A big picture of a small brain

Abstract

A detailed map of the neurons that carry information away from the mushroom bodies in the brains of fruit flies has improved our understanding of the ways in which experiences can modify behaviour.

Keywords: D. melanogaster; associative memory; behavioral valence; mushroom body; neuroscience; olfactory learning; sleep.

Figure 1.. Model of how information is processed in the mushroom body to enable it to alter behavior.

The mushroom body has three lobes (left) called α/β (blue), α′/β′ (pink) and γ (green). Each lobe is made up of projections from many Kenyon cells (KC) and is divided into five compartments (shown by the dark outlines). Each compartment (right) is defined by the projections from a limited number of dopaminergic neurons (DANs) and mushroom body output neurons (MBONs). The Kenyon cells carry sparse information about odor, while the dopaminergic neurons signal a reward or a punishment. The MBONs carry information away from the mushroom body to convergence zones in order to alter behavior. The Kenyon cells of each lobe extend through all the compartments of that lobe and form synapses with all the MBONs. However, each compartment contains a unique set of dopaminergic neurons and MBONs: this allows the information about odor to be used by several MBONs and to be modified by multiple types of dopaminergic neurons.

Figure 2.. The many types of mushroom body output neurons (MBONs).

Maps of the fly brain from Aso et al. (2014a) showing the locations of different types of MBONs, split into three groups according to the neurotransmitter chemical that they release. There are 21 types of MBONs in the fly brain: seven of these types release glutamate (shown in green in the left panel); four types release gamma-aminobutyric acid (GABA; shown in blue in the middle panel); and eight types release acetylcholine (shown in red in the right panel). The neurotransmitters released by the remaining two types are not known.