Plasticity in the nervous system

Edward Mann17th 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 circuitsOcular dominance columns

Plasticity in neural circuitsActivity-dependent rewiring in visual cortex during development

Plasticity in neural circuitsEnvironmental enrichment & spine density

Plasticity in neural circuitsAssociative 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.

Scoville & Milner (1957) J Neurol Neurosurg Psychiat

‘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’

Long-term potentiation

Bliss & Lomo (1973) J Physiol

Attractive features of LTPInput specificity

Attractive features of LTPAssociativity (& 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 inductionNMDA receptor-dependence

Mechanisms of LTP expressionIncreased AMPA receptor currents

Mechanisms of LTP maintenanceStructural 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

Synaptic plasticity based on spike rates- the BCM model

D sy

napti

c st

reng

th

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