5 mg/kg, i.m.) and ketamine hydrochloride (5 mg/kg, i.m.). The plate was anchored with dental acrylic to titanium bolts inserted in the skull. We also implanted a reference pin, the location of which was based on GSI-IX in vitro the zero coordinates defined in the stereotaxic atlas of the brain of Macaca fuscata individuals (Kusama & Mabuchi, 1970). During the surgery, heart and respiratory functions and rectal temperature were monitored (LifeScope
14; Nihon Kohden, Tokyo, Japan). A blanket heater was used to keep body temperature at 36 ± 0.5 °C. Antibiotics were administered topically and systemically for 1 week after the surgery to prevent infection. Two weeks after surgery, the monkey was retrained while the head was painlessly fixed to the stereotaxic apparatus by using the head-restraining device. The performance criterion (> 85%) was again attained within 10 days. Before recording from the pulvinar in each hemisphere, a marker consisting of a tungsten wire (diameter – 500 μm) was inserted
near the target area under anesthesia, and three-dimensional magnetic resonance imaging scans of the monkey head were performed. The 3D pictures of the monkey brain with the marker were reconstructed by computer rendering. The 3D stereotaxic coordinates of the target area were determined in reference to the marker in the 3D reconstructed brain (Asahi et al., 2003, 2006). After ABT-263 concentration the last recording session, several small marking lesions were created in the pulvinar by passing 20–30 μA of anodal current for 30 s through an electrode placed stereotaxically. Subsequently, the monkeys were deeply anesthetized with an overdose of sodium pentobarbital (60 mg/kg, i.m.) and perfused transcardially with 0.9% saline followed by 10% buffered formalin. The brains were removed from the skulls and cut into 50-μm sections containing the pulvinar. Sections were stained with Cresyl violet. The sites of electrical lesions were determined microscopically. The location of each recording site was then calculated over by comparing the stereotaxic coordinates of recording sites with
those of lesions, and were plotted on the actual tissue sections. Locations of visually responsive neurons in the two monkeys were compared on the basis of the shapes of the pulvinar nuclei, and were re-plotted on the serial sections of the pulvinar of one monkey, from 8 mm (AP8) to 5 mm anterior (AP5) to the interaural line. After the monkeys relearned the DNMS task at a > 85% correct ratio, we commenced recording neuronal activity. Neuronal activity was recorded from each hemisphere in both subjects. A glass-insulated tungsten microelectrode (0.8–1.5 MΩ at 1 kHz) was stereotaxically inserted into the pulvinar vertically to the orbitomeatal plane in a stepwise fashion by a pulse motor-driven manipulator (SM-21; Narishige, Tokyo, Japan). Only neuronal activities with a signal-to-noise ratio > 3 : 1 were recorded.
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