Anatomical and physiological properties of feedback neurons of the mushroom bodies in the bee brain.

"Feedback neurons" in the bee's mushroom body were recorded from and filled iontophoretically with either Lucifer Yellow or cobalt-hexammino-chloride (III). The neurons have complex shapes arborizing in one, or sometimes two layers of the alpha-lobe, and sometimes in the beta-lobe and pedunculus. Their axons project via the protocerebral-calycal-tract into the calyx lip and collar zones, ending as blebbed processes. Additionally these neurons also project around the alpha-lobe into the protocerebrum. More than 70% of the recorded neurons were multimodal responding to several test-stimuli. These include: light, airstreams towards the antennae and the abdomen, various odors, water and sugar-water presented to the antennae and proboscis, and mechanical stimulation of the legs. Responses were usually excitatory and in many cases showed aftereffects which lasted for many seconds. Some neurons showed spontaneous changes in their response-properties. There appeared to be no clear match between the modality of any one neuron and the anatomical features of its dendritic regions. The possible functional rôles of feedback neurons in learning and behaviour are discussed with particular reference to their structural identity as a recurrent loop from the lobes to the calyces.