PSYC1020 Lecture Notes - Lecture 8: Neuron Doctrine, Subventricular Zone, Donald O. Hebb
Ramón y Cajal
Studied growth of neurons and axons during brain development
•
Foundation of 'neuron theory'
The brain is made up of cells (neurons) and nerves are cell axons
○
Ridiculed for neuron theory but later awarded Nobel prize
○
•
Neurons do not regenerate
“In the adult centers the nerve paths are something fixed, ended and
immutable. Everything must die, nothing may be regenerated. It is for
the science of the future to change, if possible, this harsh decree.”
○
Cajal was mostly right, but not entirely
○
•
Neurogenesis - growing new brain cells
Neurons never regenerate or repair: damaged brain areas never 'regrow'
•
BUT
New neurons are constantly 'born' throughout life from neural stem
cells
○
Only two areas in adult brain
Hippocampus (learning and memory)
§
Subventricular zone for olfactory bulb
§
○
•
Synapses - forming and strengthening connections
Synaptogenesis - generation of new synapses (brain connections)
•
New synapses are constantly formed and strengthened with experience and
learning
•
Environmental enrichment - 'enriched' conditions lead to growth of
dendrites and more extensive synaptic connections
Neuroscience evidence: relates more to impoverishment than
enrichment
'super' enrichment environments are not necessarily better
§
Impoverished environments are detrimental to brain
development
§
○
•
Donald Hebb - pet rats are smarter than lab rats
Neuroplasticity: brain reorganisation with experience
Studied sensory cortex in musicians who played stringed instruments
Measured activity for index and little finger sensation for left and right
hand
○
String players had larger area on primary sensory cortex for left hand
fingers than non string players
○
Sensory cortex finger areas expand with use and experience -
homunculus
○
•
Lesioned motor cortex in monkeys and used electrical stimulation to map
hand area
With no rehabilitation: (no movement) motor cortex area for hand got
smaller - maladaptive plasticity
○
With rehabilitation: (movement training) motor cortex area for hand
expanded and movement improved
○
After damage, motor cortex can reorganise with use to recover
function -homunculus
○
•
Limbic system
Amygdala
Medial temporal lobe
○
Fear and arousal
Responds to threat/danger
§
Fear conditioning/learning phobias
§
○
•
Hippocampus
Medial temporal lobe
○
Memory
Forming new episodic memories
§
Damage causes memory loss (can't form new memories)
§
○
Spatial navigation
Mental map of familiar environment
§
○
•
Memory - patient H.M.
HM had his hippocampus removed to treat epilepsy•
Cured epilepsy but caused severe memory loss•
Led to new understanding of memory: memory is not one thing, but
different components mediated by different parts of the brain
•
Short-term memory
Lasts several seconds eg. remembering phone number long enough to
type into phone
○
(HM could 'mentally rehearse' to remember things for a few seconds)
○
•
Long-term memory•
Declarative - conscious recollection (hippocampus)
Episodic - memory of past events or 'episodes', things you've
seen and done eg. what you had for lunch yesterday, what you
did on your birthday last year
§
Semantic - facts and basic knowledge you can recall and declare
eg. paris is the capital city of france
§
○
Procedural - not for conscious recall
Skills you have learnt eg. how to ride a bike, how to sign your
name
§
(HM could learn new skills but not remember having learnt
them)
§
○
Encoding (hippocampus)
Laying down new memories for long-term storage
§
(HM could not form new memories and would immediately
'forget' everything that just happened)
§
○
Retrieval
Retrieving memories for conscious recall
§
(HM could recall memories from before surgery)
§
○
Learning and memory - strengthening synapse
connections
Long-term potentiation (LTP)
Change in the structure of synapses to give stronger signal from pre-
synaptic to post-synaptic neuron
○
Many mechanisms eg. more post-synaptic receptors
○
Focus of cellular/molecular neuroscience research on memory and
learning
○
•
Amygdala - fear learning
Classical conditioning
Eg. 1: Little Albert - conditioned to fear cute fluffy animals
Loud sound when a fluffy animal was put in front of him (hitting
a metal bar with a hammer behind his back)
§
After just a few 'pairings', started to show distress and fear as
soon as an animal was put in front of him
§
○
•
Eg. 2: rat conditioned to fear a tone
CS - tone
§
US - electric shock
§
After pairing, rat shows fear response to tone (CS) alone
§
○
Why?•
Hebb's law - 'Hebbian learning'
'Neurons that fire together wire together'
“When an axon of cell A is near enough to excite cell B and repeatedly
or persistently takes part in firing it, some growth process or metabolic
change takes place in one or both cells such that A's efficiency, as one
of the cells firing B, is increased.”
○
•
Repeated firing of pre-synaptic and post-synaptic neuron 'firing together'
strengthens synaptic connection
•
Brain 'learns' associations through repeated pairings•
Strengthens connections between paired stimuli or events•
Basis of neuroplasticity learning - brain pathways (connections) that are
used often are strengthened
•
'Grandmother cells' - all theoretical
Neurons could 'represent' a specific concept such as your grandmother•
Billions of neurons can encode billions of concepts•
Memory may be represented by groups of neurons each encoding specific
concepts or objects
•
'Jennifer Aniston' cells found in hippocampus
Recording from neurons found in epilepsy patients
○
Fire specifically to pictures of Jennifer Aniston
○
•
Spreading activation model - theory
Neurons represent a specific concept eg. grandmother cells
○
Share connections with neurons that represent related concepts
○
Activation (firing) of one neuron leads to spreading activation to
related or connected neurons
○
•
Learning and memory
Making and strengthening connections between neurons that
represent associated concepts
○
•
8A: Learning and memory: hippocampus and
amygdala
Sunday, 3 June 2018
9:42 pm
Ramón y Cajal
Studied growth of neurons and axons during brain development•
Foundation of 'neuron theory'
The brain is made up of cells (neurons) and nerves are cell axons
○
Ridiculed for neuron theory but later awarded Nobel prize
○
•
Neurons do not regenerate
“In the adult centers the nerve paths are something fixed, ended and
immutable. Everything must die, nothing may be regenerated. It is for
the science of the future to change, if possible, this harsh decree.”
○
Cajal was mostly right, but not entirely
○
•
Neurogenesis - growing new brain cells
Neurons never regenerate or repair: damaged brain areas never 'regrow'•
BUT
New neurons are constantly 'born' throughout life from neural stem
cells
○
Only two areas in adult brain
Hippocampus (learning and memory)
§
Subventricular zone for olfactory bulb
§
○
•
Synapses - forming and strengthening connections
Synaptogenesis - generation of new synapses (brain connections)•
New synapses are constantly formed and strengthened with experience and
learning
•
Environmental enrichment - 'enriched' conditions lead to growth of
dendrites and more extensive synaptic connections
Neuroscience evidence: relates more to impoverishment than
enrichment
'super' enrichment environments are not necessarily better
§
Impoverished environments are detrimental to brain
development
§
○
•
Donald Hebb - pet rats are smarter than lab rats
Neuroplasticity: brain reorganisation with experience
Studied sensory cortex in musicians who played stringed instruments
Measured activity for index and little finger sensation for left and right
hand
○
String players had larger area on primary sensory cortex for left hand
fingers than non string players
○
Sensory cortex finger areas expand with use and experience -
homunculus
○
•
Lesioned motor cortex in monkeys and used electrical stimulation to map
hand area
With no rehabilitation: (no movement) motor cortex area for hand got
smaller - maladaptive plasticity
○
With rehabilitation: (movement training) motor cortex area for hand
expanded and movement improved
○
After damage, motor cortex can reorganise with use to recover
function -homunculus
○
•
Limbic system
Amygdala
Medial temporal lobe
○
Fear and arousal
Responds to threat/danger
§
Fear conditioning/learning phobias
§
○
•
Hippocampus
Medial temporal lobe
○
Memory
Forming new episodic memories
§
Damage causes memory loss (can't form new memories)
§
○
Spatial navigation
Mental map of familiar environment
§
○
•
Memory - patient H.M.
HM had his hippocampus removed to treat epilepsy•
Cured epilepsy but caused severe memory loss•
Led to new understanding of memory: memory is not one thing, but
different components mediated by different parts of the brain
•
Short-term memory
Lasts several seconds eg. remembering phone number long enough to
type into phone
○
(HM could 'mentally rehearse' to remember things for a few seconds)
○
•
Long-term memory•
Declarative - conscious recollection (hippocampus)
Episodic - memory of past events or 'episodes', things you've
seen and done eg. what you had for lunch yesterday, what you
did on your birthday last year
§
Semantic - facts and basic knowledge you can recall and declare
eg. paris is the capital city of france
§
○
Procedural - not for conscious recall
Skills you have learnt eg. how to ride a bike, how to sign your
name
§
(HM could learn new skills but not remember having learnt
them)
§
○
Encoding (hippocampus)
Laying down new memories for long-term storage
§
(HM could not form new memories and would immediately
'forget' everything that just happened)
§
○
Retrieval
Retrieving memories for conscious recall
§
(HM could recall memories from before surgery)
§
○
Learning and memory - strengthening synapse
connections
Long-term potentiation (LTP)
Change in the structure of synapses to give stronger signal from pre-
synaptic to post-synaptic neuron
○
Many mechanisms eg. more post-synaptic receptors
○
Focus of cellular/molecular neuroscience research on memory and
learning
○
•
Amygdala - fear learning
Classical conditioning
Eg. 1: Little Albert - conditioned to fear cute fluffy animals
Loud sound when a fluffy animal was put in front of him (hitting
a metal bar with a hammer behind his back)
§
After just a few 'pairings', started to show distress and fear as
soon as an animal was put in front of him
§
○
•
Eg. 2: rat conditioned to fear a tone
CS - tone
§
US - electric shock
§
After pairing, rat shows fear response to tone (CS) alone
§
○
Why?•
Hebb's law - 'Hebbian learning'
'Neurons that fire together wire together'
“When an axon of cell A is near enough to excite cell B and repeatedly
or persistently takes part in firing it, some growth process or metabolic
change takes place in one or both cells such that A's efficiency, as one
of the cells firing B, is increased.”
○
•
Repeated firing of pre-synaptic and post-synaptic neuron 'firing together'
strengthens synaptic connection
•
Brain 'learns' associations through repeated pairings•
Strengthens connections between paired stimuli or events•
Basis of neuroplasticity learning - brain pathways (connections) that are
used often are strengthened
•
'Grandmother cells' - all theoretical
Neurons could 'represent' a specific concept such as your grandmother•
Billions of neurons can encode billions of concepts•
Memory may be represented by groups of neurons each encoding specific
concepts or objects
•
'Jennifer Aniston' cells found in hippocampus
Recording from neurons found in epilepsy patients
○
Fire specifically to pictures of Jennifer Aniston
○
•
Spreading activation model - theory
Neurons represent a specific concept eg. grandmother cells
○
Share connections with neurons that represent related concepts
○
Activation (firing) of one neuron leads to spreading activation to
related or connected neurons
○
•
Learning and memory
Making and strengthening connections between neurons that
represent associated concepts
○
•
8A: Learning and memory: hippocampus and
amygdala
Sunday, 3 June 2018
9:42 pm
Document Summary
Studied growth of neurons and axons during brain development. The brain is made up of cells (neurons) and nerves are cell axons. Ridiculed for neuron theory but later awarded nobel prize. In the adult centers the nerve paths are something fixed, ended and immutable. It is for the science of the future to change, if possible, this harsh decree. Neurons never regenerate or repair: damaged brain areas never "regrow" New neurons are constantly "born" throughout life from neural stem cells. Synaptogenesis - generation of new synapses (brain connections) New synapses are constantly formed and strengthened with experience and learning. Environmental enrichment - "enriched" conditions lead to growth of dendrites and more extensive synaptic connections. Neuroscience evidence: relates more to impoverishment than enrichment. Donald hebb - pet rats are smarter than lab rats. Studied sensory cortex in musicians who played stringed instruments. Measured activity for index and little finger sensation for left and right hand.
