Title: Fine Frequency Tuning in Monkey Auditory Cortex and Thalamus

23 The frequency resolution of auditory neurons throughout the ascending auditory pathway 24 is an important parameter for understanding how sounds are processed. It has been shown in 25 previous animal studies that the frequency tuning widths are about 1/5 octave wide in auditory 26 nerve fibers and much wider in auditory cortex neurons (Pickles, 1979; McLaughlin et al., 2008; 27 see Table 1). Psychophysical studies show that humans are capable of discriminating far finer 28 frequency differences (Oxenham and Shera 2003). A recent study suggested that this is perhaps 29 attributable to fine frequency tuning of neurons in human auditory cortex (Bitterman et al. 2008), 30 in contrast to wider frequency tunings in published animal studies. We investigated whether such 31 fine frequency tuning was restricted to human auditory cortex by examining the frequency tuning 32 width in a New World monkey species, the common marmoset, in the awake condition. We 33 show that 27% of neurons in the primary auditory cortex of awake marmosets exhibit frequency 34 tuning that is finer than the typical frequency tuning widths of the auditory nerve and 35 substantially finer than previously reported cortical data obtained from anesthetized animals. We 36 further show that such fine frequency tuning is also present in 76% of neurons of the auditory 37 thalamus in awake marmosets, and therefore may be a feature preserved or enhanced by the 38 thalamocortical circuit. Frequency tuning was narrower during the sustained response compared 39 to the onset response in auditory cortex neurons but not in thalamic neurons, suggesting that 40 thalamocortical or intracortical dynamics shape time-dependent frequency tuning in A1. These 41 findings challenge the notion that the fine frequency tuning of auditory cortex is unique to 42 human auditory cortex and that it is a de-novo cortical property, suggesting that broader 43 frequency tuning widths observed in previous animal studies may arise from the use of 44 anesthesia during physiological recordings. 45 46 47