Figure 3

Putative ascending circuitry for visceral and airway sensations. Previous studies [41] have shown that general visceral afferents project from the nucleus of the solitary tract (nTS) to the visceral sector of the thalamus (the ventral posterior parvocellular nuclei, VPPC) and onto granular and dysgranular insula cortices (GI and DI, respectively). By contrast, we propose that trigeminal (specifically Pa5) neurons receiving inputs from the trachea and larynx project to the ventral posterior thalamic nuclei (VPM/ VPL) and onto primary and secondary sensory cortices (S1 and S2, respectively). This trigeminothalamocortical pathway may be particularly important for encoding sensations arising from the airways. In addition, projections from the mediodorsal thalamus (MD) to the agranular anterior insula and lateral orbital cortices (AI and LO, respectively) likely encode affective responses associated with airways irritation. Omitted for clarity are the pontine relay nuclei which receive inputs from the medulla and project onto the VPPC and MD. See references [37, 38] for further details.