Aaron S. Geller

PyEPL: A cross-platform experiment-programming library

PyEPL (the Python Experiment-Programming Library) is a Python library which allows cross-platform and object-oriented coding of behavioral experiments. It provides functions for displaying text and images onscreen, as well as playing and recording sound, and is capable of rendering 3-D virtual environments for spatial-navigation tasks. It is currently tested for Mac OS X and Linux. It interfaces with Activewire USB cards (on Mac OS X) and the parallel port (on Linux) for synchronization of experimental events with physiological recordings. In this article, we first present two sample programs which illustrate core PyEPL features. The examples demonstrate visual stimulus presentation, keyboard input, and simulation and exploration of a simple 3-D environment. We then describe the components and strategies used in implementing PyEPL. We acknowledge support from NIH Grants MH55687, MH61975, and MH62196; NSF (CELEST) Grant SBE-354378; and the Swartz Foundation.

EEG correlates of verbal and nonverbal working memory

BackgroundDistinct cognitive processes support verbal and nonverbal working memory, with verbal memory depending specifically on the subvocal rehearsal of items.MethodsWe recorded scalp EEG while subjects performed a Sternberg task. In each trial, subjects judged whether a probe item was one of the three items in a study list. Lists were composed of stimuli from one of five pools whose items either were verbally rehearsable (letters, words, pictures of common objects) or resistant to verbal rehearsal (sinusoidal grating patterns, single dot locations).ResultsWe found oscillatory correlates unique to verbal stimuli in the θ (4–8 Hz), α (9–12 Hz), β (14–28 Hz), and γ (30–50 Hz) frequency bands. Verbal stimuli generally elicited greater power than did nonverbal stimuli. Enhanced verbal power was found bilaterally in the θ band, over frontal and occipital areas in the α and β bands, and centrally in the γ band. When we looked specifically for cases where oscillatory power in the time interval between item presentations was greater than oscillatory power during item presentation, we found enhanced β activity in the frontal and occipital regions.ConclusionThese results implicate stimulus-induced oscillatory activity in verbal working memory and β activity in the process of subvocal rehearsal.

Characterizing the ERP Old-New effect in a short-term memory task.

The early and late components of the event-related potential (ERP) Old-New effect are well characterized with respect to long-term memory, and have been associated with processes of familiarity and recollection, respectively. Now, using a short-term memory paradigm with verbal and nonverbal stimuli, we explored the way that these two components respond to variation in recency and stimulus type. We found that the amplitude of the early component (or frontal N400, FN400) showed Old-New effects only for verbal stimuli and increased with recency. In contrast, the later component (or late positive component, LPC) showed Old-New effects across a range of stimulus types and did not scale with recency. These results are consistent with the way that these same ERP components have been characterized in long-term memory, supporting the idea that some of the same processes underlie long- and short-term item recognition.

Lure similarity affects visual episodic recognition: Detailed tests of a noisy exemplar model

Summed-similarity models of visual episodic recognition memory successfully predict the variation in false alarm rates across different test items. With data averaged across subjects, Kahana and Sekuler (2002) demonstrated that subjects’ performance appears to change along with the mean similarity among study items; with high interstimulus similarity, subjects were less likely to commit false alarms to similar lures. We examined this effect in detail by systematically varying the coordinates of study and test items along a critical stimulus dimension and measuring memory performance at each point. To reduce uncontrolled variance associated with individual differences in vision, the coordinates of study and test items were scaled according to each subject’s discrimination threshold. Fitting each of four summed-similarity models to the individual subjects’ data demonstrated a clear superiority for models that take account of interitem similarity on a trialwise basis.

Temporal associative processes revealed by intrusions in paired-associate recall

Although much is known about the factors that influence the acquisition and retention of individual paired associates, the existence of temporally defined associations spanning multiple pairs has not been demonstrated. We report two experiments in which subjects studied randomly paired nouns for a subsequent cued recall test. When subjects recalled nontarget items, their intrusions tended to come from nearby pairs. This across-pair contiguity effect was graded, spanning noncontiguously studied word pairs. The existence of such long-range temporally defined associations lends further support to contextual-retrieval models of episodic association.

Eye closure causes widespread low-frequency power increase and focal gamma attenuation in the human electrocorticogram

OBJECTIVE We sought to characterize the effects of eye closure on EEG power using electrocorticography (ECoG). Specifically, we sought to elucidate the anatomical areas demonstrating an eye closure effect, and at which frequencies this effect occurs. METHODS ECoG was recorded from 32 patients undergoing invasive monitoring for seizure focus localization. Patients were instructed to close and open their eyes repeatedly. ECoG power was compared in the epochs following eye closure and opening, for various frequency bands and brain regions. RESULTS We found that at low frequencies, eye closure causes widespread power increases involving all lobes of the brain. This effect was significant not only in the α (8-12 Hz) band but in the δ (2-4 Hz), θ (4-8 Hz), and β (15-30 Hz) bands as well. At high frequencies, eye closure causes comparatively focal power decreases over occipital cortex and frontal Brodmann areas 8 and 9. CONCLUSIONS Eye closure (1) affects a broad range of frequencies outside the α band and (2) involves a distributed network of neural activity in anatomical areas outside visual cortex. SIGNIFICANCE This study constitutes the first large-scale, systematic application of ECoG to study eye closure, which is shown to influence a broad range of frequencies and brain regions.

PyParse: A semiautomated system for scoring spoken recall data

Studies of human memory often generate data on the sequence and timing of recalled items, but scoring such data using conventional methods is difficult or impossible. We describe a Python-based semiautomated system that greatly simplifies this task. This software, called PyParse, can easily be used in conjunction with many common experiment authoring systems. Scored data is output in a simple ASCII format and can be accessed with the programming language of choice, allowing for the identification of features such as correct responses, prior-list intrusions, extra-list intrusions, and repetitions.

Opioid Overdose-Related Deaths

To the Editor: Dr Bohnert and colleagues alerted the medical community to the dangers of higher opioid doses and their association with overdose death. Their study most likely missed cases of cardiac deaths from QTc prolongation, as the primary cause, methadone, was excluded from their investigation. However, the other major etiology of opioidrelated death is ventilatory suppression via opioid-induced central sleep apnea. Ventilation is consciously and reflexively controlled in the medulla with the nocturnal drive purely reflexive. If opioid ingestion is not restricted to the daytime, the suppression of ventilation by opioids can enhance the risk of nighttime hypoxemia with possible respiratory failure. Within 1 hour of ingestion of just 15 mg of oxycodone at 2 AM, precipitation of 91 central sleep apnea events occurred in a patient with chronic pain receiving longterm opiate therapy who previously showed no sleep apnea. Similarly, in a chronic pain patient taking regular hydrocodone and morphine, oxygen desaturation to 70% occurred within 2 hours following ingestion at about 1 AM of an additional 7.5 mg of hydrocodone, with events more prevalent during non–rapid eye movement (REM) sleep. Opioids prolong non-REM sleep by decreasing REM sleep duration, accentuating nocturnal breathing risks. Opioid-mediated ventilatory suppression does not attenuate with duration of use, such that patients are at risk for opioid-induced ventilatory suppression throughout their ingestion course. The suggestion from Bohnert et al to minimize opioid doses to reduce overdose-related deaths would also be useful in reducing ventilatory suppression, which is also dose dependent, although it can occur at even low doses. Dose limitation further serves patient safety and public health in that dose minimization also reduces iatrogenic dosedependent addiction as well as diminishes the risk of diversion of prescription narcotics. However, dose minimization may require clinicians to undertreat a portion of patients. If clinicians reflected on the mechanisms of death, educated patients about the ventilatory suppression risks, and informed patients not to ingest short-lasting opioids within several hours of sleep and to take long-lasting, sustainedrelease opioids in the early morning only, the risk of death might be greatly reduced.

Patient and Public Safety Maximized by Rapid Opioid Taper

of atrial fibrillation in this patient was more likely to be ascribed to an inappropriate starting dose of levothyroxine, which could have been prevented if the clinical practice was compliant with the guidelines. In this case, the current clinical practice guidelines showed excellent guidance for practice but were not well followed. Promoting compliance with these guidelines in primary clinical practice is an efficient and straightforward way to prevent the overdiagnosis and overtreatment of elderly patients with biochemically elevated thyrotropin levels. Meanwhile, studies on guidelines pertaining to overt and subclinical hypothyroidism are very insufficient and further investigations providing quality appraisal, validation, and compliance assessment of these guidelines are warranted.

To the Editor: Opioid therapy and sleep apnea

Readers comment on opioids and sleep apnea (June 2016).