Primate auditory cortex is composed of areas grouped in regions at 3 levels in a hierarchical order: core-belt- parabelt. Each region is subdivided into multiple areas. Auditory information processing proceeds through levels and through areas within every level. Information in the belt and parabelt regions diverges into parietal (dorsal) and temporal lobe (ventral), as well as different regions of prefrontal cortex. Growing evidence indicates that the representation of auditory information becomes more complex and abstract as the processing advances. This project focuses on the properties of the parabelt (PB) region on the superior temporal gyrus (STG) in macaque monkeys for two reasons. First, while PB is fairly well defined at a gross anatomical level in monkeys (e.g. it divides into caudal and rostral areas, CPB and RPB, respectively) detailed anatomical studies (architecture, intrinsic connectivity between CPB and RPB) have not been conducted. More detailed microstructural characterization of the macaque PB may help to better define the human PB. Second, while human STG has been implicated in various functions particularly related to perception of communication signals like speech, the physiological properties of the macaque PB have not been systematically studied, primarily due to the technical difficulties of accessing the macaque STG. Thus, the detailed auditory physiology of the macaque PB holds some of the key information missing in our understanding of the organization and functioning of the primate auditory cortex. Our BROAD OBJECTIVE is to characterize the physiological properties, functions and organization of the PB areas in primates. As PB areas are widely regarded as task-sensitive, we will record PB activity in monkeys performing sensory tasks that entail active discrimination of the test stimuli.
SPECIFIC AIM 1 is to systematically characterize acoustic preferences (e.g. spectral and temporal tuning) of the PB neurons by examine their responsiveness to a battery of auditory stimuli. This will provide the first ever detailed survey of basic PB physiology.
SPECIFIC AIM 2 is to characterize communication signal processing in PB. We examine neural responses to conspecific vocalization while manipulating their sensory modality or spectral/temporal domains and relate these responses to behavioral performance.
Both AIMs also allow comparisons between CPB and RPB, and between hemispheres, to provide more details about PB organization.
SPECIFIC AIM 3 is to investigate the network architecture of PB by exploring the connection patterns of PB anatomically and neurophysiologically. This will help understand how PB areas interact to process information and pass it to higher order areas. Several communication disorders (e.g. autism) implicate STG or higher level of auditory systems for its impaired functionality. Basic properties of STG (PB areas in the case of monkeys) are essential for understanding these, as well as basic sensory impairments.
The parabelt region of auditory cortex is considered as a high-level stage for human communication processing, though not yet well explored in monkeys. Delineation of its physiological and functional properties will enhance our understanding of normal communication and the mechanisms of communication disorders, as those disorders are related to neurological abnormalities in cortical regions including the parabelt.
| Kajikawa, Yoshinao; Smiley, John F; Schroeder, Charles E (2017) Primary Generators of Visually Evoked Field Potentials Recorded in the Macaque Auditory Cortex. J Neurosci 37:10139-10153 |
