Jean-Pierre Lecanuet

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.

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.

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 subjects 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 directions—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.

Effects of post-exposure anaesthesia on the retention of imprinting.

Chicks anesthetized immediately, 6 min or 15 min after the end of a 20-min imprinting session show significantly less following behavior than untreated controls, when tested 3 days later. The results are interpreted in terms of consolidation disruption, implying a consolidation period of at least 15-min duration for this type of perceptual learning.

Retroactive and proactive effects of anaesthesia on following in chicks

Abstract Halothane anaesthesia, administered after imprinting session in day old chicks, produces 2 different effects on the following response behavior tested 3 days later. First, it delays the onset of the following response for animals treated immediately after imprinting. Second, it disturbs the general performance of the following response, an effect apparently unrelated to the time of treatment. We suggest that only the first of these effects reflects a disturbance of retention.