A biophysical model of synaptic plasticity and metaplasticity can account for the dynamics of the backward shift of hippocampal place fields.

Hippocampal place cells in the rat undergo experience-dependent changes when the rat runs stereotyped routes. One such change, the backward shift of the place field center of mass, has been linked by previous modeling efforts to spike-timing-dependent plasticity (STDP). However, these models did not account for the termination of the place field shift and they were based on an abstract implementation of STDP that ignores many of the features found in cortical plasticity. Here, instead of the abstract STDP model, we use a calcium-dependent plasticity (CaDP) learning rule that can account for many of the observed properties of cortical plasticity. We use the CaDP learning rule in combination with a model of metaplasticity to simulate place field dynamics. Without any major changes to the parameters of the original model, the present simulations account both for the initial rapid place field shift and for the subsequent slowing down of this shift. These results suggest that the CaDP model captures the essence of a general cortical mechanism of synaptic plasticity, which may underlie numerous forms of synaptic plasticity observed both in vivo and in vitro.

Are free condoms associated with the frequent use of condoms among men who have sex with men?

Introduction. The National Behavioral HIV Surveillance (NHBS) is a self-reported cross-sectional survey that monitors the spread of human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS). The 2004 survey asked if the participant received a free condom, used it, and if receiving a free condom made him more likely to use a condom. The aim of this cross-sectional study is to examine the Houston MSA sub-dataset to determine if there was a self-expressed association between receiving a free condom and likelihood of using a condom at next intercourse, and to determine if the strength of that association varied by demographic subgroup.^ Methods. The Houston MSA 2004 NHBS had 502 participants who were men who have sex with men (MSM). The present analysis examined the answers to the questions: "In the past 12 months, have you received free condoms?" "Have you used any of the free condoms you received?" and "Did getting these free condoms make you more likely to use condoms during sex?".^ Results. Out of 502 participants, 500 answered the question about receiving free condoms, 406 (81.2%) answered all three questions, and 204 (50.2%) answered "yes" to all three questions. In the subgroup analyses, Hispanics were significantly less likely and men under 29 years of age were significantly more likely to report that their condom use behavior was influenced by receiving a free condom. ^ Conclusion. The effect of receipt of free condoms on likelihood of condom use varies by demographic subgroup, but these potentially important preliminary findings will require further investigation to validate them and further explicate the possible underlying dynamics.^