LTP Takes Route in the Hippocampus

fect, spreading to downregulate additional pathways. Such a model would fit especially well if olfactory signal-4040–4045. some, as it were—then cGMP concentration would be highest near stimulated receptors. Thus, L'Etoile and Bargmann speculate that such organization of olfactory transduction components might serve to physically and biochemically insulate different complexes from each other. via a different mechanism, since the effect does not require cyclase activity. One possible model is that ODR-1 binds to a protein required for butanone adaptation , titrates it, and thereby blocks adaptation. Perhaps Based on behavioral and lesion data and on the discov-signaling complexes are heterogeneous, such that com-ery of location-specific place cells in the hippocampus, plexes responding to other odors lack the protein bound O'Keefe and Nadel proposed that the hippocampus was by ODR-1 and are not affected by ODR-1 overex-the neural substrate of a cognitive map, used not only pression. for navigation but as " an objective spatial framework These results invite further experimentation. It will be within which the items and events of an organism's interesting to determine whether olfactory signaling experience are located and interrelated " (O'Keefe and components in various organisms do in fact cluster in Nadel, 1978, p. 1). Place cells are hippocampal principal discrete, spatially segregated complexes. As more is cells whose firing rate increases when the animal is at a learned about the binding specificity of odorant recep-particular location—the " place field " —in its environment, it will become more apparent ties of these cells have long been a source of fascination whether competition for receptor binding sites plays any for cognitive scientists, as they would appear to provide role in odor discrimination in various species, as has an important inroad into how learning and memory is been proposed previously (Siddiqi, 1987). It should also encoded. Most research on place cells has focused ei-be noted that many of the most interesting results from ther on the determinants of their spatial tuning (Redish, this work come from overexpression studies. Such stud-1999) or on the extent to which they encode nonspatial ies can be enormously illuminating and incisive, but ad-information (Cohen and Eichenbaum, 1993). Although a ditional insight can often be gained by complementing number of theoretical models have been proposed to them with studies of loss-of-function mutations. explain how place cells might control navigation, little Insulation of signaling pathways is likely to be critical experimental data exist to test these …