Building the brain

Question 1

How many neurones are in the brain?
How many inputs does a neuron contain?
How much neurostransmitter information is transmitted by 1 input in 3-5 milliseconds?
How many connections are in the brain?
How long can a neuron be?

Answer 1

Scale factors of the brain:
> 100 billion neurons = 10% of brain cells
> 1 neuron = 30,000 inputs
> 1 input can transmit 5,000 quanta neurotransmitter (information) in 3-5 milliseconds
> 1,000 connections
> 1 neutron can be 1-3m long

<=> if you (neuron) are in a stadium, you can touch 30,000 people at the same time

Question 2

What composes the forebrain (telencephalon)?

Answer 2

Diencephalon

• Thalamus: motivational drive, libido
• Hypothalamus: eat, drink, sleep
• very important, basic, critical functions
• needs input from the brain stem (tronc cérébral)

Cerebrum (cortical lobes)

• Occipital lobe: visual cortex (receiving and intepretation)
• Temporal lobe: auditory cortex (speech) ; memory (episodic ‘autobiographical’ ; semantic)
• Parietal lobe: primary sensory cortex (integration of sensory info ; problems in this area -> agnosia, apraxia)
• Frontal lobe: prefrontal cortex (PFC) ; primary motor cortex

Question 3

What is the prefrontal cortex (PFC)?

Answer 3

> All of the frontal lobe apart from primary motor cortex

> Higher functions that make us human:

• personality/expression
• social awareness
• goal-setting
• attentive and task-switching
• executive functioning

Question 4

What is the evolution of the nervous system?

Answer 4

Each time a new part evolved, it built on top of earlier parts
-> deep parts (under the surface of the cortex) are more ancient

1. Spinal cord and brain stem
   - sophisticated reflexes
   - autonomous organ control
2. Hypothalamus
   - basic functions (eat, drink, reproduce)
   - primal behaviours
3. Limbic and hippocampal system
   - emotional processing and memory
4. Cortical growth
   - higher cognitive processing
   - “makes us human”

Question 5

What does the hypothalamus regulate?
What are its inputs and functions?
How its critical neurotransmitter inputs?

Answer 5

> Size of an almond
Regulates a large number of primal/basic behaviours (appetite, motivation, reproduction)

Inputs:

• Sensory: taste, smell, genitals
• Eyes: light input as ‘zeitgeber’ (tells its day or night, hunt or hide) -> circadian pattern
• Hippocampal memory input
• Amygdala emotional (aversive memory) input
• Neurotransmitters: serotonin, noradrenaline -> key for appetite and motivation ; critical for the appropriate functioning of the hypothalamus

Functions:

• Sexual behaviour (core function): Hypothalamic Pituitary Axis (HPA = menstruation, spermatogenesis) ; male mounting, female hip elevation ; interpretation of pheromones
• Motivational behaviour: basic/primal (food, water, reproduction) = appetitive / consummatory motivation

Critical neurotransmitters:
- without serotonin and noradrenaline - biological side effects (found in depression)

Question 6

What is the role of the prefrontal cortex (PFC) in regards to the hypothalamus?

Answer 6

The ancient parts of our brain (hypothalamus) are very strong drivers of human behaviour
BUT our prefrontal cortex (PFC) can control and nuance them

Question 7

What are the limbic and hippocampal systems?

What do they regulate?

Answer 7

> Phylogenetically ancient systems

• with us for 100+ million years
• > sits in the ‘deep’ subcortical part of the brain

Limbic system
- ‘pure emotions’ (anger, fear, happiness)
= primal drivers

Hippocampal system
- controls function of memory
- Hippocampi (plural of hippocampus): memory formation; 3 neuronal layer of cells (usually 6) -> ancient part of brain ; connects with various regions
- Amygdalae: aversive (fearful) memory -> assists survival
(unwanted thoughts keep occurring ; thought is linked to stimulus)
(in PTSD: pathological dysfunction of the amygdala-hippocampi pathway)

Question 8

Why was the hypothalamus developed before the limbic and hippocampal systems?

Answer 8

At first, it was more important to develop a survival system for seeking food, water, and reproducing -> hypothalamus
Then, we developed an emotional system -> limbic and hippocampal systems (on top of the hypothalamus)

Question 9

What is the ‘Circuit of Papez’?

Answer 9

In the hippocampi

• long-term potentiation (LTP)
• which is necessary for the encoding, storage, and retrieval of memory

Question 10

What are Hominin and Hominids?

Answer 10

Hominin + Hominids = Humans

> Hominin: any species that came before us
Hominids: great apes

Question 11

What is sexual dimorphism?

How does it relate to the famous 4-million year old picture of anthropology saw in the lecture?

Answer 11

Sexual dimorphism:
- distinct difference in size or appearance between the sexes of an animal

Famous picture: 2 close sets of footprints

• female and male
• female’s footprints are deeper
• > hypothesis: she was carrying a child
• they were Australopithecus

Question 12

What is Australopithecus?
What was it’s lifespan, cranial capacity?
What is their evolution significance?
What are the evolutionary bipedalism advantages and disadvantages?

Answer 12

> “southern stone man”
Grandfather of Homo Sapiens
Lifespan: 4.2 - 1.2 million years ago
Cranial capacity: 3-600 cm3 (= chimpanzee)

> Evolution significance:
- they show we walked before we got smarter

> Evolutionary (bipedalism) advantages:

• walked longer distances
• moved from trees to plains
• new posture -> cooler -> more hours active
• hands free to make and carry tools, master fire
• able to get more food (than needed to survive)
• > enough energy available for brain growth and development

> Evolutionary (bipedalism) disadvantages:
- locked hips -> difficult childbirth

Question 13

What is the evolution of the genus Homo, from Australopithecus to Sapiens?

Answer 13

Australopithecus (4.2-1.2 mya)

• > Homo habilis (2.2-1.4 mya)
• > Homo erectus (1.8-1.3 mya)
• > Homo heidelbergensis (600,000-200,000 years ago)
• > Homo sapiens, neanderthal, denisova

Question 14

What are the 3 species derived from the same ancestor that were living side by side, 200,000 years ago?
What is that common ancestor?

Answer 14

Homo heidelbergensis (common ancestor)

• > 3 species:
• Neanderthal range (Europe)
• Denisova hominin (Asia)
• Homo sapiens (Africa): “wise”/”knowing” man

Question 15

What are the differences between Homo neanderthalensis and Homo sapiens?

Answer 15

Homo neanderthalensis

• complex culture
• tool making
• language
• Physical attributes: stocky (stronger than sapiens), large cranial volume (larger than sapiens)
• Hunting style: ambush larger prey
• Cognitive makeup: large occipital cortex (very good vision, including at night)

Homo sapiens

• Physical attributes: nuchal ligament (connects skull to spine), strong Achilles tendon
• > run over longer distances than neanderthal
• Hunting style: persistence hunters (chase down/follow prey over long distances)
• Cognitive makeup: smaller occipital cortex ; larger orbital frontal cortex (key to social behaviour and mentalisation) = ultimate difference

=> Sapiens: our physical attributes made us better hunters - outcompete neanderthal

Question 16

What is the genetic history from 200,000 years ago to modern day?

Answer 16

200,000 - 70,000 years ago
> 7bn people on the planet, all incredibly connected
> Event: Supervolcano (approx. 70,000 years ago)
- largest known explosion on Earth for the past 25 million years
- Lake Toba (current Indonesia)
- Mitochondrial DNA (mDNA) findings
-> population dropped to: population of 10,000 or less remained
-> all humans follow this lineage

50,000 - 12,000 years ago
> Behavioural explosion
- buried our dead
- huge increase in artwork and jewellery
> We spread from Africa, through the Levant, across the world
> Wiped out Neanderthalensis

12,000 years ago - modern day
> Neolithic revolution
- animal domestication and farming
- rise of great cities: Ur, Babylon, Jericho
- first empires: Persian, Assyrian, Egyptian
> Bronze Age
> Iron Age
> Industrial Revolution
> Scientific Revolution
> Computer and information Revolution