Bird flight is a remarkable adaptation that has allowed the approximately 10 000 extant species to colonize all terrestrial habitats on earth including high elevations, polar regions, distant islands, arid deserts, and many others. Birds exhibit numerous physiological and biomechanical adaptations for flight. Although bird flight is often studied at the level of aerodynamics, morphology, wingbeat kinematics, muscle activity, or sensory guidance independently, in reality these systems are naturally integrated. There has been an abundance of new studies in these mechanistic aspects of avian biology but comparatively less recent work on the physiological ecology of avian flight. Here we review research at the interface of the systems used in flight control and discuss several common themes. Modulation of aerodynamic forces to respond to different challenges is driven by three primary mechanisms: wing velocity about the shoulder, shape within the wing, and angle of attack. For birds that flap, the distinction between velocity and shape modulation synthesizes diverse studies in morphology, wing motion, and motor control. Recently developed tools for studying bird flight are influencing multiple areas of investigation, and in particular the role of sensory systems in flight control. How sensory information is transformed into motor commands in the avian brain remains, however, a largely unexplored frontier.

In this paper, we review the connections and physiology of visual pathways to the cerebellum in birds and consider their role in flight. We emphasize that there are two visual pathways to the cerebellum. One is to the vestibulocerebellum (folia IXcd and X) that originates from two retinal-recipient nuclei that process optic flow: the nucleus of the basal optic root (nBOR) and the pretectal nucleus lentiformis mesencephali (LM). The second is to the oculomotor cerebellum (folia VI-VIII), which receives optic flow information, mainly from LM, but also local visual motion information from the optic tectum, and other visual information from the ventral lateral geniculate nucleus (Glv). The tectum, LM and Glv are all intimately connected with the pontine nuclei, which also project to the oculomotor cerebellum. We believe this rich integration of visual information in the cerebellum is important for analyzing motion parallax that occurs during flight. Finally, we extend upon a suggestion by Ibbotson (2017) that the hypertrophy that is observed in LM in hummingbirds might be due to an increase in the processing demands associated with the pathway to the oculomotor cerebellum as they fly through a cluttered environment while feeding.

Neurons in animal visual systems that respond to global optic flow exhibit selectivity for motion direction and/or velocity. The avian lentiformis mesencephali (LM), known in mammals as the nucleus of the optic tract (NOT), is a key nucleus for global motion processing [1-4]. In all animals tested, it has been found that the majority of LM and NOT neurons are tuned to temporo-nasal (back-to-front) motion [4-11]. Moreover, the monocular gain of the optokinetic response is higher in this direction, compared to naso-temporal (front-to-back) motion [12, 13]. Hummingbirds are sensitive to small visual perturbations while hovering, and they drift to compensate for optic flow in all directions [14]. Interestingly, the LM, but not other visual nuclei, is hypertrophied in hummingbirds relative to other birds [15], which suggests enhanced perception of global visual motion. Using extracellular recording techniques, we found that there is a uniform distribution of preferred directions in the LM in Anna's hummingbirds, whereas zebra finch and pigeon LM populations, as in other tetrapods, show a strong bias toward temporo-nasal motion. Furthermore, LM and NOT neurons are generally classified as tuned to "fast" or "slow" motion [10, 16, 17], and we predicted that most neurons would be tuned to slow visual motion as an adaptation for slow hovering. However, we found the opposite result: most hummingbird LM neurons are tuned to fast pattern velocities, compared to zebra finches and pigeons. Collectively, these results suggest a role in rapid responses during hovering, as well as in velocity control and collision avoidance during forward flight of hummingbirds.

Gaede AH, Pilowsky PM. Catestatin in rat RVLM is sympathoexcitatory, increases barosensitivity, and attenuates chemosensitivity and the somatosympathetic reflex. Am J Physiol Regul Integr Comp Physiol 299: R1538 -R1545, 2010. First published October 6, 2010 doi:10.1152/ajpregu.00335.2010.-The fundamental role and corollary effects of neuropeptides that govern cardiorespiratory control in the brain stem are poorly understood. One such regulatory peptide, catestatin [Cts,], noncompetitively inhibits nicotinic-cholinergic-stimulated catecholamine release. Previously, we demonstrated the presence of chromogranin A mRNA in brain stem neurons that are important for the maintenance of arterial pressure. In the present study, using immunofluorescence histochemistry, we show that Cts immunoreactivity is colocalized with tyrosine hydroxylase in C1 neurons of the rostral ventrolateral medulla (RVLM, n ϭ 3). Furthermore, we investigated the effects of Cts on resting blood pressure, splanchnic sympathetic nerve activity, phrenic nerve activity, heart rate, and adaptive reflexes. Cts (1 mM in 50 nl or 100 M in 50 -100 nl) was microinjected into the RVLM in urethaneanesthetized, vagotomized, ventilated Sprague-Dawley rats (n ϭ 19). Cardiovascular responses to stimulation of carotid baroreceptors, peripheral chemoreceptors, and the sciatic nerve (somatosympathetic reflex) were analyzed. Cts (1 mM in 50 nl) increased resting arterial pressure (28 Ϯ 3 mmHg at 2 min postinjection), sympathetic nerve activity (15 Ϯ 3% at 2 min postinjection), and phrenic discharge amplitude (31 Ϯ 4% at 10 min postinjection). Cts increased sympathetic barosensitivity 40% (slope increased from Ϫ0.05 Ϯ 0.01 before Cts to Ϫ0.07 Ϯ 0.01 after Cts) and attenuated the somatosympathetic reflex [1st peak: 36% (from 132 Ϯ 32.1 to 84.0 Ϯ 17.0 V); 2nd peak: 44% (from 65.1 Ϯ 21.4 to 36.6 Ϯ 14.1 V)] and chemoreflex (blood pressure response to anoxia decreased 55%, sympathetic response decreased 46%). The results suggest that Cts activates sympathoexcitatory bulbospinal neurons in the RVLM and plays an important regulatory role in adaptive reflexes. baroreflex; hypoxic chemoreflex; Sprague-Dawley rat; chromogranin A THE CATECHOLAMINE release-inhibitory cleavage product of chromogranin A (CgA) was identified and named catestatin (Cts) in 1997 (23). Cts inhibits ACh-and nicotine-induced catecholamine secretion in cell culture (21, 23), and studies in humans suggest that it may play an important role in hypertension (38).Cts is unusual in its ability to function as an antagonist at neuronal nicotinic ACh receptors (nAChRs) and, possibly, other receptors, such as ␤-adrenoceptors and histamine H 1 receptors (8,14,25), as opposed to directly activating specific "Cts" receptors, as seen with other neurotransmitters and neuropeptides. Here we investigate the distribution of Cts in catecholamine-containing neurons of the brain stem and the physiological effects of Cts following microinjection into the rostral ventrolateral medulla (RVLM). The RVLM comprises a heterogeneo...

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