Thesis defense Roohollah Massoudi (Donder Series 165)

3 July 2014

Promotor: Prof.dr. J. van Opstal, copromotors: dr. M.M. van Wanrooij, dr. H. Versnel

Interaction of task-related and acoustic signals in single neurons of monkey auditory cortex

The aim of this thesis was to better understand the response properties and function of the auditory cortex (AC). To that end we performed single-unit recordings from cells in the core auditory cortex of two macaque monkeys that were trained to respond as fast as possible to a perceived modulation of complex sounds. We addressed the basic spectral-temporal tuning characteristics of AC neurons, the effect of the behavioral state of the animal on spectral-temporal and temporal envelope processing, and the interaction between acoustic information and top-down task-related signals at the single unit level of core AC.

Our findings revealed that although AC shares many spectral-temporal properties with the auditory midbrain inferior colliculus (IC), its response characteristics appeared to be more nonlinear than in the IC. We next showed that despite prominent differences in the evoked neural activity, the extracted spectrotemporal receptive fields (STRFs) remained remarkably stable during three different behavioral conditions: (i) passive exposure to sounds, vs. active engagement in an (ii) unpredictable and (iii) highly predictable sound change-detection task. By applying a broader range of temporal modulation frequencies in the same task paradigm, we showed that the different behavioral conditions affected the temporal processing capabilities of AC cells for very low (below 8 Hz) and very high (above 64 Hz) modulation frequencies. However, the tuning strength remained virtually identical for the range between about 8-64 Hz. Finally, we studied the nature of the neural interactions at the level of AC cells to acoustic and non-acoustic task-related signals. Our findings suggested a non-linear multiplicative interaction between the cell’s tuning characteristic and the top-down behavioral modulation.