Dual Coding with STDP in a Spiking Recurrent Neural Network Model of the Hippocampus
Figure 6
Putative Sharp Wave Ripple Recall Activity Following Theta Coded Learning.
(a) Typical spike raster observed in the network during recall simulations following hetero-associative learning (as described in Figure 2). Externally stimulated firing of a single neuron produces sequential recall activity in all neurons that constitute the originally learned pattern; (b) Statistics relating to hetero-associative recall for each STDP rule and plasticity modulation scheme examined. Figures shown represent data averaged over 1000 randomly initialised recall epochs with Φ = 0.05 following hetero-associative learning simulations with the (A) pair-based BCM type; (B) triplet-based BCM type; (C) pair-based non-BCM type STDP rules. Data illustrated for the relative frequency of neurons that fired before (dark grey); at the same time as (medium grey); and after (light grey) the simulated neuron encoding for the next place field on the learned route. (c) Typical spike raster observed in the network during recall simulations following auto-associative learning (as described in Figure 3). External stimulation of a random subset of (cued) neurons from each learned pattern (five out of ten, in this case) generates selective firing in (uncued) neurons that encode for the same place field/pattern after 5–10ms (depending on the plasticity rule employed during learning, and the concentration of ACh employed during recall). (d) Statistics relating to auto-associative recall for each STDP rule and plasticity modulation scheme examined. Figures shown represent data averaged over 1000 randomly initialised recall epochs following learning with the (A) pair-based BCM type STDP rule, and Φ = 0.05; (B) triplet-based BCM type STDP rule, and Φ = 0.083; (C) pair-based non-BCM type STDP rule, and Φ = 0.05. Data illustrated for the relative frequency of uncued neurons that fire within 20ms of externally cued activity in other neurons within the same pattern (dark grey) and the relative frequency of neurons in different, uncued patterns that fire within the same temporal window (light grey). (e) Typical spike raster observed in the network during recall simulations following dual coded learning (as described in Figure 5). External stimulation of a random subset of neurons from a single pattern (three out of five, in this case) produces sequential recall activity in simulated neurons that encode for each successive place field on the learned route. This neural activity pattern is reminiscent of sharp wave/ripple dynamics observed during putative recall activity in the hippocampus; (f) Statistics relating to dual coded recall for each STDP rule and plasticity modulation scheme examined. Figures shown represent data averaged over 1000 randomly initialised recall epochs with Φ = 0.111 following dual coded learning for the (A) pair-based BCM type; (B) triplet-based BCM type; and (C) pair-based non-BCM type STDP rules. Data illustrated for the relative frequency of neurons that fired before (dark grey); at the same time as (medium grey); and after (light grey) the first action potential in any simulated neuron encoding for the next place field on the learned route.