Neural facilitation

Neural facilitation, also known as paired pulse facilitation, is a concept in neuroscience where an increase in the postsynaptic potential (EPP or EPSP) is evoked by a second impulse.

The phenomena of paired-pulse facilitation (PPF) and depression (PPD) are well known short-term forms of synaptic plasticity. They are expressed in electrophysiological experiments as changes in the amplitude of a test EPSC evoked by a second presynaptic spike that follows the first (conditioning) one in the paired-pulse paradigm. The second PSP can be up to five times the size of the first. Successive PSPs can grow the original PSP several dozen times within a second in some synapses. Facilitation often occurs with a build and decay time course of about 100 milliseconds.

Facilitation has been shown to be a phenomenon that occurs solely at the presynaptic side of a synapse, where synaptic vesicles containing neurotransmitter are released from a pool. As such, facilitation is thought to be the result of an increase in probability of vesicle release from this pool. Early experiments by Del Castillo & Katz in 1954 and Dudel & Kuffler in 1961 showed that facilitation was possible at the neuromuscular junction even if transmitter release does not occur. Experiments by Katz & Miledi in 1968 demonstrated that the presence of calcium ions was necessary for both facilitation and neurotransmitter release. This led to the residual Ca²⁺ hypothesis: that facilitation is caused by an action of calcium remaining in the nerve terminals after the conditioning stimulus. Calcium channels are present in neurons which are capable of allowing calcium to flow in.

The presence of PPF or PPD is dependent on the types of synapses and the experimental conditions. It varies strongly according to the interval between the conditioning and test pulses.

Short-term plasticity can be responsible for cognitive abilities involving temporal processes, eg. the determination of: order, duration, and interval.^{[citation needed]}

This is an example of a dynamic synapse.

References

• Zucker, Robert S.; Regehr, Wade G. (2002), "Short-Term Synaptic Plasticity", Annu. Rev. Physiol. 64: 355–405, doi:10.1146/annurev.physiol.64.092501.114547, PMID 11826273 .
• Katz, B; Miledi, R (1968), "The role of calcium in neuromuscular facilitation", J. Physiol. 195 (2): 481–492, PMC 1351674, PMID 4296699, http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1351674 .
• Del Castillo, J; Katz, B (1954), "Statistical factors involved in neuromuscular facilitation and depression", J. Physiol. 124 (3): 574–585, PMC 1366293, PMID 13175200, http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1366293 .
• Dudel, J; Kuffler, SW (1968), "Mechanism of facilitation at the crayfish neuromuscular junction", J. Physiol. 155 (3): 530–542, PMC 1359873, PMID 13724751, http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1359873 .