Can the developing auditory system adapt to hearing loss using multiple adaptive strategies? A hearing loss in one ear changes some of the cues to sound location (the binaural cues that rely on differences between the sound heard by each ear) but leaves others intact (the cues that rely only on the sound heard by the ear with normal hearing). Previously, we showed that developing ferrets adapt to a hearing loss in one ear by learning to rely more on the cues to sound location that are unaffected by hearing loss. We now show that these ferrets can also localize sounds correctly using the cues that have been changed by hearing loss. This means that the developing brain (primary auditory cortex) can use multiple adaptive strategies to adapt to hearing loss. It also helps explain some of the apparent differences between experiments in birds and mammals. This suggests that many different species may use the same adaptive strategies. Finally, our results provide insight into the way in which sound location is represented by populations of neurons in the brain. Previous work had suggested that sound location is represented by the difference in neural activity between the two hemispheres. Although this may be true at the level of the brainstem, it does not appear to be true in the cortex.

Keating P, Dahmen JC, King AJ (2015) Complementary adaptive processes contribute to the developmental plasticity of spatial hearing. Nature Neuroscience 18:185-187.

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How is sound localization affected by previous experience? This review paper outlines recent advances in our understanding of this topic and identifies some of the most promising directions for future research.

Keating P, King AJ (2015) Sound localization in a changing world. Current opinion in neurobiology 35:35-43.

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In the midbrain, do neighbouring neurons like similar things? Decades of research have shown that neighouring neurons often respond to similar sound frequencies, which can produce maps of frequency in the brain. However, recent research has shown that this organization may break down at a very fine spatial scale in the auditory forebrain. This paper shows a complementary result for the auditory midbrain. Certain aspects of frequency organization (a boundary between different sub-divisions of the inferior colliculus) can be seen at a very fine spatial scale but are invisible at a coarser spatial resolution. This can be seen using a technique called calcium imaging, which makes individual neurons light up when they are active.

Barnstedt O, Keating P, Weissenberger Y, King AJ, Dahmen JC (2015) Functional microarchitecture of the mouse dorsal inferior colliculus revealed through in vivo two-photon calcium imaging. Journal of Neuroscience 35:10927-39.

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Can adult humans adapt to a hearing loss in one ear using multiple strategies? Sound localization is impaired by a hearing loss in one ear. But during development, ferrets adapt to this type of hearing loss using multiple adaptive strategies. This paper shows that adult humans also use multiple adaptive strategies for adapting to a hearing loss in one ear, provided they are given appropriate training on a sound localization task. These adaptive strategies appear to be independent of one another, with some individuals relying more on one adaptive strategy than the other. This suggested to us that these adaptive strategies might rely more on different sets of neurons. This is precisely what we found when we recorded from neurons in ferrets reared with a hearing loss in one ear.

Keating P, Rosenior-Patten O, Dahmen JC, Bell O, King AJ (2016) Behavioral training promotes multiple adaptive processes following acute hearing loss. Elife 5:e12264

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