PSY260 L2 Learning and Plasticity

core nervous system functions

collect sensory information

process information

generate behaviour from given input (motor output)

parts of the nervous system

central nervous system

peripheral nervous system

enteric nervous system

central nervous system

brain and spinal cord

peripheral nervous system

somatic: controls voluntary motor movement and relays sensory information

autonomic: sympathetic (fight or flight) and parasympathetic (rest and digest)

enteric nervous system

“second brain", controls the gastrointestinal system

information processing in the cortex: posterior vs anterior

sensory information processing starts from posterior

• basic details, sensory information

information becomes more abstract as it passes to more anterior areas

• what do I know about these details? what opinions do i have about this object? how do i relate to this object?

information processing in the cortex: medial vs lateral

processing in medial tends to be internally-focused or self-referential

• “me in the centre”

lateral areas tend to be externally-focused or related to external stimuli, task-oriented processing

• “what is around me”

• what do i sense

• what tasks must i accomplish

what lobes are shown here?

counter clockwise from the upper left:

frontal

primary motor cortex (the fold between frontal and parietal)

parietal

occipital

cerebellum

brainstem

temporal lobe

frontal lobe

executive functions, controlling complex actions

decision making, problem solving, planning

more rostral: planning, more caudal: doing (as we move toward the primary motor cortex)

parietal lobe

touch, feeling, sense of space

occipital lobe

vision

temporal lobe

hearing and memory

near a lot of memory-related structures which communicate with each other

what is shown in this picture?

clockwise from rostral:

basal ganglia

thalamus

amygdala

hippocampus

basal ganglia

subcortical structure

reward-based learning, modulating movement

includes caudate nucleus (striatum), putamen, nucleus accumbens, etc

thalamus

subcortical structure

transmits sensory info to sensory cortices

ALL SENSORY INFO GOES HERE FIRST

amygdala

subcortical structure

emotion

important for fear-based learning

hippocampus

subcortical structure

memory consolidation (memory moves from short-term → long term storage)

reflexes

innate responses not done consciously

the simplest expression of the 3 nervous system functions:

• stimulus → little processing → response

hardwired, innate, involuntary

processing of reflexes

often handled solely in the spinal cord

interneurons allow for rapid responses that can bypass the brain

immediately activates motor neuron as opposed to first brain processing

common sensory pathway

sensory organ → thalamus → primary sensory cortex

primary sensory cortex function

specialized for initial processing, then relays to other cortical areas

• frequency, tone, basic details

• understanding/conceptualizing

label this image

clockwise from rostral:

• primary motor cortex

• primary somatosensory cortex

• primary visual cortex

• primary auditory cortex

voluntary motor output pathway

primary motor cortex (M1) in frontal lobe → down spine

inputs to M1 to form behavioural plans can include:

• frontal lobes — planning and logical thinking

• cerebellum, basal ganglia — refinements of motor program

comparative neuroanatomy

comparing brains across species gives insight into brain function

bigger isn’t necessarily better — relative proportions and size reflect different specialization for each niche

• birds have a disproportionally large cerebellum compared to humans — flying requires motor refinement and balance

• humans have a disproportionally large cerebral cortex — higher order thinking, processing

we look at bird and rodent brains in addition to focus of human brain

neocortex: outside lobes recently evolutionarily developed for higher order thinking

lesion analysis approach

very rarely do we intentionally lesion human brain tissue unless there is a medical reason (epilepsy, hippocampus to stop seizures)

• compare functions before and after surgery within a single subject

we recruit patients with lesions in similar areas and study what shared symptoms they have

we recruit patients with similar symptoms and study what shared areas of damage they have

• no two lesions are the exact same

• both methods infer the responsible area

lesion analysis results

data can be messy — no two lesions are exactly the same, no two brains respond the same way to damage

• non-human controlled lesions can be done instead to ensure consistency

magnetic resonance imaging (MRI) approach

strong magnetic field aligns subset of atoms in tissue

computer measures signals emitted by different tissues and create photographs

magnetic resonance imaging (MRI) results

extremely detailed structural 3d model of the living brain

safe (no radiation)

has revolutionized medical, scientific research into the brain

good spatial resolution, no temporal (just a photo)

functional magnetic resonance imaging (MRI) approach

detect changes in blood flow to different parts of the brain Blood Oxygen Level Dependent response

indirect measure of neural activity (relying on the assumption that more blood flow = more activity),

• estimates timeline on a broad scale — takes time for O2 to replenish

functional magnetic resonance imaging (MRI) results

allows for functional 3d modelling of the brain over time during tasks or at rest

has revolutionized medical and scientific research into the brain

good spatial, less good temporal

electroencephalogram (EEG) approach

electrodes on the scalp with gel conductor detects electrical charges from neural activity

electroencephalogram (EEG) results

relatively portable, inexpensive, easy to use

good temporal (better than MRI), low spatial

• measures from the surface — unknown how deep signals come from

• scalp can distort

magnetoencephalogram (MEG) approach

electrodes on the scalp record magnetic field produced by electrical currents in the brain

smaller than MRI but still needs dedicated space

magnetoencephalogram (MEG) results

expensive, difficult to use, not portable

better spatial resolution than EEG (magnetic fields don’t get as distorted by the scalp)

more accurate measures closer to the scalp

good temporal resolution

excitatory neurons neurotransmitter

glutamate

makes it more likely for cells around to fire

inhibitory neurons neurotransmitter

gamma-aminobutyric acid (GABA)

makes it less likely for cells around to fire

glial cells

provide support to nerve cells

• structurally, functionally

form myelin sheath

label this image

label this image

axon conducts action potentials away from the cell body

myelin sheath cover the axon and help signal travel faster

nodes of ranvier allow signal to jump across rapidly

action potential

resting potential is negative

if stimulus threshold is reached, sodium channels open, and Na+ ions enter the cell

at around 40 mV, K+ ions exit the cell

neuron becomes hyperpolarized (refractory period)

• very unlikely to meet stimulus threshold during this phase

back propagation

echo of electricity rippling out to dendrites — telling dendrites it has fired

EPSPs

excitatory post-synaptic potential caused by neurotransmitters

a temporary depolarization of the postsynaptic membrane caused by inflow of ions

makes the neuron more likely to fire an action potential

neural communication: chemical

NTs are contained in synaptic vesicles in the terminal of the presynaptic neuron

action potential causes them to fuse with the cell membrane and release NTs into the synaptic cleft

NTs bind to receptors on the post-synaptic neuron

examples of neurotransmitters

modulatory (controlling other NTs)

• acetylcholine

• dopamine

• norepinephrine

GABA (inhibitory)

glutamate (excitatory)

hebbian plasticity

Hebb’s theory on how neurons change over time

proposed that synaptic connections are determined competitively like natural selection

• cells that fire together wire together

• cells out of sync lose their link

suggests an experience-based “natural selection” for the most useful synaptic connections — the most useful synaptic connections survive

repeated experience with a stimulus may help neurons tuned to that stimulus “win” and expand their synaptic connections

• tuned especially (not exclusively) to particular stimuli

cells that fire together…

“wire together”

two neurons that fire at the same time are more likely to connect and trigger each other

cells out of sync

“lose their link”

neurons not firing are more likely to die

long-term potentiation

when a neuron connection is used repeatedly, synapses between them get stronger

sprouting of new synaptic contacts between co-activated neurons

• new synaptic bulbs can be formed

more vesicles formed, more AMDA receptors, more glutamate emitted and received, more F-actin to provide more structure to cell (BIGGER)

long-term depression

when a neuron connection is used very little, or they fire at different times, synapses between them get weaker

to limit unnecessary connections, retracting/dismantling of synaptic contacts between non-cooperating neurons

fewer vesicles formed, less AMDA receptors, less glutamate emitted/received, less F-actin (SMALLER)

pruning unnecessary associations

examples of unnecessary associations

phobias

unneeded memories, emotions

examples of neural plasticity in effect

make more/less transmitter

have more/fewer receptors

make synapses bigger/smaller

eliminate synapses/make new synapses