ABSTRACT
Relatively little is still known about the sense of taste, or contact chemoreception,
compared with other sensory modalities, despite its importance to many aspects of animal
behaviour. The central projections of the sensory neurons from bimodal contact chemoreceptors
(basiconic sensilla) were compared with those from mechanosensory tactile hairs located
on similar regions of the middle leg of the locust. Basiconic sensilla are multiply innervated,
containing one mechanosensory and several chemosensory neurons, whereas tactile hairs are
innervated by a single mechanosensory neuron. We show that the sensory neurons from
tactile hairs form a complete 3-dimensional somatotopic map in the mesothoracic ganglion.
Sensory neurons from hairs located on the coxa projected to a region near the midline of the
ganglion with neurons from hairs located on progressively more distal parts of the leg
arborizing in successively more lateral regions of neuropil. All the neurons from basiconic
sensilla, both mechanosensory and chemosensory, also projected in a similar, strictly somatotopic,
manner, and the arbors from these neurons overlapped considerably with those from
tactile hairs on equivalent parts of the leg to form a continuous region. Thus, the position of
a receptor on the leg is preserved in the central nervous system not only for the mechanosensory
neurons from both tactile hairs and basiconic sensilla but also for chemosensory neurons.
We could observe no anatomical features or small differences in projection region
between sensory neurons from individual basiconic sensilla consistent with differences in
modality.

Indexing terms: chemoreception; gustation; mechanoreception; sensory neuron; locust