Lecture 4: neuroanatomy and neuroimaging Flashcards
Major components of the CNS
- Forebrain
- Diencephalon
- Mesencephalon / midbrain
- Metencephalon / Hindbrain
- Medulla oblongata
- Spinal cord
Grey vs. white matter
Grey matter consists of cell bodies and white matter consists of myelinated axons, connecting the neurons throughout the CNS/PNS.
Afferent vs. Efferent connections
- Afferent: going towards the brain (Afferent –> Arrives at the brain).
- Efferent: going away from the brain (Efferent –> Exits the brain ).
Gyri and sulci
The wrinkled surface of the cortex has gyri (bumps in the wrinkles) and sulci / fissures (grooves or space between the wrinkels).
Ventricles
The space where the cerebrospinal fluid is circulating through the brain. It takes away toxins.
Directional planes of the brain
- Axial plane: looking at the brain from above.
- Sagittal plane: looking at the brain from the side. (Saggital = Side).
- Coronal: looking at the brain from the front/back.
Subcortical pathways
- Basal ganglia
- Thalamus
- Limbic system
Functional pathways
Functions are often implemented as pathways or circuits, involving multiple brain regions. Sometimes function connectivity cannot easily be determined with neural structures. Examples of functional pathways are:
- visual
- auditory
- somatosensory
- motor
Most behaviours include many functions, thus involving many pathways simultaneously.
Visual pathways
- The dorsal pathway (WHERE): is used for spatial information, damage in this area leads to impaired perception of movement and spatial neglect.
- The ventral pathway (WHAT): is used for object recognition. Damage in this area leads to impairment in object or facial recognition.
Limbic circuit
Involved in emotional colouring of experiences. Starts and ends in the hypothalamus and consists of the hippocampus, hypothalamus and amygdala.
Anatomical images of brain structures
- X-rays: CT, angiography etc.
- MRI: differentiating tissue types, CT’s are not good at this.
- D-MRI: diffusion through white matter tracts.
Direct vs. indirect measures of activation of brain function
- Indirect measures: through blood circulation or oxygen levels (MRI, fMRI, PET, CT).
- Direct measures: measures of neuronal firing/ electrical signals in the brain (EEG, MEG, ECoG).
X-rays
Distinguish bone/tissue form fluid/air. There are different types of X-rays:
- Radiography: small dose of radiation. Rays are absorbed to a different extent by different tissue types. Single projection, good images of bones.
- CT: moderate dose of radiation beams. Cross-sections and better resolution through multiple projection, soft tissue is NOT visible with X-rays.
- Angiography: imaging blood vessels using contrast agents.
Magnetic Resonance Imaging (MRI)
Does NOT use any radiation. Contrast agents are sometimes useful but not necessary. Also images the soft tissue and the different types of tissue. Has a wide range of contrast mechanisms: tissue characteristics, water diffusion, oxygen saturation.
T1 vs. T2- weighted scans
- T1 scans: contrast between grey and white matter.
- T2 scans: contrast between tissue and fluid.
Diffusion-weighted MRI (D-MRI)
Looking at how the water moves in the brain.
fMRI
Measures oxygen saturation with the BOLD-response. Different weights of MRI makes it sensitive to oxygen-level changes. Repeated scanning over time is a temporal resolution. You can interpret fMRI results by overlaying the scan with a statistical map at look at the differences.
PET / SPECTS
Looks at blood flow. A radioactive tracer allows imaging of blood flow patterns using gamma rays. It’s a subtract method with a limited number of trials (one-shot method).
Electrophysiological signals
Electrical reactivity related to neural firing can be detected in 2 ways:
1. Directly with invasive electrodes (in brain surgery).
2. From the scalp if the summation is sufficient and the neurons are approximately alligned.
Examples:
- EEG: electrodes on the scalp.
- MEG: better source estimation than EEG and measures magnetic field potentials.
- ECoG: directly on the cortex.
Time and space
- EEG is very good at TIME (when something is happening in the brain).
- MRI is very good at SPACE (where something is happening in the brain.
