Hebbian analysis of the transformation of medial entorhinal grid-cell inputs to hippocampal place fields.

The discovery of grid cells in the medial entorhinal cortex (MEC) permits the characterization of hippocampal computation in much greater detail than previously possible. The present study addresses how an integrate-and-fire unit driven by grid-cell spike trains may transform the multipeaked, spatial firing pattern of grid cells into the single-peaked activity that is typical of hippocampal place cells. Previous studies have shown that in the absence of network interactions, this transformation can succeed only if the place cell receives inputs from grids with overlapping vertices at the location of the place cell's firing field. In our simulations, the selection of these inputs was accomplished by fast Hebbian plasticity alone. The resulting nonlinear process was acutely sensitive to small input variations. Simulations differing only in the exact spike timing of grid cells produced different field locations for the same place cells. Place fields became concentrated in areas that correlated with the initial trajectory of the animal; the introduction of feedback inhibitory cells reduced this bias. These results suggest distinct roles for plasticity of the perforant path synapses and for competition via feedback inhibition in the formation of place fields in a novel environment. Furthermore, they imply that variability in MEC spiking patterns or in the rat's trajectory is sufficient for generating a distinct population code in a novel environment and suggest that recalling this code in a familiar environment involves additional inputs and/or a different mode of operation of the network.

Minority preferences and disease types for non-emergent emergency department usage in a CHIP population

Background. Of the over five million annual pediatric visits to U.S. emergency departments, one-third to one-half are for non-emergent conditions. Minorities are more likely to utilize the emergency department (ED) for non-emergent conditions. Very little research has analyzed the role of illness type, perceived need, or family preferences in explaining this disparity. ^ Objectives. This study examined racial-ethnic differences in preferences for care among non-emergent users of the ED. ^ Research design. A random selection of pediatric non-emergent ED users within a single CHIP managed care plan were surveyed regarding attitudes and health care preferences. Preferences for ED utilization were analyzed by racial-ethnic category, controlling for illness type, child and guardian age, education level, language, and perceived need. ^ Results. A total of 250 families were surveyed. Most respondents reported having a regular doctor, satisfaction with their physician, and ready access to their physician. Fifteen percent of White, 39% of Hispanic, and 38% of Black families reported they preferred the emergency department for ill care. In multivariate analysis, Whites families were significantly less likely to prefer the emergency department for ill visits (odds ratio, 0.12; 95% confidence interval 0.03-0.55) compared to Blacks and Hispanics. ^ Conclusions. Racial-ethnic disparities in non-emergent ED utilization may be partially explained by different preferences for care. ^ Key words: children, emergency department, preferences for care, disparities ^