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

cultured synapses) is stimulus-dependent - the longer the stimulation the much longer the
endocytosis takes (21), (22) (the experimental results plotted in Figure 11 result from complete
depletion of the RRP). The authors in (22) found that the time for endocytosis was 56 ms after
single-vesicle exocytosis but could increase to 8.3 seconds after longer stimulation suggesting
that subliminal stimulation may only lead to an incomplete tagging that lasts a tenth of a second.
Second, this split in short and long time scales of endocytosis may also correspond to the two
phases of short term memory (3).

5. Appendix I

Typically the endocytosis curves are fit with two exponentials that each has an
associated time constant presumably with the hope in mind that there are one or perhaps two
unknown biochemical reactions with a corresponding energy barrier. To check whether the
customary double exponential fit is an appropriate fit, I tabulated some of the exponential fitting
time constants for the experiments of Figure 10 in Table 1. There seems to be little correlation of
the time constants suggesting that a double exponential fit is inappropriate. In contrast, the
logarithmic fits of Figure 11 give slopes that are very similar and thus seem more appropriate.

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