Short Term Memory May Be the Depletion of the Readily Releasable Pool of Presynaptic Neurotransmitter Vesicles

Time (s)

Figure 12. Vesicle recovery from slow cells (filled squares) and fast cells (filled diamonds)
from (16) (the average over the two is shown in Figure 11) with the memory curve in filled circles.

4. Summary

Exocytosis in a presynaptic terminal occurs until the action potentials have stopped or all
the vesicles in the RRP have released their transmitter under prolonged firing of the action
potentials. In our model, a word is read causing prolonged firing which in turns depletes the
RRPs of the presynaptic terminals. The short term memory trace of a word is the particular
pattern of RRP depleted presynaptic terminals. The particular pattern should be related to the
long term memory version of the word. After the action potential firing has slowed down,
endocytosis causes the word to decay from short term memory. If the endocytosis is allowed to
finish (the word is not read again), the pattern of exhausted postsynaptic terminals is gone and, in
our model, the short term memory of the word is gone.

The evidence presented includes corresponding qualitative and quantitative functional
forms for tagging (exocytosis) and tagging decay (endocytosis). Two more fact supports our
finding. First, the failure to effect human memory using subliminal stimulation has a parallel in the
endocytosis. The time course of endocytosis of a variety of synapse (including hippocampal

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