Multichannel cochlear implant is the first neural prosthesis to bring electronic technology
effectively and safely into a direct physiological relation with the central nervous
system and human consciousness.[1 ]
Among children, classical candidates to cochlear implantation are those presenting
bilateral severe to profound hearing loss when amplification benefits are limited
to the optimal auditory and language development.[2 ]
[3 ]
Despite the remarkable contribution to the access of speech sounds, cochlear implant
outcomes vary considerably depending on several factors.[4 ] Sharma et al.[5 ] (2002) suggested that a critical period of plasticity existed for developing brain
connections, and early surgical intervention has been indicated ever since. Nevertheless,
just 'opening' the doorway of the brain (the ears) to receive sounds may not be enough
to allow their interpretation.[6 ]
Once the hearing loss is diagnosed, an early intervention program should begin to
promote receptive and expressive language development. This program will require the
child to be educated to maximally use hearing with the cochlear implant.[1 ]
[7 ]
[8 ]
Listening presupposes an intentional activity. In listening, one is actively trying
to focus on some sounds. In contrast, hearing may happen without necessarily paying
attention or intention. It is possible to hear something even when you don't want
to hear it and try not to hear it. The brain pathways used in 'listening' and simply
hearing are different. When listening, in addition to paying attention to what we
hear, it implies finding the pathways that lead to attributing representation to that
sound, that could be a meaning or a feeling stored in memory. To hear, it is enough
to detect, sound can pass through the ear and reach the temporal lobe, without connecting
to symbolic or meaningful associations. When one really 'want' to listen, must pay
attention, intention, and trigger association pathways to the 'end point' where there
must have stored information, so that the input message can be compared to previous
listening experiences, be understood and ́make sensé. At the extreme, one may put
all the attention and intention into listening to someone talking in Russian, while
nothing that was heard was understood, if one does not have meaningful stored information.
Thus, to understand, it is necessary that the brain has a stored arsenal to be able
to interpret the sound.
In the first years of life, everyone who is born with normal hearing thresholds, may
be able to hear 'everything' and will store auditory experiences associated with sensations,
emotions, and daily experiences that, through repetition and routine, will allow the
creation of a significant arsenal (Flexer, 2011).[6 ] The 'meaningful arsenal' is achieved with emotional bonding among the family members
(that will give the motivation to the intention to hear, or listening) and is the
basis of language. Language will be transmitted as speech (oral language) when a connection
among the ascending auditory pathways, meaningful association pathways and the descending
motor efferent pathways are linked. The language is accumulated with the experiences
that generate the processing of several stations, regardless of the way it will be
expressed.
ASHA[9 ] summarizes some expected landmarks in the auditory and speech development ([Table 1 ]) in children with typical hearing. Although they may have thresholds within normal
ranges, they only respond reflexively to loud sounds during the first three months
of life. They begin to imitate speech sounds only after more than 7 months of repeated
auditory experiences and motor maturity in the tongue and mouth, revealing the connection
between the afferent auditory and the efferent speech motor pathways. They will point
out body parts around 12 months old, after taking at least 365 baths or showers, listening
in a pleasant and playful environment with their parents and caregivers.
Table 1
Expected markers in the development of listening and speaking skills during the first
2 years of life[9 ]
Hearing and comprehension
Speech
Birth to 3 months
Startles with loud sounds
Be quiet or smile when spoken to
Makes pleasant sounds
Smile when sees mom/dad
4 to 7 months
Moves eyes in the direction of sounds
Notices toys that make noise
Babbles different speech sounds
Vocalizes while playing
7 to 12 months
Turn and look in the direction of the sound source
Starts responding to requests ('come here')
Babbling has both long and short sounds.
Imitates different speech sounds
1 to 2 years
Points to some body parts
Follows simple orders (where's the shoe)
Says a new word every month
Uses 1-2 word phrases and questions
Hence, the construction of language is the result of countless experiences and situations
stored and associated by synaptic connections, that are potentiated by emotions and
hormones.[10 ]
As mentioned earlier, when the child is born with severe to profound hearing loss
and conventional amplification hearing aids are not able to stimulate all the tonotopic
regions of the cochlea and cochlear nerve with speech sounds, the cochlear implant
will be indicated to allow access to the necessary acoustic cues. This may allow the
development of auditory skills, the experience of representative situations, culminating
in oral language.[11 ]
Diagnosis at birth or in the first month is very important so that the necessary actions
for intervention are taken in time, that is, before 3 to 6 months, to allow this children
have the meaningful experiences almost at the same time as their hearing peers.[7 ] The more adequate the auditory and linguistic development before the CI, the better
the evolution after the surgery. As important as the diagnosis is the supporting and
counseling of families. Families that are “paralyzed” in the diagnosis, not knowing
how to deal with deaf children, without the adequate guidance might unconsciously
becoming “mute families”. One of the possible reactions or tendencies when dealing
with someone that may not be hearing us, may be 'not talking'. “What is the point
of talking”, one may ask themselves, “if he/she won't listen to me'”. The importance
of supporting families involved in the child's rehabilitation process has been reinforced
and proven in numerous studies.[4 ]
[10 ]
[11 ]
[12 ]
[13 ]
[14 ]
[15 ]
[16 ] Lind-Combs & Holt[15 ] (2022) conducted a study with 62 dyads of children with typical hearing and with
hearing loss using conventional hearing aids or cochlear implants, between 3 and 8
years of age. They found that the vocabulary used by the family associated with a
mental state (such as: I think that, I feel that) positively affected the inhibitory
control of children using hearing devices. Hence, not only language development is
impacted by family communication style, but the whole cognitive development.
The great contribution of rehabilitation is precisely to establish a partnership,
strengthening guidance and advice to families of children with hearing loss to transform
the home into a stimulating environment.
Thus, in addition to the the age at diagnosis and intervention with conventional hearing
aids before 3 to 6 months of age, adequate and desired oral language development after
early cochlear implantation will only happen when:
There is adequate family involvement and communication,
Residual hearing is effectively harnessed with hearing aids before the CI, while the
greater the degree of hearing loss, the shorter the deprivation time should be,
Etiology allows proper insertion of electrodes and sufficient and adequate neural
density of ganglion cells for electrical stimulation
The Map (programming) in the speech processor is adequate to allow optimized access
to speech sounds and features
There are no other associated handicaps
Appropriate school and rehabilitation quality
Adequate nonverbal intelligence
And CI usage during all the waking hours, that is to say an average of 10 hours a
day.
Pianesi et al.[17 ] (2016) warned that the risk of lack of oral language development can be identified
in the first 6 months after CI, due to slow development of auditory skills identified
by IT-MAIS. Silva-Comerlatto[18 ] has also studied 230 Brazilian kids with severe to profound hearing loss, and stablished
the landmarks for auditory and oral language after cochlear implants. Therefore, children
who do not demonstrate development in the first 6 months after CI should be considered
as 'red flags' and actions such as the verification of the intervention (rehabilitation
and family communication), speech processor programming and hours of use should be
investigated.
Robbins[19 ] (2005) proposed a list of Red flags for both groups of children implanted early
and late in life, up to 12 months after CI, that may also serve as markers for taking
actions after cochlear implantation. Our proposal is that, if there is no expected
evolution, a list of reasons may be reviewed to allow the identification of the aspects
that may be driven ([figure 1 ]).
Fig. 1 Checklist of reasons for the development below expectations. Legend: SOE. Spread
of excitation; Rehab. Rehabilitation
In summary
Cochlear implant is a remarkable solution to open the doorway to the brain,[6 ] but the factors that influence the development of oral language, that is, auditory
and communicative skills in severe to profound deaf children, transcend the age of
the cochlear implant surgery.
Furthermore, we must have in mind that in very early cochlear implantation, many other
additional handicap diagnoses may appear later, after the surgery, including Autism
Spectral Disorders.[20 ]
[21 ]
Considering the individuality and characteristics of each child, it is the responsibility
as the multidisciplinary team, including pediatricians, otorhinolaryngologists, speech
therapists, social workers, psychologists, to offer support and the best possible
guidance to the children and their families.
