O cérebro de um bebê nasce imaturo e é uma máquina de aprendizagem! Passa por uma modelagem durante o desenvolvimento e recebe informações do ambiente, construindo seus circuitos neuronais e sinapses. Os sistemas sensoriais são a nossa porta de entrada, como a audição.
A PLASTICIDADE NEURONAL é a capacidade do sistema nervoso de se reorganizar em resposta aos sentidos. O aumento do estímulo causa um crescimento das sinapses durante os primeiros quatro anos de vida e diminuem posteriormente, a chamada PODA NEURAL ou NEURONAL.
A plasticidade neuronal é fundamental na abordagem da surdez, pois muda a entrada sensorial e causa uma reorganização plástica no cérebro conforme o estímulo.
Na surdez congênita, a plasticidade diminui com a idade e não pode ser substituída ou controlada pelo cérebro e a terapia tardia torna-se menos eficiente.
Vários tipos de períodos sensíveis no desenvolvimento cerebral já foram identificados:
-períodos em que a experiência é necessária para o desenvolvimento de uma determinada habilidade (períodos sensíveis para o desenvolvimento);
-períodos em que o sistema é vulnerável pela manipulação da experiência como a privação monocular (períodos sensíveis para danos);
-períodos em que a terapia (compensação de um déficit) só é parcialmente possível após determinada idade por ter sido perdida (períodos sensíveis para recuperação);
-um tipo distinto de período sensível deve ser adicionalmente diferenciado: períodos de recuperação da privação total.
A completa privação sensorial desde o nascimento deixa o sistema sensorial funcionalmente “ingênuo”, que é distinto da experiência juvenil anormal (como privação monocular ou estrabismo). Deixa o sistema sensorial privado funcionalmente incompetente para desempenhar sua função. Na experiência anormal, o sistema sensorial manipulado ainda é usado para controlar a função, mas está sujeito a entrada de estímulo anormal (input). O estado “ingênuo” abre a possibilidade de reorganização transmodal dos circuitos neuronais, processos degenerativos (funcionais e morfológicos) e outros processos que não ocorrem se o sistema permanecer funcional (embora com entrada ou input anormal).
Portanto, quanto mais precoce a surdez, maiores são as consequências no sistema nervoso central. Quando ela ocorre ainda na vida intrauterina, os déficits são mais extensos e afetam todo o sistema auditivo, tanto periférico (a cóclea) quanto o central (nervo coclear e córtex auditivo temporal no cérebro). Ao nascimento, os danos são menos extensos, mas ainda assim afetam o desenvolvimento cortical. É a SURDEZ PRÉ-LINGUAL, aquela que ocorre antes da aquisição da fala e linguagem.
No adulto, o cérebro já tem memória auditiva pelos estímulos recebidos anteriormente quando a entrada ou input eram normais ou presentes, ainda que parcialmente, portanto os déficits são menores, a chamada surdez PÓS-LINGUAL. Evidentemente, quanto maior o tempo de surdez, maiores as consequências da privação sonora e pior o resultado do tratamento, seja ele por aparelhos auditivos convencionais ou mesmo o implante coclear.
Portanto, quanto mais precoce for o tratamento, maior a estimulação no período crítico e menor a perda de sinapses no cérebro, melhorando os resultados de discriminação sonora (compreensão dos sons) e o desenvolvimento da fala e linguagem. A indicação do IMPLANTE COCLEAR pode ocorrer já a partir de 6 meses de idade, contanto que se tenha CERTEZA do diagnóstico da surdez e da falta de acesso aos sons da fala com os aparelhos auditivos convencionais nas várias avaliações fonoaudiológicas comportamentais que sempre devem ser feitas, o que chamamos de TERAPIAS DIAGNÓSTICAS, ou seja, terapias para estímulo mas ao mesmo tempo para se avaliar o resultado com os aparelhos auditivos e o ganho funcional auditivo.
Lembramos sempre que o implante coclear não faz entender, faz ouvir, já que ouvimos com os ouvidos, mas entendemos com o cérebro, o qual precisa de estimulação intensa durante os primeiros anos de vida para que todas as capacidades cognitivas e sensoriais possam se desenvolver adequadamente.
Por todos estes motivos é que apoiamos fortemente os projetos de Triagem Auditiva Neonatal Universal (TANU) e todas as ações de divulgação e conscientização sobre o diagnóstico precoce da surdez!
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