Figure 4.

Structural changes associated with LTP and LTD. (A) Synaptic strength correlates with spine volume and the area of the postsynaptic density (orange). Note that the PSD in potentiated synapses is often perforated. (B) LTP can also lead to the appearance of new spines. Within 30 min of triggering LTP (30 stimuli applied to the presynaptic axon at 10-sec intervals paired with depolarizing current injection into the postsynaptic neuron; black bar) of a synaptic connection in the hippocampus, new spines appear. (Panel created from data adapted from Engert and Bonhoeffer 1999.)