E-Cigarette Demand: Impact of Commodity Definitions and Test–Retest Reliability

Introduction Behavioral economic demand provides a multidimensional understanding of reinforcement. Commodity purchase tasks are an efficient method for measuring demand in human participants. One challenge in translating these procedures to electronic nicotine delivery systems (ENDS or e-cigarettes) is defining commodity units given the lack of standardization in the e-cigarette marketplace. Aims and Methods The purpose of this study was to directly compare methods of operationalizinge-cigarette purchases, puffs, cartridges, and mLs liquid, using a within-subject design. Participants (N = 132) reporting past week e-cigarette use were recruited using crowdsourcing. Purchase tasks were completed operationalizing e-cigarette units as puffs or cartridges at baseline and puffs or mLs liquid at a 3-month follow-up. Results Bivariate associations supported convergent and discriminant validity with the largest effect size correlations for intensity and elasticity observed for the puff version. Interaction models suggested that product preferences moderated the relationship between time-to-first use and cartridge demand with larger effect size correlations among persons reporting a preference for JUULs, but weaker relationships among persons reporting other device preferences. Puff intensity (rxx = .61) and elasticity (rxx = .62) showed good test–retest reliability for participants reporting stable consumption, but poor test–retest reliability for individuals with changed consumption levels (intensity rxx = −.08; elasticity rxx = −.10). Conclusions This study highlights the relevance of commodity definitions in the e-cigarette purchase task. Puffs as an experimental commodity may provide flexibility for studying e-cigarette demand in heterogenous or unknown populations, whereas more tailored or personalized approaches like cartridge or mL-based tasks will likely be helpful when studying known subgroups. Implications The commodity purchase task procedure is widely used for understanding cigarette and e-cigarette demand in nicotine dependence research. This study evaluates the importance of operational definitions of e-cigarette commodities in the purchase task (ie, puffs, cartridges, or mLs liquid). Puffs may provide a more flexible commodity unit when evaluating e-cigarette demand in general or heterogenous populations, whereas device-specific units may prove more valuable when studying populations with consistent and known product use.

Coding of Tactile Response Properties in the Rat Deep Cerebellar Nuclei

In the lateral hemispheres of the cerebellar cortex, somatosensory responses are represented in a finely grained fractured somatotopy. It is unclear, however, how these responses contribute to the ultimate output of the cerebellum from the deep cerebellar nuclei (DCN). Robust responses of DCN neurons to somatosensory stimuli have been described, but a detailed examination of their somatotopic arrangement and stimulus coding properties is lacking. To address these questions, we recorded extracellular, single-unit activity in the DCN of ketamine-anesthetized rats in response to air-puff stimuli aimed at six different orofacial and forelimb locations. In additional experiments, the duration and intensity of air-puff stimuli to the ipsilateral upper lip were systematically varied. Overall, we found that DCN neuron responses to air puff stimuli showed combinations of three distinct response components: a short-latency spike response, a pronounced inhibition, and a long-latency increase in firing. Individual neurons responsive to air-puff stimulation exhibited any combination of just one, two, or all three of these response components. The inhibitory response was most common and frequently consisted of a complete cessation of spiking despite a high spontaneous rate of baseline firing. In contrast to published findings from cerebellar cortical recordings, the receptive fields of all responsive neurons in the DCN were large. In fact, the receptive field of most neurons covered the ipsi- and contralateral face as well as forepaws. Response properties of individual neurons did not reliably indicate stimulus intensity or duration, although as a population DCN neurons showed significantly increasing response amplitudes as air-puff intensity or duration increased. Overall, the responses were characterized by a distinct temporal profile in each neuron, which remained unchanged with changes in stimulus condition. We conclude that the responses in the DCN of rats to air-puff stimuli differ substantially from cerebellar cortical responses in their receptive field properties and do not provide a robust code of tactile stimulus properties. Rather, the characteristic temporal response profile of each neuron may be tuned to control the timing of a specific task to which its output is linked.

Thalamic VPM nucleus in the behaving monkey. II. Response to air-puff stimulation during discrimination and attention tasks

1. Single-unit activity was recorded in the ventral posterior medial (VPM) thalamic nucleus of awake monkeys while they performed detection and discrimination tasks involving tactile air-puff stimuli presented to the face. Neuronal responsiveness was compared directly with the monkey's discriminative performance. In addition, neuronal activity was compared when the monkey's attention was directed to the air-puff stimulus and when it was directed to a concurrent visual stimulus. 2. Neurons responding to the air-puff stimuli were classified as slowly adapting (SA), rapidly adapting (RA), inhibitory (IN), or multimodal (MM), according to their responses to manual and thermal stimulation, as well as their adaption rates to the air puff. Of 47 neurons responsive to air-puff stimulation and studied extensively in the behavioral task, 14 were classified as RA, 15 as SA, 6 as IN, and 12 as MM. The 12 MM neurons were so classified because, in addition to air puff, they responded to noxious heat, innocuous cooling, or noxious pinch. 3. Neurons from each class had restricted contralateral receptive fields localized within one division of the trigeminal nerve. There was no systematic difference in receptive-field size among groups. 4. A prominent difference in tactile responsiveness of MM neurons was response latency. Although the mean latency for RA, SA, and IN neurons was not significantly different (6.1, 9.1, and 12.2 ms, respectively), the mean latency for MM neurons was significantly longer than that for each of the other neuronal categories (28.8 ms; Ps < 0.001). These data suggest that the excitatory tactile afferent input to MM neurons is different from that to low-threshold neurons. 5. For RA, SA, and MM neurons the frequency of the neuronal discharge evoked by the air-puff stimulation was proportional to the intensity of the air puff. Thus responses of each neuronal class coded air-puff stimulus intensity. 6. The monkeys' ability to detect air-puff stimuli of various intensities was compared with the frequency of neuronal responses to those stimuli. Both the percent success in detecting differences in air-puff intensity and the detection latency were highly correlated with neuronal response frequency. The responses of all three excitatory neuronal categories corresponded well with the monkey's performance. Thus any or all of RA, SA, and MM neurons could play a role in the discrimination of air-puff intensities.(ABSTRACT TRUNCATED AT 400 WORDS)