Abstract
In the early sensory and motor areas of the cortex, individual neurons transmit information about specific sensory features via a peaked response. This concept has been crystallized as “labeled lines,” to denote that axons communicate the specific properties of their sensory or motor parent cell. Such cells also can be characterized as being polarized, that is, as representing a signed quantity that is either positive or negative. We show in a model simulation that there are two important consequences when learning receptive fields using such signed codings in circuits that subtract different inputs. The first is that, in feedback circuits using labeled lines, such arithmetic operations need to be distributed across multiple distinct pathways. The second consequence is that such pathways must be necessarily dynamic, i.e., that synapses can grow and retract when forming receptive fields. The model monitors the breaking and growing of new circuit connections when their synapses need to change polarities and predicts that the rate of such changes should be inversely correlated with the progress of receptive field formation.
Highlights
Most neural sensory circuits are faced with the issue of representing negative quantities and there are different strategies for doing so
While the fact of synaptic growth and retraction is well established from experiments (Smythies, 2002; Trachtenberg et al, 2002; Stettler et al, 2006; Bourne and Harris, 2007, 2008; Yamahachi et al, 2009), we demonstrate how often it happens in the context of an algorithm for receptive field formation that monitors the synapse changes quantitatively throughout the receptive field formation process
We show that, depending on the individual cases that arise, the modified synapses may be on different neurons
Summary
Most neural sensory circuits are faced with the issue of representing negative quantities and there are different strategies for doing so. In contrast to the VOR’s spike rate encoding, the cortex uses a very different coding strategy where two neurons represent the different polarities of a quantitative feature, one for positive and one for negative. In their original experiments, Wiesel and Hubel (1966) characterized a cell’s peaked response to a stimulus feature as a labeled line, and we use the phrase signed labeled lines to note that the quantities are part of a two-cell representation for signed numbers. It turns out that this coding strategy poses difficulties for feedback circuits that use subtraction, since the desired circuit depends on the relative magnitudes of the minuend and subtrahend
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