Assistant Professor
Department of Physiology and Biophysics
UCD at Fitzsimons
RC-1 North Tower, P18-7120. PO Box 6511, Mail Stop F8307. Tel (303) 724-0625. Fax (303) 724-4501.
Email daniel.tollin@UCHSC.edu

Dan's Curriculum vitae

Behavioral and physiological mechanisms of binaural and spatial hearing

The goal of the work in my lab is to understand the neural mechanisms of auditory perception with particular emphasis on how sources of sounds are localized.  Because the peripheral receptors of the ear have no mechanism to directly sense sound location on their own (unlike the topographic organization of the retina), location must be computed at more central levels.  This makes sound localization a fascinating neurocomputational problem, particularly from a developmental perspective.  Our experiments seek answers to at least four basic questions:

1. What are the acoustical cues to sound source location and what are their physical bases?
2. How are the acoustical cues represented and transformed in the activity patterns of neurons in the various nuclei of the ascending auditory pathway?
3. How are the neural representations of the cues used by observers to determine location?
4. How do each of these aspects of hearing develop?

I use a multidisciplinary approach to tackle these questions employing both experimental and theoretical techniques including human and animal psychophysics, extracellular physiology, signal detection and information theory, systems identification techniques, acoustic transfer function measurement and modeling, digital filter design and estimation, acoustic signal design, and physiological systems modeling.

Fig. 1  Illustration of a frontal section through the brainstem showing the ascending pathways through the nuclei of the superior olivary complex that are believed to be responsible for encoding interaural level differences (ILDs).  Neurons of the lateral superior olive (LSO) receive bilateral inputs from both ears.  The input from the ipsilateral ear via the spherical bushy cells (SBCs) is excitatory (open symbols) but the input from the contralateral ear via the globular bushy cells (GBCs) of the contralateral anteroventral cochlear nucleus (AVCN) is inhibitory (filled symbols) due to the additional synapse in the ipsilateral medial nucleus of the trapezoid body (MNTB).  The interplay of the ipsilateral excitation and contralateral inhibition confers on LSO neurons sensitivity to ILDs.  LSO neurons send excitatory projections to the contralateral inferior colliculus (IC) and dorsal nucleus of the lateral lemniscus (DNLL) and inhibitory projections (not shown) to the ipsilateral IC and DNLL.  The color bar and shading indicates the tonotopic organization and shows that the neurons comprising the MNTB and LSO are sensitive to predominantly high frequency sounds.

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LAB PERSONNEL

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