Toolbox/Lecture 9

Multielectrode array
Multi-electrode arrays are used to stimulate and record extracellular electrical activity in many recording sites. This multi-unit approach offers the advantage of simultaneously recording tens or even hundreds of neurons at the same time; one can choose to analyze the activity of a single cell or any combination of cells. The technology can be used to record electrophysiological data both in vivo and in vitro.

Toads
The toad’s stereotyped prey capture response was studied in order to better understand how releasers, features of a stimulus that activate a fixed action pattern, are detected. For the toad, the fixed action pattern was orienting its head towards potential prey and the releaser was a cardboard cutout that resembled a worm. Three different types of stimuli were placed in front of the frog and moved in a horizontal plane. The toad’s orienting response for each stimulus was measured. When a rectangular cardboard stimulus was moved across the toad’s visual field in the direction of its long axis, the so-called “worm” configuration, a strong orienting response was elicited. When a rectangular cardboard stimulus was moved across the toad’s visual field in the direction of its short axis, the so-called “anti-worm” configuration, no response was elicited. When the stimulus was a square piece of cardboard, the toad moved toward it if the square was small and moved away from it if the square was large, the shift in orientation taking place at the point where the square stopped being viewed as prey by the toad and started being viewed as a predator. A type of tectal neuron called TH5(2) which demonstrated frequent impulses in response to the worm configuration, infrequent impulses in response to the anti-worm configuration, and impulses of decreasing frequency in response to square stimuli of increasing size is a strong candidate for the feature detector.