fan-shaped body [FBbt_00003679]

fan-shaped body

ID: FBbt_00003679

The largest synaptic neuropil domain of the adult central complex, located posterior to the ellipsoid body and anterior to the protocerebral bridge (Hanesch et al., 1989; Wolff et al., 2015). The fan-shaped body is composed of a rough 2-dimensional grid of layers and columns (Hanesch et al., 1998; Wolff et al., 2015; Hulse et al., 2021). Eight horizontal layers, numbered bottom to top, form a fan shape and can be divided into vertical columns (sometimes called staves, slices or segments) (Ito et al., 2014; Wolff et al., 2015). An additional, much narrower, 9th layer, which lacks a columnar organization, sits dorsal to layer 8 (Wolff et al., 2015). The number of columns varies for different neuronal types (Scheffer et al., 2020). (Hanesch et al., 1989, Wolff et al., 2015, Kahsai and Winther, 2011, Lin et al., 2013, Hulse et al., 2021, Ito et al., 2014)

Previously thought to be 8 slices per hemisphere numbered from 1-8 medial to lateral - arranged in 4 closely associated pairs (Ito et al., 2014). Each of the two neighboring slices (1-2, 3-4, 5-6, 7-8) are associated more closely because they receive small-field columnar neurons generated by the same neuroblasts, forming four groups on each side of the midline, from lateral to medial: segment pair W, X, Y and Z (Boyan and Williams, 2011; Ito and Awasaki, 2008). Six to nine layers can be identified, depending on the staining that is used (Hanesch et al., 1989; Young and Armstrong, 2010; Kahsai and Winther, 2011, Lin et al., 2013, Wolff et al., 2015). Recent papers divide the FB into 9 layers (Wolff et al., 2015; Scheffer et al., 2020).