Discrete somatotopic representation and neural response properties in hummingbird and zebra finch forebrain nuclei

Abstract

Somatosensation allows animals to perceive the external world through touch, providing critical information about physical contact, temperature, pain, and body position. Somatosensory pathways, particularly those related to the rodent vibrissae, have been well-studied in mammals, illuminating principles of cortical organization and sensory processing 1,2. However, comparative studies across diverse vertebrate species are imperative to understand how somatosensory systems are shaped by evolutionary pressures and specialized ecological needs. Birds provide an excellent model for studying the evolution of somatosensation, as they exhibit remarkable diversity in body plans, sensory capabilities, and behavior. Prior work in pigeons3-6, parrots7, and finches8 have identified general tactile-responsive regions within the avian telencephalon. Yet how somatosensory maps and response properties vary across key avian groups remains unclear. Here, we aimed to elucidate somatotopic organization and neural coding in the telencephalon of Annas hummingbirds (Calypte anna) and zebra finches (Taeniopygia guttata). Using in vivo extracellular electrophysiological techniques, we recorded single and multi-unit activity in telencephalic regions of anesthetized hummingbirds and finches. We stimulated the beak, face, trunk, wings, and hindlimbs with controlled tactile stimuli and mapped somatosensory receptive fields. We found distinct representations of body regions distributed across multiple somatosensory zones, with surprising differences in relative areas devoted to key body surfaces, potentially as related to behavioral significance. Highlights{square} Somatosensation provides birds with critical information for behaviors necessary to survival including foraging and flight. {square}In vivo extracellular physiological recordings were used to monitor tactile responses in contralateral forebrain nuclei corresponding to the feather deflection in hummingbirds and finches including to air puff stimuli. {square}Both hummingbirds and finches show distinct separation of body and head receptive field representation in different nuclei. {square}A continuous somatotopic arrangement can be found in both the rostral Wulst (corresponding to the wings and body) and in nucleus basorostralis (corresponding to the head and beak), with particularly enlarged representations of the wing leading edge and the foot.