Figure 12.

The expression of and implications for activity-dependent plasticity manifolds

Behavioral context-dependent afferent inputs to the DG recruit a subset of granule cells, which elicit action potentials in theta-burst patterns. The findings from our study (within yellow box) show that TBF reduces sub-threshold excitability, but contrastingly increases supra-threshold excitability. Mechanistically, induction of this form of plasticity is dependent on cytosolic calcium influx through L-type VGCCs and InsP₃Rs. The expression of TBF-induced contrasting plasticity in sub- and supra-threshold excitability is an outcome of conjunctive plasticity in multiple ion channels: HCN, K_ir, and NaP. The enhanced supra-threshold excitability in the subset of contextually recruited cells (which manifested TBF) could result in the emergence of “engram cells” (highlighted in red in the top panel of granule cells), which encode for this specific behavioral context. The concomitant reduction in sub-threshold excitability, on the other hand, provides overall homeostatic balance in this subset of cells, to counteract the enhanced firing and enable stable encoding in this subset of granule cells.