Receptive field sizes and neuronal encoding bandwidth are constrained by axonal conduction delays
Fig 8
Conduction velocity and stimulus dynamics constrain meaningful population sizes of LIF model neurons.
A—C Mutual information between stimulus and response estimated from the population responses of LIF-model neurons (see sketches in Fig 1A). These models assume 1D populations with a density of 2000 neurons per m of the sensory surface. Model parameterization was completely arbitrary and identical for all model neurons (see Methods). The models were driven with the same frozen noise sequences with spectral power in the ranges 0–100 Hz, 100–200 Hz and 200–300 Hz (dashed, dash-dotted, and dotted lines, respectively). Each model had the same amount of (independent) noise added to the driving stimulus. Three realistic conduction velocities were simulated and compared to the unrealistic instantaneous conduction (blue solid line in all figures, “without delay”). With decreasing conduction velocity the encoding performance drops at smaller populations. High-frequency encoding is most sensitive to spread in conduction delays. The “harmonic” structure seen in A is a consequence of the stimulus’ auto-correlation. A: Conduction velocity of 7 ms−1, as described for some visual fibers in the monkey corpus callosum [55]B: 25 ms−1 for example measured in squid giant axons [18], C: 50 ms−1 as estimated above for P-unit afferents.