Long-term frequency tuning of local field potentials in the auditory cortex of the waking XXXX .

@entity2198 @entity840
The goal of our study was to determine the extent of changes in frequency tuning in the auditory cortex over weeks. The subjects were awake adult male @entity840 (n = 8) bearing electrodes chronically implanted in layers IV-VI of primary auditory cortex. Tuning was determined by presenting sequences of pure tone bursts (approximately 0.97-41.97 kHz, -20 to 80 dB, 100-ms tone duration, 5-ms rise-fall, 800-ms intertone intervals, 1.5-s intersequence interval) either in 0.5-octave steps (n = 5, 14 probes) or 0.25-octave steps (n = 3, 9 probes) delivered to the ear contralateral to recording sites. Tuning curves were determined for local field potentials (LFPs), which were tuned to frequency (negative potential, latency to peak 15-20 ms), repeatedly for up to 27 days (0.5 octave) or 12 days (0.25 octave). @entity2198 ( @entity2198 ), best frequency at 10 and 30 dB above absolute threshold (BF10, BF30), threshold (TH), and bandwidth (10 dB above threshold; BW) were measured. Absolute amplitude often decreased across weeks, necessitating normalization of amplitude. However, there were no significant trends in tuning over days for @entity2198 , BF10, or BF30 for either the half- or the quarter-octave group. Both groups exhibited random daily variations in frequency tuning, the quarter-octave group revealing larger variations averaging 0.228, 0.211, and 0.250 octave for @entity2198 , BF10, and BF30, respectively. Therefore, frequency tuning in waking animals does not exhibit directional drift over very long periods of time. However, daily tuning variations on the order of 0.20-0.25 octave indicate that the peaks of tuning curves ( @entity2198 , BF) represent a preferred frequency range rather than a fixed frequency.
