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Plasticity in the nervous system
Edward Mann
17th Jan 2014
Lecture Plan
• How interactions with the environment change the brain
• Activity-dependent synaptic plasticity in the hippocampus
• Mechanisms of hippocampal synaptic plasticity
• Cellular learning rules – spike rate or spike timing?
Plasticity in neural circuits
Ocular dominance columns
Radioactive tracing
of OD
Plasticity in neural circuits
Activity-dependent rewiring
cortex during
Effectinofvisual
monocular
development
deprivation
Normal
inject non-deprived inject deprived eye
eye
Plasticity in neural circuits
Environmental enrichment & spine density
Plasticity in neural circuits
Associative learning through changes in synaptic weights
Lecture Plan
• How interactions with the environment change the brain
• Activity-dependent synaptic plasticity in the hippocampus
• Mechanisms of hippocampal synaptic plasticity
• Cellular learning rules – spike rate or spike timing?
Effects of bilateral temporal lobectomy
- patient H.M.
‘In summary, this patient appears
to have a complete loss of memory
for events subsequent to bilateral
medial temporal-lobe resection 19
months before, together with a
partial retrograde amnesia for the
three years leading up to his
operation’
Scoville & Milner (1957) J Neurol
Neurosurg Psychiat
Long-term potentiation
Bliss & Lomo (1973) J Physiol
Attractive features of LTP
Input specificity
Attractive features of LTP
Associativity (& Cooperativity)
Lecture Plan
• How interactions with the environment change the brain
• Activity-dependent synaptic plasticity in the hippocampus
• Mechanisms of hippocampal synaptic plasticity
• Cellular learning rules – spike rate or spike timing?
Mechanisms of LTP induction
NMDA receptor-dependence
Mechanisms of LTP expression
Increased AMPA receptor currents
Mechanisms of LTP maintenance
Structural plasticity?
Enger & Bonhoeffer (1999) Nature
Lecture Plan
• How interactions with the environment change the brain
• Activity-dependent synaptic plasticity in the hippocampus
• Mechanisms of hippocampal synaptic plasticity
• Cellular learning rules – spike rate or spike timing?
Hebb’s postulate
When an axon of cell A is near enough to excite
a 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
D synaptic strength
Synaptic plasticity based on spike rates
- the BCM model
Postsynaptic spike rate
Spike timing-dependent plasticity
Bi & Poo (1998) J Neurosci
Spike rate and spike time encoding in the
hippocampus
Burgess & O’Keefe (2011)
Current Opinion in Neurobiology
Compression of behavioural sequences for storage
via STDP
Dragoi (2013)
Replay of spike sequences during sleep
From Daoyun Ji
Conclusion
• Neurons have the capacity to store information encoded by
both spike rates and spike timing
• Understanding the biological basis of memory will require
massively parallel recordings of both cellular and synaptic
activity
• Advances in engineering and mathematical modelling are
required to generate and interpret this data