Cholinergic suppression of transmission may allow combined associative memory function and self-organization in the neocortex

Selective suppression of transmission at feedback synapses during learning is proposed as a mechanism for combining associative feed(cid:173) back with self-organization of feed forward synapses. Experimental data demonstrates cholinergic suppression of synaptic transmission in layer I (feedback synapses), and a lack of suppression in layer IV (feed(cid:173) forward synapses). A network with this feature uses local rules to learn mappings which are not linearly separable. During learning, sensory stimuli and desired response are simultaneously presented as input. Feedforward connections form self-organized representations of input, while suppressed feedback connections learn the transpose of feedfor(cid:173) ward connectivity.