Researchers from the Centre for Neural Circuits and Behaviour and the Dept of Pharmacology, together with co-workers in New York have published and tested a novel theory of synaptic plasticity. Reliable memory formation and retrieval is dependent on long term modification of neuronal connections. Such modifications can be manifested by both pre and postsynaptic changes. However, these are highly variable and for many years the relative contributions of neurotransmitter release and subsequent detection on these changes has remained enigmatic.
Writing in the prestigious journal Neuron, Costa et al., propose that long term plasticity works by most efficiently optimizing the synapse to achieve the desired outcome. In this way the initial state of the synapse determines the ratio of pre and post synaptic modifications. This can be illustrated using examples from development where many synapses lack functional receptors and are ‘silent’. In these cases, it makes sense for long term plasticity to primarily occur through post synaptic modification. However, if functional postsynaptic receptors are present then it becomes more probable that plasticity will occur through presynaptic mechanisms such as control of neurotransmitter release.
The authors tested the new theory in a range of experimental situations and found that it fitted well with the observed results.
Previous models ignored the issue of pre/post synaptic variability whereas this new work provides insights into it. This draws a picture where the changes in plasticity are brought about by an efficient balance of pre and post synaptic modifications to provide the optimal result.
This work suggests that not only "neurons that fire together wire together", but also that their pre and postsynaptic terminals are optimised together.- Dr Rui Ponte Costa