L17: Cognitive Neuroanatomy Flashcards
What makes human brains special?
So among primates, human brains are the heaviest. They’re about 2.87 pounds.
They also contain the most neurons among primates, between 86 and 100 billion neurons.
Encephalization quotient
a measure that compares an animal’s actual brain mass to the brain mass expected based on body size, predicted by a mathematical relationship between brain and body mass
Humans have an EQ of 7-8 - the highest of any species by far
Problems with EQ:
The EQ of the African Elephant is 1.3, which is the same as that of a walrus, camel, or squirrel,despite the fact that african elephants show more complex behavior than these animals
Capuchin monkeys have a higher EQ than great apes, however great apes demonstrate greater behavioral flexibility and cognitive capacity than capuchin monkeys
Cerebral cortex theory
This finding supports the hypothesis that larger absolute number of neurons in the human cerebral cortex is correlated with the superior cognitive abilities of humans compared to other large-brained mammals
Human cerebral cortex
High cell density
Primarily compartmentalized local-circuit interconnectivity
Fast transmission of neural signals
What anatomical features of the human cortex contribute to these properties?
Macroanatomical features: cortical folding
Microanatomical properties: cellular organization
Macroanatomical features of human cortex
Surface area of human cerebral cortex - 2.5 square feet
Each hemisphere has roughly the same surface area as a medium pizza
Human brains are highly gyrencephalic
About 60-70% of the human cortical surface is tucked within sulci
The complex cortical folding of the human brain confers a greater surface area to volume ratio
Two major benefits of greater surface to volume ratio
Head size: a larger cerebral cortex can fit within the limited space of the human skull. Without such folding, the head would need to be significantly larger to accommodate the same amount of cortical tissue, making childbirth much more difficult
Shorter Communication Paths: The folding structures helps to reduce the distance that electrical signals need to travel between specific brain regions, minimizing the time it takes for these signals to transmit
Electrical signals take less time to get to their destination
Functional localizers
a task where you show a participant in the scanner certain types of stimuli.
If you are interested in looking at where in the brain faces are processed then you show the participants images of faces.
Can see if there is one specific area that responds selectively to faces
Why would macroanatomical features such as sulci predict the boundaries of functional regions?
Sulci often predict transitions in cytoarchitecture, or the organization, size, and shape of neurons across the layers of the cortex
Predict transitions in cortical gray matter
What do cortical layers have to do with function?
The functional characteristics of brain regions are determined by the physical arrangement of neurons and neural circuits
Each layer of cortex has specific characteristics with respect to the physical arrangement of neurons and their connectivity
The prominence of certain cortical layers differ between regions, conferring specific computations to different regions of the cortex
6 anatomically distinct layers of the cerebral cortex
Molecular layer: sparse, small neurons (local connections between adjacent neurons and cortical regions)
External granular layer: small granular neurons that are densely packed
External pyramidal layer: small and medium-sized pyramidal cells whose axons project to ipsi- and contralateral cortical regions
Internal granular layer: small granular neurons that are densely packed and receive input from other regions of the brain. Most prominent in primary sensory cortices
Internal pyramidal layer: main output layer containing large pyramidal cells projecting to cortical and subcortical regions. Prominent in primary motor cortex
Polymorphous layer: neuronal cell bodies of different shapes projecting primarily to subcortical regions
V1
Primary visual cortex (V1) receives
segregated input from LGN ganglion
cells that preserve their topographic
organization in order to represent the fine details of the visual world with
high fidelity. This means that layer IV of V1 receives a large amount of
input.
M1
Primary motor cortex sends a large amount of output projections to pyramidal tracts and the striatum to exert a high level of control over skeletal muscle, resulting in a prominent layer V in M1
Primary visual cortex
Highest cell density in cortex
Heavily myelinated
Columnar organization
These features give rise to inflexible, highly stereotyped, rapid processing of visual information - which is important for maintaining a stable representation of your visual world
Observer independent methods
quantify cytoarchitecture in the
human ventrotemporal cortex
identified two cytoarchitectonically
distinct regions on either side of
the mid-fusiform sulcus that were
not accounted for in an
observer-dependent atlas defined
by classic histological methods
