Research

Research Interests 

Hearing relies on the brain’s ability to represent auditory information. We use multiple approaches to investigate this function in owls and chicken. Birds are not just fascinating creatures but offer advantages for understanding the neural coding and computations underlying hearing.
  

Projects 

Brain representation of auditory space: The biased owl   

Although owls can very accurately localize sounds near the center of gaze, they underestimate the direction of sources in the periphery.  This behavioral bias is also observed in other animals and in humans. This behavior and the underlying neural implementation can be predicted by statistical inference; Brian Fischer showed that the mapping of auditory space in the owl’s midbrain could explain how statistical inference takes place. These conditions are likely in other cases, as shown by studies of the oblique effect in visual perception in humans. To perform statistical inference, it is critical that the brain represents the relationship between sensory information and the environment, as well as the statistics of the environment. We plan to elucidate how this happens in collaboration with Brian Fischer and Terry Takahashi.
                                                                   
 
                                           
  
                                                                        Adjusting tonotopy through weighting by reliability to represent space  
                                                                                               (modified from Cazettes et al 2014)
 
 
 
                                                                   
       Non-uniform spatial tuning and surround bias in the owl's midbrain                                                        Representation of space predicted by Bayesian theory   
               (modified from Knudsen 1982 and Wang et al 2012)                                                                                      (modified from Fischer and Pena 2011)
                 

Coding sound identity together with space and time   

The auditory system encodes both the identity and location of sounds. The spectral features over time are essential for identifying sounds, such as in vocalizations. However, this information must be encoded in parallel with cues about sound direction, such as differences in time and level between the ears. Our studies examine how information flows and how enhanced selectivity for ‘what’ and ‘where’ emerges in the ascending auditory system.     

 Computations underlying auditory spatial tuning: Models of human sound localization materialized in the owl’s brain  

The plausibility of sound-localization models remains in question. Our studies in barn owls directly address this issue. In the owl’s brain, the signals collected by the ears are compared to infer sound direction. This computation underlies the highly efficient ability of owls to catch prey in darkness. In fact, the owl’s brain performs many of the operations proposed in sound localization models. Cross-correlation describes the response of neurons to the extent that theorems apply; averaging-like processes reduce noise; multiplication underlies the selectivity of space-specific neurons. Thus, a bird’s brain possesses tremendous power to understand neural computations. The question how the evolutionary pressure for optimality has driven the owl’s brain to achieve elegance in a mathematical sense guides our long-term plans.  
 
 

 





Interaural time and level differences determine the receptive field of ICx cells in auditory space.
(modified from Pena and Konishi 2002)


 

Techniques used in the lab 

Electrophysiology
We are interested in recording techniques that may help us address scientific questions. We have used in vivo intracellular recordings to investigate space selectivity in the owl’s brain and in vivo cell-attached recording in auditory coincidence detectors to overcome the difficulty in isolating coincidence detector neurons. We developed in vitro recordings in chicken to bridge our systems approach and cellular and synaptic mechanisms. 

                                                                             
                                                                                                               In vitro recording in the chicken midbrain.  
                                                                                                                   (modified from Penzo and Pena 2009)


Intracellular labeling and in vivo recording of a space-specific neuron.                                                                                              (modified from Pena and Konishi 2001)