Why Study Neuroscience?Neuroscience: study of the nervous system

physical structure and physical processes

1. Scientific interest – how to get a complete picture Thoughts algorithms neurons molceules

2. Test psychology/linguistics theories Example: visual buffer idea, test what is active in brain Example: test for existence of language module

3. Find out something about cognitive architecture Capabilities of a proposed architecture depend on physical structure Knowing structure/processes should give an idea of architecture

4. Important to understand relationship:physical structure information processing capabilities

Improve treatments for damage (accident or disease) Know human limits

Better learning methods Better computer systems to support humans (compensate for weakness)

Study at Different Scales

1m – CNS

10cm – systems (vision system)

1cm – maps (don’t know much about this)

1mm – networks (don’t know much about this)

100m – synapses (know a bit about this)

1Å – molecules (neurotransmitters)

Central Nervous System

Cerebrum

Cerebellum

Brain stem

Compare Brains of Other Animals Human similar to rat or monkey Early research tried to find special neural cells which

were unique to humans Didn’t find any

…But human brain bigger Seems not special cells,

but more of them and more connections

Animal Encephalization quotient

Man 7.4–7.8

Bottlenose dolphin 5.3

Chimpanzee 2.2–2.5

Whales 1.8

Gorilla 1.5–1.8

Fox 1.6

African elephant 1.3

Dog 1.2

Squirrel 1.1

Cat 1.0

Horse 0.9

Sheep 0.8

Mouse 0.5

Rabbit 0.4

Brain Development Macaque monkeys born with 60% of brain size Chimpanzee – 46% Human – 25%...

Brain growth rate of foetus same… but… Human brain continues growth at rapid fetal rate for 2 yrs

Child has higher density of connections Gradually eliminated Reach adult values by about 10yrs

Windows for development 8 months can distinguish two foreign language sounds 12 months cannot Strabismus can be corrected in early years Infants born without callosum compensate (other pathways?)

Brain Development Plasticity of brain in children

Language impairment produced by brain injurycan recover if before age 5

Infants who had left half brain removedmany linguistic functions normal

Synapses

Repeated stimulation can increase synaptic strengths For days or even weeks Learning?

Release neurotransmitter chemicals Excitatory Inhibitory

Neurochemical Systems At least 40 different substances Serve a multitude of different functions 2 types

Neurotransmitter act in synapse

Neuromodulator Act more globally … but extremely specific functions Nanogram of angiotensin II : intense and prolonged drinking Acts as trigger

Neurochemical Systems Psychoactive drugs

Mimic/enhance/disrupt effects of body’s neurochemicals

Molecular structures may resemble neurotransmitters LSD similar to seratonin Mescaline similar to dopamine Cocaine blocks reuptake of neurotransmitter

More neurotransmitter remains in synapse to stimulate further

Fascinating Brain Facts… 100,000,000,000 = 1011 neurons

100 000 are irretrievably lost each day

Number of Synapses about 1014 – or a bit more Each neuron connects to 10,000 -150,000 others Every person on planet make 200 000 phone calls

same number of connections as in a single human brain in a day

Grey part folded to fit - would cover surface of office desk The gray cells occupy only 5% of our brains

95% is taken up by the communication network between them

About 2x105km of wiring Pulses travel at more than 400 km/h (250 mph) 2% of body weight… but consumes 20% of oxygen All the time! Even when sleeping Any loss of oxygen… cells die in minutes…

Damage permanent in adults

Mapping Functions to Brain Areas See what disabilities result from specific physical

damage In humans wait for accident In animals do damage deliberately

To see where axons terminate Inject dye, transported along axon Slice up brain and examine under microscope

Insert microelectrodes Into a single neuron Monitor changes in electrical potential

Brain imaging While patient is doing a particular task

Imaging Positron Emission Tomography (PET)

Inject radioactive glucose Gets absorbed by active regions Get the subject to do a task for about two minutes Record image

Functional magnetic resonance imaging (fMRI) Hemoglobin: metalloprotein red blood cells Carries oxygen Hemoglobin diamagnetic when oxygenated

paramagnetic when deoxygenated

More Brain Facts…In right-handed individuals (91% of people)Right side of the brain controls:

musical talent, fantasy, imagination, dreams, drawing and painting.

Left side of the brain controls: mathematical ability, ability to solve logic problems, language skills, remembers names, dates, and facts

Maps change with experience Microelectrodes to map monkey’s hand and fingers area Trained monkey rotating disk for food reward After 20 weeks… Brain area for hand had expanded markedly

Mapping Functions to Brain Areas

Innate or Learned? Nature or Nurture? Major neural pathways very similar in all mammals

Suggests genetic hardwiring

Study of eye in water flea Made cloned insects (genetically identical) Studied neurons Same number of sensory neurons,

and connect to same number of cells Different number of synapses,

and shape of axons

Similar results for pigeons Final system could be quite different in cloned animals

Neuropsychology Tries to discover relationships between

Neuroscience and Psychology …or between : Cognitive models of information processing And structures and processes in the brain

Examples: Study functions of people who have suffered brain damage Build an artificial neural network to solve some problem

(In a biologically plausible way) Then damage the network Study the results and compare with real patients

Imaging techniques (as discussed before)

Neuropsychology studying Alexia Alexia: damage to brain causes loss of ability to read

Ability to read and write can be affected, while speech is normal

Theoretical model of reading: dual route(parallel processing) Lexical route – retrieve words from a lexicon Phonological route – sound out words

Neuropsychology studying Alexia Phonological route

Group word into syllables (by vowels/consonants) Convert syllables to proper phonemes Evident in children sounding words Some patients have difficulty pronouncing unfamiliar words Example: non-words like “troat” Otherwise no problem reading “Phonological deficit hypothesis”

Lexical route Identify base root: antiabortion anti-abort-ion Access Lexical memory to recall proper pronunciation of parts Some patients have difficulty accessing lexicon Must pronounce out word Difficulty with exceptions: yacht, come, have “Dyseidetic” or “visual dyslexia”

Neuropsychology is Difficult Usually have a dodgy cognitive model of a process Must find a match between this and multiple possible brain

implementations Evidence from patients who have suffered damage difficult…

Damage can affect many areas Patients often on medication with not entirely clear effects Patients “grouped” together with “same” damage often different Example: Trauma and tumour quite different Imaging Scans have limited accuracy Patient’s age very relevant

One solution: case study with individuals

Relationship With Artificial Neural Networks ANN typically leave out many aspects of real networks

Real neurons generate sequences of action potentials Frequency and phase significant (ANN has a simple number output) Real networks have multiple neurotransmitters Many distinct types of neurons with different shapes (ANN has one type) Real networks have microcircuits Compute complex nonlinear functions (ANN usually a sum) Maybe synapse should be unit rather than neuron

Some success: trained a network to recognise object position relative to eye direction Used hidden layer in ANN Resulting values closely resembled measurements from macaque

monkey neurons