Influence of auditory experience on the development of brain stem auditory-evoked potentials in mallard duck embryos and hatchlings.

The development of brain stem auditory-evoked potentials (BAEP) was studied in devocalized ducklings reared in auditory isolation and in vocal ducklings exposed to enhanced species-specific auditory stimulation with embryonic contact-contentment calls (CTs). Thresholds and latency of BAEP wave P1 in the mute ducklings indicated that even short-term auditory deprivation affected the development of auditory sensitivity, substantially reducing the rate of decline in BAEP thresholds and latencies of P1, especially in the low-frequency (500 and 750 Hz) and high-frequency (above 2.0 kHz) ranges. The ducklings exposed to enhanced stimulation, on the other hand, showed an accelerated decline in BAEP thresholds and latencies of P1 across all test frequencies, with the most marked influence on low (below 1.5 kHz) and high (above 2.5 kHz) frequencies. The influence of species-specific auditory experience had its most potent effect during the embryonic critical period for postnatal auditory perceptual (behavioral) development, at which time the embryo produces and hears a special low-frequency (1.5-2.5 kHz) version of its own contact-contentment vocalization.

Development of brainstem auditory pathway in mallard duck embryos and hatchlings.

The development of the brainstem auditory evoked potential (BAEP) was studied in mallard duck (Anas platyrhynchos) embryos and hatchlings from 5-6 days before hatching through two days after hatching in response to tone pips of different frequencies. BAEPs showed a different time of onset and a different rate of development for low, middle, and high frequencies. Although auditory sensitivity in the mid-frequency range (1.0, 1.5, 2.0, and 3.0 kHz) appeared 1-2 days later than in the low-frequency range, development of the BAEPs in the mid-frequency range was almost complete by hatching. In contrast, the development of auditory sensitivity in the low- and high-frequency ranges continued to develop after hatching. Accelerated development of BAEPs to middle frequencies during the embryonic period and to high frequencies after hatching was correlated with the ducklings' exposure to their own mid-frequency and high-frequency vocalizations before and after hatching, respectively.

Development of auditory sensitivity of altricial birds: absolute thresholds of the generation of evoked potentials.

The thresholds of the generation of EP in the L field of two to nine day old pied flycatcher nestlings in response to monotonal bursts of varied frequency were investigated. The entire range of auditory sensitivity was divided into three channels on the basis of the character of the age-related dynamics of the thresholds (two to nine days of life): low-frequency (0.3-1.6 kHz), middle- (1.5-4.0 kHz), and high-frequency (5.0-8.0 kHz). Widening of the auditory range in the direction of high frequencies on the 4th to 5th days of nest life was demonstrated. It was shown that the development of auditory sensitivity continues in all three channels in the post-embryonic period (two to nine days after hatching), and that each of these is characterized by its own thresholds time course.

[The development of hearing sensitivity in altricial birds: the absolute thresholds of the generation of evoked potentials]. / Razvitie slukhovoi chuvstvitel'nosti nezrelorozhdaiushchikhsia ptits: absoliutnye porogi generatsii vyzvannykh potentsialov.

Thresholds of field L auditory evoked potentials EP were studied in 1.5-9-day-old nestlings of pied flycatcher in response to pure tone signals of different frequencies. According to the tendencies of age dynamics of auditory EP thresholds (2-9 days of life) all hearing range was divided into three separate channels: low-frequency (0.3-1.0 kHz), intermediate-(1.5-4.0 kHz) and high-frequency (5.0-8.0 kHz) ones. The widening of the hearing range in its high-frequency part was demonstrated on days 4-5 of life. The development of auditory sensitivity was shown to continue within all three channels in postembryonic period (days 2-9 post-hatching), each of the channels being characterized by its own age dynamics of auditory EP thresholds. Reproduction of tape-recorded species song during days 1-3 post-hatching resulted in significant decrease of auditory EP thresholds.

[Role of a species-specific acoustic environment in the development of hearing in nestlings]. / Rol' vidospetsificheskoi akusticheskoi sredy v razvitii slukha ptentsov.

Main parameters were studied of the acoustic evoked potentials (EPs) from L field of the caudal neostriatum of altricial nestlings of 2-8 days to pure tones in the range of species-specific signals. It has been established that auditory EPs to the tones of different frequencies differ by the terms of appearance and the degree of maturity. At every of the revealed stages of the auditory ontogenesis, including the stage of completely formed auditory sensitivity, such parameters of auditory EPs, as latencies of different phases, amplitude-temporal pattern and the course of recovery curve are different for the tones of different frequencies. The earliest to appear are the responses to the tones 0.2-4.0 kHz, corresponding to the energy of alimentary signals. Responses to tones of higher frequencies corresponding to the spectrum of other species-specific signals appear later, but the speed of their formation is higher than in the responses to the tones of low frequencies. It is suggested that the higher speed of sensitivity maturation in the high-frequency region is determined by ecologically conditioned afferentation, the function of which is fulfilled by nestlings own vocalization.

[Relation between the defensive behavior of altricial nestlings and the parameters of an alarm signal. Neuroethologic approach]. / Zavisimost' oboronitel'nogo povedeniia nezrelorozhdaiushchikhsia ptentsov ot parametrov signala trevogi. Neiroétologicheskii podkhod.

The acoustic organization of the defensive behaviour was studied in Pied Flycatcher nestlings. Electrodes were chronically implanted into the field L and the neck muscles for auditory EPs and EMG recordings. A well developed defensive reaction which under natural conditions is elicited by species-specific alarm call, could be artificially provoked by monotonal 4.5-6 kHz bursts with repetition frequency of 4-0,8/s. The tone frequency was shown to be the critical acoustic parameter permitting the altricial nestlings to identify alarm vocalization and differentiate it from alimentary signals. The role of the burst repetition frequency is restricted to maintaining the tonic defensive activation in the course of the alarm signal presentation. Certain correlation was found between the time of regeneration of excitability in auditory structures and the burst repetition frequency in the species specific alarm signal.

[Formation of visual evoked potentials and development of visually guided behavior in the Ficedula hypoleuca nestling]. / Formirovanie zritel'nykh vyzvannykh potentsialov i razvitie zritel'no napravliaemogo povedeniia ptentsov duplognezdnikov.

Age dynamics of evoked potentials (EPs) of Wulst area of the dorsal hyperstriatum (functional analogue of mammalian visual cortex) was investigated in 2-7 days old nestlings. EPs in response to light stimuli, with the duration and intensity imitating natural alimentary signals for 5-7 days-old nestlings, were recorded parallel with the behaviour. It was found that the development of the visual system in precocious nestlings became completed in postembryonal ontogenesis. The most essential changes in the parameters of visual EPs occur between 2.5 and 4 days of nest life. By the end of the 4-th day the EPs parameters resemble those of the definite EPs. During the same period the visually directed form of the alimentary behaviour appears for the first time. Both the visual EPs and the visually directed alimentary behaviour first appear in the ontogenesis in response to the second component of two-fold luminosity change--the natural signal of alimentary behaviour.

[Auditory evoked potentials and acoustically-directed behavior of nestlings]. / Slukhovye vyzvannye potentsialy i akusticheski-napravliaemoe povedenie ptentsov.

Characteristics of auditory evoked potentials (EP) were studied in 1.5 to 7.5 days old Pied Flycatchers nestlings (Ficedula hypoleuca) with chronically implanted electrodes in the field L (analogue of the mammal's auditory cortex). EPs simultaneously with behaviour were recorded in nestlings under conditions similar to natural, in response to "feeding" calls and pure tones of different frequency and intensity. It was found that EP generation thresholds do not depend on the sum total of factors which influence the organization of feeding behaviour. The EP generation threshold is by 13-36 dB (for different frequencies) below that of the appearance of feeding responses in nestling with a maximum high motivation. It is suggested that the realization of inborn behaviour with a signal basis needs not only an integration (formed in the process of embryogenesis) of a definite sensory input with a complex of structures of the "feeding centre", but also the presence of a massive modality-specific inflow.

[Visual evoked potentials of fledglings to ecologically significant stimuli]. / Zritel'nye vyzvannye potentsialy ptentsov na ékologicheski znachimye stimuly.

A study was made of the structure of evoked potentials in the Wulst of the dorsal hyperstriatum in five- to eight-day old nestlings in response to ecologically determined visual stimuli significant for the alimentary behaviour, within the range of their intensity natural fluctuation. It was established that the parameters of the visual evoked potentials correlate with the rate of behaviour manifestation, which depends on the level of alimentary motivation. At a low motivation level (and under Nembutal anaesthesia), latencies of all response components depend on the energetic parameters of the stimuli and to a maximum degree so -- the primary component latencies. At a high level of alimentary motivation, dependence of the response components latencies on the stimuli parameters is pronounced to a much lesser degree, and still less for the primary component. It is assumed that when the subsequent behavioral response is present, evoked potentials are more linked to the processes of organization and realization of behaviour than to the parameters of affective stimulation.

[Development of species specific acoustic sensitivity in hole-nester fledgelings]. / Razvitie vidospetsificheskoi zvukovoi chuvstvitel'nosti u ptentsov duplognezdnikov.

A study was made of acoustic sensibility of hole nestlings to species-specific signals of adult birds. It has been established that the final formation of sensibility to such signals is not completed in the embrional period of development, but continues, at least during the first half of life in the nest. In the embrional period, the formation of sensibility is concluded only within the spectrum of the "alimentary" signal complex, providing for adequate alimentary behaviour of the nestlings immediately after hatching. In the early postembrional period, the formation of acoustic sensibility in the spectrum of other species-specific signals (alarm signals) is completed in parallel with the organization of behavioral reactions controlled by these stimuli.

[Role of natural sensory factors in organization of feeding behavior using fledgling development as an example]. / Rol' estestvennykh sensornykh faktorov v organizatsii pishchevogo povedeniia na primere razvitiia ptentsov

A change in the composition of natural sensory stimuli, triggers of the alimentary functional system of Muscicapa hypoleuca nestlings, was studied throughout their nest life. In the first five days the alimentary reaction is elicited by a complex of acoustic stimuli. From the fifth to the eighth day the reaction appears in response to a momentary change of illumination. From the ninth to the thirteenth day two stimuli are involved in the organization of the alimentary reaction: a trigger stimulus-a momentary change of illumination, and a directional stimulus-a mobile silhouette of the bird. On the thirteenth to the fifteenth day the alimentary reaction appears only in response to the bird's movement. It is assumed that the successive change of trigger stimuli in one and the same alimentary functional system is determined by a successive involvement of increasingly complicated sensory mechanisms. The time periods of involvement may vary with a change of environmental factors.