3.14 Neuroimaging Techniques

Study of Brain Structure and Function

Introduction

  • Discussion of the various methods used to study the brain's structure and function.

  • Importance of advancing technology in neuroscience and psychology.

  • Division of neuroimaging techniques into two main categories: structural (static) and functional (dynamic).

Structural Neuroimaging Techniques

  • Techniques used to visualize the brain's structure, shape, and size.

CT Scan (Computed Tomography)

  • Utilizes X-rays to create images of the brain.

  • X-rays penetrate different tissues at varying speeds.

    • Calculations based on speed differences provide insights into brain structure.

  • Useful for identifying lesions or areas of damage in the brain after accidents.

MRI (Magnetic Resonance Imaging)

  • Generates high-resolution images of the brain.

  • Involves placing a patient in a large magnetic tube.

    • Measures magnetic properties to create detailed brain images.

  • Commonly depicted in media (television, films).

DTI (Diffusion Tensor Imaging)

  • Specifically visualizes white matter tracts (myelinated axons) in the brain.

  • Produces colorful images representative of brain injury effects (e.g., concussions).

  • Helpful in identifying and isolating damage to white matter for therapeutic direction.

  • Provides insights into functional circuits and brain region interactions.

Functional Neuroimaging Techniques

  • Techniques that measure brain activity patterns and function.

EEG (Electroencephalogram)

  • Involves placing electrodes on a person's head with a specialized cap.

  • Measures surface-level electrical activity of the brain.

  • Helps identify areas of activity during specific tasks or cognitive functions.

    • Electric activity generates waveforms; changes can be linked to cognitive processes (e.g., attention).

PET Scan (Positron Emission Tomography)

  • Requires the injection of radioactive glucose into the patient before imaging.

  • Radioactive glucose acts as a tracer for brain energy usage; active areas draw in glucose and radioactivity.

  • Helps ascertain which brain regions are activated during tasks.

  • Clarification of common misconceptions about the safety of radiation in PET scans.

    • Mention of daily exposure to radiation from natural sources and travel (e.g., flying).

fMRI (Functional Magnetic Resonance Imaging)

  • Hybrid method combining structural and functional techniques.

  • Utilizes magnetic resonance imaging to produce images while assessing blood oxygenation levels in brain regions.

  • Active regions in the brain use more oxygen, allowing for activity mapping.

    • Example of visual response measurement through light signaling and activity in the occipital lobe.

  • Signal averaging: multiple trials are conducted to account for noise from random thoughts or distractions.

  • Colors in fMRI images (red/orange for high activity) represent involvement in cognitive tasks.

Limitations of fMRI

  • Recognition that fMRI data are correlational, not causal.

    • Just because an area shows activity does not mean it is necessary for task performance.

    • Other unmeasured areas may play a significant role in cognitive tasks.

  • Caution against inferring direct causes from correlational data.