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Articles and Reports

Duke University Primate Experiments

Visual and Saccade-Related Activity in Macaque Posterior Cingulate Cortex

J Neurophysiol 92: 3056-3068, 2004.

Heather L. Dean1, Justin C. Crowley4,5 and Michael L. Platt1,2,3

1Department of Neurobiology, 2Center for Cognitive Neuroscience, and 3Department of Biological Anthropology and Anatomy, Duke University Medical Center, Durham, North Carolina 27710; and 4Department of Biological Sciences and 5Center for the Neural Basis of Cognition, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213

Animal subjects

Two adult male rhesus macaques (Macaca mulatta) were used as subjects in these experiments. All animal procedures were developed in association with Duke University Medical Center veterinarians and were approved by the Duke University Institutional Animal Care and Use Committee. These procedures were designed and conducted in compliance with the Public Health Service's Guide for the Care and Use of Animals.

Surgical procedures

A head-restraint prosthesis and scleral search coil (Fuchs and Robinson 1966; Judge et al. 1980) were implanted in an initial aseptic surgical procedure performed under isoflurane anesthesia. First, the dorsal rostrum of the skull was exposed and six 2.5-mm holes were drilled through the skull with standard orthopedic surgical instruments. These holes were then tapped for 3.5-mm fine-thread orthopedic cortical bone screws. Sterile orthopedic bone cement (Biomet; Palacos) was used to bond a stainless steel head post (Crist Instruments) lowered to just above the skull surface to 6 titanium screws (Zimmer) inserted into the tapped holes. The Teflon-insulated scleral search coil (Cooner Wire AS634) was implanted beneath the conjunctiva, passing just rostral to the insertions of the extraocular muscles (Judge et al. 1980). The wire exited the conjunctiva temporally, exited the orbit subdermally, was embedded in the bone cement that formed the restraint prosthesis, and terminated in a gold and plastic electrical connector (Winchester Electronics/Litton). After surgery, animals received analgesics for a minimum of 3 days. Antibiotic prophylaxis was initiated intraoperatively and continued for 710 days. Animals were given a 4- to 6-wk recovery period after surgery.

A second aseptic surgical procedure was performed once animals could reliably execute all the behavioral tasks used in the study. A stainless steel recording chamber (Crist Instruments) was positioned stereotaxically perpendicular to the horizontal plane over a 15-mm craniotomy and bonded to 46 additional orthopedic bone screws and the original implant with orthopedic bone cement. The recording chamber was centered stereotaxically at position 0,0, the intersection of the midsagittal and interaural planes (cf. Olson et al. 1996). Postoperatively, animals received analgesics for a minimum of 3 days and antibiotics for 710 days. The recording chamber was kept clean with daily antibiotic washes and sealed with replaceable sterile Cilux caps. Single-cell recording experiments began after a 1-wk postoperative period.

Behavioral techniques

Access to water was controlled during training and testing, and animals were habituated to head restraint and trained to perform oculomotor tasks for a fruit-juice reward using a custom-built software interface (Ryklin Software). Visual stimuli consisted of light-emitting diodes (LEDs; LEDtronics), which could be illuminated to appear red, green, or yellow to normal human observers. The LEDs were fixed on a tangent screen placed 144.78 cm (57 in.) from the eyes of the animal, forming a grid of points, separated by 1, spanning 49 horizontally and 41 vertically. These LEDs could be illuminated within 1 ms and extinguished within 7 ms by the computer system controlling the experiments.

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