Lecture 4: neuroanatomy and neuroimaging

Question 1

Major components of the CNS

Answer 1

• Forebrain
• Diencephalon
• Mesencephalon / midbrain
• Metencephalon / Hindbrain
• Medulla oblongata
• Spinal cord

Question 2

Gray matter

Answer 2

Consists of cell bodies, they are organised in layers:
- 6 cortical cell body layer, covering the hemispheres.
- Subcortical deep seated ganglia and nuclei

Question 3

White matter

Answer 3

Consists of the myelinated axons, connecting the neurons throughout the CNS/PNS. The majority of white matter consists of:
- Cortico-cortical connections: short fibres between areas.
- Commisural fibres: cross to the other hemisphere.
- Projection fibres: may connect ot subcortical regions, cerebellum or spinal cord.

Question 4

Afferent vs. Efferent connections

Answer 4

• Afferent: going TOWARDS the brain (Afferent –> Arrives).
• Efferent: going AWAY from the brain (Efferent –> Exits).

Question 5

Gyri and sulci

Answer 5

The wrinkled surface of the cortex has gyri (bumps in the wrinkles) and sulci / fissures (grooves or space between the wrinkels. They are landmarks on the brain and they are always quite visible. Based on these fissures you can identify the brain regions and gyrus.

Question 6

Subcortical structures / areas (under the surface of the brain)

Answer 6

• Basal ganglia
• Thalamus
• Limbic system

Question 7

Ventricles

Answer 7

The space where the cerebrospinal fluid is circulating through the brain. It takes away toxins.

Question 8

Directional planes of the brain

Answer 8

• Axial plane: horizontal view of the brain.
• Sagittal plane: looking at the brain from the side.
• Coronal / frontal plane: looking at the brain from the front.
• Dorsal: towards the back of the body.
• Lateral: away from the median.
• Anterior: in front of the brain.
• Posterior: behind the brain.
• Median midline of the brain.

Question 9

Functional pathways

Answer 9

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 or motor pathways. Most behaviours include many functions, thus involving many pathways simultaneously.

Question 10

Visual pathways

Answer 10

• 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.

Question 11

Auditory pathways

Answer 11

Signal crosses in the brainstream, processen bilaterally. Signals spread to various cortical and subcortical regions for further processing. The evidence for multiple pathways seperating sound identification and spatial hearing in the ventral and dorsal streams.

Question 12

Somatosensory pathways

Answer 12

There are different pathways for different types of stimuli:
- Touch, pressure, position and vibration crosses over in the lower medulla, terminating in the somatosensory cortex.
- Pain and temperature crosses over in the cervical spinal cord, terminating in the brainstem.

Question 13

Motor pathways

Answer 13

• Movement planning originates in the frontal premotor and supplementary motor areas.
• Movement execution involves the basal ganglia, cerebellum and primary motor areas.

From limb specific areas in the precentral gyrus, signals pass through the internal capsule to the muscles, crossing over in the medulla. Injury leads to movement problems or paralysis.

Question 14

Limbic circuit

Answer 14

Involved in emotional expression. Starts and ends in the hypothalamus. The hippocampus, the cingulate cortex and the interior nuclei of the thalamus are also part of this circuit.

Question 15

Anatomical images of brain structures

Answer 15

• X-rays: CT, angiography etc.
• MRI: differentiating tissue, CT’s are not good at this.
• D-MRI: diffusion through white matter tracts.

Question 16

Measures of activation of brain function

Answer 16

• Indirect measures: through blood circulation or oxygen levels (fMRI, PET, fNIRS.
• Direct measures: measures of neuronal firing/ electrical signals in the brain (EEG, MEG, ECoG, invasive line electrodes).

Question 17

X-rays

Answer 17

Distinguish bone 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. Cross-sections and better resolution through multiple projection, soft tissue is NOT visible with X-rays.
- Angiography: imaging blood vessels using contrast agents.

Question 18

Magnetic Resonance Imaging (MRI)

Answer 18

Does NOT use any radiation. Contrast agents are sometimes useful but not necessary. Also images of the soft tissue and the different types of tissue. Has a wide range of contrast mechanisms: tissue characteristics, water diffusion, oxygen saturation.

Question 19

Core mechanism of MRI

Answer 19

Nuclear magnetic resonance = measuring spins of hydrogen atoms / protons. Proton density differs over tissue types (ex. fatty tissue, fluid). Protons behave somewhat differently in different tissue types. Protons behave somewhat differently in different tissue types:
- T1 recovery: how fast the protons get back up.
- T2 recovery: how long it takes the protons to be in sinc again.

Question 20

T1 vs. T2- weighted scans

Answer 20

• T1 scans show a good contrast between grey and white matter.
• T2 scans show a good contrast between CSF and brain tissue (most used).

Question 21

Diffusion-weighted MRI (D-MRI)

Answer 21

Looking at how the water moves in the brain. There is diffusion tensor imaging (DTI) and diffusion spectrum imaging (DSI).

Question 22

fMRI

Answer 22

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.

Question 23

PET / SPECTS

Answer 23

Look 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).

Question 24

Electrophysiological signals

Answer 24

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.

Question 25

Time and space

Answer 25

• 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.