Real Time Multiplicative Memory Amplification Mediated by Whole-Cell Scaling of Synaptic Response in Key Neurons
Fig 10
Whole-cell balanced amplification had a considerable impact on the probability that very short voltage transients would elicit a spike.
A. An alpha function-like time course of increased rate activation of excitatory synapses was induced (tau = 12 ms, multiplication factor = 5) resulting in brief (half time ~ 30 ms) excursions of voltage bumps. B. For each trace (30 bumps of voltage elevations) the probability of eliciting a spike was calculated before and after whole cell balanced amplification. The simulation parameter space was spanned by varying the resting membrane potential, the synaptic strength, and the activation frequency of the synapses as indicated in the Materials and Methods. Binning the probabilities in all conditions resulted in highly non-linear amplification, where bumps that had a low likelihood of eliciting a spike were amplified to threshold values with probabilities of 50%. Using Eq 2 we tested whether the multiplication of σ and by a factor of 1.7 could account for the simulation results. β was set such that the maximum frequency was 100 Hz or 150 Hz [58] at values where the average current was 3σ more depolarized than threshold (a range in which sodium channels still do not undergo pronounced inactivation). The parameter space (35 different sets of simulations) was spanned by varying
(0.4–0.9, similar to the values obtained in the simulations) and the threshold
(0.5–3.7), yielding results that spanned the same area as the simulations. The values of
are indicated by color coding, and the values of β are indicated by solid lines (max firing frequency of 150 Hz) and double lines (max firing frequency of 100 Hz). C. Binning these calculated values based on the probability before whole-cell amplification yielded a curve that was similar to the simulated curve.