Week 8 Flashcards
What is the protomap hypothesis and what is the protocortex hypothesis?
Protomap:
- Postulates that the early cortex has an inherent, predefined template for development of cortical areas
Protocortex:
- That the cortex is a blank slate and that the identity of individual cortical areas in specified by incoming afferents
There is evidence for both. E.g., There is prespecified tissue in the VZ, however, transplantation studies show reprogramming is possible
The 3 theories of map formation are:
a - Induction models
b - Cytodifferentiation models
c - Neighbour matching models
What do each of these postulate?
a) Incoming axons have inherent information that specifies their orderly mapping within the target tissue
b) The existence of molecular cues on incoming axons that match them with corresponding cues on target cells
c) Incoming axons contain signals that are more similar between adjacent cells than distant ones. Neighbouring target cells have the ability to distinguish these signals and selectively establish contact with incoming axons carrying similar signals
What is the chemoaffinity hypothesis and what theory(s) of map formation does it support?
- Postulates the presence of labelling molecules on BOTH axons and target cells
- Found by rotating an eye of a frog 180deg
- Supports both the neighbour matching model and the cytodifferention model
Ocular dominance bands in primary visual cortex:
a) are present in all layers of the cortex
b) are formed as a result of visual experience during the critical period
c) are formed before birth in mammals but can be affected by early visual experience
d) are the last feature of the visual cortex to be susceptible to visual experience
C
Which of the following is expressed in a temporo-nasal gradient in retinal cells?
a) Ephrin A5
b) EphA5
c) EMX2
e) FGF8
B
Retinal waves:
a) are required for the formation of ocular dominance bands in layer 4 of primary visual cortex
b) are required to induce a shift in ocular dominance to monocular deprivation
c) synchronize activity of neurons within a single eye
d) synchronize activity of neurons of the two eyes
C
Feature maps:
a) are representations of the physical features of a stimulus
b) are exemplified by the sensory and motor homunculi in human cortex
c) all develop independent of visual experience
d) are dependent on Eph-ephrin gradients
A
Dark rearing:
a) abolishes the development of ocular dominance bands
b) disrupts the development of direction-selective maps
c) allows for the study of visual cortex development in the absence of visual input
d) b & c
D
Direction-selective maps:
a) are an example of topographic maps
b) develop at the same time as ocular dominance bands
c) are dependent on visual experience
d) develop 4 weeks before orientation selective maps
C
Orientation-selective maps:
a) are abolished by dark-rearing
b) cannot be visualised using optical imaging
c) were first discovered by Hubel and Wiesel
d) are a sub-map of direction selective maps
C
What is a feature map?
Representation of a physical feature of a stimulus such as the colour of an object
What is a topographical map?
Representation of a spatial stimuli on a sensory surface. E.g., in motor systems, they specify locations in the brain in which activity causes movement of a region
Example: Cochlear of the inner ear, facial pad of a mouse and the associated sensory neurons of the whiskers
What is the role of EMX2 in spatial positioning of cortical areas?
What does Emx2 ablation cause?
- EMX2 is present in a gradient, with HIGH levels of expression at the posterior regions of the cortex and low expression at the anterior.
- Emx2 ablation results in anterior expansion. Hyper activity results in posterior expansion
The olfactory bulb develops not using molecular gradients. How does development of the olfactory bulb work?
- OSNs express one type of OR
- Each OSN connects a particular subset of neuronal targets in the OB called glomeruli
- All the OSNs that can detect coffee for example, although randomly assorted in the nose, all connect to the same glomeruli #
- Done through cytodifferentiation
Retinotectal maps are an example of WHAT kind of map development?
Fine map development
