Long-term synaptic plasticity N500, 6 Sept., 2016
We just finished describing short-term synaptic changes
What about long-term changes?
How does the brain store information?
Outline Origins of the synaptic hypothesis of memory The hippocampus and the tragic case of H.M. The discovery of Long term potentiation (LTP) Associative and Hebbian LTP Spike-timing dependent plasticity (STDP) Induction and expression Long-term depression (LTD) The BCM rule
Outline Origins of the synaptic hypothesis of memory The hippocampus and the tragic case of H.M. The discovery of Long term potentiation (LTP) Associative and Hebbian LTP Spike-timing dependent plasticity (STDP) Induction and expression Long-term depression (LTD) The BCM rule
S.Seung, MIT
S.Seung, MIT
S.Seung, MIT
Outline Origins of the synaptic hypothesis of memory The hippocampus and the tragic case of H.M. The discovery of Long term potentiation (LTP) Associative and Hebbian LTP Spike-timing dependent plasticity (STDP) Induction and expression Long-term depression (LTD) The BCM rule
The case of H.M. Surgery to prevent continued epileptic seizures Both hippocampi removed Unable to learn new declarative information Can learn new motor skills: golf, mirror writing
S.Seung, MIT
S.Seung, MIT
Outline Origins of the synaptic hypothesis of memory The hippocampus and the tragic case of H.M. The discovery of Long term potentiation (LTP) Associative and Hebbian LTP Spike-timing dependent plasticity (STDP) Induction and expression Long-term depression (LTD) The BCM rule
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So it looks like synapses change in longterm ways. What next?
Outline Origins of the synaptic hypothesis of memory The hippocampus and the tragic case of H.M. The discovery of Long term potentiation (LTP) Associative and Hebbian LTP Spike-timing dependent plasticity (STDP) Induction and expression Long-term depression (LTD) The BCM rule
Learning Meat Bell Meat, Bell Saliva Saliva
Learning Meat Bell Bell Saliva Saliva
A post-synaptic potential (psp)
An action potential (spike)
Typical LTP protocol
Associative properties, like Aristotle and James suggested
As Hebb predicted!
Just as Hebb suggested
Sensitive to temporal contiguity, like Pavlov observed
Outline Origins of the synaptic hypothesis of memory The hippocampus and the tragic case of H.M. The discovery of Long term potentiation (LTP) Associative and Hebbian LTP Spike-timing dependent plasticity (STDP) Induction and expression Long-term depression (LTD) The BCM rule
LTP can be temporally very precise Bi and Poo, 1998
Why is STDP important?
Why is STDP important?
Synaptic strength Why is STDP important? time Fire early -> get stronger -> fire earlier Fire late -> get weaker -> fire later
Why is STDP important?
Outline Origins of the synaptic hypothesis of memory The hippocampus and the tragic case of H.M. The discovery of Long term potentiation (LTP) Associative and Hebbian LTP Spike-timing dependent plasticity (STDP) Induction and expression Long-term depression (LTD) The BCM rule
Mechanisms of expression
Outline Origins of the synaptic hypothesis of memory The hippocampus and the tragic case of H.M. The discovery of Long term potentiation (LTP) Associative and Hebbian LTP Spike-timing dependent plasticity (STDP) Induction and expression Long-term depression (LTD) The BCM rule
Long-term depression (LTD)
Outline Origins of the synaptic hypothesis of memory The hippocampus and the tragic case of H.M. The discovery of Long term potentiation (LTP) Associative and Hebbian LTP Spike-timing dependent plasticity (STDP) Induction and expression Long-term depression (LTD) The BCM rule
High frequency LTP
Low frequency LTD
Test pulse at 0.067 Hz: no change
Synaptic change (%) The BCM theory of synaptic plasticity + 0.1 1 10 100 Frequency (Hz) -
BCM predicts a leftward shift for lower spontaneous activity % = Light reared = Dark reared
BCM predicted the data % = Light reared = Dark reared A new type of LTP
Timing induced LTP
Timing induced LTD
Unresolved issues Asymmetry of induction: 120 vs. 900 pulses What causes the shape of the BCM curve? Frequency results did not predict timing results Timing results do not say why 1 Hz unpaired induces LTD, yet 0.1 Hz unpaired induces no change