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).

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).