Science
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Aversive classical conditioning of Aplysia californica, a gastropod mollusk suited for neurobiological study, produces a learned reaction to the chemosensory conditioned stimulus that is expressed as a marked facilitation of four defensive responses: two graded reflexes (head and siphon withdrawal), an all-or-none fixed act (inking), and a complex fixed action pattern (escape locomotion). In addition, the conditioned stimulus produces a concomitant depression of at least one appetitive response, feeding. These extensive and selective actions of the conditioned stimulus in Aplysia resemble the actions of conditioned fear stimuli in higher mammals and suggest that the functional equivalent of fear occurs in invertebrates and thus may be an adaptive mechanism that is widespread in the animal kingdom.
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Electromyographic studies of brachiation in the gibbon controvert deductions, based on dissection, about the purported functions of muscle chains in the hylobatid forelimb. Neither force conduction distally along the components of the chains nor simultaneity of muscular contraction occurs in brachiation. Rather, the unique structure of the forelimb is probably the result of evolved changes in the short head of biceps brachii to enhance its role as a forearm flexor.