Spike-timing-dependent plasticity

The core idea of neuroscience is that learning takes place by changes in the strength of synapses. A method to account for how this may occur was proposed in 1949 and is termed as Hebb’s rule. This states that all the synapses between two neurons become stronger when both of the neurons are activated at similar time. The Synapses that show this kind of plasticity are known as to be Hebbian, and can mediate the associative learning as they act as coincidence detectors which relate firing of the presynaptic and postsynaptic cell. The Hebb’s rule is summarize by the aphorism; “what fires altogether, wires altogether.”

Numerous mechanisms to take about synaptic modifications are now known which either raise synaptic weighting, long-term potentiation (LTP); or reduce synaptic weighting, long-term depression (LTD). These are illustrations of spike-timing-dependent plasticity (STDP), modifications to synaptic weighting which are fashioned by accurate timing of neural activity. LTP and LTD are both long lasting, but the other are more transient varieties of STDP exist.

Both the LTP and LTD take place in the hippocampus, the LTP is also seen in the neocortex, amygdala, and at the other sites in the nervous system, whereas LTD also takes place in the cerebellum and spinal cord. Both needs that activity in the pre- and postsynaptic cell takes place within a narrow time window of 10–20 ms. When the presynaptic spike takes place before the postsynaptic spike the outcome is LTP, but if the presynaptic spike follows the postsynaptic spike then the LTD ensues. The vital conditions required for synchrony to trigger STDPs are supplied by the gamma and theta frequency oscillations and the phase relations between them.

The LTP and LTD are regarded as cellular substrates of learning. A few neuroscientists have argued that most, if not all; excitatory synapses in the CNS are capable of the STDPs. If so, then learning is a basic property of the easiest neural networks.