Editing Barrel cortex (section)

== Anatomy and connectivity of the barrels ==
[[File:Barrel cortex pathways.jpg|thumb|200px|Sensory information flows in parallel pathways from whiskers to cortex.]]

The barrels of the barrel cortex were named because the densities of cells resembled [[barrel]]s. That is, they are collected into cylindrical shapes that are narrowed at the top and bottom. The centre of the barrel is designated the hollow, and the spaces between the barrels are the septa (singular: septum).<ref name="ReferenceA"/>

Sensory information flows from whisker follicles to barrel cortex via the [[trigeminal nerve nuclei]] and the thalamus. Barrel-like divisions can be seen in some, but not all parts of the trigeminal nuclei (where they are called barrelets) and the thalamus (where they are called barreloids). The [[trigeminal nerve]] carries afferent fibres from the follicles into the brainstem where they connect to neurons in four different trigeminal nerve nuclei: principal, interpolar, oral, and caudal.

Projections from the trigeminal nuclei to the thalamus are split into pathways designated [[lemniscus (anatomy)|lemniscal]], extralemniscal, and paralemniscal. In the lemniscal pathway, axons from the principal trigeminal nucleus cross over the midline and project to “barreloids” in the thalamus, specifically in the dorsomedial section of the ventroposterior medial nucleus (VPMdm). Neurons in VPMdm project mainly to barrels in layer 4 of primary somatosensory cortex (S1). In the extralemniscal pathway, neurons of the interpolar nucleus project to the ventrolateral section of the ventroposterior medial nucleus (VPMvl). Neurons in VPMvl project to septa between the barrels and to [[secondary somatosensory cortex]] (S2). The paralemniscal pathway runs from the interpolar trigeminal nucleus via the posterior nucleus (POm) of the thalamus to S2 and to diffuse targets in barrel cortex, especially layer 5.

Each pathway also has secondary projections to other layers within barrel cortex and other regions of cortex, including motor cortex.<ref>[[#refBosmanWhiskers|Bosman et al., 2011]]</ref> These different pathways are thought to transmit different modalities of sensory information from the whisker.<ref name="Fox, 2008"/><ref>[[#refDiamonWhatWhere|Diamond et al., 2008]]</ref>