Figure 14.

Adaptation in a visual pathway prevents deterioration of SNR. Arrays of rods, cones (P) and bipolar cells (B) transduce a noisy stimulus and transmit their response through noisy synapses (N). The ganglion cell collects signals from many cones to reduce noise (Tsukamoto et al., 1990). The synapses would saturate (S) without adaptation, which originates in biochemical feedback in the outer segments of rods and cones, potassium channels in cones and bipolar cells (looped arrows), and feedback from horizontal cells and amacrine cells (dashed arrows). Center-surround receptive fields for 2 layers of neurons presynaptic to ganglion cell are generated by their local circuits, for the purpose of adaptation to prevent saturation of synapse and and masking by noise. The 2 layers of center-surround processing both contain subtractive and divisive components and therefore interact in a complex manner. The ganglion cell center-surround receptive field is the convolution of the presynaptic receptive fields and their synaptic weighting functions (Smith & Sterling, 1990). Spike generator adds noise when creating spike train that saturates at high spike rates.