Questions about STDP as a General Model of Synaptic Plasticity

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Computational Neuroscience

Background:

• Spike-timing-dependent plasticity (STDP) posits that the precise timing between pre- and postsynaptic activity dictates synaptic potentiation or depression.
• Most STDP studies use artificial current injection to evoke postsynaptic spikes, which may not reflect natural neuronal function.

Purpose of the Study:

• To critically evaluate the role of sodium (Na+) spikes in STDP under more physiologically relevant conditions.
• To explore alternative dendritic depolarizing events that may govern long-term potentiation (LTP) and long-term depression (LTD).

Main Methods:

• Review of existing literature on STDP, focusing on studies using physiologically evoked spikes.
• Analysis of experimental data where postsynaptic spikes are triggered by excitatory postsynaptic potentials (EPSPs).
• Comparison of plasticity induction under conditions with and without Na+ spike blockade.

Main Results:

• Under realistic conditions (EPSP-evoked spikes), results often contradict STDP predictions.
• Low-frequency stimulation can induce LTD irrespective of Na+ spike generation, contrary to STDP's LTP prediction.
• LTP induction with pre-before-post timing is sometimes possible without Na+ spikes, indicating they are not essential.

Conclusions:

• Sodium spikes may play a facilitative role in LTP/LTD but are not strictly necessary.
• Dendritic calcium (Ca2+) spikes, EPSPs, and NMDA receptor-mediated events are likely more critical for plasticity.
• It is premature to consider STDP-like processes as the main regulators of bidirectional synaptic plasticity.