Lecture 4/5: Cytoarchitecture and Cytoarchitecture Maps Flashcards
Cytoarchitecture
- Cytoarchitecture is the structure and organization of the neurons in the cortex.
- Some of the characteristics we look at are size of cells, types of cells, density of cells and a couple of things related to the organization of cells (cellular collums, layers)
- we want to study cytoarchitecture because there is not much known and what is known is not very certain at the moment. → hardly any research done on the cytoarchitecture inside the sulci.
How do we study cytoarchitecture?
1) Slice a part of brain
2) Stain the gray matter (ex: Nissl Stain → just stains cell bodies)
3) Look up close on microscope
How can we see the cerebral microstructure?
In order to see the cerebral microstructure, we must stain the cell bodies.
Golgi stains: stains 10% of neurons, but stains them completely (the ones it does stain, stains them very well)
Nissl Stain: stains the cell bodies of all neurons (by staining the endoplasmic reticulum).
Weigert Stain: Stains the myelin of the axons (the white matter) → myeloarchitectonic
What can you use stains for?
- Specific parts inside the cell bodies
- receptors
- neurotransmitters
- dendritic spines
Types of cortex
1) Allocortex (old cortex): anywhere from 3-4 cortical layers (not your traditional 6 layers).
2) Neocortex (new cortex): 6 cortical layers
ex: Area 44 and 45
Layers of Neocortex
Layer I (molecular layer): comprised of a few scattered neurons. Present troughout the cortex in the brain.
Layer II (external granular layer): dense layer of very small round pyramidal neurons which sometimes appear to be granular.
Layer III (external pyramidal layer): pyramidal neurons which get larger the deeper into the cortex they go.
Layer IV (internal granular layer): small round cells.
→ a lot of the input comes in (most noteable characteristic of neocortex).
Layer V (internal pyramidal layer): pyramidal neurons, often denser in the upper part than in lower part.
Layer VI (multiform layer): Spindle-shaped neurons/ modified cells, the lower part often blends with the white matter.
Layer III → main output layer from cortical to cortical areas.
Layer V → main output from cortical to subcortical areas.
Types of Neocortex
Granular neocortex: Fully formed granular IV.
Ex: area 45 and 47/12
- Subset of granular neocortex called Hypergranular cortex (koniocortex): granular layer IV and the rest of the layers are granular in appearance.
Ex: area 3b (primary somatosensory cortex) - so many inputs coming into sensory areass so all the neurons are structured like granular cells to receive a bunch of inputs.
Area 17 (primary visual cortex)
Area 41 (primary auditory cortex)
Dysgranular cortex: Slightly granular layer IV interupted by pyramidal cells from III and V.
eg: area 44
Agranular cortex: no granular layer IV
eg: area 4 and area 6
- The best stain to use for cytoarchitectonic analysis of the cortex is?
- When stimulating the exposed cortex of patients undergoing surgery, Dr. Wilder Penfield found that the precentral gyrus contains
- Which of the following lack the typical six layers found in neocortex?
- Which of the following was considered the main language pathway for many years?
- Fill in the blanks: The globus pallidus lies ___ to the thalamus but ___ to the putamen
1) The Nissl stain
2) A map of the body corresponding to voluntary motor control
3) the pyriform cortex, the hippocampus, and the cortex of the cingulate gyrus
4) the arcuate fasciculus
5) lateral, medial
Area 47/12
- Typical 6 layers
- Good granular layer IV
- Area involved active memory retrieval (with area 45)
- granular cells in layer IV are much smaller than pyramidal cells.
Area 45
- Distinct granular layer IV
- Large pyramidal cells in the lower part of layer III called gamma (I) cells by Economo and Koskinas
- Active memory retrieval and processing area
- Some definitions of Broca’s area include area 45.
The differentiation of area 45 from area 47/12 is in the bottom of layer III (layer 3C) → there are dark spots: bigger + more darkly stained.
Area 44
- Dysgranular layer IV (interupted layer IV)
- Broca’s area proper
- Electrical stimulation to this area .can cause speech arrest
Area 6VR
- Premotor area (premotor cortex)
- No layer IV (sometimess there is a space where layer IV could of been)
- Agranular cortex
- Difficult to distinguish layers.
Area 4 (medial surface)
- Agranular area
- Largest neurons (feet neurons) in the brain are in layer V, called Betz cells
- Poor border with the white matter, even seen in anatomical MRI
- Thick cortical ribbon
- Primary motor area
Betz cells
Following the homonculus, as you move down, the size of the cells changes because it doesn’t have to go as far.
Orofacial → quite small cells (smallest)
Hand → smaller
Foot → largest
Area 3b
→ similar to area 17 and 41
* Hypergranular cortex (very small)
* Very distinct layer IV
* All other layers appear granular
* Thin cortical ribbon
* Primary somatosensory area
Differences in cytoarchitectonic composition and organization (what we see structurally) leads to…
Differences in cytoarchitectonic composition and organization (what we see structurally) leads to differences in functions.
agranular areas = motor related areas
hypergranular areas = sensory areas
frontal granular area = processing area
Things develop out of the central sulcus
Obstacles to the study of cytoarchitecture.
- Non-optimal sectioning (need to start with good sections.
- Not being able to analyse an entire brain.
- Cutting artifact (if you cut it more thick, it will show that there iss a lot of cells)
- Staining artifact
- Quantitative analysis are difficult
- Labour intensive
- Accesibility (Expense, Access to brain,Process it)
Optimal vs Non-optimal angles of cut
Optimal Cutting: Cutting the cortical tissue perpendicularly to the direction of the sulci or gyri to obtain clear views of the cytoarchitectonic layers (cuting perpendicular to the sulci or gyri that you are intersted in).
* Some of what we do in the lab involves the optimal cutting around sulci of interest for cytoarchitectonic analysis.
* We use neuronavigation techniques to plan each part of the brain that will be processed based on sulci of interest.
→ Use MRI to help navigate
→ optimize the blocking using anatomical MRIs and neuronavigation techniquess (see what we have before going into the tissue)
Brodmann’s Map
- The gold standard?
- one brain
- cytoarchitecture
- No stated criteria (never said why each area is different)
- No accounting for sulci
- No homologies between anumal species (did not do comparitive cytoarchitecture)
Why are we using the naming convention from a 100+ year old map?
* The study of neural cytoarchitecture began with the invention of the Nissl and Golgi stains at the end of the 19th century when allowed us to see neurons for the first time.
* By the early 1900s, scientists worked away and were able to come up with the first cytoarchitectonic maps
Campbell (1905)
- In 1905, Campbell created the first complete cytoarchitectonic map of the human brain.
- He talks about the importance of optimal cutting
- In his map, there is some representation of different neurons
Brodmann followed with his map.
Economo and Koskinas (1925)
- Economo and Koskinas published their extensive map and atlas in 1925.
- This work took around two decades to complete.
- Much of their nomenclature is still used today with regards to areas in the parietal and temporal lobes.
- They justified what they did → justified procedures and nomenclature.
- nomenclature = Fabcde…, Pabcde…, Tabcde…, Oabcde…
Sarkisov (1949)
- used brodmann numbering system
- Similar to Economo and Koskinas map
By the 40s and 50s, the study of cytoarchitecture and cortical anatomy had slowed down considerably.
→ War was happening
→ Behaviourism: People were focused on behaviour and not the brain.
Nevertheless, the study of some structural/functional relationships was progressing.
Penfield
- Founded MNI (montreal neuro institute)
- He was doing micro stimulation of the cortex when doing surgery.
Homunculi
- Developed by Penfield → he came up with the homunculus
At this time they wanted to create a common space for neurosurgeons so that they could talk and discuss about the brain areas and their patients/cases.
