The entorhinal cortex (EC), with connections to the hippocampus, amygdala, and neocortex, is a critical, yet still underexplored, contributor to fear memory. Previous research suggests possible heterogeneity of function among its lateral (LEC) and medial (MEC) subregions. However, it is not well established what unique roles these subregions serve as the literature has shown mixed results depending on target of manipulation and type of conditioning used. Few studies have manipulated both the LEC and MEC within the same experiment. The present experiment systematically manipulated LEC and MEC function to examine their potential roles in fear memory expression. Long-Evans rats were trained using either trace or delay fear conditioning. The following day, rats received an N-methyl-D-aspartate (NMDA)-induced lesion to the LEC or MEC or received a sham surgery. Following recovery, rats were given an 8-min context test in the original context. The next day, rats were tested for tone freezing in a novel context with three discrete tone presentations. Further, rats were tested for hyperactivity in an open field under both dark and bright light gradient conditions. Results: Following either LEC or MEC lesion, freezing to context was significantly reduced in both trace and delay conditioned rats. LEC-lesioned rats consistently showed significantly less freezing following tone-offset (trace interval, or equivalent, and intertrial interval) in both trace and delay fear conditioned rats. Conclusions: These data suggest that the LEC may play a role in the expression of a conjunctive representation between the tone and context that mediates the maintenance of post-tone freezing.
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Click to increase image sizeClick to decrease image size This article is part of the following collections: The Fibonacci Sequence Additional informationNotes on contributorsArthur T. BenjaminArthur Benjamin (benjamin@math.hmc.edu) earned his B.S. in Applied Mathematics from Carnegie Mellon and his Ph.D. in Mathematical Sciences from Johns Hopkins where he studied discrete optimization under Alan J. Goldman. Since 1989, he has taught at Harvey Mudd College, where he is currently an associate professor. He is editor of the Spectrum book series for MAA, and an Associate Editor of Mathematics Magazine. He was recently awarded the MAA's Haimo Award for distinguished college teaching.Jennifer J. QuinnJennifer Quinn (jquinn@oxy.edu) is an Associate Professor of Mathematics at Occidental College in Los Angeles. She earned her degrees from Williams College, University of Illinois, Chicago, and the University of Wisconsin, Madison continually moving the "Quinn family center of gravity" west. Her primary research interests are combinatorics and graph theory. Lately she has been having great fun hosting The Number Years, a mathematical game show co-created with Occidental graduate Eric Libicki and Art Benjamin.
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Retrograde amnesia following disruptions of hippocampal function is often temporally graded, with recent memories being more impaired. Evidence supports the existence of one or more neocortical long-term memory storage/retrieval site(s). Neurotoxic lesions of the medial prefrontal cortex (mPFC) or the dorsal hippocampus (DH) were made 1 day or 200 days following trace fear conditioning. Recently encoded trace fear memories were most disrupted by DH lesions, while remotely encoded trace and contextual memories were most disrupted by mPFC lesions. These data strongly support the consolidation theory of hippocampus function and implicate the mPFC as a site of long-term memory storage/retrieval.
Abstract Patients diagnosed with posttraumatic stress disorder (PTSD) present with a spectrum of debilitating anxiety symptoms resulting from exposure to trauma. Women are twice as likely to be diagnosed with anxiety and PTSD compared to men; however, the reason for this vulnerability remains unknown. We conducted four experiments where we first demonstrated a female vulnerability to stress‐enhanced fear learning (SEFL) with a moderate, acute early life stress (aELS) exposure (4 footshocks in a single session), compared to a more intense aELS exposure (15 footshocks in a single session) where males and females demonstrated comparable SEFL. Next, we demonstrated that this female vulnerability does not result from differences in footshock reactivity or contextual fear conditioning during the aELS exposure. Finally, using gonadectomy or sham surgeries in adult male and female rats, we showed that circulating levels of gonadal steroid hormones at the time of adult fear conditioning do not explain the female vulnerability to SEFL. Additional research is needed to determine whether this vulnerability can be explained by organizational effects of gonadal steroid hormones or differences in sex chromosome gene expression. Doing so is critical for a better understanding of increased female vulnerability to certain psychiatric diseases.
The Mathematical Association of America presented the 2016 Gung and Hu Award for Distinguished Service to Mathematics to Dr. George Berzsenyi for his remarkable career promoting the art of problem solving, creating national and international mathematical talent searches, supporting mathematical competitions, and empowering generations of high school students to pursue their mathematical and scientific passions. George is a native of Hungary and came to the United States as a high school student in 1957 following the end of the Hungarian Revolution of 1956. He completed his education in Texas, including a Ph.D. in mathematics at Texas Christian University. He taught at universities in Texas and Louisiana prior to moving to Indiana to chair the Department of Mathematics at Rose-Hulman Institute of Technology (RHIT), where he is now Professor Emeritus.
The occurrence of incompressible quantum fluid states of a two dimensional system is a result of electron--electron interactions in a highly degenerate fractionally filled Landau level. Novel quasiparticles (QP's) called composite Fermions (CF's) have allowed a simple single particle description of the most prominent incompressible states. Residual interactions among these QP's are investigated. These interactions determine the type of "daughter states" that can occur at the next generation. We demonstrate that at certain values of the QP filling factor nu_QP, Laughlin correlations among the QP's give rise to states of the standard CF hierarchy. At other values of nu_QP pairing of QP's is found leading to a novel hierarchy of incompressible states.
