Inhibitory Replay and E Firing

Abstract

We replayed inhibitory spike recordings from three frozen MNIST PING classifiers after either independent-spike jitter or shared shifts within fixed clock windows. At 14 ms jitter, mean E rates were 0.007 Hz under independent shifts and 68.318 Hz under window shifts, with each I neuron’s spike count preserved. Accuracy declined under both interventions. Replay interrupted responsive feedback, so these measurements do not isolate synchrony or a gamma-specific mechanism.

Results

Replay perturbations diverge

At 14 ms jitter, independent shifts reduced mean E firing to 0.007 Hz, whereas fixed-window shifts gave 68.318 Hz. The three reused networks retained their I-spike counts, but replay prevented inhibition from responding to E activity.

Methods

1. Models. We reused three independently trained PING networks, initialized with training seeds 42–44.

2. Trials. We tested each network-condition combination on the same 1,000 MNIST test images. The main figure represents 36,000 condition-level trials, or 33,000 distinct simulations because both arms shared the zero-jitter control.

3. Simulation. We presented each image for 200 ms using a 0.1 ms timestep. We encoded pixel intensities as spike trains with a maximum input rate of 25 Hz, fixed across all training replicates and perturbation conditions. Full-intensity pixels therefore had a 25 Hz encoding rate; lower intensities scaled this rate proportionally.

4. Independent jitter. We gave every inhibitory spike an independent Gaussian time shift, using $\sigma = 0 , 0.5 , 1 , 2 , 5 , 9 ,$ and $14$ ms.

5. Group jitter. We divided the timeline into fixed 22.8 ms windows and gave every inhibitory spike within a window the same shift, using $\sigma = 0 , 1 , 3 , 7 ,$ and $14$ ms. The window spanned 228 simulation steps, obtained by rounding the period of the fixed 43.95 Hz reference to the 0.1 ms grid; windows were not detected gamma cycles.

6. Boundaries. We reflected independent spikes that left the 200 ms interval back into it individually. For group jitter, we reflected the shared displacement once so that the group remained intact.

7. Collisions. We moved same-neuron spikes landing on the same timestep to the nearest unused in-range timestep. No spikes were removed.

8. Measurements. We recorded accuracy and mean excitatory and inhibitory firing rates. Curves show the mean across the three training seeds.

9. Range restriction. We retained larger jitter values as boundary-sensitivity results but excluded them from the main figure because reflection became a substantial part of the intervention.