Measurement Techniques and Instrumentation

Experiments were performed under animal care and experimental guidelines that conformed to those set by the National Institutes of Health. Only a brief description of the animal preparation, maintenance, and surgical procedures is given here because they have been fully described elsewhere (Nordhausen et al., 1996; Warren et al., 2001). Felines were inducted with Telazol, cannulated, intubated, and their heads immobilized. The animals were artificially ventilated and anesthesia was maintained with halothane (approximately 0.8% during recording). The visual cortex was exposed by a 1- to 2-cm-diameter craniotomy and the dura reflected. Paralysis was established with pancuronium bromide (0.1 mg/kg/h, i.v.). The pupils were dilated, the nictitating membranes were retracted, and the eyelids were sutured open. Gas-permeable contact lenses were placed in each eye to protect the corneas. The retinas were back-refracted onto a tangent screen and the locations of retinal landmarks were recorded on the screen to locate the area centralis (Bishop et al., 1962; Nikara et al., 1968).

An acute configuration of the Utah Electrode Array (Cyberkinetics Neurotech-nology Systems, Inc. Foxborough, MA) was used for all experiments. An electron micrograph of the UEA and a light micrograph of the implant array system are shown in figure 3.1.

The fabrication and characteristics (Jones et al., 1992) as well as the pneumatic insertion technique (Rousche and Normann, 1992) of the UEA are described elsewhere. For the array used, the 1.5-mm-long electrodes were arranged in a 10 x 10 grid with 0.4-mm spacing between adjacent electrodes. The electrode impedance measured with a 1-kHz, 100-nA, sinusoidal signal ranged between 200 and 400 kW, with the typical impedance around 300 kW. The UEA was implanted to a depth of approximately 1 mm at the junction of the lateral and posterior lateral gyri.

Neural activity as well as the state of the visual stimulus was recorded by a 100-channel data acquisition system (Cyberkinetics Neurotechnology Systems, Inc.). This system filtered (250-7500 Hz) and digitized the neural signals. Further details of the data acquisition system are available elsewhere (Guillory and Normann, 1999). In the experiments described in this chapter, we collected data from both eyes and recorded activity on 98 of the possible 100 electrodes. No data were recorded on the remaining two channels because these two amplifiers had known problems.

Figure 3.1

The Utah Electrode Array (UEA) consists of 100, 1.5-mm-long electrodes that project from a 0.25-mm-thick, 4 x 4 mm silicon substrate (see inset). The array is connected to a connector board by 100, 25-|m-diameter insulated wires.

Figure 3.1

The Utah Electrode Array (UEA) consists of 100, 1.5-mm-long electrodes that project from a 0.25-mm-thick, 4 x 4 mm silicon substrate (see inset). The array is connected to a connector board by 100, 25-|m-diameter insulated wires.

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