Abstract
The negative phototaxic behavior of planaria (turns and contractions) is augmented when light is paired with an electrical field. Ii has been suggested that this phenomenon represents a learning process (Thompson and McConnell, 1955), i.e., that planaria can be conditioned to associate light and electrical stimuli. This conclusion is based on the tacit assumption that planaria are not sensitized by the electrical field used in conditioning procedures. However, it has been shown that this assumption is incorrect; planarian negative phototaxic behavior is augmented by light and shock that are temporally unrelated (Brown et al., 1966b). This finding suggests that modified planarian behavior, widely attributed to “learning,” actually represents sensitization. It has been suggested that the augmented phototaxis (conditioned response) of planaria is transferable to other worms by ingestion (McConnell, 1962), and that it is evident in both head and tail sections regenerated from conditioned, bisected worms, because both types of regenerate display similar exaggerated behavior in response to light stimuli (McConnell et al., 1959). However, when head and tail sections were regenerated in the presence of ribonuclease, tail sections were less light responsive (showed “less resistance to extinction”) than head sections following regeneration.
Published Version
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