Lecture 19: Measuring Activity of the CNS

Electroencephalography (EEG)

• Measures electrical activity of the brain

• Post-synaptic activity of 1000s or more neurons

• Event-related brain potentials (ERP)

• Excellent temporal resolution BUT “inverse problem”

• Fast measurement technique → measures electro-activity in milliseconds

• Doesn’t allow you to localize brain area → very poor spatial resolution

• Measure technique time locked to sensory, cognitive, or motor event.

• Hundreds of trials

• Going above 0 voltage → increase; going below 0 voltage → decrease

Positron Emission Tomography (PET)

• Nuclear imaging technique

  • Injected with radioactive (isotope) trackers

• Measures physiological changes → metabolism, blood flow, glucose uptake

• Primarily used as diagnostic tool → identify specific neurodegenerate diseases

• Very poor spatial resolution

Which is the healthy brain and which is the Alzheimer’s brain?

• Scan 1 → healthy participant

• Scan 2 → Alzheimer’s Disease; slight reduction in overall cortical and subcortical regions of the brain

Which is the healthy brain and which is the Parkinson’s brain?

• Scan 1 → healthy participant

• Scan 2 → Parkinson’s Disease

What was neuroimaging originally used for and what does it do now?

• Originally to localize function in the brain

• Now clinical to look at onset and progression of neuro-degenerate diseases like Alzheimer’s and Parkinson’s

Functional Magnetic Resonance Imaging (fMRI)

• Measures brain activity by identifying changes in blood flow

  • Brain activity and blood flow linked

• Bold signal

• System level of the brain

• All about structure and function

• Measuring neural activity in brain by proving good spatial resolution but terrible temporal resolution

• A little slow → ~1 second

• Participant tapping finger → fMRI sees primary motor cortex active, able to evaluate bold signal through blood oxygen level → magnet spins biomolecules and blood cells in brain (carrying O2) able to measure spin frequency and determine where there is significant uptake of blood

Near-Infrared Spectroscopy

• Technique using light to detect changes in oxygenated (and deoxygenated) hemoglobin in blood.

• Decrease in oxygenation of the blood cells as a function of exercise → cells using more oxygen

Transcranial Magnetic Stimulation (TMS, rTMS)

• Non-invasive brain stimulating technique in which a changing magnetic current induces electrical activity at a specific region of the brain

• “Virtual” lesion technique → disrupts or facilitates neural activity in the brain

  • If disrupt is virtual lesion → area doesn’t work for a couple milliseconds

• Increases or decreases localized brain activity

• Single pulse creates scotoma (small area where you can’t see) in visual cortex → no processing of visual information

Purdue Pegboard Test Findings

• 1 and 3 Hz groups showed better functional recovery at every assessment

• 1 Hz to unimpaired Hz has the greatest recovery

TMS and Visual Spatial Neglect

• One treatment of 5 Hz, 15 days later

• Difference of severity of visual spatial neglect → gradually faded back to baseline