Egocentric and allocentric representations in auditory cortex

• Published in: PLoS biology Vol. 15; no. 6; p. e2001878
• Main Authors: Town, Stephen M., Brimijoin, W. Owen, Bizley, Jennifer K.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 15.06.2017; Public Library of Science (PLoS)
• Subjects: Acoustic Stimulation; Animals; Auditory cortex; Auditory Cortex - cytology; Auditory Cortex - physiology; Auditory Cortex - radiation effects; Auditory system; Behavior, Animal - radiation effects; Biology and Life Sciences; Brain; Coding; Cortex (auditory); Data collection; Electric Stimulation; Electrodes, Implanted; Electroencephalography; Evoked Potentials, Auditory - radiation effects; Exploratory Behavior - radiation effects; Female; Ferrets; Head; Head movement; Head Movements - radiation effects; Information processing; Localization; Locomotion - radiation effects; Medicine and Health Sciences; Models, Neurological; Models, Psychological; Modulation; Movement; Neural circuitry; Neurons; Neurons - cytology; Neurons - physiology; Neurons - radiation effects; Open source software; Physiological aspects; Position measurement; Representations; Roles; Sound; Sound localization; Sound Localization - radiation effects; Spatial Behavior - radiation effects; Spatial Processing - radiation effects; Tuning; University colleges
• ISSN: 1545-7885; 1544-9173; 1545-7885
• DOI: 10.1371/journal.pbio.2001878

A key function of the brain is to provide a stable representation of an object's location in the world. In hearing, sound azimuth and elevation are encoded by neurons throughout the auditory system, and auditory cortex is necessary for sound localization. However, the coordinate frame in which neurons represent sound space remains undefined: classical spatial receptive fields in head-fixed subjects can be explained either by sensitivity to sound source location relative to the head (egocentric) or relative to the world (allocentric encoding). This coordinate frame ambiguity can be resolved by studying freely moving subjects; here we recorded spatial receptive fields in the auditory cortex of freely moving ferrets. We found that most spatially tuned neurons represented sound source location relative to the head across changes in head position and direction. In addition, we also recorded a small number of neurons in which sound location was represented in a world-centered coordinate frame. We used measurements of spatial tuning across changes in head position and direction to explore the influence of sound source distance and speed of head movement on auditory cortical activity and spatial tuning. Modulation depth of spatial tuning increased with distance for egocentric but not allocentric units, whereas, for both populations, modulation was stronger at faster movement speeds. Our findings suggest that early auditory cortex primarily represents sound source location relative to ourselves but that a minority of cells can represent sound location in the world independent of our own position.