Download Signal learning

English Programm 2009/10
Neurobiology of Learning
Bottom-up:
Neuronal mechanisms of learning
Classical Conditioning
Conditioning Typ S
„Signal learning“
Unconditioned Stimulus
UCS
UR
Unconditioned Reaction
Iwan Petrowitsch Pawlow (1849-1936)
Inhibition:
Conditioned Stimulus
Conditioned Stimulus
CS
CS
Conditioned Stimulus
CR
CS
CR
Unconditioned Reaction
Conditioned Reaction
UR
UCS
Unconditioned Reaction
Unconditioned Stimulus
Lack of Reinforcement results in fading of the reaction
Inhibiton is an active process
Reaction
CS
CR
Trial
Spontaneous Recovery
Axiety can be seen as a
conditioned emotion and
strategies of Pawlow´s theory
can be applied:
Behavior Therapy
John B. Watson (1878-1950)
Bliss & Lomo (1973): LTP
First observation of facilitation of
synaptic transmission after
high frequency stimulation of the
presynaptic neuron.
Long-term potentiation LTP remains
stable for many weeks
Hebb postulate for learning (1949):
Facilitation of synaptic transmission
is the neuronal basis of learning
NMDA receptor responds maximally if:
NMDA receptor
[N-methyl-D-aspartate receptor]
Glutamat binds to it
Neuron is depolarized
Maximal influx of Na + and Ca+ + ions
triggering enzymes [protein kinases]
Evidence that LTP
is involved in learning:
The critical factor is the co-occurence of
firing in presynaptic and postsynaptic cells
Reconfirmed for NMDA by Bi & Poo 2001
LTP triggers structural changes:
• Increased number of synapses
LTP occurs at synapses participating in learning
• Increased size of synapses
Conditioning produces LTP-like changes
• Increased number of NMDA receptors
Mutant mice with little LTP have learning difficulties
E. R. Kandel Nobelpreis 2000
The molecular biology of memory storage:
A dialogue between gens and synapses.
[Science 2001]
Their functions are well known
Aplysia has 20 000 neurons only
Sea-slug Aplysia
Kandels modell for learning was the
withdrawl reflex of the gill of Aplysia
The motoneuron L7 controls
quick withldraw of the gill
Nucleus
Sensory
neuron
Serotonin
Receptor
Motor
neuron
Sipho-System: 24 sensory neurons
connected with 6 motoneurons
controlling the withdrawl of the gill
New connections are seen after
application of Serotonin only
Reinforcement by
increased release
of glutamat
Basis of short term memory is an
increased release of neurotransmitter.
Tissue cultures for simple learning networks
New synaptic junctions
Information from DNA
Anatomical changes
Long term memory is based
on new synaptic junctions
Why growth takes place in activated synapses
only was studed on branched axons
Serotonin
cAMP
Proteinkinases A
activates protein CREB 1
inducing gene expression
Serotonin
cAMP
MAF-Kinases
deactivates protein CREB 2
gen-expression
Gen-expression results in production of
(silent) mRNA
The prionlike protein CPEB [cytoplasmatic
polyadenylation element-binding Protein]
converts recessive into dominant mRNA.
Only application of serotonin
effected synaptic modifications
Proteins reach all synapses. Only in
serotonin-stimulated regions mRNA
is activated and growth takes place.
Somatosensory
representation in
the Owl Monkey
Neuronal Plasticity:
Structual changes can even alter
the size of cortical projection areas
[M. M. Merzenich 1990]
Sensibility training
for several weeks
Somatosensory
areas before (l)
and after (r)
training
Formation of new nerve cells takes
place also postnatal. First discovered
by Nottebohm in the brain of birds.
Fernando Nottebohm: New nerve cells follow certain glial fibres
Instrumental Conditioning
Similar effects were recently
observed also in the human brain
Edward L. Thorndike (1874-1949)
Burrhus F. Skinner (1904-1990)
Positive Reinforcement
Conditionierung Typ R
„Reaction-Learning“
Spontaneous Behavior
Increase of Probability
Spontaneous Behavior
Learning by Reinforcement
Negative Reinforcement
Fading in
Fading out
Olds & Milner
Self-Stimulation
Positive
Negative
Reward Centers
Decrease of Probability
Top-down:
Psychology of cognitive learning
The mesotelencephalic dopamine system:
Nigrostriatal pathway (green) and
mesocorticolimbic pathway (red)
Hermann Ebbinghaus
Material
Curve of forgetting
“Overlearning“ does not
increase long term memory
Time
Material
Material
5
10
20 . . .
Memory interference
Time
Time
Control
Hubert Rohracher:
Retroactive Inhibition
Consolidation
“The brain learns longer
than consciousness”
Proactive inhibition
Postmental excitations
Papez Circle – Limbic System
Hippocampus
Amygdala
Fornix
Gyrus cinguli
Corpus mamillare