Maturation of fetal responses to music.

Maturation of fetal response to music was characterized over the last trimester of pregnancy using a 5-minute piano recording of Brahms' Lullaby, played at an average of 95, 100, 105 or 110 dB (A). Within 30 seconds of the onset of the music, the youngest fetuses (28-32 weeks GA) showed a heart rate increase limited to the two highest dB levels; over gestation, the threshold level decreased and a response shift from acceleration to deceleration was observed for the lower dB levels, indicating attention to the stimulus. Over 5 minutes of music, fetuses older than 33 weeks GA showed a sustained increase in heart rate; body movement changes occurred at 35 weeks GA. These findings suggest a change in processing of complex sounds at around 33 weeks GA, with responding limited to the acoustic properties of the signal in younger fetuses but attention playing a role in older fetuses.

Maternal depression and increased fetal activity.

Pregnant women with (n = 45) and without (n = 45) symptoms of depression (CES-D score of 16 or more) were provided ultrasound examinations during the second and third trimesters. An analysis of variance on the cross-sectional data yielded a significant diagnosis by gestational month interaction effect (P < 0.05). The fetuses of depressed mothers spent significantly more time being active during the fifth, sixth and seventh gestational months than fetuses of non-depressed mothers. A stepwise regression analysis revealed that 35% of the variance in time being active could be accounted for by the combined depression and trait anxiety scores of the mothers. These findings suggest that maternal depression correlated with increased fetal activity. These data also highlight the need for research on the potential effects of stress hormones on fetal activity.

Fetal discrimination of low-pitched musical notes.

Cardiac responses of 36- to 39-week-old (GA) fetuses were tested with a no-delay pulsed stimulation paradigm while exhibiting a low heart rate (HR) variability (the HR pattern recorded when fetuses are in the 1f behavioral state). We examined whether fetuses could discriminate between two low-pitched piano notes, D4 (F(0) = 292 Hz/292-1800 Hz) and C5 (F(0) = 518 Hz/518-300 Hz). Seventy percent of all fetuses reacted to the onset of the first note (D4 or C5) with the expected cardiac deceleration. After heart rate returned to baseline, the note was changed (to C5 or D4, respectively). Ninety percent of the fetuses who reacted to the note switch did it with another cardiac deceleration. Control fetuses, for whom the first note did not change, displayed few cardiac decelerations. Thus, fetuses detected and responded to the pulsed presentation of a note and its subsequent change regardless of which note was presented first. Because perceived loudness (for adults) of the notes was controlled, it seems that the note's differences in F(0) and frequency band were relevant for detecting the change. Fetuses' ability to discriminate between spectra that lay within the narrow range of voice F(0) and F(1) formants may play an important role in the earliest developmental stages of speech perception.

What sounds reach fetuses: biological and nonbiological modeling of the transmission of pure tones.

In utero transmission of external and maternal sounds has been studied in pregnant women and in an animal model of human species, the sheep. These works, especially the most recent ones, suggest that local and environmental factors interfere in such a way that signals are attenuated in a complex manner as frequency increases. The present work investigated whether a plain rubber sphere which was filled with water could be considered as a reliable nonbiological model in a study describing the characteristics of sound transmission. A sweeping pure tone, presented externally, was measured inside the rubber sphere using a high signal-to-noise ratio experimental hydrophone. A paradigmatic three components curve was observed between 100 and 20,000 Hz. In the first component of the curve (low to midfrequencies between 100 and 1,000 Hz), the intensity of the inside signal remained stable. The second component of the curve was composed of higher frequencies with the inside pressure falling gradually, demonstrating attenuation of the external signal. The third component of the curve appeared above a critical frequency, the value of which depended on several model and environment parameters. In this component, a series of rapid peaks and drops of the inside high frequency pressure was observed, indicating the presence of resonance systems. Analyses were carried out on the effects of several acoustical parameters, including: the size of the sphere, the location of the hydrophone in the sphere, the distance between the signal source and the hydrophone, the location of the external reference microphone, and the acoustical structure of the environment. These parameters allowed for the definition of their respective roles in the in-utero transmission of external sounds. These data were then compared with measurements performed within a biological model--ewes--under close acoustical settings. The comparisons confirmed the validity of the measurements, suggesting that the model may be useful in studies of sound transmission in utero.

Fetal sensory competencies.

A growing body of evidence is available about the functioning of fetal sensory systems during gestation. This article aims at reviewing data concerning (i) the presence of potential sensory stimulation in the fetal milieu, (ii) the sequential functional development of the sensory systems and (iii) physiological and behavioral responses of fetuses to various types of stimulation. Human data are compared with data collected in other mammalian species. Most studies have investigated auditory and chemosensory (olfactory and gustatory) responsiveness of the fetus in the second half of gestation. They demonstrate that (i) motor and heart rate responsiveness depends on gestational age and characteristics of stimulation; (ii) fetal sensory experience has short- and long-term effects at morphological, functional and behavioral levels (for example transnatal learning). The clinical consequences of the fetal sensory functioning are developed.

Decelerative cardiac responsiveness to acoustical stimulation in the near term fetus.

Human fetal cardiac responses (36-39 weeks gestational age) to brief, repeated vocal stimuli (male or female voice uttering the same sentence), given at 90-95 dB SPL ex utero (around 20-30 dB less in utero) during a state of low fetal heart rate (FHR) variability, were examined using highly conservative statistical criteria taking into account each subject's prestimulus FHR variability. Subjects exposed to either of the two stimuli displayed significantly more decelerative heart rate (HR) changes compared to control subjects receiving no stimulation. The decelerative changes started during the first seconds following the onset of stimulation and reached their amplitude peak within 10 or 20 sec, depending on the subject. The direction--HR acceleration or deceleration--and the amplitude of the response depended on prestimulus HR variability only, not on prestimulus level. No major difference was found between the effects of the two voices. The data are compared to previous studies demonstrating fetal decelerative changes to acoustic stimuli of less than 105 dB SPL. The choice of an objective criterion to define an HR response and the possible orienting response nature of the decelerative change are discussed.

[Nasal chemoreception in utero: preliminary experiences in fetal sheep]. / Chimioréception nasale in utero: expériences préliminaires chez le foetus ovin.

Intranasal injections of a fragrant solution of 2-methyl-2-thiazoline elicited significant heart rate decelerations in late pregnancy fetal sheep, while the injection of a control fluid (isotonic saline) had no effect. This result indicates that the ovine fetuses are able to detect nasally administered odorants, as previously demonstrated in the fetuses of murine rodents.

Fetal cardiac and motor responses to octave-band noises as a function of central frequency, intensity and heart rate variability.

Accelerative and decelerative cardiac responses and motor responses (leg movements) of 37-40 weeks (G.A.) fetuses are analyzed as a function of the frequency of three octave-band noises (respectively centered at 500 Hz, 2000 Hz and 5000 Hz) and of their intensity level (100, 105, 110 dB SPL, ex utero), during high (HV) and low (LV) heart rate (HR) variability pattern states. In both states, increasing the frequency and/or the intensity of the acoustic stimulation: (i) increases the ratios and amplitudes of accelerations, and the motor response ratios, (ii) reduces deceleration ratios and motor response latencies. Cardiac and motor reactiveness are higher in HV than in LV with acceleration ratios always greater than motor ones. However, when a high intensity and/or frequency is used, the reactiveness differences between states disappears. Low intensity and/or frequency stimulation levels induce a majority of decelerations.

[Fetal perception and discrimination of speech stimuli; demonstration by cardiac reactivity; preliminary results]. / Perception et discrimination foetales de stimuli langagiers; mise en évidence à partir de la réactivité cardiaque; résultats préliminaires.

Human fetuses (35-38 ws GA), exposed to a repeated pair of syllables, either [ba] [bi] or [bi] [ba], at 95 dB SPL when in a low heart rate variability state, display a significant heart rate deceleration. Changing the order of the syllables in the pair, [ba] [bi] becoming [bi] [ba] (or the reverse), induces a new cardiac deceleration. This suggests that fetuses demonstrate auditory discrimination abilities for speech units like syllables.

Fetal responses to acoustic stimulation depend on heart rate variability pattern, stimulus intensity and repetition.

Fetuses (37-40 wks DA) were exposed to three successive presentations of a 5-s high-pass filtered (800 Hz) pink noise either at 105 dB or at 110 dB SPL. Stimulations were given during high or low variability heart rate (HR) patterns (HV or LV) which presumably correspond mostly to active and quiet sleep episodes, respectively. The proportion of fetuses showing cardiac response (CR) was always greater than the proportion showing leg movement (LM) but the presence of an accompanying leg movement always increased the amplitude of CR, independent of HR pattern, stimulus repetition and intensity. Fetal reactiveness always diminished with stimulus repetition but diminished more on the three examined dimensions (CR ratio, LM ratio and CR amplitude) with LV infants than with HV infants, and more with the 105 dB stimulus than with the 110 dB stimulus. More importantly, stimulus parameters and HR patterns interacted. At 110 dB in HV, neither the median amplitude of the CRs nor the probability of a CR changed over trials but the probability of a concommittant LM decreased. At 110 dB in LV, repetition induced a decrement on all three response dimensions from the second trial onwards. At 105 dB in HV, LM decreased rapidly, as much as at 110 dB in LV. Thus, state, as reflected by HR pattern, plays a significant role in determining the occurrence and the amplitude of the CR and the occurrence of a LM which, in turn, will enhance the CR amplitude.

Feasibility of prenatal hearing test.

Variability in foetal responses to sound stimulations is described and the effect of the different factors involved in this reactivity, in particular the physical characteristics of the stimulus and state of alertness of the foetus, is discussed. Results obtained with a high pass filtered pink noise at a 106, 109 and 113 dB SPL on 37-40 week foetuses are given to illustrate this dependency. For all tested levels, responsiveness was reduced after repetition of the stimulus. This was observed even at 113 dB when stimulation was preceded by a series of lower level stimuli to which foetuses were (or became) unresponsive. Motor responses (lower limb movements) were the first and the most affected by stimulus repetition, followed by cardiac response decrement--but with a lower proportion of non-responses, especially at 113 dB. Consequently, with this specific stimulus, cardiac reactivity seems a more reliable parameter to examine when more than one stimulus is needed to ascertain foetal hearing. It was also demonstrated that foetuses were much less reactive when stimulated during low heart rate variability sequences than during high heart rate variability. Testing of prenatal hearing seems feasible in utero and should be a promising method for detecting gross hearing impairment once the influence of each biophysical parameter has been carefully studied.

Selective effects of post-imprinting anaesthesia on choice-test behaviour.

Day-old chicks which are submitted to a halothane anaesthesia immediately after a 10 min. exposure to a moving model are less likely than non-treated chicks to approach this model in subsequent tests given 24 and 48 hours later. They may be unable to approach any model or they may approach the other model presented in the test situation. Modulation of responses at test depends on strength of imprinting which itself depends on attractiveness of the model and amount of following displayed during the exposure session. Results of this experiment corroborate previous results showing disruptive effects of halothane anaesthesia on behaviour in imprinted chicks, effects which are stronger if chicks had a poor visuo-motor experience at exposure session. Imprinting as a gradual acquisition process is suggested by detailed analysis of results of control and treated chicks.