Hemispheric interaction during lateralized auditory processing in humans: effects of task difficulty, training and age

• Applicant: Dr. Nicole Angenstein
• Subject Area: Clinical Neurology; Neurosurgery and Neuroradiology
• Term: from 2011 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 192660229

The left and the right auditory cortex are differentially specialized for the processing of fundamental acoustic features and auditory tasks. For the processing of complex sounds, e.g. speech, a number of acoustic features need to be evaluated simultaneously. As a consequence both the left and the right auditory cortex are involved in the processing of such complex sounds and consequently, hemispheric interaction is required. The degree of hemispheric involvement does not solely depend on the acoustic properties of the stimuli but is also influenced by other factors, such as task difficulty, experience from prior training and age. The aim of my project is to systematically determine the effects of these three factors on the lateralization of processing in the human auditory cortices and on the hemispheric interaction by using functional magnetic resonance imaging (fMRI). In particular, the degree of hemispheric involvement will be determined by the contralateral noise procedure that I have developed and validated in the previous funding period. Hemispheric interactions will be studied by connectivity analyses. The results of these analyses will be correlated with diffusion tensor imaging (DTI) measures of the anatomical fine structure of the corpus callosum as the main structure for interhemispheric transfer of information. Based on the results of the previous funding period, two different tasks will be contrasted that require vastly different hemispheric involvement and as a consequence different levels of hemispheric interaction: First, the categorization of tones based on their direction of frequency modulation (FM) will be applied, which relies on a dominant involvement of the right auditory cortex. Second, the sequential comparison of tones based on their FM direction will be applied, which involves both the left and the right auditory cortex to a substantial degree and therefore, requires stronger hemispheric interaction than the categorization task. For the two tasks, the effect of task difficulty on hemispheric involvement and hemispheric interaction will be investigated by comparing three levels of difficulty. Then, the effects of training will be determined by repeated fMRI measurements of the same participants. Finally, the effects of aging in combination with training will be investigated by repeated measurements of older adults. The results of the project will help to answer many of the still open questions regarding hemispheric specialization and its functional consequences. This knowledge is a prerequisite to develop new strategies for maintaining and regaining speech competence of older adults especially in noisy environments as well as of brain damaged patients with deficits in auditory and language processing.

• DFG Programme: Research Grants