Fig. 1.

MDGL network schema. (A) Six diametrically paired circles (labeled A–F) represent six types of spiking neurons, each defining a population of units on the basis of differential synaptic and modulatory connection and affinity statistics. Inhibitory and excitatory synaptic connections are cartooned here by faint curving lines, while both TD and local modulatory connections are indicated by arrow-spray glyphs representing secretion of TD and local modulatory ligands and activation of modulatory GPCRs, all differentially color coded as captioned. Learning tasks are defined by temporal patterns of the indicated spike inputs and outputs, as described in Fig. 3. (B) Six cell types based on excitatory vs. inhibitory synaptic actions, regular vs. adaptive spiking, and internal-only vs. output connectivity. Excitatory and inhibitory cells are further distinguished by which NP-like modulators they secrete, while only output cells are directly responsive to the dopamine-like TD modulator. (C) Cell-type–specific channels of local modulatory signaling established by activity-dependent secretion of two different modulatory ligands and two differentially selective receptors. (D) An error/reward-encoding TD signal impacts target neurons and synapses both 1) directly via activity-dependent secretion of TD ligand and 2) indirectly via activity-dependent secretion of local modulatory ligands.