Lecture 17 Brain and behaviour

Question 1

Nervous system in humans: basics

Answer 1

Central Nervous System (CNS)
-brain
-spinal cord

Peripheral Nervous System (PNS)
-Peripheral nerves: connect the CNS with the somatic(skin, muscles, skeleton) and autonomic(heart/blood vessels, internal organs, glands…) nervous system

Question 2

neurons

Answer 2

Sensory neurons➢Detect external stimuli

Motor neurons➢Control muscle movements

“Connector” neurons➢Relay signal

Neuron/glia ratio ~1:1 ~170 million brain cells

Question 3

The discovery of nerve cells

Answer 3

✓Discovered end of 19thcentury using Golgi staining that stains sparsely the whole cells

✓Golgi and Cajal shared the Nobel Prize for Physiology and Medicine in 1906 for their work on the structure of the nervous system

Question 4

Nervous system across phylae

Answer 4

Bilaterian- Ceohalisation (head and tail)

coordinated behaviours
- hydra, jellyfish, sponges

Question 5

Invertebrate

Answer 5

Invertebrate
-Nerve net, nerve ring(diffuse nerve cells)
-Cephalisation: CNS (ganglia, nerve chord, “proto-brain” [cerebral ganglia])

Question 6

Vertebrate

Answer 6

✓Functional division (CNS/PNS)
✓Distinct brain structures
✓Use-dependent changes (e.g., size)

Question 7

what does the nervous system allow for

Answer 7

Nervous system allows sensorimotor behaviour

Question 8

Origin of the nervous system: earliest known CNS

Answer 8

was in the early Cambrian- 520 million years ago

Question 9

earliest known CNS

Answer 9

✓Alalcomenaeusfossil dated 520-million-year-old with extremely well-preserved CNS
✓Belong to the megacheirans (“great appendage”), an extinct class of arthropods

✓Discovery helped clarify that the segment of proto-brain that innervates GA is the same as in the fangs of modern-days spiders and scorpions

Question 10

Origin of the nervous system: how did it appear?

Answer 10

✓From jellyfishes to humans, neurons have the same fundamental morphology and function
✓The “raison d’être” of nerve cells is to transmit signals to other neurons = communicate. ➢Fundamental unit of the nervous system = synapses

In humans:~86 million neurons~1015million synapses

Question 11

Synapses are small ‘computers’

Answer 11

Synapses host numerous (~2000) specialised proteins and protein complexes, which are essential for the release and interpretation of the neurotransmitter signals

Question 12

Synaptic proteins precede synapses

Answer 12

Components of the synapses are present in single cells and do participate in cell-cell communication

Phylogenetic tree depicting taxonsof current relevance to synapse evolution
- Ursynapse is the key point in the phylogenetic tree

Question 13

Vertebrate brain
Origin of the vertebrate brain

Answer 13

Haikouichthys(extinct): 530-million-year-old fossil (~3cm):
➢Protovertebrae
➢Mass of cartilage around primitive brain

✓Growth of body → evolution of myelinwhich allows more rapid transduction of nerve signals further away
➢Specialisation of glial cells = oligodendrocytes [CNS]/Schwann cells [PNS])
➢Specialisation of sensory and motor organs
-Complexification of behaviours

✓Evolution of homologous brain regions with specialised functions
➢E.g., cerebellum stabilises body in the water or on land
✓Different evolution for different lineages➢Land animals have developed cerebrum
-Development of cortex in mammal

Question 14

development of cortex

Answer 14

✓Significant development of the cortex
oApparition of circumvolutions
o~90% of the human brain

✓Cortical functions evolved according to ecological niche

Question 15

Sensory and motor homunculi

Answer 15

✓Representation of the entire body on the surface of the primary somatosensory and motor cortices

✓Cortical surface devoted to a specific organ depends on its usage
➢Homunculi: the body how the brain sees it
- in humans the sensory sees the whole body but especially the hands and mouth and ears
-the motor homonucli especially sees the hands and mouth and smell

Question 16

What makes us human?

Answer 16

What is special about our brain that is not found in other mammals or even primates?

-humans have the highest brain to body/volume ratio

rapid evolution of brain size & frontal lob

Prefrontal cortex:
✓Executive function
✓Motivation
✓Speech & language
✓Working memory
✓Risk assessment
✓Decision making
✓Social behaviour

Question 17

What event in human evolution seems to be at the origin of the rapid expansion of the brain of primates and why?

Answer 17

➢Fire→ cooked food = more calories in minimum time
➢Allows to increase number of neurons (high energy cost) without spending more time searching for food
➢More time to develop new abilities

Question 18

What makes us human: size matters but…

Answer 18

the density of neurons per brain size in humans is 7x higher than that of African bush elephants and is generally more dense than that of non-primates

Question 19

Example of corvids (crows) and parrots

Answer 19

✓Use tool
✓Plan action
✓Resolve complex (and new) problem = transfer of knowledge
✓Recognize themselves in mirror (self-conscious?)

Question 20

What makes Brain size and brain cell density intelligent

Answer 20

Evolved brains help to make predictions and plans and develop behaviours to fulfil long-term goals
✓Language
✓Use of tools

Question 21

Interim summary

Answer 21

❖Nervous system evolved during the Cambrian period and exist in 3 main forms
✓Primitive nerve net and nerve ring (Cnidarian –e.g., Hydraand jellyfish)
✓CNS/ganglia with cephalisation (bilaterian clade)
✓CNS/brain + PNS (vertebrates subphylum)

❖Evolution of the nervous system allowed diversification and complexification of behaviours

❖Vertebrates have developed a brain which functions evolved according to ecological niche (e.g., sensorimotor cortical specialisation, prefrontal cortex in humans)

❖The brain of ‘intelligent’ species have an increased brain/body size and brain cell density

Question 22

Evolution of behaviour: basics

Answer 22

✓A behaviour is an internally generated response to an external or internal stimulus

✓It is (in most cases) produced by the nervous system

✓As other phenotypic traits, behaviour can evolve through natural selection because:
➢It can be inherited as (partially) determined by genes
➢It varies across individuals
➢It serves the fitness of individual

Question 23

How to study evolution of behaviour?

Answer 23

Behavioural ecology explores the evolutionary significance of behaviour

1.How does it work?
2.How does it develop?
3.How/why did it evolve?
4.What is its adaptive value

Question 24

The case of bird song(≠ calls)

Answer 24

1.How does it work? Mechanisms?

2.How does it develop? Ontogeny?

3. How did it evolve? Phylogeny?
4. what is its adaptive value? fitness?

Neurons/circuits/genes involved

Early exposure to an adult “tutor” is needed to learn

Advertise their quality to mates & competitors and mark territory(increase fitness)

Song structure changes during evolution

Question 25

Does sleep have an evolutionary significance? How does it work?

Answer 25

✓Produced by the brain
✓Coordinate the response of the organism to a combination of internal and external stimuli:
➢‘Fatigue’ (sleep pressure)
➢Circadian rhythms
➢Light
➢Genetics

Question 26

do all animals sleep?How do we define sleep (behaviour)?

Answer 26

Behavioural description of sleep

1.Sleep is a quiescent behavioural state associated with:
✓reduced sensory responsiveness to weak stimuli (≠ immobility during wake)
✓rapid reversibility in response to strong stimuli (≠ physiological and pathophysiologic quiescent states such as torpor, hibernation, and coma)

2. Preventing sleep leads to more or ‘deeper’ sleep (= sleep homeostasis)

Question 27

Sleep phylogeny

Answer 27

✓Some form a sleep-like state has been described in all animals studied so far (in 6 out of 36 known phyla…)

✓Likely to have appeared early in animal evolution

✓Nerve cells, but not a brain nor CNS, are required for sleep behaviour

Question 28

Adaption of sleep behaviour

Answer 28

Sleep behaviour and duration can vary significantly across species due to factors such as:

➢Environmental factor (e.g.temperature)
➢Dietary requirements
➢Migration periods
➢Mating behaviour

Sleep adapts and will happen no matter what

Question 29

What is sleep’s adaptive value?

Answer 29

“The evolutionary persistence of sleep, in the face of apparent costs of vulnerability to predation and absence of foraging or reproduction, suggests that it has an essential function.”

“If sleep doesn’t serve an absolutely vital function, it is the biggest mistake evolution ever made.”

Sleep serves a fundamental role for metabolic coordination/allocation

Sleep allows “a temporal structure and organizational principle for coping with the energetic and chemical demands of life, given the constraints of time and space.”

Given the prevalence of sleep across animals and the diversity of the animal kingdom and their respective physiological demands, there is a considerable chance that sleep evolved to accumulate several different adaptive functions, which occurrence during sleep is advantageous and provides benefits in an organism-specific manner.

• evolution is the addition of new functions to a core function- resulting in adaptive functions

Question 30

Current views on sleep function(s)

Answer 30

-Restorative function (immune/growth/waste clearance)

-Energy conservation/allocation (metabolic)

-Neuroplasticity (development/memory