iBCS: 3. A Biopharmaceutics Classification System for Orally Inhaled Drug Products.

In this article, we specify for the first time a quantitative biopharmaceutics classification system for orally inhaled drugs. To date, orally inhaled drug product developers have lacked a biopharmaceutics classification system like the one developed to navigate the development of immediate release of oral medicines. Guideposts for respiratory drug discovery chemists and inhalation product formulators have been elusive and difficult to identify due to the complexity of pulmonary physiology, the intricacies of drug deposition and disposition in the lungs, and the influence of the inhalation delivery device used to deliver the drug as a respirable aerosol. The development of an inhalation biopharmaceutics classification system (iBCS) was an initiative supported by the Product Quality Research Institute (PQRI). The goal of the PQRI iBCS working group was to generate a qualitative biopharmaceutics classification system that can be utilized by inhalation scientists as a "rule of thumb" to identify desirable molecular properties and recognize and manage CMC product development risks based on physicochemical properties of the drug and the deposited lung dose. Herein, we define the iBCS classes quantitatively according to the dose number and permeability. The proposed iBCS was evaluated for its ability to categorize marketed inhaled drugs using data from the literature. The appropriateness of the classification of each drug was assessed based on published development, clinical and nonclinical data, and mechanistic physiologically based biopharmaceutics modeling. The inhaled drug product development challenges for each iBCS classification are discussed and illustrated for different classes of marketed inhaled drugs. Finally, it is recognized that discriminatory laboratory methods to characterize regional lung deposition, dissolution, and permeability will be key to fully realizing the benefits of an iBCS to streamline and derisk inhaled drug development.

In Vitro Drug Delivery of a Fixed-Dose Combination of Fluticasone Furoate/Umeclidinium/Vilanterol from a Dry Powder Inhaler.

Background: Dry powder inhalers (DPIs) require patients to impart sufficient energy through inhalation to ensure adequate dose emission, medication deaggregation, and resultant particle sizes suitable for lung deposition. There is an ongoing debate regarding the level of inspiratory effort, and therefore inspiratory flow rate, needed for optimal dose delivery from DPIs. Materials and Methods: The delivered dose (DD) and fine particle fraction (FPF) for each component of fluticasone furoate/umeclidinium/vilanterol (FF/UMEC/VI) 100/62.5/25 µg and FF/UMEC/VI 200/62.5/25 µg ELLIPTA DPIs were assessed at flow rates of 30, 60, and 90 L/min. Electronic lung (eLung) (eLung; an electronic breathing simulator) assessments were conducted to replicate inhalation profiles representing a wide range of inhalation parameters and inhaled volumes achieved by patients with chronic obstructive pulmonary disease (COPD) or asthma of all severity levels. Timing and duration of dose emission were assessed using a particle detector located at the entrance of an anatomical throat cast attached to the eLung. Results: During DD assessment, a mean of >80% of the nominal blister content (nbc) was emitted from the ELLIPTA DPI at all flow rates. In Next Generation Impactor assessments, the observed mean DD across flow rates for FF/UMEC/VI 100/62.5/25 µg ranged from 85.9% to 97.0% of nbc and 84.0% to 93.5% for FF/UMEC/VI 200/62.5/25 µg. In eLung assessments, 82.8% to 95.5% of nbc was delivered across the PIF range, 43.5 to 129.9 L/min (COPD), and 85.1% to 92.3% across the PIF range, 67.4 to 129.9 L/min (asthma). The FPF (mass <5 µm; % nbc) for each component was comparable across all flow rates and inhalation profiles. Dose emission timings indicated that near-complete dose emission occurs before reaching PIF. Conclusions: Dose delivery assessments across all flow rates and inhalation profiles indicate that patients with all severity levels of COPD or asthma can achieve the required inspiratory effort for efficient delivery of all components of FF/UMEC/VI from the ELLIPTA DPI. Dose emission profiles suggest rapid and near-complete dose delivery from the ELLIPTA DPI before reaching PIF.

iBCS: 2. Mechanistic Modeling of Pulmonary Availability of Inhaled Drugs versus Critical Product Attributes.

This work is the second in a series of publications outlining the fundamental principles and proposed design of a biopharmaceutics classifications system for inhaled drugs and drug products (the iBCS). Here, a mechanistic computer-based model has been used to explore the sensitivity of the primary biopharmaceutics functional output parameters: (i) pulmonary fraction dose absorbed (Fabs) and (ii) drug half-life in lumen (t1/2) to biopharmaceutics-relevant input attributes including dose number (Do) and effective permeability (Peff). Results show the nonlinear sensitivity of primary functional outputs to variations in these attributes. Drugs with Do < 1 and Peff > 1 × 10-6 cm/s show rapid (t1/2 < 20 min) and complete (Fabs > 85%) absorption from lung lumen into lung tissue. At Do > 1, dissolution becomes a critical drug product attribute and Fabs becomes dependent on regional lung deposition. The input attributes used here, Do and Peff, thus enabled the classification of inhaled drugs into parameter spaces with distinctly different biopharmaceutic risks. The implications of these findings with respect to the design of an inhalation-based biopharmaceutics classification system (iBCS) and to the need for experimental methodologies to classify drugs need to be further explored.

iBCS: 1. Principles and Framework of an Inhalation-Based Biopharmaceutics Classification System.

For oral drugs, the formulator and discovery chemist have a tool available to them that can be used to navigate the risks associated with the selection and development of immediate release oral drugs and drug products. This tool is the biopharmaceutics classification system (giBCS). Unfortunately, no such classification system exists for inhaled drugs. The perspective outlined in this manuscript provides the foundational principles and framework for a classification system for inhaled drugs. The proposed classification system, an inhalation-based biopharmaceutics classification system (iBCS), is based on fundamental biopharmaceutics principles adapted to an inhalation route of administration framework. It is envisioned that a classification system for orally inhaled drugs will facilitate an understanding of the technical challenges associated with the development of new chemical entities and their associated new drug products (device and drug formulation combinations). Similar to the giBCS, the iBCS will be based on key attributes describing the drug substance (solubility and permeability) and the drug product (dose and dissolution). This manuscript provides the foundational aspects of an iBCS, including the proposed scientific principles and framework upon which such a system can be developed.

Isolating the Neural Substrates of Visually Guided Attention Orienting in Humans.

The neural processes that enable healthy humans to orient attention to sudden visual events are poorly understood because they are tightly intertwined with purely sensory processes. Here we isolated visually guided orienting activity from sensory activity using event-related potentials (ERPs). By recording ERPs to a lateral stimulus and comparing waveforms obtained under conditions of attention and inattention, we identified an early positive deflection over the ipsilateral visual cortex that was associated with the covert orienting of visual attention to the stimulus. Across five experiments with male and female adult participants, this ipsilateral visual orienting activity (VOA) could be distinguished from purely sensory-evoked activity and from other top-down spatial attention effects. The VOA was linked with behavioral measures of orienting, being significantly larger when the stimulus was detected rapidly than when it was detected more slowly, and its presence was independent of saccadic eye movements toward the targets. The VOA appears to be a specific neural index of the visually guided orienting of attention to a stimulus that appears abruptly in an otherwise uncluttered visual field.SIGNIFICANCE STATEMENT The study of visual attention orienting has been an important impetus for the field of cognitive neuroscience. Seminal reaction-time studies demonstrated that a suddenly appearing visual stimulus attracts attention involuntarily, but the neural processes associated with visually guided attention orienting have been difficult to isolate because they are intertwined with sensory processes that trigger the orienting. Here, we disentangled orienting activity from sensory activity using scalp recordings of event-related electrical activity in the human brain. A specific neural index of visually guided attention orienting was identified. Surprisingly, whereas peripheral sensory stimulation is processed initially and predominantly by the contralateral visual cortex, this electrophysiological index of visual orienting was recorded over the cerebral hemisphere that was ipsilateral to the attention-capturing stimulus.

Quantifying volume conducted potential using stimulation artefact in cortico-cortical evoked potentials.

BACKGROUND: Cortico-cortical evoked potentials (CCEP) are a technique using low frequency stimulation to infer regions of cortical connectivity in patients undergoing Stereo-electroencephalographic (SEEG) monitoring for refractory epilepsy. Little attention has been given to volume conducted components of CCEP responses, and how they may inflate CCEP connectivity. NEW METHOD: Using data from 37 SEEG-CCEPs patients, a novel method was developed to quantify stimulation artefact by measuring the peak-to-peak voltage difference in the first 10 ms after CCEP stimulation. Early responses to CCEP stimulation were also quantified by calculating the root mean square of the 10-100 ms period after each stimulation pulse. Both the early CCEP responses and amplitude of stimulation artefact were regressed by physical distance, stimulation waveform, stimulation intensity and tissue type to identify conduction related properties. RESULTS: Both stimulation artefact and early responses were correlated strongly with the inverse square of the distance from the stimulating electrode. Once corrected for the inverse square distance from the electrode, stimulation artefact and CCEP responses showed a linear relationship, indicating a volume conducted component. COMPARISON WITH EXISTING METHODS: This is the first study to use stimulation artefact to quantify volume conducted potentials, and is the first to quantify volume conducted potentials in SEEG. A single prior study utilizing electrocorticography has shown that parts of early CCEP responses are due to volume conduction. CONCLUSIONS: The linear relationship between stimulation artefact amplitude and CCEP early responses, once corrected for distance, suggests that stimulation artefact can be used as a measure to quantify the volume conducted components.

Using Polar Ion-Pairs to Control Drug Delivery to the Airways of the Lungs.

The rapid absorptive clearance of drugs delivered to the airways of the lungs means that many inhaled medicines have a short duration of action. The aim of this study was to investigate whether forming polar ion-pairs can modify drug absorption to slow down clearance from the airways. Salbutamol was used as a model drug and was formulated as ion-pairs in an aqueous solution with three negatively charged hydrophilic counterions: sulfate (molecular weight (MW) 142), gluconate (MW 218), and phytate (MW 736) (association constants of 1.57, 2.27, and 4.15, respectively) and one negatively charged hydrophobic counterion, octanoate (MW 166) (association constant, 2.56). All of the counterions were well tolerated by Calu-3 human bronchial epithelial cells when screened for toxicity in vitro using conditions that in silico simulations suggested maintain >80% drug-counterion association. The transport of salbutamol ion-pairs with higher polar surface area (PSA), i.e., the sulfate (PSA 52%), gluconate (PSA 50%), and phytate (PSA 79%) ion-pairs, was significantly lower compared to that of the drug alone (PSA 30%, p < 0.05). In contrast, the octanoate ion-pair (PSA 23%) did not significantly alter the salbutamol transport. The transport data for the gluconate ion-pair suggested that the pulmonary absorption half-life of the ion-paired drug would be double that of salbutamol base, and this illustrates the promise of increasing drug polarity using noncovalent complexation as an approach to control drug delivery to the airways of the lungs.

Comparing connectivity metrics in cortico-cortical evoked potentials using synthetic cortical response patterns.

BACKGROUND: Cortico-Cortical Evoked Potentials (CCEPs) are a novel low frequency stimulation method used for brain mapping during intracranial epilepsy investigations. Only a handful of metrics have been applied to CCEP data to infer connectivity, and no comparison as to which is best has been performed. NEW METHOD: We implement a novel method which involved superimposing synthetic cortical responses onto stereoelectroencephalographic (SEEG) data, and use this to compare several metric's ability to detect the simulated patterns. In this we compare two commonly employed metrics currently used in CCEP analysis against eight time series similarity metrics (TSSMs), which have been widely used in machine learning and pattern matching applications. RESULTS: Root Mean Square (RMS), a metric commonly employed in CCEP analysis, was sensitive to a wide variety of response patterns, but insensitive to simulated epileptiform patterns. Autoregressive (AR) coefficients calculated by Burg's method were also sensitive to a wide range of patterns, but were extremely sensitive to epileptiform patterns. Other metrics which employed elastic warping techniques were less sensitive to the simulated response patterns. COMPARISON WITH EXISTING METHODS: Our study is the first to compare CCEP connectivity metrics against one-another. Our results found that RMS, which has been used in many CCEP studies previously, was the most sensitive metric across a wide range of patterns. CONCLUSIONS: Our novel method showed that RMS is a robust and sensitive measure, validating much of the findings of the SEEG-CCEP literature to date. Autoregressive coefficients may also be a useful metric to investigate epileptic networks.

Connectivity of the human insula: A cortico-cortical evoked potential (CCEP) study.

OBJECTIVE: The human insula is increasingly being implicated as a multimodal functional network hub involved in a large variety of complex functions. Due to its inconspicuous location and highly vascular anatomy, it has historically been difficult to study. Cortico-cortical evoked potentials (CCEPs), utilize low frequency stimulation to map cerebral networks. They were used to study connections of the human insula. METHODS: CCEP data was acquired from each sub-region of the dominant and non-dominant insula in 30 patients who underwent stereo-EEG. Connectivity strength to the various cortical regions was obtained via a measure of root mean square (RMS), calculated from each gyrus of the insula and ranked into weighted means. RESULTS: The results of all cumulative CCEP responses for each individual gyrus were represented by circro plots. Forty-nine individual CCEP pairs were stimulated across all the gyri from the right and left insula. In brief, the left insula contributed more greatly to language areas. Sensory function, pain, saliency processing and vestibular function were more heavily implicated from the right insula. Connections to the primary auditory cortex arose from both insula regions. Both posterior insula regions showed significant contralateral connectivity. Ipsilateral mesial temporal connections were seen from both insula regions. In visual function, we further report the novel finding of a direct connection between the right posterior insula and left visual cortex. SIGNIFICANCE: The insula is a major multi-modal network hub with the cerebral cortex having major roles in language, sensation, auditory, visual, limbic and vestibular functions as well as saliency processing. In temporal lobe epilepsy surgery failure, the insula may be implicated as an extra temporal cause, due to the strong mesial temporal connectivity findings.

Nocturnal motor events in epilepsy: Is there a defined physiological network?

OBJECTIVE: Paroxysmal nocturnal movements in epilepsy are a recognised phenomenon, however, the mechanisms that produce them and the effect of the underlying epilepsy still remains elusive. In this study, 10 patients were studied to define the cerebral networks corresponding to these movements and explore how epileptiform activity modulated them. METHODS: We compared the change in power of the 25-250 Hz frequency band using event-related synchronization of all stereo-EEG electrodes implanted, during a baseline segment, during nocturnal movements and seizures. RESULTS: The underlying network activated during these paroxysmal movements comprised the insula, anterior cingulate, premotor areas and orbitofrontal regions. Three groups emerged, (1) complete overlap, (2) no overlap and (3) partial overlap of ERS changes of the epileptogenic zone within the proposed network and correlation of semiology between nocturnal movements and seizures. CONCLUSION: We conclude that nocturnal movements are due to a complex interplay within this physiological network of defined anatomical regions. Epileptic activity had significant impact on nocturnal movements but was not required for generation. SIGNIFICANCE: Where the semiology of the first clinical sign of a seizure consistently matches a patient's nocturnal movements, we suggest that the underlying epileptogenic zone is potentially located within this defined network.

Automatic detection of the epileptogenic zone: An application of the fingerprint of epilepsy.

BACKGROUND: The successful delineation of the epileptogenic zone in epilepsy monitoring is crucial for achieving seizure freedom after epilepsy surgery. NEW METHOD: We aim to improve epileptogenic zone localization by utilizing a computer-assisted tool for the automated grading of the seizure activity recorded in various locations for 20 patients undergoing stereo electroencephalography. Their epileptic seizures were processed to extract two potential biomarkers. The concentration of these biomarkers from within each patient's implantation were then graded to identify their epileptogenic zone and were compared to the clinical assessment. RESULTS: Our technique was capable of ranking the clinically defined epileptogenic zone with high accuracy, above 95%, with a true to false positive ratio of 1:1.52, and was effective with both temporal and extra-temporal onset epilepsies. COMPARISON WITH EXISTING METHOD: We compared our method to two other groups performing localization using similar biomarkers. Our classification metrics, sensitivity and precision together were comparable to both groups and our overall accuracy from a larger population was also higher then both. CONCLUSIONS: Our method is highly accurate, automated and non-parametric providing clinicians another tool that can be used to help identify the epileptogenic zone in patients undergoing the stereo electroencephalography procedure for epilepsy monitoring.

In vitro investigation on the impact of airway mucus on drug dissolution and absorption at the air-epithelium interface in the lungs.

Although the mucus layer is the first biological barrier encountered by inhaled drugs upon their deposition in the upper airways, its potential impact on drug dissolution and absorption in the lung has hardly been investigated. Bio-relevant in vitro models were therefore used to assess the role of airway mucus in the fate of drug particles at the air-epithelium interface. Salbutamol and indomethacin were used as model Biopharmaceutics Classification System (BCS) class III and class II drugs, respectively. Dry powders were reproducibly aerosolised using a PennCentury™ Dry Powder Insufflator onto multiple air-liquid interfaced layers of the broncho-epithelial cell line Calu-3 or thin layers of porcine tracheal mucus mounted onto Transwells® inserts, as well as on empty Transwells®. Comparison of the permeation profiles of the two drugs indicated that mucus acted as a barrier for salbutamol transport but increased that of indomethacin, suggesting it facilitates the dissolution of poorly soluble drugs. In presence of Calu-3 layers, the permeability of salbutamol was even more restricted while indomethacin transport was enhanced further. This study demonstrates mucus distinctly affects the absorption characteristics of drugs with different physico-chemical properties. Hence, drug-mucus interactions should be considered during the development of inhaled drugs.

Considerations in performing and analyzing the responses of cortico-cortical evoked potentials in stereo-EEG.

This review aims to highlight key considerations when performing cortico-cortical evoked potentials (CCEPs) using stereo-electroencephalography (SEEG) for network mapping and show its clinical applicability to presurgical evaluations. The parameters for performing stimulation and safety aspects have been investigated in electrocorticography (ECoG) and deep brain stimulation (DBS), but not as extensively in SEEG. A review of current literature was performed, with an attempt made to emphasize practical insights from all modalities of intracranial stimulation. This paper reviews physical stimulation parameters, highlights safety limits, and considers the influence of changing common stimulation parameters. These factors are put into the context of CCEPs in SEEG. Given the paucity of direct research in this area, studies utilizing low frequency stimulation, DBS, and ECoG are incorporated along with the fundamental principles of electrical engineering. In addition, postprocessing considerations are reviewed, including electrode localization, application of digital filters, baseline selection, application of connectivity metrics, and higher order network analysis. The aim is to guide CCEP stimulation as well as to provide an understanding of the underlying principles of this technique. At present, there are few articles detailing the design of low-frequency stimulation paradigms, especially in the setting of SEEG. Providing a review of the fundamentals and postprocessing considerations when performing CCEPs in SEEG will increase the accessibility of this technique.

Inability to suppress salient distractors predicts low visual working memory capacity.

According to contemporary accounts of visual working memory (vWM), the ability to efficiently filter relevant from irrelevant information contributes to an individual's overall vWM capacity. Although there is mounting evidence for this hypothesis, very little is known about the precise filtering mechanism responsible for controlling access to vWM and for differentiating low- and high-capacity individuals. Theoretically, the inefficient filtering observed in low-capacity individuals might be specifically linked to problems enhancing relevant items, suppressing irrelevant items, or both. To find out, we recorded neurophysiological activity associated with attentional selection and active suppression during a competitive visual search task. We show that high-capacity individuals actively suppress salient distractors, whereas low-capacity individuals are unable to suppress salient distractors in time to prevent those items from capturing attention. These results demonstrate that individual differences in vWM capacity are associated with the timing of a specific attentional control operation that suppresses processing of salient but irrelevant visual objects and restricts their access to higher stages of visual processing.

In Vitro Dosing Performance of the ELLIPTA® Dry Powder Inhaler Using Asthma and COPD Patient Inhalation Profiles Replicated with the Electronic Lung (eLung™).

BACKGROUND: To evaluate the in vitro dose delivery characteristics of approved asthma and chronic obstructive pulmonary disease (COPD) therapies delivered via the ELLIPTA(®) dry powder inhaler across inhalation endpoints representative of the target patient population, using the Electronic Lung (eLung™) to replicate inhaler-specific patient inhalation profiles that were previously recorded in vivo. METHODS: Selected profiles, representative of the range of inhalation endpoints achieved by patients with all severities of asthma and COPD, were replicated using the eLung breathing simulator in conjunction with an oropharyngeal cast. A Next Generation Impactor was coupled to the eLung to determine the aerodynamic particle size distribution of the ex-throat dose (ETD) of asthma and COPD therapies delivered via the ELLIPTA inhaler. Delivered dose (DD), ETD, and fine particle dose (FPD; defined as a mass of active substance less than 5 µm) were determined for fluticasone furoate (FF)/vilanterol (VI) 100/25 µg and 200/25 µg (asthma and COPD), umeclidinium (UMEC)/VI 62.5/25 µg (COPD only), FF 100 µg and 200µg monotherapy (asthma only), and UMEC 62.5 µg monotherapy (COPD only). RESULTS: Inhalation profiles replicated by eLung covered a wide range of peak inspiratory flow rates (41.6-136.9 L/min), pressure drops (1.2-13.8 kPa), and inhaled volumes through the inhaler (0.7-4.2L). DD was consistent across the range of patient representative inhalation parameters for all components (FF, VI, and UMEC) of each therapy assessed; although ETD and FPD were also generally consistent, some small variation was observed. Dose delivery was consistent for each of the components, whether delivered as mono- or combination therapy. CONCLUSIONS: The in vitro performance of the ELLIPTA inhaler has been demonstrated for the delivery of FF/VI, UMEC/VI, FF monotherapy, and UMEC monotherapy. Across a range of inspiratory profiles, DD was consistent, while ETD and FPD showed little flow dependency.

Effect of Disease Severity in Asthma and Chronic Obstructive Pulmonary Disease on Inhaler-Specific Inhalation Profiles Through the ELLIPTA® Dry Powder Inhaler.

BACKGROUND: Two studies were undertaken to characterize the maximal effort inhalation profiles of healthy subjects and patients with asthma or chronic obstructive pulmonary disease (COPD) through a moderate-resistance dry powder inhaler (DPI). Correlations between inhaler-specific inhalation characteristics and inhaler-independent lung function parameters were investigated. METHODS: Healthy subjects (n = 15), patients with mild, moderate, or severe asthma (n = 45), and patients with mild, moderate, severe, or very-severe COPD (n = 60) were included in the studies. Inhalation pressure drop versus time profiles were recorded using an instrumented ELLIPTA® DPI or bespoke resistor component with equivalent resistivity. Inhaler-independent lung function assessments included pharyngometry, spirometry, plethysmography, and diffusion. RESULTS: For the inhaler-specific inhalation profiles, the mean maximal effort peak inspiratory flow rates (PIFRs) varied across the subgroups from 65.8-110.6 L/min (range: 41.6-142.9). Peak pressure drop, PIFR, inhaled volume, and average inhalation flow rate (primary endpoints) did not differ markedly between healthy subjects and patients with asthma or mild COPD. Moderate, severe, and very-severe COPD patients demonstrated lower mean peak pressure drops, PIFRs and inhaled volumes, which tended to decrease with increasing COPD severity. Severe and very-severe COPD patients demonstrated shorter mean inhalation times compared with all other participants. Inhaler-independent lung function parameters were consistent with disease severity, and statistically significant (p < 0.05) strong correlations (R > 0.7) with components of the inhaler-specific inhalation profiles were observed in the COPD cohort; correlations in the asthma cohort tended to be weaker. CONCLUSIONS: All participants achieved a maximal effort PIFR ≥ 41.6 L/min through the moderate resistance of the ELLIPTA inhaler. Patients with asthma achieved similar inhalation profiles to healthy subjects, but increasing COPD severity tended to reduce a patient's inhalation capability. Correlation analyses suggest that some lung function parameters may be a useful indicator of ability to inhale efficiently through a moderate-resistance DPI, such as the ELLIPTA inhaler.

Development of an in vitro model to assess deposition of aerosol particles in a representative replica of the rat's respiratory tract.

BACKGROUND: Small rodents continue to be the mainstay for the assessment of pharmacological and toxicological data of inhaled therapeutics. For meaningful interpretation of the results information about deposition of aerosol particles in the respiratory tract is warranted, but not trivial to obtain for animals with nose-only aerosol exposure. The purpose of this study was to develop and evaluate a general method to characterize the deposition of inhaled test particles in an in vitro model (IVR) of the rat's respiratory tract. METHODS: A highly detailed, realistic and representative image using micro-CT scanning technology was obtained and the generated morphological data was used to construct a plastic replica of the average rat respiratory tract. The model was connected to a rodent ventilator, which allowed the breathing frequency (f, min(-1)) and tidal volume (V(T), mL) to be varied as required. Polydisperse fluorescent microsphere particles with an average mass median aerodynamic diameter (MMAD) of 3.1 µm and geometric standard deviation (GSD) of 2.2 µm were used as model compound. RESULTS: Comparison of the experimental data for total and regional deposition levels with predicted outputs using the in silico MPPD model showed reasonably good relative agreement between the two models. The predictions were closest to the experimental values when default respiratory conditions of f=102 breaths/min and V(T) of 2.0 mL were used. Moreover, the IVR model revealed good correlation with published in vivo data. CONCLUSION: Using the IVR model allows an easy, fast and reasonably precise estimation of the inhaled dose in rodent inhalation studies. The IVR has the potential to be used along with live rats in inhalation exposure studies, and thus provides the unique possibility to run an internal standard for dose deposition in the respiratory tract in each inhalation experiment. This should contribute to enable a greater understanding of drug pharmacokinetics and dynamics in rats and may improve dose extrapolation from animals to humans.

Object-substitution masking modulates spatial attention deployment and the encoding of information in visual short-term memory: insights from occipito-parietal ERP components.

If object-substitution masking (OSM) arises from mask representations replacing target representations, OSM should impede the formation of representations in visual short-term memory (VSTM). We utilized event-related potentials to examine the effect of OSM on target processing. An N2pc was observed on trials with delayed-offset masks, indicating that focused attention was directed to the target. The sustained posterior contralateral negativity (SPCN), an index of VSTM storage, was observed in delayed-offset trials only on trials with correct responses. This supports the hypothesis that inaccurate performance on delayed-offset trials arises from a failure to encode the target in VSTM. On co-termination trials, accuracy was high and neither the N2pc nor SPCN was observed. This indicates that, in the absence of masking, the task was accomplished by maintaining a diffuse attentional state that enabled the joint encoding of the potential target items.

Spatial layout of letters in nonwords affects visual short-term memory load: evidence from human electrophysiology.

The sustained posterior contralateral negativity (SPCN) was used to investigate the effect of spatial layout on the maintenance of letters in VSTM. SPCN amplitude was measured for words, nonwords, and scrambled nonwords. We reexamined the effects of spatial layout of letters on SPCN amplitude in a design that equated the mean frequency of use of each position. Scrambled letters that did not form words elicited a larger SPCN than either words or nonwords, indicating lower VSTM load for nonwords presented in a typical horizontal array than the load observed for the same letters presented in spatially scrambled locations. In contrast, prior research has shown that the spatial extent of arrays of simple stimuli did not influence the amplitude of the SPCN. Thus, the present results indicate the existence of encoding and VSTM maintenance mechanisms specific to letter and word processing.

Mental rotation requires visual short-term memory: evidence from human electric cortical activity.

The purpose of the present study was to seek evidence that mental rotation is accomplished by transforming a representation held in visual short-term memory (VSTM). In order to accomplish this goal, we utilized the sustained posterior contralateral negativity (SPCN), an electrophysiological index of the maintenance of information in VSTM. We hypothesized that if mental rotation is accomplished by transforming a representation held in VSTM, then the duration that this representation is maintained in VSTM should be related to the degree to which the representation must be rotated to reach the desired orientation. Therefore, the SPCN should offset at progressively longer latencies as the degree of rotation required increases. We tested this prediction in two experiments utilizing rotated alphanumeric characters. Experiment 1 utilized a normal versus mirror discrimination task that is known to require mental rotation. Experiment 2 utilized a letter versus digit discrimination, a task that does not require mental rotation. In Experiment 1, the offset latency of the SPCN wave increased with increases in the angle of rotation of the target. This effect indicates that targets were maintained in VSTM for longer durations as the angle of rotation increased. Experiment 2 revealed that target orientation did not affect SPCN offset latency when subjects did not adopt a mental rotation strategy, confirming that the effects on the SPCN latency effects observed in Experiment 1 were not due to the mere presentation of rotated patterns. Thus, these two experiments provide clear evidence that mental rotation involves representations maintained in VSTM.