Figure 6.

Proposed model of somatovisceral convergence of thin afferents onto lamina I neurons. Somatic (blue) and visceral (red) afferents converge directly onto a lamina I projection neuron (PN) and a lamina I local circuit neuron (LCN), where somatic and visceral processing pathways merge together. Lamina I LCNs can be both inhibitory⁵¹ and excitatory²⁷ and can directly synapse on PNs.²⁷ Intercalated excitatory (+) and inhibitory (−) neurons are shown by smaller circuits; their laminar location is not known. The excitatory intercalated neurons may amplify the primary afferent-driven input to a PN. The inhibitory intercalated neurons may play diverse roles, eg, disinhibit a PN by supressing activity in a rhythmic inhibitory LCN, or induce reciprocal inhibition of somatic or visceral inputs. At the same time, other PNs receive somatic- or visceral-specific inputs.