WO2001049176A1

WO2001049176A1 - Method and device for determining and/or treating congenital deafness

Info

Publication number: WO2001049176A1
Application number: PCT/GB2001/000028
Authority: WO
Inventors: James Dexter; Steve Evans
Original assignee: The Babycalm Partnership
Priority date: 2000-01-05
Filing date: 2001-01-05
Publication date: 2001-07-12
Also published as: AU2690101A

Abstract

There is described a method of detecting and/or measuring congenital deafness in an infant which comprises applying a 'pulse' pattern in the frequency range 70-700 Hz to an ear of the infant detecting the relaxation response in a portion of a limb. There is also described an instrument comprising an audible sound transmitter adapted to deliver a high frequency 'pulse' wave pattern in the range of from 70 to 700 Hz and a computer programme product adapted to deliver such a high frequency 'pulse' pattern in the range of from 70 to 700 Hz.

Description

METHOD AND DEVICE FOR DETERMINING AND/OR TREATING CONGENTINAL DEAFNESS

This invention relates to a novel method for determining and/or treating congenital deafness in a mammal, e.g. children and apparatus for achieving this. The invention also includes a method for inducing a specific memory in a mammal and apparatus for achieving this.

Congenital deafness, e.g. in children, has long been a problem. It has been established that a common cause of congenital deafness is incomplete development of some or all of the auditory nerves connecting between the cochlea and the brain. Moreover, current methods of determining congenital deafness in a child mean that the disorder is generally not determinable until the infant is approximately 18 months old. by which time the deafness has lead to further problems, including speech and social interaction difficulties. In many cases the first indication of hearing difficulties are detected through speech deficits.

Estimates of the date at which the human foetus begins to hear currently range between 16 and 24 weeks gestational age (GA). depending, ter alia, upon the kind of sound presented and the exact criterion according to which hearing is deemed to be present. At 20 weeks GA. the human cochlea reaches a developmental state similar to that in other mammals when responses to sound can be evoked, and sounds may be encoded and messages sent along the auditory pathways.

Abundant anecdotal evidence exists regarding the effect of sound heard prenatal ly upon the behaviour of the new-born infant. For example, in 16^th century Europe, it was believed that sounds, conversations and especially music heard by the unborn child affected the personality and disposition of the baby after birth.

More recently. Hepper, "An examination of fetal learning before and after birth'^", Irish Journal of Psychology 1991 : 12. 95-107; observed postnatal behavioural reactions to the theme tune of a popular television programme, confirming that the new-born infant is able to recognise a specific piece of music heard only before birth. He used a well-known and popular television theme tune broadcast widely in the UK. The experimental group consisted of mothers who regularly watched Neighbours and the control group of mothers who did not. The experimental group reacted with a reduction in movement and heart rate by comparison to controls. The method confirmed that auditory learning occurs prenatal ly but did not shed light on the gestational stage at which the capacity for hearing and memory develops.

In a later study, Shahidullah & Hepper. "The developmental origins of foetal responsiveness to an acoustic stimulus" Journal of Reproductive and Infant

Psychology 1993; 1 1 : 135-142; found that the human foetus was able to respond to sound generated externally from as early as 19 weeks GA. In their investigation various pure tones ranging from 100 Hz to 3000 Hz were presented to foetuses aged between 19 and 35 weeks. Foetal movements were tracked using ultra-sound techniques. The foetus typically responded to sound with a quickening of movement and an increase in heart rate. Flowever a movement of the foetus in response to sound does not indicate the existence of memory; equally, non-response to sound in behavioural experiments does not imply deafness.

Foetal learning/memory is currently believed to begin at 24 weeks with the establishment of neuronal connections within the cortex. However, we have found that the precortical foetus has the ability to recognise certain sound wave patterns. The use of certain wave patterns has long been used, although not fully understood, in lullabies. Traditionally, lullabies would have been taught to a pregnant female, who will then repeat the lullaby when the infant is born and it would have a noticeable calming effect on the infant.

This process rarely takes place in modern western developed countries although it is still very much the case in less developed countries, for example in Africa and the Far East, e.g. China. More particularly, we have fouid that a precortical foetus has the ability to recognise wave patterns that represent ihe high frequency end of a heart beat pattern. A mammalian heart beat or pulse will generally produce a characteristic frequency output (see Fig. l ). We have established that, in particular, a precortical foetus, that is a foetus at the developmental stage prior to the development of the cortex of the brain (which usually occurs at about 24 weeks gestation) can detect and store in the form of memory descending musical intervals. The recognition behaviour displayed by the new-born to such music first heart prenatally can tell us a great deal about the foetal auditory system. For example, for the new-born to recognise the music it would require an ear and developed cochlea capable of detecting a range of sounds and frequencies, auditory pathways capable of transmitting the encoded sounds to the brain and an area of the brain capable of storing the encoded information in such a way as to allow the encoded and stored information to be recalled at some later date in the form of memory. The existence of memory can be ascertained by the very specific observable and measurable behaviour which is demonstrated by the newborn. Indeed, we have found that such recognition can start to develop as early as 16 weeks in human gestation

More importantly, we have found that the use of a structured 'pulse' of descending musical intervals in the range of between 70 and 700 Hz ( fundamental frequencies) can be detected and stored in a precortical foetus. These memories can trigger recognition behaviour in the infant upon birth. The musical patterns transmitted will have a wide frequency spectrum and this can assist in the stimulation of auditory nerve growth across the hearing range. The postnatal behaviour triggered by the prenatal stimulation can then be used to identify hearing deficits in the new-born.

According to a first feature of the invention we provide a method of detecting and/or measuring congenital deafness in an infant which comprises applying a 'pulse' pattern in the frequency range 70-700 Hz to an ear of the infant detecting the relaxation response in a limb. Our research has also shown that veiy specific non cortical behaviour is associated with recognition of prenatal sounds, in particular musical patterns This makes it possible to identify whether or not a new-born baby has the capacity to hear within any given frequency range by measuring the electrical activity in a limb, preferably the calf muscle, of the infant The methods used capitalise on the fact that, unlike other methods where the baby has to respond to any stimulus by moving, which requires detailed motoi control, in this case the measurement is of relaxation which occurs without the need for detailed motor response or control Therefore if the amount of electrical activity in the calf muscle decreases in response to the sound then a practitioner can be certain that the infant has heard the music

By adjusting the tonal lange and iiequencv of the signal altei birth it becomes possible to test the full range of the baby^'s hearing capacity

The method of invention allows the early recognition of dealness. in an infant and also permits measurement of the extent of the deafness, for example, in many infants the deafness is often only in the high frequency range and once the precise restricted range has been measured steps can be taken to convert high frequency sounds into low frequencv sounds

Thus according to a furthci ieatuie oi the invention we provide a method of treating deafness in an infant which compπses the application ol a hearing aid adapted to convert high fiequency sound into low frequency sound

The low frequency receptors in the cochlea and the low frequency transmission paths within the auditory nerve develop after birth, this makes it possible to correct deficits in the auditory system by focussing on the newly developing pathways making it possible to retrain the brain during the plasticity period of development b> utilising the low frequency system as high frequency transmitters It is an especially advantageous feature of the present invention that the treatment can be applied to very young infants, i.e. less than two years of age, or 18 months old or less, or 12 months old or less, or even less than 6 months old. or as envisaged within three days of the birth, prior to hospital release.

We have also found that in pregnant mothers who have a history or risk of congenital deafness the frequency range of the musical patterns can act to enhance the auditory environment and act as a stimulus to the growth of auditory nerves both in the brain and the cochlea. Moreover, the wave pattern also introduces pattern recognition in the auditory thalamic region of the thalamus of the precortical foetus. Thus, if the same pattern is replayed to the infant in which the pattern recognition has been established this can produce a specific memory response, usually of comfort or calmness.

Thus according to a further feature of the invention we provide a method of inducing the development of the auditory nerves in a foetus which comprises exposing the foetus to a high frequency 'pulse' wave pattern.

The high frequency sound is preferentially in the range of from 70 to 700 Hz. We also provide an instrument, e.g. an audible sound transmitter, adapted to deliver such a wave pattern. Conventionally known instrumentation may be used but programmed to deliver the desired high frequency 'pulse' wave pattern. Therefore, according to a further feature of the invention we provide a computer programme product adapted to deliver a high frequency 'pulse^' pattern.

We also provide an instrument, e.g. an audible sound transmitter, programmed with a computer programme as hereinbefore described.

According to a further feature of the invention we provide a method of inducing a specific memory in the auditory thalamic region of the thalamus of a mammal, e.g. a human, which comprises the steps of: (i) exposing a precortical mammalian foetus to a wave pattern between 16 and 24 weeks gestation (for a human foetus);

(ii) exposing the mammalian infant to the same wave pattern within the first five weeks (for a human infant) after birth; and

(iii) subsequently exposing the mammal to the same wave pattern and frequency at the desired time so as to produce a specific memory response.

The induction of a specific memory response may utilise a wide variety of music of varying tones, wavelength band widths, vibroacoustic or airborne presentations. Thus the sound may be encoded so as to effectively send one or more messages along the auditory pathway. As such, the method of the invention may have very wide utility. In the most preferred embodiment of the invention the method is used to enable babies and infants to be calmed when in a stressed state. Thus the wave pattern is selected so as to reflect a pulse pattern as hereinbefore described.

According to a further feature of the invention we provide an instrument suitable for use in the preferred method of the invention.

The instrument is preferably adapted to operate over a frequency range of from 70 to 700 Hz, not including the frequencies of any natural harmonics.

The overall volume range of the instrument of the invention is preferentially set at a fixed level for all operations. Thus the minimum level is 70db and maximum is 90db output. Thus, the instrument may have an output average volume of 88db and the tolerance of the volume level is l Odb. The average volume of 88 dB ensures that the sound will be heard by the foetal ear but not be damaging to the developing auditory system. The instrument of the invention is preferably adapted to play one or two musical compositions. Although the du -ation of these compositions may vary, each is preferably up to 10 minutes in curatbn. Furthermore, the instrument may be adapted to record, store and replay a message of up to 3 minutes duration. The recording, storing and replaying means with which the instrument is provided may comprise any conventional means known er se. Such means would be readily know to one skilled in the art.

The device instrument of the invention may be mains powered and/or battery powered, although a battery powered version is preferred. Importantly, the instrument is self contained requiring no external connections for normal operation.

Such a device preferentially comprises a computer programme product as hereinbefore described.

In the context of this application 'High Frequency' is intended to be viewed as the higher frequencies within the audible vocal range. 'Low frequency^' is also to be viewed in the same way.

According to a further feature of the invention we provide the use of an audible sound transmitter adapted to deliver a high frequency 'pulse' wave pattern in the manufacture of an instrument as hereinbefore described.

The invention will now be described by way of example only.

Example 1

Ontogenesis of auditory perception and memory at twenty weeks' gestation Fifteen pregnant women participated voluntarily. Ten were recruited at about 12 weeks GA and were allocated to the Experimental Groups. Five were recruited at about 36 weeks GA and were allocated to the Control Group.

Three pieces of traditional folk music, here called Music A. B and C. were selected according to the following criteria: (i) they include frequent repetitions of melodic- rhythmic fragments; (ii) they sound characteristically different from one another: and (iii) each piece sounds homogeneous, without changes of texture, tempo or mood. None of the music had been heard by the participating mothers prior to the experiment.

The 10 experimental mothers were each given 2-cassette tapes, one of Music B and one of Music C. The music on each tape lasted for 16 minutes. Each mother was asked to listen to the whole of one tape each day during her 2 P¹ gestational week (i.e., 7 times, from GA = 20 weeks to GA = 21 weeks obstetric date). The other tape was listened to during the 31 ^s' week. Exact listening times and comments were recorded in a diary. Cassette tapes were returned to the experimenters at the end of each experimental week.

Five of the experimental mothers ( Experimental Group 1 ) heard Music B during week 21 and Music C during week 31 . The other 5 (Experimental Group 2) heard Music C during week 21 and Music B during week 31. The 5 control mothers heard neither piece prior to postnatal testing.

Experimental mothers were asked to adjust the sound level of the music to be "loud enough to be heard above a washing machine on the spin-dry cycle and yet not loud enough to annoy the neighbours^"'. Our intention was to achieve time-averaged SPLs in the range of 70 to 90 dB with a minimum of technical intervention, given that: (i) sounds reaching the foetal ears from outside the mother^'s body are affected very little (attenuated or enhanced by only a few dB) below about 500Hz. with attenuation growing by a few dB per octave toward higher frequencies; and (ii) the 20-week foetus, if sensitive to sound, is most sensitive to a narrow range of frequencies centred near 250 Hz. The music produced by the cassette player both during prenatal exposure and postnatal testing covered a wide range of spectral frequency.

All babies were born healthy and without complications. Two to three weeks after birth, all babies heard a tape recording of all 3 pieces of music. Babies were observed individually, and heard each piece of music once only. The tape lasted for 18 minutes and was the same for all babies. It consisted of 3 minutes of silence. 3 minutes of Music A (control music), 3 minutes of silence, three minutes of Music B. 3 minutes of silence, and 3 minutes of Music C. Three minutes may be regarded as the minimum period required to accurately determine a baby's behavioural state. The experiment began when the mother considered the baby to be happy and attentive.

The baby lay next to a portable tape player, parallel to the body at a distance of about 0.7 m. Side-mounted speakers played the music at a comfortable level (50-60 dB SPL at the baby's head). The baby was video-recorded throughout. Both experimenter and mother were present. Mothers remained quiet during stimulus presentation but were free to signal if they wished to interrupt, for example if the baby became distressed. If an interruption occurred the presentation continued from the beginning of the preceding silent period. There were 6 such interruptions: 1 baby from the Control Group (restarting in silent period 3). 2 from Experimental Group 1 ( 1 restarting in silent period 2 and 1 restarting in silent period 3) and 3 from Experimental Group 2 (2 restarting in period 2, and 1 in period 3).

Behavioural states were assessed using leg movements as a measure of overall movement. Kicks are clearly visible and can be easily defined for observational analysis as moments of maximum leg extension. Each video was watched without interruption by two independent observers, who recorded each individual leg kick for each leg separately. Observers were unfamiliar with the study and did not hear the video soundtracks. The number of kicks during each 3 -minute period were counted and averaged over the two legs and the 5 babies in each group. Kick counts were normalised by dividing by the total number of kicks in the session and multiplying by 6, the number of 3- minute periods.

As previously observed, babies kicked more frequently during silent periods than during music, E(l ,72) = 23, P < 0.001. Kick rates during each silent period were consistent for each baby, E(2.36) = 0.03, P = 0.98. nor did kick rates vary across the 3 groups, E(2.36) = 1 .4. P - 0.26. Data for silent periods were therefore omitted from subsequent analysis.

The pattern of results for the 3 different musical periods differed between the 3 groups. E(4,36) = 5.8. P < 0.002; kick rates for the control group steadily increased (presumably, an effect of habituation to unfamiliar sounds) whilst the kick rates for the experimental groups remained roughly constant or decreased. By comparison to the control babies, the experimental babies reacted to Music B and Music C (heard before birth) with a highly significant reduction in kick rates, E(2,24) = 12.6, P < 0.001. On average, kick rates for control babies were more than twice those of both experimental groups. Thus, as previously observed, prenatal exposure to music affected postnatal behaviour, with kick rates decreasing in response to familiar stimuli.

The existence of both hearing and memory is widely accepted at 30 weeks GA, enabled by relatively advanced neuronal connections, but disputed at 20 weeks GA. On this basis, we had expected the foetus to be more capable, of hearing, encoding, and remembering patterns of sound at 30 weeks than at 20 weeks. Our results failed to support this prediction. When kick counts during presentations were summed separately over all babies who had been exposed to that music during week 21 and week 31. no significant difference was observed, E(1.19) = 2.0, P = 0.17. This result is consistent with an ontogenesis for both hearing and memory prior to 20 weeks GA. At twenty weeks GA. neurone I connections in the cortex have yet to develop. On this basis it is highly unlikely that the auditory cortex played any role in memory for the auditory stimuli presented during week 21. Between weeks 16 and 26 the ascending pathways from the cochlea nerve to the inferior colliculus undergo extensive expansion and collateralization. Higher nuclei in the auditory pathways in the region of the inferior colliculus and the auditory thalamus may have memory capacity. Due to the earlier development of myelinisation in the auditory pathways than in other sensory systems and the resultant higher processing speed achieved, the region of the inferior colliculus and the auditory thalamus may play an important role in auditory perception and memory, at least until the end of the first postnatal year.

Claims

1 . A method of detecting and/or measuring congenital deafness in an infant which comprises applying a 'pulse^' pattern in the frequency range 70-700 Hz to an ear of the infant detecting the relaxation response in a portion of a limb.

2. A method according to Claim 1 characterised in that the portion of a limb is a calf muscle.

3. A method according to Claim 1 characterised in that the relaxation response is an electrical activity response.

4. A method according to Claim 1 characterised in that by adjusting the tonal range and frequency of the signal the lull range of a baby^'s hearing capacity is measured.

5. A method of treating deafness in an infant which comprises the application of a hearing aid adapted to convert low frequency sound into high frequency sound or high frequency sound into low frequency sound.

6. A method according to Claim 5 characterised in that the treatment is applied to an infant of less than two years of age.

7. A method of inducing the development of the auditory nerves in a foetus which comprises exposing the foetus to a high frequency 'pulse" wave pattern.

8. A method according to Claim 7 characterised in that the high frequency sound is preferentially in the range of from 70 to 700 Hz.

9. An instrument comprising an audible sound transmitter adapted to deliver a high frequency 'pulse' wave pattern in the range of from 70 to 700 Hz.

10. A computer programme product adapted to deliver a high frequency 'pulse' pattern in the range of from 70 to 700 Hz.

1 1. An instrument comprising an audible sound transmitter programmed with a computer programme according to claim 10.

12. A method of inducing a specific memory in the auditory thalamic region of the thalamus of a mammal, e.g. a human, which comprises the steps of;

(i) exposing a precortical mammalian foetus to a wave pattern between 16 and 24 weeks gestation (for a human foetus);

13. A method according to Claim 12 characterised in that a wide variety of music of varying tones, wavelength band widths, vibroacoustic or airborne presentations is used.

14. A method according to Claim 12 characterised in that the sound is encoded so as to effectively send one or more messages along the auditory pathway.

15. A method according to Claim 12 characterised in that it enables a baby or infant to be calmed when in a stressed state.

16. A method according to Claim 12 characterised in that the wave pattern is selected so as to reflect a pulse pattern.

17. An instrument suitable for use in conjunction with the method of claim 12.

18. An instrument according to Claim 17 characterised in that the instrument is adapted to operate over a frequency range of from 70 to 700 Hz.

19. An instrument according to Claim 17 characterised in that it is adapted to operate at a volume level of no greater than 88 dB.

20. An instrument according to Claim 17 characterised in that it comprises a computer programme product according to claim 10.

21. The use of an audible sound transmitter adapted to deliver a high frequency 'pulse' wave pattern in the manufacture of an instrument according to Claim 17.

22. A method or an instrument substantially as described with reference to the accompanying examples.