Figure 1.

Synaptic plasticity as the cellular basis of memory? (A) Schematic of long-term potentiation (LTP) and long-term depression (LTD). Upon a diverse array of stimuli, the dendritic spine undergoes marked structural change, which is accompanied with the dynamic change in actin polymerization and the increase in surface AMPA receptor in the postsynaptic density (PSD). (B) The synaptic weights determined by (de)potentiation provide a scalar quantity representing the circuit that can be preferentially retrieved in response to the activation of upstream cell ensembles. When Spine #1 is potentiated, the probability of action potential of Neuron #3 would increase. When both Spine #1 and Spine #2 are potentiated, Neuron #3 is more likely to fire as a part of cell ensemble. In contrast, when Spine #3 is potentiated and Spine #1 is depotentiated, Neuron #4, instead of Neuron #3, is more likely to fire.