Principles of Neuroscience Lecture 24 Brain Evolution

Question 0

What are the three ways we can compare brain size? Which is the most useful?

Answer 0

Size of brain
Brain to body weight ratio
Encephalisation factor - the most useful. This tells us how far off the average for the species’ size its brain is

Question 1

What did Cuvier say about brain size?

Answer 1

All else being equal, smaller animals have a greater body to brain weight ratio

Question 2

What is special about cartilaginous fish?

Answer 2

These have a very steep slope for the graph of brain vs. body weight

Question 3

Describe differential regional size in the brain of different animals

Answer 3

In vertebrates, the relative sizes of different regions in the brain varies

Eg. Humans have, most importantly, a very large neocortex, whilst other animals have an olfactory lobe that is bigger than ours

Question 4

What is meant by “a rat is a monkey is a human”?

Answer 4

This is saying that all these animals have the same functional regions in the brain, which are also organised in a similar way, they are just different sizes

Question 5

Which area of the brain is fairly unique to higher animals?

Answer 5

Neocortex

Question 6

How does brain architecture in simple, as well as very large animals, compare with human?

Answer 6

Not vastly different, as we might expect

Goldfish: everything that is present in humans is here, it is just more dense and miniature

Whale: lack the lamination that we see in humans

Question 7

Describe differences in gyrification in different monkeys

Answer 7

As brain size and complexity increases, there is an increase in gyrification

Question 8

Describe differences of cortical thickness in different monkeys

Answer 8

As the brain size and complexity increases, there is no increase in the thickness of the cortical layer

Question 9

What is special about hominids?

Answer 9

They have a very large brain, with a very large neocortex

Question 10

What are the three different trajectories of brain vs. body weight?

Answer 10

Monkeys: not a steep slope
Australopithecines: also, they did not show a huge expansion in brain size over the years
Hominids: huge increase in brain size over the years

Question 11

Why is a big brain better?

Answer 11

More cells
Better connectivity
Greater differentiation of cell types
Different cytoarchitecture

Question 12

Describe migration of hominids

Answer 12

Out of Africa to Middle East, then Europe and Asia

Question 13

What is interesting about Homo Florensis?

Answer 13

Despite being alive not that long ago, they had a tiny brain

Question 14

On which trajectory is Homo Florensis? (Body vs. brain weight?)

Answer 14

It is ambiguous, we can’t tell whether it is a hominid or an Australopithecine

Question 15

Why are big brains associated with higher function?

Answer 15

.

Question 16

Describe how we can look at evolutionary changes in terms of epigenetic effects

Answer 16

Monkeys and humans appear to be quite related when we look solely at the genetic material
However, it is more useful to look at the expression of these genes. This shows us to be not so closely related

Question 17

What were the evolutionary pressures for an expansion of brain size?

Answer 17

1. Social interaction is selected for, which is a feature of a bigger brain
2. Better survival for those with a big brain

Question 18

What are the costs of having a larger brain?

Answer 18

1. Long gestation period, and babies are helpless for a long time: thus, it’s a burden on the mother
2. With a bigger brain, there is more chance of mutation or damage
3. Birth becomes very difficult, because the birth canal is barely wide enough for the brain

Question 19

What does comparison of parcellation in macaques and humans indicate?

Answer 19

If we look at the Brodmann’s areas in macaques and humans, we see there is much Homology.
The structure of the brain is very similar, there is not one thing that humans have that monkeys do not

Question 20

How did human brains expand?

What mechanisms are there for brain growth?

Answer 20

They don’t grow at a faster rate, they just grow for longer

Question 21

Describe how sexual pressures may select for a bigger brain

Answer 21

Bower bird: collect and sort materials for the nest to attract females for mating
A big brain is required for such behaviour.
Thus a bigger brain is selected for

In humans, we could compare this to humour, wit, cleverness etc. those with these traits may have had a larger brain, and these individuals were more likely to mate

Question 22

What is the mechanism for growing a larger brain?

Answer 22

Over expression of beta catering will cause rats to grow a bigger brain