Biomedical subjects

W S Pritchard

Publications and source records attributed to W S Pritchard.

At least 19 recordsLinked to original sources

PubMed2001

Effects of smoking/nicotine on performance and event-related potentials during a short-term memory scanning task.

RATIONALE: Nicotine absorbed from cigarette smoke shortens reaction time (RT) in a wide variety of cognitive tasks. However, relatively few studies have tried to isolate the specific stage(s) of information processing affected by smoking/nicotine. OBJECTIVE: The present study was designed to investigate the effect of smoking/nicotine on the short-term memory (STM) scanning stage of information processing in minimally abstaining smokers. Both RT and event-related potentials (ERPs) were measured. METHODS: A Sternberg-type STM-scanning task was performed before and after smoking each of two cigarettes. One cigarette had a 0.05-mg nicotine yield ("denicotinized") and the other had a 1.1-mg yield ("nicotine-yielding"). On each trial, either 2, 3, or 4 consonants were displayed as a memory set. After a brief interval, a single probe consonant was displayed. If the probe was in the memory set (positive probe) a right button press was required, and if the probe was not in the memory set (negative probe) the left button was pressed. RESULTS: Smoking the nicotine-yielding cigarette but not the denicotinized cigarette shortened RT. However, memory-scanning speed, as estimated from the increase in RT as a function of increasing set size, was not differentially affected by the two types of cigarettes. For the ERPs, smoking the nicotine-yielding but not the denicotinized cigarette (a) reduced N200 latency to both the memory-set stimuli and negative probes, (b) increased N200 amplitude to negative probes and P300 amplitude to both types of probes, and (c) produced a sustained negative shift in memory-set ERP amplitude beginning around 600 ms post-stimulus. CONCLUSION: While smoking/nicotine shortened probe RT, it did not affect the speed of STM scanning. Moreover, the ERP-latency effects obtained for the probes were small relative to the effects of smoking/nicotine on RT, suggesting that smoking/nicotine shortens RT primarily by affecting response-related processes.

Adult↗

PubMed2000

Distinguishing withdrawal relief from absolute facilitation: commentary on Bell et al.

A recent article in this journal by Bell and colleagues (Bell SL, Taylor RC, Singleton EG, Henningfield JE, Heishman SJ, Nicotine & Tobacco Research 1:45-52, 1999) studied the effects of smoking on cognitive performance using an overnight smoking abstention design. They interpreted their results for a two-letter search task (poorer performance following abstention that was improved by smoking) as indicating 'nicotine withdrawal-induced cognitive impairment' (p. 50). However, in this commentary, we point out that overnight-abstention experimental designs cannot distinguish withdrawal relief from absolute facilitation of performance (or a combination of the two). We suggest two approaches to resolving the issue of the nature of smoking/nicotine's effects on human cognitive performance.

Cognition Disorders↗

PubMed2000

Nonlinearity in human resting, eyes-closed EEG: an in-depth case study.

The question of nonlinearity in the human electroencephalogram (EEG) is important, since linear methods of EEG analysis are more well-developed and computationally faster than nonlinear methods. Furthermore, the presence or absence of nonlinearity has important theoretical implications for understanding the nature of the brain's oscillatory activity. Using a linear summary measure as a control, we report a failure to reject the null hypothesis of a (largely) stationary linear-Gaussian process for normal, resting, eyes-closed EEG from a single participant. We found significant evidence of nonlinearity at two occipital sites (O1 and O2) where the 8-12.5 Hz alpha rhythm was prominent. However, this element of nonlinear structure appeared trivial, as (1) we found no evidence of time irreversibility at these loci, and (2) best-fitting linear models accounted on-average for over 94% of the variance in the data with nonlinear modeling doing no better. Half of the remaining variance could be accounted for by nonstationarity. While our findings technically apply only to the one individual tested, his EEG was typical of those seen under the conditions that we employed.

Alpha Rhythm↗

PubMed1999

Little evidence that "denicotinized" menthol cigarettes have pharmacological effects: an EEG/heart-rate/sujective-response study.

RATIONALE: A substantial portion of cigarette smokers prefer menthol-flavored cigarettes. To date, however, no studies have examined whether menthol in cigarettes has central pharmacological effects. OBJECTIVE: We investigated psychophysiological and subjective effects of smoking menthol versus non-menthol cigarettes in both menthol and non-menthol smokers. To assess these effects independently of the immediate effects of nicotine, all cigarettes employed were "denicotinized" (FTC nicotine yield = 0.06 mg). METHODS: The psychophysiological measures were EEG and heart rate (HR). The subjective measures assessed mental alertness, muscular relaxation, anxiety/nervousness, and how much a participant wanted to smoke one of his usual brand of cigarettes. Menthol and non-menthol smokers participated in a single session in which each participant smoked both a menthol and a non-menthol denicotinized cigarette (order balanced across participants). The psychophysiological and subjective measures were recorded before and after smoking each cigarette. RESULTS: Out of 48 F-ratios spanning 22 analyses of variance involving the critical interaction between pre-/post-smoking and menthol/non-menthol cigarette, only one unambiguously fit a "pharmacological" pattern, a result indistinguishable from a type-I statistical error. We report evidence that menthol smokers may be chronically less aroused and more sensitive to the effects of nicotine than non-menthol smokers. CONCLUSIONS: We found little evidence that menthol in cigarettes has central pharmacological effects.

Adolescent↗

PubMed1999

A double blind study of the effects of smoking on heart rate: is there tachyphylaxis?

RATIONALE: Smoking following overnight abstention reliably increases heart rate (HR), an effect due to nicotine absorption. The effect of subsequent cigarettes on HR is less than that associated with the first cigarette of the day, an indication of tachyphylaxis (acute tolerance). To date, smoking/HR studies have not been conducted double-blind. Instead, control conditions have included non-smoking or some type of "sham" smoking (puffing on an unlit cigarette or a straw). OBJECTIVE: We investigated the HR response to smoking and its time course using double-blind methodology. METHODS: HR was recorded in overnight-abstaining participants before and after smoking the first, second and third cigarette of the day (40 min between each cigarette) in two sessions. The experimental manipulation involved replacing the second cigarette of one session with a very low nicotine-yield cigarette (0.05 mg; FTC method) compared with the other five cigarettes (1.1-mg nicotine yield). RESULTS: Smoking increased HR by 15, 8 and 7 beats/min (bpm) in the session where all three cigarettes had the higher yield. The comparable values for the session in which the second cigarette had the lower yield were 15, -1 and 11 bpm. CONCLUSIONS: In the session where all three cigarettes had the higher yield, larger increase in HR after smoking the first than the second or third cigarettes indicates tachyphylaxis. The HR response in the other session was smaller for the third cigarette than the first cigarette, indicating that a period greater than 80 min would be needed before the HR response was fully restored.

Adult↗

PubMed1999

Dynamics underlying rhythmic and non-rhythmic variants of abnormal, waking delta activity.

OBJECT: We applied a new test, nonlinear cross prediction (NLCP), to investigate whether or polymorphic delta activity (PDA) and frontal intermittent rhythmic delta activity (FIRDA) reflect linear or nonlinear brain dynamics. Furthermore realistic models were constructed to explain the dynamical properties of PDA and FIRDA. METHODS: Forty-nine EEG time series with FIRDA and 40 time series with PDA were studied with the NLCP algorithm. This characterizes a time series in terms of its predictability, amplitude asymmetry, and time asymmetry, with the latter two measures reflecting nonlinearity. Parameters of an EEG model proposed by Lopes da Silva were adjusted to obtain time series resembling PDA and FIRDA. RESULTS: FIRDA was more predictable than PDA. Most PDA segments could not be distinguished from linearly filtered noise. In contrast, FIRDA activity showed strong evidence of nonlinear dynamics. These dynamical properties of PDA and FIRDA could be reproduced by the Lopes da Silva model. PDA and FIRDA reflect a point attractor and a limit cycle attractor, respectively, perturbed by dynamical noise. CONCLUSION: Experimental analysis and modeling of the data suggest that PDA and FIRDA reflect fundamentally different types of brain dynamics. While PDA is filtered noise, reflecting low-level, random input to cortical networks, FIRDA may reflect limit-cycle oscillations due to increased excitation.

Adult↗

PubMed1999

On the validity of spatial embedding: a reply to Pezard et al.

Careful consideration of the issues raised by Pezard and colleagues (in this issue of Psychophysiology) allows for the conclusion that spatial embedding may be valid as a method of dynamical reconstruction. However, two problems with the technique cannot be ignored. First, spatial embedding of EEG invariably involves linear cross-correlation among channels, which distorts the dynamical reconstruction due to compression toward the main state-space diagonal. Further, before spatially embedding across a set of channels, one must first check for at least "similar" dynamics among them, using, for example, a measure such as estimated mutual dimension. Measuring a "whole cortex" state via spatial embedding may also be possible in principle, except for the nontrivial obstacle of separating local dynamics that are heterogeneous across the cortex from activity reflecting the "unified field" of the cortex as a whole.

Cerebral Cortex↗

PubMed1999

P300 and response selection: a new look using independent-components analysis.

PURPOSE: The most prevalent current view of the functional role of the P300 component of the event-related potential (ERP) is that it indexes strategic processing related to context updating. Using independent-components analysis (ICA), the present study examined the role of P300 in the tactical process of response selection. METHODS: In a task crossing manipulations of perceptual difficulty (PD) and response-selection difficulty (R-SD), ICA was employed to measure not only P300 latency, but its onset and duration as well. RESULTS: Increased PD delayed P300 latency and onset in parallel, while increased R-SD lengthened P300 duration. CONCLUSIONS: The latency and onset results suggest that the often-cited covariation of P300 latency with stimulus-evaluation time is secondary to effects on processing stages preceding P300. The results for duration indicate that P300 is involved in response selection, suggesting that it is not a unitary phenomenon. While P300's well-known relation to stimulus probability indicates a strategic role, our findings indicate a tactical role as well.

Adult↗

PubMed1997

Segregation of the thalamic alpha rhythms from cortical alpha activity using the Savit-Green S-statistic and estimated correlation dimension.

The large-amplitude, occipital alpha rhythm of the human electroencephalogram (EEG) is associated in normal subjects with a state of relaxed wakefulness. We analyzed resting eyes-open and eyes-closed human EEG data using three measures: power in the 8-12-Hz alpha frequency band, estimated correlation dimension (D2), and the Savit-Green S-statistic. At occipital loci, two groups of points were evident in the scatterplot of S vs. estimated D2. Group A was of higher dimension and consisted of predominantly eyes-open records. Group B was of lower dimension and consisted of more eyes-closed than eyes-open records. Furthermore, Group B had a broad range of alpha power, with alpha power being negatively correlated with estimated D2 (higher alpha power associated with lower dynamical complexity). In contrast, Group A had a very small range of low alpha power, and was positively correlated with estimated D2 (higher alpha power associated with increased dynamical complexity). Our results indicate that Group B EEG (the alpha rhythm) and Group A EEG (EEG containing 'other' alpha activity) have fundamentally different dynamical properties.

Adult↗

PubMed1996

Faster P300 latency after smoking in visual but not auditory oddball tasks.

In two separate experiments, P300 was recorded from overnight-abstaining smokers before and after smoking. In the first experiment, 32 subjects counted forward by ones and counted backwards by threes upon presentation of a rare tone burst (20%) in a stream of standard tones. There were no changes in P300 amplitude or latency pre- to post-smoking (1.1-mg FTC nicotine-yield cigarette). In the second experiment, 29 subjects completed auditory and visual oddball tasks before smoking, after smoking a low nicotine-yield cigarette (0.05 mg), after smoking a higher nicotine-yield cigarette (1.1-mg), and after smoking a second 1.1-mg cigarette. In the visual oddball task, P300 latency decreased after smoking the first higher-yield cigarette relative to both pre-smoking and post smoking the lower-yield cigarette. This effect was maintained after smoking the second higher-yield cigarette. In the visual task, P300 amplitude increased after smoking the first higher-yield cigarette (from a lower baseline level) in a group of subjects with larger changes in tidal-breath CO but not in a group with smaller changes in CO. There were no effects of smoking on P300 amplitude or latency in the auditory tasks of either the first or second experiment.

Adult↗

PubMed1996

Examining the relation between usual-brand nicotine yield, blood cotinine concentration and the nicotine- "compensation" hypothesis.

Eight data sets relating usual-brand nicotine yield (FTC method or equivalent) to blood cotinine concentration are reviewed with respect to the so-called nicotine-"compensation" hypothesis, i.e., that all smokers achieve a specific level of nicotine in their blood, regardless of the FTC nicotine yield of the cigarette smoked. The data from the studies reviewed here indicate wide variability in blood cotinine concentrations over the range of FTC nicotine yields and that the nicotine-compensation hypothesis is not supported. On average, blood cotinine concentrations are found to be roughly midway between complete compensation (all smokers absorb equal amounts of nicotine regardless of FTC nicotine yield) and the value expected if there was no compensation (i.e., smokers absorb an amount of nicotine exactly equal to the FTC yield). As a result of individual smoking-behavior differences (number of cigarettes smoked, puff volume, puff frequency inhalation volume and depth, etc.), the data indicate that, on average, smokers achieve roughly 50% lower blood cotinine concentrations than predicted by the nicotine-compensation hypothesis.

Cotinine↗

PubMed1996

Assessing the sensory role of nicotine in cigarette smoking.

Thirty-two subjects were tested in five double-blind sessions (16 subjects in the morning following overnight smoking abstention, and 16 in the afternoon following ad-lib smoking). In each session, subjects smoked one of five experimental (EX) cigarettes having the following FTC nicotine/"tar' yields in mg: 0.08/8.5, 0.17/9.1, 0.37/9.8, 0.48/9.8, and 0.74/10.4. In a sixth session, subjects smoked a 0.71/8.6 commercial "light' (CL) cigarette that was their usual brand. Before and after smoking, subjects subjectively rated their desire to smoke a cigarette of their usual brand and had blood samples drawn. Following smoking, subjects rated the cigarette on a variety of sensory dimensions; they also rated smoking satisfaction. Analysis of variance indicated that nicotine played an important sensory role for a variety of dimensions related to cigarette taste and sensory impact but not perceived draw. Principal-components analyses indicated that sensory factors were at least as important as nicotine pharmacology (indirectly indexed by the pre-to post-smoking rise in blood nicotine concentration) when considering smoking's overall effects on satisfaction, product acceptance, and reduction in desire to smoke.

Adult↗

PubMed1996

Use of non-linear EEG measures to characterize EEG changes during mental activity.

Non-linear EEG analysis provides a possibility for studying the dynamical changes in cortical networks related to mental activity. In this study the correlation dimension D2 was used to study local changes in complexity, and the mutual dimension Dm was used to assess changes in the dynamical coupling between different brain areas. EEGs were recorded in 25 healthy subjects under three conditions: (1) eyes closed, (2) eyes open, and (3) mental arithmetic with eyes closed (serial subtraction of 7s from 1000). In the eyes-closed condition, D2 was lower at parieto-occipital sites. D2 increased during the eye-open and arithmetic conditions. Contrary to the D2, the Dm showed no regional differences in the eyes closed condition. A clear increase in Dm was seen during eyes open and arithmetic. We conclude that both the correlation dimension and the mutual dimension are very sensitive to EEG changes during simple visual information processing and during mental arithmetic. However, these measures seem to be relatively non-specific, and correlate only weakly with performance on the arithmetic task.

Adult↗

PubMed1996

Application of dimension estimation and surrogate data to the time evolution of EEG topographic variables.

Dimensional complexity (estimated correlation dimension) was measured for two topographic EEG time series: (a) the time evolution of global field power (GFP) and (b) the time evolution of sequential dissimilarity (SQD) for resting, eyes-closed and eyes-open data. Eyes-closed GFP and eyes-closed/open SQD all had an element of nonlinearity in their dynamics as evidenced by increased dimensional complexity associated with the phase-angle randomization, Gaussian surrogate-data procedure. However, none of the three gave any evidence of being deterministic chaotic processes. Eyes-open GFP dimensional complexity could not be distinguished from a linear-stochastic process.

Adult↗

PubMed1996

On the validity of estimating EEG correlation dimension from a spatial embedding.

We demonstrate by using simulations that spatial embedding of single-variable time series data does not reliably reconstruct state-space dynamics. Instead, correlation dimension estimated from spatially embedded data is largely a measure of linear cross-correlation in the data set. For actual electroencephalographic (EEG) data, we demonstrate a high negative correlation between spatial correlation dimension and the average amount of lag-zero cross-correlation between "nearest-neighbor" embedding channels (the greater the cross-correlation, the lower the dimension). We also show that the essential results obtained from spatially embedding EEG data are also obtained when one spatially embeds across a set of highly cross-correlated stochastic (second-order autoregressive) processes. Although, with appropriate surrogate data, correlation dimension estimated from spatially embedded data detects nonlinearity, its use is not recommended because correlation dimension estimated from temporally embedded data both reconstructs state-space dynamics and, with appropriate surrogate data, detects nonlinearity as well.

Algorithms↗

PubMed1996

Effects of cigarette smoking on EEG spectral-band power, dimensional complexity, and nonlinearity during reaction-time task performance.

Electroencephalogram (EEG) and heart rate (HR) were recorded while individuals performed visual and auditory go/no-go reaction time (RT) tasks. Overnight-abstaining smokers smoked two types of cigarettes in a single morning session. The first type was smoked once and had a nicotine yield of 0.05 mg. Two cigarettes of the second type (1.1 mg) were smoked. Four recordings were made: presmoking, postsmoking 0.05 mg, and postsmoking each 1.1 mg. HR was increased only by the first 1.1-mg cigarette. Smoking both the 1.1-mg cigarettes decreased RT. Smoking the first 1.1-mg cigarette increased EEG power in the beta2 band. A flexible effect of smoking the first 1.1-mg cigarette on EEG dimensional complexity (DCx) was obtained at locus Cz. Specifically, DCx was (a) raised when the presmoking level was low, (b) not affected when the presmoking level was intermediate, and (c) lowered when the presmoking level was high. Surrogate-data testing indicated the presence of nonlinearity in the EEG data that was not affected by smoking. Decreased RT was associated with increased DCx in the visual task only.

Adult↗

PubMed1996

Psychophysiological and subjective effects of cigarettes having varying nicotine yields but relatively constant "tar' yields.

Thirty-two subjects were tested in five double-blind sessions-16 subjects in the morning (a.m.) following overnight smoking abstention, and 16 in the afternoon (p.m.) following ad lib smoking. In each session, subjects smoked 1 of 5 cigarettes having the following FTC nicotine/'tar' yields in mg: 0.08/8.5, 0.17/9.1, 0.37/9.8, 0.48/9.8, and 0.74/10.4. On a pre- to postsmoking basis, blood nicotine and heart rate increased with nicotine yield. The effect of nicotine yield on changes in self-rated anxiety was an inverted-U function, but this effect was possibly confounded by baseline differences. The following effects on EEG spectral-band magnitude were also obtained: (1) nicotine yields > or = 0.17 mg decreased delta; (2) nicotine yields of 0.37 and 0.48 mg decreased theta in a.m. subjects; (3) nicotine yields > or = 0.37 mg decreased alpha, the effect being greater in a.m. subjects; (4) no effect of yield on beta 1 was obtained; (5) nicotine yields of 0.48 and 0.74 mg increased the Cz-minus-T5 differential in beta 2. Pre- to postsmoking changes in this measure of beta 2 were not correlated with either blood nicotine or anxiety.

Adolescent↗

PubMed1995

Measuring "chaos" in the brain: a tutorial review of EEG dimension estimation.

The technique of dimension estimation is currently a leading application of nonlinear dynamics (popularly termed "chaos theory") to EEG analysis. A tutorial review of this technique is presented along with some elementary background concepts from nonlinear dynamics. Practical aspects of applying dimension estimation to EEG data are also reviewed, and the possible role of deterministic chaos in brain function is discussed.

Brain↗