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Methamphetamine (MA) is a highly addictive stimulant with recent upward trends in prevalence and associated public health problems. Drug demand, as assessed by hypothetical purchasing tasks, has been useful in addictions research and may help our understanding of the factors influencing MA use. However, no studies have assessed MA demand using current models of demand. The purpose of the current study was to assess demand for MA using a hypothetical drug purchasing task. Given high rates of cigarette smoking among MA users, it was of interest also to assess and compare demand for MA relative to cigarettes. Participants consisted of non-treatment-seeking volunteers with MA use disorder (N = 18), of whom 17 reported daily smoking. Results showed the exponentiated demand model provided a good fit to consumption data. Results from Bayesian generalized linear modeling demonstrated multiple positive relationships (posterior probability ≥75%) between self-reported drug use (days MA used in the past 30 days, cigarettes smoked per day) and indices of demand for each drug (Qo, Omax, Pmax, and break point). Comparing MA to cigarettes, results from Bayesian generalized linear mixed modeling revealed greater abuse liability for MA compared to cigarettes (posterior probability ≥99%) based on α and essential value. Overall, the findings of the current study support the feasibility and validity of the exponentiated demand model for assessing demand for drugs among individuals with MA use disorder. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Background and Objectives: Delay discounting is associated with numerous clinically significant aspects of substance use disorders (SUDs). Recent studies have demonstrated that different models for assessing discounting may result in disparate conclusions. The current study compared two discounting tasks: money now versus money later (M-M) and methamphetamine now versus money later (MA-M) among non-treatment seeking individuals (N = 59) with methamphetamine use disorder (MAUD). Results from each task were assessed using three different models for assessing delay discounting., Methods: Discounting data were fit to three models of discounting, log k using Mazur's hyperbolic formula, area under the curve (AUC), and an alternative AUC model in which the delay values have been log transformed (AUClog)., Results: For both discounting tasks, the distribution of model-related outcomes were normally distributed when using log k and AUClog, but skewed for AUC. Discounting in the MA-M task was significantly greater compared to the M-M task when using log k and AUClog but not AUC., Conclusion: To our knowledge, the current study is the first to report significantly greater discounting in a MA-M relative to M-M discounting task among individuals with MAUD, an outcome consistent with other psychomotor stimulants and drugs of abuse., Scientific Significance: The differential results observed across the three discounting models reaffirm potential issues with AUC noted in recent studies and highlight that researchers must be cautious when deciding on their final model of discounting. (Am J Addict 2018;XX:1-8)., (© 2018 American Academy of Addiction Psychiatry.)

Delay discounting describes how a reward loses value as a function of increasing delay to its receipt and has been reliably associated with a variety of vulnerable populations including those with substance use disorders (SUDs). Two commonly used models to assess delay discounting in the field of SUDs include log k derived from Mazur's hyperbolic equation and area under the curve (AUC). In the current study, we compared log k with AUC on delay discounting data obtained from non-treatment seeking, cocaine- and methamphetamine-dependent volunteers. We specifically chose this population in order to obtain a distribution of relatively steep discounters. The results show that the relationship between AUC and log k is better described by a quadratic rather than a linear function. In other words, changes in discounting, as measured by AUC and log k , are reflected differently across a range of obtained responses. Additionally, the distribution of AUC values was skewed, which appears to be more likely among populations exhibiting greater discounting. Finally, closer examination of indifference points revealed that AUC was almost perfectly predicted by the area from the two longest delays, with relatively less input from shorter delays. Given these results, researchers should exercise additional caution when deciding which method to assess discounting data and how final results are to be interpreted, particularly when dealing with relatively high rates of discounting. High rates of discounting are likely in populations with impulsive disorders such as those with SUDs.

A number of studies have established that transcranial direct current stimulation (tDCS) modulates cortical excitability. We previously demonstrated polarity dependent changes in parietal lobe blood oxygen level dependent (BOLD) fMRI in a group of young adults during a spatial navigation task [15]. Here we used resting state functional connectivity (rsFC) to examine whether analogous changes were also evident during the resting state. Participants were randomized to either a parietal-anodal, frontal-cathodal (P+F-) or the opposite montage (P-F+) and received 20min of tDCS (2mA) before undergoing resting-state fMRI. rsFC was evaluated between the groups by placing a seed in the medial superior parietal lobule (mSPL), which was under the target electrode. rsFC between the mSPL and a number of other areas involved in spatial navigation, scene processing, and sensorimotor processing was significantly higher in the P+F- than the P-F+ group. Thus, the modulatory effects of tDCS were evident during rest and suggest that stimulation primes not just the underlying neocortex but an extended network that can be recruited as necessary during active task performance., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Background: Allocentric navigation declines with age and neurologic disease whereas egocentric navigation does not; differences that likely arise from maladaptive changes in brain regions mediating spatial (parietal cortex; hippocampus) but not procedural processing (caudate nucleus). Transcranial direct current stimulation (tDCS) holds promise for treating such decline given its ability to modulate neuronal excitability, but its effects have yet to be examined on spatial navigation., Objectives/hypotheses: Using healthy young adults as a model, Study 1 intended to validate a novel spatial navigation paradigm using functional magnetic resonance imaging (fMRI). Using these data to determine targets for tDCS, Study 2 aimed to determine if 1) stimulation modulates activation in a polarity-specific manner; 2) stimulation results in global and/or task-specific activation changes; 3) activation changes are accompanied by changes in effective connectivity., Methods: All participants underwent fMRI while learning allocentric and egocentric environments. Twelve participants completed Study 1. In Study 2, 16 participants were randomized to 20 min of tDCS (2 mA) using a montage with the anode over PZ and cathode over AF4 (P+F-) or the reverse montage (P-F+)., Results: Study 1 revealed that distinct networks preferentially mediate allocentric and egocentric navigation. Study 2 revealed polarity-dependent changes in activation and connectivity. The P+F- montage increased these measures in spatial regions, especially during allocentric navigation, and the caudate nucleus. Conversely, the P-F+ montage increased activation and connectivity in lateral prefrontal cortices and posterior hippocampus., Conclusions: These findings support the neuromodulatory effects of tDCS in non-motor areas and demonstrate proof-of-principle for ameliorating age- and disease-related decline in navigational abilities., (Published by Elsevier Inc.)

Acute intermittent porphyria (AIP) is an autosomal dominant genetic defect in heme synthesis. Patients with this illness can have episodic life-threatening attacks characterized by abdominal pain, neurological deficits, and psychiatric symptoms. Feigning this illness has not been reported in the English language literature to date. Here, we report on a patient who presented to the hospital with an acute attack of porphyria requesting opiates. Diligent assessment of extensive prior treatment records revealed thirteen negative tests for AIP.

Advances in structural and functional neuroimaging techniques have unquestionably improved understanding of the development and progression of Alzheimer disease (AD), with evidence supporting regional (and network) change that underlies cognitive decline across the "healthy" aging/mild cognitive impairment (MCI)/AD spectrum. This review focuses on visual rating scales and volumetric analyses that could be easily integrated into clinical practice, followed by a review of functional neuroimaging findings suggesting that widespread cerebral dysfunction underlies the learning and memory deficits in MCI. Evidence of preserved neuroplasticity in this population and that cognitive rehabilitation techniques may capitalize on this plasticity to improve cognition in those with MCI is also discussed., (Published by Elsevier Inc.)

Objectives: To examine interface pressure characteristics for two alternating air cell mattresses used for pressure ulcer prevention and treatment in a spinal cord injury population., Design: Prospective evaluation of Dynamic Flotation System (DFS) mattress and the Pegasus Airwave Mattress. Subjects acted as their own controls., Setting: Veterans Affairs Medical Center Spinal Cord Injury Unit., Participants: Convenience sample of 15 subjects with spinal cord injuries., Interventions: Minimum, maximum, and average interface pressures, and interface pressure range were measured by use of a force-sensing array system. The sacrum was chosen as the area of interest. Recordings lasted 9.5-10 minutes. Analyses were performed on 19 subjects in the supine and 45-degree upright positions for both mattresses., Results: Maximum and average interface pressures and interface pressure ranges were significantly higher, whereas minimum interface pressures were significantly lower on the Pegasus vs the DFS. For either mattress, the 45-degree position resulted in significantly greater interface pressures. There was no consistent correlation found between interface pressures and body mass index., Conclusions: Interface pressure characteristics of these two mattresses are very different, and neither mattress retains performance in the 45-degree position. Which interface pressure characteristic is most clinically relevant remains undetermined. Avoidance of the 45-degree sitting position is recommended.