An intracellular Ca2+ subsystem as a biologically plausible source of intrinsic conditional bistability in a network model of working memory.

We have developed a firing rate network model for working memory that combines Mexican-hat-like synaptic coupling with intrinsic or cellular dynamics that are conditionally bistable. While our approach is in the spirit of Camperi and Wang (1998) we include a specific and plausible mechanism for the cellular bistability. Modulatory neurotransmitters are known to activate second messenger signaling systems, and our model includes an intracellular Ca(2+) handling subsystem whose dynamics depend upon the level of the second messenger inositol 1,4,5 trisphosphate (IP3). This Ca(2+) subsystem endows individual units with conditional intrinsic bistability for a range of IP3. The full "hybrid" network sustains IP3-dependent persistent ("bump") activity in response to a brief transient stimulus. The bump response in our hybrid model, like that of Camperi-Wang, is resistant to noise-- its position does not drift with time.