Fig. 14.

The auditory belt fields of awake macaque exhibit a range of temporal properties; population MTFs for the belt reveal no clear trend in rate tuning, but a possible transformation in temporal tuning from low-pass in core, to band-pass in belt. A: cumulative distributions of pure-tone response latency are illustrated for belt fields CM, M, and L (bold lines in black, medium gray, and light gray respectively) with the core fields included for reference (reproduced from Fig. 8B; AI and R are fine lines in black and medium gray). As described in the text, minimum latencies in CM (n = 11) were shorter than those in neighboring AI (and all other fields), M (n = 14) was intermediate between the core fields (and in fact did not differ significantly from AI), and neurons in L (n = 15) had long latencies similar to those in the core field R. Comparisons between belt fields did not reach significance because relatively few neurons gave sufficiently robust tone responses for a significant minimum latency to be measured. B: cutoff frequencies for SAM divide the fields into 2 rough classes, 1 with high temporal precision to AM and 1 without. Neurons in CM (n = 17), like AI, tended to exhibit synchrony to high rates of modulation relative to belt fields M and L (n = 25 and 18, respectively) where neurons had lower cutoffs similar to those in R. Legend in A applies to both panels. C: population rate MTF, conventions as in Fig. 13A. For clarity, core data are not shown. D: population temporal MTF shows a common peak at 5 Hz in belt fields; conventions as in Fig. 13B (core data are reproduced as fine lines for comparison). At low modulation frequencies (<5 Hz) where synchrony predominates in the core fields, synchrony is rare in the belt. The median point at which 50% of the population is in synchrony is higher in caudal auditory cortex (∼30 Hz in AI, ∼60 Hz in CM) than in rostral, lateral, and medial fields (core field R, and belt fields L and M, all ∼10 Hz).