neuron while animal is doing specific and you can tell exactly how this neuron responds to the stimuli • Disadvantages? Enormously difficult to do these studies; recording of single neuron and none of its input/output connectivity

What are some examples of genetic manipulation?

• Knockout in CA1 > Impaired fear conditioning • Knockout NMDA receptors in CA1 ○ Joe Tsien did this • Poor memory • Doogie mice ○ Inserted gene for NMDA receptor in CA1 (dramatic effect in memory just by inserting one gene) ○ Better memory

What are the logic & limitations of a lesion?

• Logic: If area is involved in function, lesion > deficits • Multiple areas involved, including white matter ○ Broca's Pt.; Alzheimer's, Huntington's, TBI, stroke • Variability between patients ○ Exact location of all injuries may be uncertain ○ May even be true of animal lesion studies • Behavioral compensation (Taub; 1st 1 arm then the other) • Functionally related areas may compensate ○ Interconnected with related functions that may compensate • Functional differences between species ○ You may think you're in a homologous species when you're not • Downstream effects (Brain is a network!!!) ○ Parkinson's disesase= degeneration of neurons in basal ganglia (BG: Initiation and speed of movement: DBS > improvement) • Other: Mass effects, acute swelling, inflammation, metabolic changes; Effects may be due to much more than local damage • LEGIONS ARE NOT THE BEST TO STUDY BRAIN FUNCTION

What does a PET scan do?

• Measures blood flow, oxygen use, and sugar (glucose) metabolism: Correlated w/ activity • Not used much anymore because you need a cyclotron to generate • Need cyclotron; radioactive label • Poor temporal and spatial resolution

What is an example of mistaking the difference between correlation and causation?

• PTSD and Brain Size ○ PTSD > Decreasing Size? ○ Decreasing Size > PTSD? • Twin Study ○ Non-PTSD twin also correlated (in PTSD severity) ○ Small hippocampus is risk factor for PTSD

Difference between single and double dissociation?

• Single Dissociations: Often used; 1 task harder/more sensitive? ○ Pt. vs. controls; Lesion may affect memory, attention, depression (other functions=> may not be looking at what you think you're looking at) • Double Dissociations: Temporal (Familiarity deficits, not recency); Frontal (opposite) • DD: Much more convincing; Deficit is selective

What does the Transcranial Magnetic Stimulation do?

• Used to briefly disrupt cognitive processing ○ Can excite or inhibit (brief focal lesion) cortex (diff parameters) • Greater impact on surface cortical areas ○ Effects localized (1.0-1.5cm^3 (quite focal excitation/inhibitions; downstream effects?)

What does the Stroop effect demonstrate?

• What is the color of the ink? DV: Reaction Time • Word & color both represented; Word interferes • How brain represents & processes info; Not where the processing occurs (there's no way to know without doing other manipulations)

What is an example of Single cell recordings in humans?

• i.e. Halle Berry neuron • Recordings from hippocampal neuron in epilepsy patient • Neuron also active when imagining Halle Berry

What are the effects of Transcranial Direct Current Stimulation?

• tDCS • Low-level DC current between 2 electrodes on scalp • Excitation under the anode • Inhibition under cathode • Poor spatial resolution: Stimulation over large area • Effects short-lived • Simple, cheap; DIY community • Depression? • Brain enhancement? • Placebo effects?

What does Diffusion Tensor Imaging (DTI) show?

- Shows White Matter Tracts: Connectivity between regions

The spatial resolution of an MRI IS ____ to that of a CT scan

Superior

What are optogenetic methods?

• Using Light to Manipulate Neuronal Activity • Insert genes into specific neurons ....i.e. A, B Hippocampal neurons activated ....C Amygdala: Less fearful

What does the memory comparison behavioral studies tell us?

- Mental processing takes time • Memory comparison (i.e. 1-4 letters, delay period, and show letter and say whether this letter was in the group of letters shown earlier ○ Presented with 1, 2 or 4 letters; memorize ○ Delay, then probe letter; Was it shown previously? ○ DV: Reaction time increases with set size ○ Target letter compared sequentially, not in parallel ○ Visuomotor Rotation: Linear increment in reaction time Ss perform a mental rotation that ^s with angle

What can Magnetic Resonance Imaging do?

Can distinguish white & gray matter & CSF

If I say the word "grass," you may immediately think of its distinct shape, the smell of grass clippings, and the fact that it is a type of plant. This phenomenon, which was illustrated in Posner's letter-matching task, demonstrates that humans:

Develop multiple representations of the same stimulus

The term ________ is used to describe the situation in which group 1 is impaired on task X and unimpaired on task Y and group 2 is impaired on task Y and unimpaired on task X. In contrast, the term ________ is used when group 1 is impaired on task X and unimpaired on task Y and group 2 is unimpaired on both tasks X and Y.

Double dissociation, Single dissociation

Research questions about the time course of cognition are better addressed using methods like ________, whereas questions about the anatomy of cognition are better addressed using methods like ________.

ERP, fMRI