Hippocampal theta frequency is a somewhat neglected topic relative to theta power, phase, coherence, and cross-frequency coupling. Accordingly, here we review and present new data on variation in hippocampal theta frequency, focusing on functional associations (temporal coding, anxiety reduction, learning, and memory). Taking the rodent hippocampal theta frequency to running-speed relationship as a model, we identify two doubly-dissociable frequency components: (a) the slope component of the theta frequency-to-stimulus-rate relationship (“theta slope”); and (b) its y-intercept frequency (“theta intercept”). We identify three tonic determinants of hippocampal theta frequency. (1) Hotter temperatures increase theta frequency, potentially consistent with time intervals being judged as shorter when hot. Initial evidence suggests this occurs via the “theta slope” component. (2) Anxiolytic drugs with widely-different post-synaptic and pre-synaptic primary targets share the effect of reducing the “theta intercept” component, supporting notions of a final common pathway in anxiety reduction involving the hippocampus. (3) Novelty reliably decreases, and familiarity increases, theta frequency, acting upon the “theta slope” component. The reliability of this latter finding, and the special status of novelty for learning, prompts us to propose a Novelty Elicits Slowing of Theta frequency (NEST) hypothesis, involving the following elements: (1) Theta frequency slowing in the hippocampal formation is a generalised response to novelty of different types and modalities; (2) Novelty-elicited theta slowing is a hippocampal-formation-wide adaptive response functioning to accommodate the additional need for learning entailed by novelty; (3) Lengthening the theta cycle enhances associativity; (4) Even part-cycle lengthening may boost associativity; and (5) Artificial theta stimulation aimed at enhancing learning should employ low-end theta frequencies.

This article addresses the need for the United States to reduce emissions from the transportation sector. In order to concisely evaluate the political discussion of promoting renewable energy use and discouraging reliance on fossil fuels, this article focuses on the adoption of electric and hybrid vehicles as a means of illustrating the larger policy challenge of how to maximize policy effectiveness at reducing emissions while minimizing economic disruption. The article estimates the magnitude of electric and gas-powered vehicles purchases in response to either a subsidy or a tax and discusses the positive and negative outcomes of each policy approach. The article finds that while a tax on carbon emissions may be most effective in removing gas-powered vehicles from the road, it will disproportionately affect lower-income households. Implementing substantial subsidies for electric vehicles, funded through a smaller tax on carbon emissions, is suggested as a solution to reduce the regressive impacts of a standalone carbon tax.

People with criminal records in the United States continue to face limited employment opportunities due to social stigma and legal barriers. In contrast to the civilian sector, the military conducts a "whole person" evaluation to screen potential recruits and regularly hires people with felony and misdemeanor records. Moreover, evidence suggests that the military serves as a socially integrative institution and may facilitate desistance from future crimes. However, critics argue that the military exacerbates inequalities by subjecting marginalized communities to the unequal burden of service. Using the data obtained from the Army, we examine the relative risks of combat exposure and casualties between enlisted soldiers with and without criminal records who joined between 2002 and 2009. The results suggest that soldiers with felony and misdemeanor records are more likely to be assigned to combat occupations than those without criminal records. We also find that among soldiers assigned to positions with low combat exposure, ex-offenders face a higher risk of death compared to those without criminal records. Findings do not dispute the idea that the military facilitates desistance from future crimes and provides second chances to people with criminal records, but reaffirm the fact that military service costs lives and limbs.