Yawning: no effect of 3-5% CO2, 100% O2, and exercise.

Using human college-age subjects, the present study tested the commonly cited but previously untested hypothesis that yawning is facilitated by higher than normal levels of CO2 or lower than normal levels of O2 in the blood by comparing the effect on yawning of breathing 100% O2 and gas mixtures with higher than normal levels of CO2 (3 or 5%) with compressed air, the control condition. If yawning is a response to heightened blood CO2, the CO2 mixtures should increase yawning rate and/or duration. If low blood O2 produced yawning, breathing 100% O2 should inhibit yawning. The CO2/O2 hypothesis was rejected because breathing neither pure O2 nor gases high in CO2 had a significant effect on yawning although both increased breathing rate. A second study found that exercise sufficient to double breathing rate had no effect on yawning. The two studies suggest that yawning does not serve a primary respiratory function and that yawning and breathing are triggered by different internal states and are controlled by separate mechanisms.

Comparative analysis of the development of wing-flapping and flight in the fowl.

The development of wing-flapping rate, lateral flight, wing area, and the ratio of wing area to body weight are described in the Japanese quail (Coturnix coturnix japonica) and three chickens (Gallus gallus) to determine common developmental phenomena and to assess the effects of domestication. The chickens were the White Leghorn (a commercial egg producer), the Cornish X Rock (a commercial meat producer), and the Red Jungle fowl (the probable ancestor of domestic chickens). All birds performed drop-evoked wing-flapping on the day of hatching, at least 1 week before lateral flight was possible. Flapping rate of chickens doubled between hatching (approximately 4-6 Hz) and 13 days (approximately 9-12 Hz), after which it leveled off. Japanese quail (JQ) maintained a high flapping rate (approximately 11-13 Hz) during the 21 days after hatching. The Jungle fowl (JF) and JQ flapped the fastest and the White Leghorn (WL) and Cornish X Rock (CR) chickens flapped the slowest. The JF, WL, and JQ developed lateral flight at 7-9 days. The CR first flew 1-2 weeks later but subsequently became flightless. The WL, JF, and JQ had similar ratios of wing area to body weight; the ratios increased to a peak at 11-15 days and later declined. The ratio of the very heavy, essentially flightless, CR was approximately one-half that of the flighted JQ, WL, and JF. The wing-flapping frequencies of the domestic WL and CR chickens approximated that of the JF, suggesting that domestication did not affect the motor pattern generator for flight. The artificial selection of the CR for high body weight drastically diminished its flight performance by producing an unfavorable ratio of wing area to body weight. The JF and the domestic WL both flew well and had similar ratios. Domestication affected flight performance but not the neural circuitry producing wing-flapping. The central nervous system is much more conservative in its response to selection than the peripheral effector structures that it drives.

Chicken muscular dystrophy: an inherited disorder of flight.

Dystrophic (University of California, Davis, line 413) and normal control (Davis, 1. 412) chicks (Gallus domesticus) between 7 and 49 days old were tested for flight-related pathology and righting ability. Drop-evoked lateral flight developed in control chicks between 7 and 13 days. Dystrophic chicks never developed lateral flight. Both dystrophic and control chicks showed drop-evoked wing-flapping on the day of hatching. Also, dystrophic chicks had a normal but slightly higher drop-evoked flapping rate than controls at 13 days. Thus, the neural circuits that initiated and generated the rate of drop-evoked wing-flapping, present in dystrophic chicks at birth, were intact at 13 days, when deficiencies in lateral flight and righting ability were already present. The righting behavior of control chicks was superior to that of dystrophic chicks at all ages from 7 to 49 days.

Preflight development of bilateral wing coordination in the chick (Gallus domesticus): effects of induced bilateral wing asymmetry.

The performance of bilaterally synchronous wing-flapping by chick hatchlings suggests but does not prove the existence of a bilateral coordinating mechanism. The present research tests for bilateral coordination by using the technique of induced asymmetry. The onset of bilateral wing coordination was defined as the age when induced bilateral asymmetry produced by right wing amputation, immobilization, or weighting influenced the drop-evoked flapping rate of the left wing. Unilateral right wing immobilization or weighting immediately before testing reduced the flapping rate of the contralateral left wing of 3-5 day chicks, the youngest examined. Weighted and unweighted wings flapped synchronously. Therefore, a mechanism which acts across the body midline to synchronize wing-flapping by slowing the rate of the more rapidly flapping wing to match that of its slower contralateral partner was present by 3-5 days. This is several days before the onset of flight. The flapping rate of the left wing of chicks that had their right wing amputated on Day 1 was similar in rate to that of intact chicks when tested at 7 and 13 days. "Wing-flapping" on the amputated side of some unilateral amputees was made visible by a prosthesis attached to the stump of the amputated wing. Bilaterally coordinated flapping in the unilateral amputees indicated that the sensory and trophic periphery of a given wing and flight-related adaptive significance are not necessary for the postnatal production of bilaterally synchronized wing-flapping. However, the slowed flapping produced by unilateral wing weighting or immobilization indicates that wing-flapping rate is modulated by sensory feedback, even at preflight stages.

Wing-flapping develops in chickens made flightless by feather mutations.

Two lines of mutant, domestic chickens (scaleless and delayed feathering), flightless because they lack flight feathers, were used to evaluate the influence of flight-related experience and adaptation on the development of wing-flapping. Most testing was at 13 days because normally feathered control chicks of this age flap at adult rates and can fly. By 13 days, the wing-flapping rates of the flightless, mutant chicks and the normally feathered and flight-competent control chicks were similar. Therefore, normal adult rates of wing-flapping developed in the absence of flight-related behavioral consequences. Drop-evoked wing-flapping was probably initiated by vestibular mechanisms: feather-related mechanoreceptor and visual cues were not necessary because flapping was initiated by naked, scaleless chicks which were deprived of visual input by masking their eyes or by testing in a darkened room. The possible role of feather mutations in the evolution of avian flightlessness is also considered.

Development of wing-flapping and flight in normal and flap-deprived domestic chicks.

Lateral flight evoked by dropping appeared 7-9 days after hatching. Drop-evoked bilaterally symmetrical wing extension and slow, low-amplitude wing-flapping were present by Day 1. Flapping rate measured using strobophotography increased up to approximately 13 days. Normal wing-flapping rates and lateral flight distances were achieved by chicks whose wings were immobilized with elastic bandages from Day 1 until immediately before testing at 13 days, indicating that wing movement is not necessary for the postnatal development of basic wing-flapping and flight. The ratio of wing area to body weight, a morphological index of wing-lift efficiency, rapidly increased up to 13 days and slowly declined through 49 days. The peaking of this ratio at 13 days corresponds to the age at which lateral flight is well established and wing-flapping rate is at its maximum. Thus, the development of wing morphology, wing-flapping rate, and flight are strongly and positively correlated.

Development of between-limb movement synchronization in the chick embryo.

Spontaneous between-limb movement synchronization is described as the amount of concurrent limb movement observed in 7--19-day chick embryos. At early stages, a wing moved as often with the ipsilateral leg as with the contralateral wing. Later, between-girdle (ipsilateral wing-leg) synchronization progressively decreased and within-girdle (wing-wing) synchronization increased, especially after 15--17 days. Bilaterally synchronized movements of the wings as in flapping and of the legs as in walking appeared at embryonic stages. Both wing and leg motility increased between 7 and 13 days and declined until hatching. The wings and legs were equally active except at 17 and 18 days when the wings moved more frequently than the legs. The left and right wings were equally active. These behavioral events reflect developmental changes in the motor outflow of the central nervous system.

Crossing the midline: limits of early eye-hand behavior.

The development of the ability to extend the hand across the body midline to contact a visually presented object was examined in 48 normal, full-term, 9--20-week infants. One of the infant's arms was restrained while the behavior of the contralateral, unrestrained arm was observed. Results indicate that infants can first contact objects placed in front of the ipsilateral shoulder, then at the body midline, and later in front of the contralateral shoulder. Between 9 and 17 weeks, success at contacting objects at the midline progressed from 33% to 93%. During this interval, the success in contacting objects presented in front of the contralateral shoulder increased from 0% to 71%. By 18--20 weeks, all infants contacted objects in all three positions. These findings indicate that visually directed hand extension and reaching skills progress from the ipsilateral to include the bilateral and later the contralateral domains. The results are considered in regard to the development of bilateral coordination and complementarity.

Formation of cockroach interganglionic connectives: an in vitro analysis.

Individual ganglia of the cockroach embryo (Periplaneta americana) were explanted on clean glass coverslips immersed in a chemically defined liquid medium and incubated for periods up to eight weeks. Substantial, straight interganglionic connections were formed between: (1) rows of ganglia arranged in the normal in vivo configuration; (2) rows of ganglia placed in abnormal orders; (3) rows of ganglia which never form connections in vivo because they occur singly in the embryo; and (4) rows of ganglia in natural sequences but which have had their rostro-caudal axes rotated 90 degrees in relation to the line of the row. Therefore fascicles and interganglionic connectives were formed without regard to normal in vivo relationships. Daily observations with a Nomarski microscope indicated that several processes are involved in connective formation. (1) Initial outgrowth is in a random, radial pattern. (2) Intersecting fibers from adjacent ganglia are deflected toward each others' perikarya. (3) Initially bowed fiber connectives are straightened, perhaps by increases in fiber tension or by fiber shortening which may be brought about by neuronal or extraneuronal (glial) processes. (4) Outgrowing fibers follow already established fiber pathways. The present results indicate that fiber-fiber and fiber-target interactions play a significant role in the formation of interganglionic connectives. In this system, the spatial relationships between ganglia determine the patterns and varieties of permissible neuronal connections. Thus, major, straight nerve trunks may be formed between adjacent ganglia which are growing out fibers on a glass surface submerged in a liquid medium which offers minimal orientation cues and provides a growth substrate vastly different and simpler than that encountered by outgrowing fibers in vivo.