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The present review examines the role of perirhinal cortex (PRC) in Pavlovian fear conditioning. The focus is on rats, partly because so much is known, behaviorally and neurobiologically, about fear conditioning in these animals. In addition, the neuroanatomy and neurophysiology of rat PRC have been described in considerable detail at the cellular and systems levels. The evidence suggests that PRC can serve at least two types of mnemonic functions in Pavlovian fear conditioning. The first function, termed "stimulus unitization," refers to the ability to treat two or more separate items or stimulus elements as a single entity. Supporting evidence for this perceptual function comes from studies of context conditioning as well as delay conditioning to discontinuous auditory cues. In a delay paradigm, the conditional stimulus (CS) and unconditional stimulus (US) overlap temporally and co-terminate. The second PRC function entails a type of "transient memory." Supporting evidence comes from studies of trace cue conditioning, where there is a temporal gap or trace interval between the CS offset and the US onset. For learning to occur, there must be a transient CS representation during the trace interval. We advance a novel neurophysiological mechanism for this transient representation. These two hypothesized functions of PRC are consistent with inferences based on non-aversive forms of learning., (Copyright © 2012 Wiley Periodicals, Inc.)

Persistent-firing neurons in the entorhinal cortex (EC) and the lateral nucleus of the amygdala (LA) continue to discharge long after the termination of the original, spike-initiating current. An emerging theory proposes that endogenous persistent firing helps support a transient memory system. This study demonstrated that persistent-firing neurons are also prevalent in rat perirhinal cortex (PR), which lies immediately adjacent to and is reciprocally connected with EC and LA. Several characteristics of persistent-firing neurons in PR were similar to those previously reported in LA and EC. Persistent firing in PR was enabled by the application of carbachol, a nonselective cholinergic agonist, and it was induced by injecting a suprathreshold current or by stimulating suprathreshold excitatory synaptic inputs to the neuron. Once induced, persistent firing lasted for seconds to minutes. Persistent firing could always be terminated by a sufficiently large and prolonged hyperpolarizing current; it was prevented by antagonists of muscarinic cholinergic receptors (mAChRs); and it was blocked by flufenamic acid. The latter has been suggested to inhibit a Ca(2+) -activated nonspecific cation conductance (G(CAN) ) that normally furnishes the sustained depolarization during persistent firing. In many PR neurons, the discharge rate during persistent firing was a graded function of depolarizing and/or hyperpolarizing inputs. Persistent firing was not prevented by blocking fast excitatory and inhibitory synaptic transmission, demonstrating that it can be generated endogenously. We suggest that persistent-firing neurons in PR, EC, LA, and certain other brain regions may cooperate in support of a transient-memory system., (Copyright © 2011 Wiley Periodicals, Inc.)

Posttraumatic stress disorder (PTSD) is common following the experience of a natural disaster and sleep disturbance is an important influence on its course in adults, but little research is available examining sleep and PTSD in youths. This study's objective was to evaluate the role of sleep disturbance and the developmentally influenced factor of fear of sleeping alone in the maintenance of posttraumatic stress (PTS) symptoms in youths. Deidentified data of 191 Hurricane Katrina survivors ages 8 to 15 were used in this study. We found cross-sectional relationships of sleep disturbance and fear of sleeping alone with PTS symptom severity. Longitudinal analysis also indicated that general sleep disturbance at 24 months (T1) was predictive of PTS symptoms severity at 30 months (T2) even after adjusting for PTS symptom severity at T1, age, sex, and continued disrepair to the home. These results have implications for intervention strategies among youth exposed to traumatic events., (Copyright © 2011 International Society for Traumatic Stress Studies.)

Evolving relationships between electrical conductivity (EC) and sodium adsorption ratio (SAR) in reconstructed soils at surface mines have been insufficiently documented in the literature. Some minesoils (i.e., rootzone material) are classified as saline, sodic, or saline-sodic and are considered unsuitable for revegetation. Weatherable minerals such as calcite and gypsum are common in alkaline minesoils and on dissolution tend to mitigate elevated SAR levels by maintaining or increasing electrolytes in the soil and providing sources of exchangeable calcium and magnesium. Topsoils (i.e., coversoils) contribute to mitigation of sodic conditions when soluble cations are translocated from coversoils into the underlying minesoils. This study evaluated the weathering characteristics of minesoils sites from three surface coal mines in northwestern New Mexico and northeastern Arizona. Minesoils were grouped into 11 classes based on EC and SAR. After 6 to 14 yr, differences between upper and lower halves of the coversoils suggest general increases occurred with EC, SAR, chloride (Cl(-)), and sulfate (SO(4)(2-)) with depth. Within the reclaimed minesoils, there were several significant (P < 0.05 or < 0.10) relationships among EC and SAR that related to Minesoil Class. Lower SAR levels with corresponding increases in EC compared to baseline minesoils were more apparent in upper minesoil depths (0-5 and 5-15 cm). Minesoil anion concentrations suggested coversoil leachates and gypsum dissolution influenced EC and SAR chemistry. Over time, chemical changes have increased the apparent stability of the saline and sodic reclaimed minesoils studied thereby reducing risks associated with potential aggregate slaking and clay particle dispersion.

Whole-cell recordings from 140 pyramidal neurons in layer V of rat perirhinal cortex (PR) revealed three distinct firing patterns: regular spiking (RS, 76%), burst spiking (BS, 9%), and late spiking (LS, 14%). LS neurons have not previously been reported in layer V of any cortical region. LS cells in layer V of PR exhibited delays of up to 12 s from onset of a depolarizing current step to spike threshold, followed by sustained firing. In contrast, pyramidal cells in layer V of other cortical regions contain only RS and BS cells. Within PR, the percentage of LS neurons in layer V differs markedly from what we previously observed in layers II/III (50% LS) and VI (90% LS). Morphologically, BS neurons in layer V of PR had thick primary apical dendrites that terminated in a tuft within layer I, whereas RS and LS cells had relatively thin primary apicals that terminated either diffusely or in a layer I tuft. At holding potentials near rest, PR neurons exhibited small (approximately 15 pA), inward, spontaneous postsynaptic currents (PSCs) that were indistinguishable among the three cell types. Currents evoked by minimal stimulation of layer I were about 2.8 times larger than the spontaneous PSCs. Evoked currents had unusually long onset latencies with little variation in latency, consistent with monosynaptic responses evoked by stimulation of unmyelinated fibers. The prevalence of LS cells in combination with the long-latency monosynaptically evoked PSCs suggested that PR is not a region of rapid throughput. This is consistent with anatomical data suggesting that PR is a higher-level association cortex. These data further advance an emerging picture of PR as a cortical region with a unique distribution of cell types different from other cortical regions.

Much of the current interest in the hippocampus concerns a rapid and persistent form of synaptic plasticity, called long-term potentiation (LTP), that is a candidate substrate for some of the mnemonic functions of this structure. There are at least two kinds of LTP in the hippocampus. One form is found at the synapse between the mossy fibers of the granule cells and the pyramidal neurons of the CA3 region. Attempts to examine the mechanism underlying this form of LTP have yielded contradictory conclusions. The authors show how the complex circuitry of the dentate gyrus and adjacent hippocampus may have caused the contradictions. To overcome problems introduced by the circuitry, a specific set of procedures and criteria for evoking and identifying mossy fiber responses is proposed. Use of these or similar procedures and criteria will improve the design and interpretation of experiments on mossy fiber LTP and allow more informative comparisons among species and brain regions and across laboratories.

In this study we compared the results of measurement of duodenogastric reflux using 24-hour intragastric pH monitoring and nasogastric aspiration with analysis of bile acid and alpha amylase concentrations. Eight patients were studied at least 5 months after biliary and/or gastric surgery. The correlation coefficient of pH and bile acid concentration was 0.36 (p less than 0.001) and of pH and amylase concentration was 0.48 (p less than 0.001). If a pH greater than 4.0 was taken to indicate duodenogastric reflux this had a sensitivity of 84% compared with either high bile acid or amylase concentration. Bile acid concentration has been the "standard" method of measuring duodenogastric reflux. pH monitoring is relatively simple to perform, causes little patient distress, and can measure episodes of duodenogastric reflux over a continuous 24-hour period.