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Adams & Cox Simple Proofreading Circuit
 

Summary: Adams & Cox
Simple Proofreading Circuit
Hebbian Proofreading the J-I connection is Hebbian but not completely specific, K is a coincidence detector
which gates the plasticity of the Hebbian connection using an outer product ruleThis circuit can apply to any
feedforward cortical network that must accurately learn complex input statistics. In the case of the feedforward
connections from thalamus to middle layers of cortex, the coincidence-detecting K cell would be a layer 6
"simple" cell. It would show "double simplicity" because it would receive inputs from both a layer 4 simple cell
and from the relay cells that form monosynaptic connections on its layer 4 partner, and would only fire when both
sets of inputs fire. This arrangement corresponds to that found biologically (e.g. Sherman and Guillery; Callaway).
The layer 6 cell would then innervate both the relay cells that generate its simple responses, and the layer 4 simple
cell; these feedback pathways would conjunctively enable the plasticity of the relevant relay-to layer 4
connection, by neuromodulatory glutamate release from drumstick synapses. There is anatomical and
physiological evidence for these pathways (Sherman Guillery; Callaway etc), but our model goes beyond available
evidence.
Adams & Cox
Push-Pull Proofreading Circuit
Simple proofreading lowers the error rate but cannot guarantee avoidance of an error catastrophe, because even at a reduced
error rate, unfavorable input statistics may occur, leading to loss of all previous learning. The cortex has to take everything
the environment throws at it, learning when opportunities arise, yet maintaining its existing interpretations (the
"stability/plasticity dilemma"). This can be achieved using a more sophisticated version of the basic proofreading circuit,

  

Source: Adams, Paul R. - Department of Neurobiology and Behavior, SUNY at Stony Brook

 

Collections: Biology and Medicine