Supporting Information

Files in this Data Supplement:

Chair/Restraining Apparatus. The monkey chair was designed by Crist Instruments (Hagerstown, MD) in collaboration with the authors. The design, based on a previous Crist Instruments model, was adapted to optimize comfortable restraint of awake animals and PET scan compatibility. Several materials were tested before the construction of the chair to assure optimal rigidity and minimal signal attenuation; low atomic-number materials (acrylic and graphite) were selected. The chair included an adjustable base to allow for animals of different sizes, and an adjustable back support to increase the comfort of the animal when tilted backward into the PET scanner. The chair was attached to a table constructed of aluminum, with casters to facilitate the positioning of the animal. The table was equipped with a base with hinge joints over which the chair was fixed, allowing the animal to be tilted back for proper placement in the scanner.

Animal Training. The study required that the animals be maintained in a relaxed state while listening to auditory stimuli in the PET-scan environment. To accomplish this goal, each animal was habituated to the chair and to the PET-suite environment by using the training sequence described below. Several months before training, an acrylic headpost was surgically implanted in each animal to restrict head motion during scanning. During each training session, the animal was taken from its cage and placed in the chair by using a pole-and-collar method:

(i) Habituation to passive sitting in the chair in a training room with head restrained (vertical position; no stimuli presented).

(ii) Habituation to passive sitting in the chair in a training room with head restrained (tilted backward 70° , the position required for scanning; no stimuli presented).

(iii) Habituation to passive sitting in the chair in a training room with head restrained [tilted backward 70° while acoustic stimuli were presented: nonbiological sounds (broadband noise bursts) and conspecific calls (grunts)].

(iv) Acclimation to the PET-scanner suite while passively sitting in the chair with head restrained (tilted backward 70° , positioned in the scanner; no stimuli presented).

(v) Habituation to the PET-scanner suite while passively sitting in the chair with head restrained [tilted backward 70° , positioned in the scanner while acoustic stimuli were presented: nonbiological sounds (broadband noise bursts) and conspecific calls (grunts)].

These habituation-training phases took ≈6 months to complete. Habituation training was accomplished solely with positive reinforcement (using fruits and juice). The categories of acoustic stimuli used during training were not used in the study reported in the manuscript.

Stimuli. All coo and scream exemplars were high-quality digitized vocalizations. The calls were recorded by M.D.H. and many field assistants from 1987–1999 from rhesus monkeys living in a seminatural habitat on the island of Cayo Santiago, Puerto Rico. Thus, all callers were unfamiliar to our subjects. The calls selected for this study were given by several different individuals and represent the best exemplars of each type.

The sounds were amplitude-normalized, and the stimulus sequences were created and presented by using SIGNAL software (Engineering Design, Berkeley, CA). Sounds were broadcast with a DAQCard-6062E (National Instruments, Austin, TX) and a Powered Partners AV570 speaker (Advent, Benicia, CA) (frequency response: 40–30 kHz) with broadcast values at 1.5 m as follows. Nonbiological sounds: mean amplitude of 68.0 dB sound pressure level (SPL) and range of 50.66–83.0 dB SPL. Coos: mean amplitude of 67.33 dB SPL and range of 54.66–83.5 dB SPL. Screams: mean amplitude of 65.0 dB SPL and range of 50.0–86.66 dB SPL.

A pilot study was performed in one animal to establish an adequate stimulus presentation structure for the sound blocks of acoustic stimuli to maximize auditory-cortex activity. During PET-scan data acquisition, the monkey listened passively to blocks of broadband noise bursts, with variable time intervals between bursts. Interstimulus intervals (ISI) were either (i) short (a mean of 0.875 sec, randomly jittered between 0.5 and 1.25 sec) or (ii) long (a mean of 1.75 sec, randomly jittered between 1 and 2.5 sec). The total length of the stimulus block was tested for two durations (15 and 30 sec). Sound amplitude was kept constant for all conditions.

Analysis of these data indicated that the short ISI (0.5–1.25 sec) and the stimulus-block duration of 30 sec elicited the strongest activation of auditory cortex (STG). This stimulus-block structure was used for all acoustic stimulus blocks presented in the study.