Correlation of neural response properties with 1 auditory thalamus subdivisions in the awake marmoset 2 3 4 5

28 As the information bottleneck of nearly all auditory input that reaches the cortex, the 29 auditory thalamus serves as the basis for establishing auditory cortical processing streams. The 30 functional organization of the primary and non-primary subdivisions of the auditory thalamus is 31 not well characterized, particularly in awake primates. We have recorded from neurons in the 32 auditory thalamus of awake marmoset monkeys and tested their responses to tones, band-pass 33 noise, and temporally modulated stimuli. We analyzed the spectral and temporal response 34 properties of recorded neurons and correlated those properties with their locations in the auditory 35 thalamus, thereby forming the basis for parallel output channels. Three MGB subdivisions were 36 identified and studied physiologically and anatomically, though other medial subdivisions were 37 also identified anatomically. Neurons in the ventral subdivision (MGV) were sharply tuned for 38 frequency, preferred narrowband stimuli and were able to synchronize to rapid temporal 39 modulations. Anterodorsal subdivision (MGAD) neurons appeared well-suited for temporal 40 processing, responding similarly to tone or noise stimuli but being able to synchronize to the 41 highest modulation frequencies and with the highest temporal precision among MGB 42 subdivisions. Posterodorsal subdivision (MGPD) neurons differed substantially from the other 43 two subdivisions, with many neurons preferring broadband stimuli and signaling changes in 44 modulation frequency with non-synchronized changes in firing rate. Most neurons in all 45 subdivisions responded to increases in tone sound level with non-monotonic changes in firing 46 rate. MGV and MGAD neurons exhibit responses consistent with providing thalamocortical 47 input to core regions whereas MGPD neurons are consistent with providing input to belt regions. 48