The development of the neural projections responsible for sound frequency representation in the central auditory system.
The understanding of language, and the abilities to read and write are skills which develop in children based on the proper function of the senses of hearing and vision, as well as a range of higher-level brain processing mechanisms. Brain cell (neuron) activity, or rather the collected activity of arrays of neurons, forms the fundamental building blocks of the very complex brain functions required for language and reading skills. This proposal concerns the development and function of these arrays of neurons, particularly those concerned with hearing. The research focuses on a very fundamental aspect of the structure of the auditory system, namely the way in which complex sounds such as speech are coded and represented in the auditory brain.
Speech sounds are received by the cochlea of the inner ear and the frequency components in the sounds are immediately analyzed and represented as a pattern of electrical signals in the array of neurons that make up the cochlear nerve (VIIIth cranial nerve). This pattern of neural activity, which represents the speech signal, is transmitted through the lower parts of the brain (brain stem, midbrain, and thalamus) to the auditory centres of the cerebral cortex. Thus the speech signal is now represented at the levels of the brain where it can be identified, compared with stored memory patterns, correlated with visual images etc. It is at this level of the brain where the representations of speech signals can be strung together, with certain rules which define language, and where these patterns can be correlated with visual images of the written word.
This structure of the auditory pathways which allow the speech sounds to be coded in the brain is called the “tonotopic” organization. Without a good tonotopic organization to transmit speech information from the ears to the cortex, there will be poor speech understanding, and abnormal development of language and literacy skills. It is the development of these tonotopic representations in the auditory brain that the researchers wish to study. They will look at how the normal tonotopic pathways develop, as well as what can go wrong in early development to produce an inadequate system, i.e. one which would result in an impairment of language and reading skills later in life.