Frequency map variations in squirrel monkey primary auditory cortex.
OBJECTIVE
The goal of this work is to understand the neural basis for cortical representation of hearing in highly vocal primates to gain insights into the substrates for communication. Variation patterns in frequency representation among animals are incorporated into an explanatory model to reconcile heterogeneous observations.


METHODS
Prospective.


METHODS
Thirty-four squirrel monkeys underwent microelectrode mapping experiments in primary auditory cortex (AI) using tone pip stimuli. Characteristic frequency (CF) was extracted from the excitatory frequency receptive field. Frequency maps were reconstructed using Voronoi-Dirichlet tessellation. The spatial locations (rostral vs. caudal) of highest CF isofrequency contours (minimum length 1 mm) and highest CF neuronal clusters on the temporal gyral surface were analyzed.


RESULTS
Isofrequency contours at least 1 mm long with CFs greater than 2.9 kHz (75% cases) are accessible on the temporal gyrus. Variability of the highest CF isofrequency contours accessible on the temporal gyrus has an interquartile range from 2.9 to 5.1 (mean 4.3) kHz. The highest CF isofrequency contours are located mainly in rostral AI, whereas the highest CF neuronal clusters flanking fully expressed isofrequency contours are equally distributed in rostral and caudal locations.


CONCLUSIONS
Squirrel monkey AI frequency map variations are sizeable across animals and small within single animals (interhemispheric comparison). AI frequency map variations, modeled as translations and rotations relative to the lateral sulcus, are independent transfers. Caution must be exercised when interpreting nominal frequency map changes that are attributed to hearing loss and auditory learning effects.
Coleman Memorial Laboratory and W. M. Keck Center for Integrative Neuroscience, Division of Otology, Neurotology and Skull Base Surgery, University of California, San Francisco, California 94143, USA. scheung@ohns.ucsf.edu
Steven W
SW
Cheung
D000818:Animals; D001303:Auditory Cortex / Q000033:anatomy & histology* / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D004558:Electric Stimulation / Q000295:instrumentation; D007839:Functional Laterality; D006311:Hearing Disorders / Q000503:physiopathology; D007858:Learning; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology; D011446:Prospective Studies; D012453:Saimiri; D013702:Temporal Lobe / Q000033:anatomy & histology / Q000502:physiology