Cerebral Cortex Advance Access originally published online on October 9, 2006
Cerebral Cortex 2007 17(8):1766-1781; doi:10.1093/cercor/bhl088
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First-In–First-Out Item Replacement in a Model of Short-Term Memory Based on Persistent Spiking
Center for Memory and Brain, Department of Psychology and Program in Neuroscience, Boston University, Boston, MA 02215, USA
Address correspondence to R.A. Koene, Center for Memory and Brain, Department of Psychology and Program in Neuroscience, Boston University, 64 Cummington Street, Boston, MA 02215, USA. Email: randalk{at}bu.edu.
Persistent neuronal firing has been modeled in relation to observed brain rhythms, especially to theta oscillations recorded in behaving animals. Models of short-term memory that are based on such persistent firing properties of specific neurons can meet the requirements of spike-timing–dependent potentiation of synaptic strengths during the encoding of a temporal sequence of spike patterns. We show that such a spiking buffer can be simulated with integrate-and-fire neurons that include a leak current even when different numbers of spikes represent successive items. We propose a mechanism that successfully replaces items in the buffer in first-in–first-out (FIFO) order when the distribution of spike density in a theta cycle is asymmetric, as found in experimental data. We predict effects on the function and capacity of the buffer model caused by changes in modeled theta cycle duration, the timing of input to the buffer, the strength of recurrent inhibition, and the strength and timing of after-hyperpolarization and after-depolarization (ADP). Shifts of input timing or changes in ADP parameters can enable the reverse-order buffering of items, with FIFO replacement in a full buffer. As noise increases, the simulated buffer provides robust output that may underlie episodic encoding.
Key Words: gamma rhythm • integrate-and-fire neurons • persistent firing • sequence buffer • short-term memory • theta rhythm
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