Orienting in 3D space

Ninad Kothari

In the natural world, most animals interact and orient to objects in three dimensional space. Previous work has implicated the midbrain superior colliculus (SC) in orienting an animal towards salient stimuli in two dimensions (azimuth and elevation). The majority of prior work on the SC has employed 2 dimensional, artificial stimuli which has limited the relevance of these studies to real-world, three dimensional conditions. Using the flying echolocating bat as a model, we provide evidence for the role of the superior colliculus as a sensorimotor integration center for orienting an animal in 3D space.

Experimental Design

To understand the role of the SC in 3D orienting behaviors we utilized the following experimental setup.

1) Bats are trained to fly across the room and land on a platform where they are rewarded.
2) High speed video cameras (Miro, Vision Research) and motion capture systems (Vicon) are used to reconstruct the flight trajectory of the bat and also capture the 3D head aim vector while the bat is flying.
3) Ultrasonic microphones (Pettersson Elektronik) are used to capture the bats sonar vocalizations and beam pattern.
4) Once bats are trained to perform the behavior, a 16 channel NeuroNexus probe is chronically implanted into the right superior colliculus.
5) A TBSI telemetry system linked with Plexon A/D are used to record neural data.

The problem of understanding echo sensory space in a flying bat

Understanding the time when echoes reach the bats and from which spatial direction the echoes originate in 3D space (i.e. which objects are ensonified by the bats sonar vocalizations and at what time the echoes from the ensonified objects reach the bat) is a difficult problem to solve. Using the reconstructed flight trajectory, sonar beam aim and knowledge of the 3D position of objects in space, we developed an acoustic echo model which gives us the following information about the echo sensory space of the bat.
     1) Time when echoes arrive at the bats ears
     2) 3D direction from which the echo originated.
We call this the Echo Model.
Correlating the neural spike times with the output of the echo model enables us to develop an understanding of the role of the SC in orienting in 3D space.

Results

Once the bat's echo acoustic scene is recreated we computed spatial tuning profiles of different neurons.
The figure below shows spatial tuning profiles of 2 simultaneously recorded neurons during one experimental session.


Copyright@2017 Batlab, Johns Hopkins University
Questions and comments to wxian1@jhu.edu

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