Fine functional organization of auditory cortex revealed by Fourier optical imaging

Abstract

We provide an overall view of the functional tonotopic organization of the auditory cortex in the rat. We apply a recently developed technique for acquiring intrinsic signal optical maps, Fourier imaging, in the rat auditory cortex. These highly detailed maps, derived in a several-minute-long recording procedure, delineate multiple auditory cortical areas and demonstrate their shapes, sizes, and tonotopic order. Beyond the primary auditory cortex, there are at least three distinct areas with fine-scale tonotopic organization, as well as at least one additional high-frequency field. The arrangement of all of these cortical areas is consistent across subjects. The accuracy of these optical maps was confirmed by microelectrode mapping in the same subjects. This imaging method allows fast mapping of the auditory cortex at high spatial resolution comparable to that provided by conventional microelectrode technique. Although spiking activity is largely responsible for the evoked intrinsic signals, certain features of the optical signal cannot be explained by spiking activity only, and should probably be attributed to other mechanisms inducing metabolic activity, such as subthreshold membrane phenomena.optical imaging of intrinsic signals ͉ rat ͉ tonotopy ͉ cortical maps

Arc expression and neuroplasticity in primary auditory cortex during initial learning are inversely related to neural activity

“…Although the increases in Arc expression in A1 of animals that had just learned the task were robust, such changes did not generalize to the entire cortex, because the percentage of Arcexpressing neurons remained low in the perirhinal cortex, which is located just ventral of the auditory-responsive fields (0.92 ± 0.13%) (25,26).…”

“…Cranial bone was thinned over A1. Images were collected as described previously (26). A 4-s sound stimulus was used, and the speaker was positioned 12 in in front of the nose on the interaural plane and 0°vertical.…”

Gene Expression Identifies Distinct Ascending Glutamatergic Pathways to Frequency-Organized Auditory Cortex in the Rat Brain

“…Auditory stimuli used for multiunit recordings were flat spectrum noise tokens (Ͻ5 ms rise time, 50 ms duration) delivered via a TDT RX6 multifunction processor at 96 kHz . Auditory stimuli used for Fourier intrinsic imaging were a continuous sequence of 16 pure tones (50 ms duration, 5 ms rise and decay time, 250 ms interstimulus interval) from 2 to 32 kHz (0.25 octave steps) with a 4 s period in ascending or descending order (Kalatsky et al, 2005;Polley et al, 2007;Higgins et al, 2010;Storace et al, 2010Storace et al, , 2011 delivered via a Lynx Studio Technology professional audio card at 98 kHz.…”

“…Fourier optical imaging was used to map tone frequency response organization in auditory cortex. Images were acquired with a Dalsa 1M30 CCD camera with a 512 ϫ 512 pixel array covering a 4.6 ϫ 4.6 mm 2 area (Kalatsky et al, 2005;Polley et al, 2007;Higgins et al, 2010;Storace et al, 2010Storace et al, , 2011. Surface vascular patterns were imaged with a green (546 nm) interference filter at a 0 m plane of focus.…”

“…Several mammals including humans have multiple "core" fields outside the primary (A1) auditory cortical field (Formisano et al, 2003;Schreiner and Winer, 2007;Hackett, 2011). Gerbils, guinea pigs, and rats have overlapping hearing ranges and similar frequency organization of A1 relative to the anterior auditory field (AAF) and a third ventral field with distinct frequency organization (Wallace et al, 2000;Kalatsky et al, 2005;Donishi et al, 2006;Budinger and Scheich, 2009). In the rat, this ventral field is called the suprarhinal auditory field (SRAF) (Polley et al, 2007).…”