Engram

linotte dunce rutabaga amnesiac LRN —I—► STM —I—► MTM

dCREB2-b CXM - LTM

V radish

Fig. 27 Genetic dissection has unveiled multiple 'phases in the 'acquisition and the 'consolidation of memory in the fruit fly. (a) Four functionally distinct phases are proposed to underlie the memory curve observed in normal flies trained to avoid a shock-associated odour: STM, short-term memory; MTM, middle-term memory; ARM, memory that is resistant to anaesthesia; LRN, learning; LTM, long-term memory. STM decays the fastest and LTM the slowest. (b) A scheme showing where in the pathway different mutants and pharmacological manipulations exert their primary disruptive effects: linotte, a mutant defective in a putative 'protein kinase; dunce, a mutant defective in a form of the enzyme that degrades cAMP, cAMP-dependent phosphodiesterase; rutabaga, a mutant defective in the form of the enzyme that produces cAMP, adenylyl cyclase (this form of the enzyme is sensitive to 'calcium and may serve as a 'coincidence detector of the 'neurotransmitter and calcium signals); amnesiac, a mutant defective in the production of a peptide that stimulates cAMP synthesis; radish, the product of which is yet unidentified; dCREB2-b, flies engineered to express an antagonist of the transcription factor 'CREB; CXM, flies treated with the 'protein synthesis inhibitor cyclo-heximide.The figure is adapted from Dubnau and Tully (1998). For the molecular defects in the indicated mutants, see Dura et al. (1995; linotte), Byers et al. (1981; dunce), Dudai et al. (1983), Livingstone et al. (1984) (rutabaga), and Waddell et al. (2000; amnesiac).

of Drosophila (Corfas and Dudai 1990; Davis 1993; Waddell et al. 2000; Zars et al. 2000; Dubnau et al. 2001). This search for the "engram is not too easy, for reasons including the fact that the brain and the thoracic ganglion of the fruit fly are small and compact. "Functional neuroimaging methods, similar to those already in use in the "honeybee, may facilitate the task.

Selected associations: CREB, Intracellular signal trans-duction cascade, Neurogenetics, Simple system

1On the virtues of working with flies in general, see Dethier (1962).

2The accumulative body of knowledge, procedures, traditions, and rituals of the drosophilists provides an interesting example of scientific sub'culture (Kohler 1994;Weiner 1999).

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