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E Gordon

Publications and source records attributed to E Gordon.

At least 73 records · Page 4Linked to original sources
PubMed1998

Decrement of the N1 auditory event-related potential with stimulus repetition: habituation vs. refractoriness.

We examined whether the amplitude decrement traditionally found for the N1 peak of the event-related potential (ERP) with repetition of auditory stimuli results from the process of habituation or from the refractory period of the neural elements underlying the N1 response. These competing accounts of the process underlying the N1 decrement with repetition differ in terms of the predicted effects of variations in stimulus repetition and interstimulus interval (ISI). These predictions were examined using a short-term habituation design with a factorial combination of stimulus repetition and ISI. Forty-five subjects received 21 stimulus trains, each consisting of seven innocuous tones, all at 1 kHz except the sixth, which was a 1.5-kHz tone. Each subject was assigned to one of three ISI conditions (either 1, 3 or 10 s). The results provide little support for the view that N1 response decrement with stimulus repetition reflects a process of habituation. The present results provide greater support for the view that this decrement is based on the separate refractory periods or recovery cycle processes of at least two neural generators contributing to activity in the N1 peak latency range.

Acoustic Stimulation↗
PubMed1998

Dynamic spectral analysis of event-related potentials.

This paper presents a new method for the identification of individual event related potential (ERP) components in both frequency and time domains. Using the similar basis function (SBF) algorithm the method provides a time to frequency transform, representing a frequency domain equivalent of the component waveform. Notable features of the SBF algorithm are that it allows for unevenly spaced sampled functions in both the time and frequency domains, and estimates of spectral densities are obtained by numerical computation of finite Fourier integrals. Application of this method to ERP data from 20 normal subjects demonstrated a similar shape of component amplitude frequency characteristics for traditional late component waveforms (N1, P2, N2 and P3). On this basis, a low-frequency band was found where the component amplitude frequency characteristic was described by a Gaussian function, while the component phase frequency characteristic was a linear function of frequency. These relationships are interpreted as frequency domain equivalents of the component. Transformed to the time domain, they provided an analytical description of the ERP as the sum of positive- and negative-going monopolar waves. The study points to similar mechanisms underlying these component waveforms, and analytically defines dynamic properties for the components both in the frequency and time domains.

Adult↗
PubMed1998

Prestimulus EEG alpha phase synchronicity influences N100 amplitude and reaction time.

The influence of the level of prestimulus alpha phase synchronicity on the N100 component and reaction time (RT) was examined, in target auditory oddball data from 25 normal subjects. Alpha phase synchronicity is a new measure consisting (for a given stimulus presentation) of the angular or circular variance of the alpha phase at stimulus onset across the parieto-occipital sites. The lower the angular variance, the higher the phase synchronicity (the more closely in phase the alpha activity across these sites) and vice versa. Subaveraged event-related potentials (ERPs) were formed for high and low prestimulus alpha phase synchronicity stimulus presentations. N100 amplitude was significantly greater in the high than the low phase synchronicity subaverages. In addition, RT was significantly reduced in the high prestimulus alpha phase synchronicity cases. Alpha phase synchronicity reflects an aspect of brain state that influences subsequent stimulus processing.

Adult↗
PubMed1998

Dysfunctions of automatic (P300a) and controlled (P300b) processing in Parkinson's disease.

P300 Event Related Potentials components (P300a and P300b) were investigated using an auditory oddball paradigm (with a button press response to target stimuli) in 15 Parkinson's disease patients and 50 normal controls whilst simultaneously measuring electrodermal activity. Cluster analysis showed that the first 10 target stimuli generated the largest skin conductance responses. The first 10 single-trial ERP epochs were therefore analysed as an ERP sub-average for each individual. The P300a component (associated with the automatic 'Orienting Reflex') was expected to be most prevalent in this sub-average (compared with sub-averages of subsequent blocks of 10 target stimuli). Twenty-nine out of 50 normal controls (58%) elicited a P300a in the first 10 target sub-average, compared with only 2 out of 15 Parkinson's disease subjects (13%). The conventional P300b component (associated with controlled processing) was found to be significantly delayed for all sub-averages for the Parkinson's disease group when compared with controls. These preliminary findings suggest a possible dysfunction in both automatic and controlled processing in this disorder.

Adult↗
PubMed1998

Relative impact of oxidative stress on the functional competence and genomic integrity of human spermatozoa.

Reactive oxygen metabolites are known to disrupt sperm-oocyte fusion, sperm movement, and DNA integrity; however, the relative sensitivities of these elements to oxidative stress are unknown. In this study these factors were assessed in human spermatozoa exposed to increasing levels of oxidative stress achieved through the stimulation of endogenous oxidant generation with NADPH or direct exposure to hydrogen peroxide. At low levels of oxidative stress, DNA fragmentation was significantly reduced while the rates of sperm-oocyte fusion were significantly enhanced. As the level of oxidative stress increased, the spermatozoa exhibited significantly elevated levels of DNA damage (p < 0.001) and yet continued to express an enhanced capacity for sperm-oocyte fusion. At the highest levels of oxidative stress, extremely high rates of DNA fragmentation were observed but the spermatozoa exhibited a parallel loss in their capacities for movement and oocyte fusion. These studies emphasize how redox mechanisms can either enhance or disrupt the functional and genomic integrity of human spermatozoa depending on the intensity of the oxidative stimulus. Because these qualities are affected at different rates, spermatozoa exhibiting significant DNA damage are still capable of fertilizing the oocyte. These results may have long-term implications for the safety of assisted conception procedures in cases associated with oxidative stress.

DNA↗
PubMed1998

Quantified EEG activity in adolescent attention deficit hyperactivity disorder.

The aim of this study was to explore elements of the maturational and cortical hypoarousal models in adolescent ADHD, by examining EEG activity in a rest eyes open condition, in 26 adolescent unmedicated ADHD males and 26 age and sex matched normal controls. ADHD adolescents were found to have increased anterior EEG absolute theta activity and reduced posterior relative beta activity compared with controls. These results lend some support to the continuation of a maturational lag and reduced cortical arousal in adolescent ADHD. These measures need to be further explored using concomitant EEG with electrodermal measures of arousal.

Adolescent↗
PubMed1998

Epileptic seizures progressing into nonepileptic conversion seizures.

BACKGROUND: Epileptic and nonepileptic seizures can occur in the same patient, but usually occur at different times. In 1885, Gowers suggested that minor seizures can elaborate into hysterical seizures, but the concurrence of epileptic and nonepileptic seizures is not well documented. METHODS: We reviewed all patients with nonepileptic seizures documented with video-EEG recordings at our center to identify those with temporally associated epileptic seizures. RESULTS: Four patients were identified in whom video-EEG-documented epileptic seizures were temporally associated with nonepileptic seizures. In one woman, the nonepileptic event followed an absence seizure. Given the high frequency of absence seizures, the occurrence of the nonepileptic seizure may have been coincidental. In three patients, the seizures were partial and arose from right frontotemporal regions. In these patients, epileptic seizures were infrequent. CONCLUSIONS: Epileptic and nonepileptic seizures can be temporally related, and in patients with partial seizures, there may be a pathophysiologic relation in which ictal changes facilitate the development of conversion symptoms. Ictal activation or disinhibition of emotions or impulse control may contribute to these nonepileptic events.

Adult↗
PubMed1998

Fast and slow reaction time changes reflected in ERP brain function.

A number of studies have examined the average late component Event Related Potential (ERP) and Reaction Time (RT) in response to multiple target stimuli (across-trial averages). This study demonstrates within-trial differences in ERP brain function associated with relatively fast and slow RTs in 50 normal subjects. A conventional auditory oddball paradigm (with a 1 ISI) was employed. Increased ERP N100 and N200 amplitude (and decreased P200 amplitude), as well as earlier P200, N200 and P300 latency were found in the fast compared with the slow ERP subaverages. These results show the potential to elucidate temporal and spatial dynamics of brain function associated with changes in performance, in conventional "cognitive" paradigms applicable to both health and disease states.

Acoustic Stimulation↗
PubMed1998

EEG alpha phase at stimulus onset significantly affects the amplitude of the P3 ERP component.

Analysis of the relationship between prestimulus EEG alpha phase and the subsequent ERP has proved difficult because of the non-Euclidean nature of phase measurements. In this study, we employed a conventional P3 templating method of single-trial analysis to identify the P3 component in target auditory oddball data from 25 normals. As in previous studies, the absence or near absence of P3 from a subset of single-trials was clearly demonstrated. We investigated this phenomenon to determine whether those single-trials with a large P3 had a different prestimulus alpha phase from those with a small or no P3. Statistical analysis of phase required the use of circular statistical analysis and the development of a new form of topographic mapping, circular topography. The alpha phase at stimulus onset in single-trials with a large P3 was significantly different from that in single-trials with a small or no P3 (p = .02).

Acoustic Stimulation↗
PubMed1998

Fast and slow reaction times and associated ERPs in patients with schizophrenia and controls.

A number of studies have examined across-trial averaged late component. Event Related Potentials (EPR) and Reaction Times (RT) in response to multiple target stimuli. In this study, within-trial relatively fast and slow sub averages are additionally examined, in 20 patients with schizophrenia and 20 age and sex matched controls. A conventional auditory oddball paradigm. Across-trial ERP average analysis showed smaller N200 amplitude and delayed latency (but larger P200 amplitude) in patients with schizophrenia compared with controls. Within-trial ERP analysis revealed a number of additional findings. Controls showed distinctive differences in fast compared with slow ERP sub averages (smaller P200 amplitude, increased N200/P300 amplitudes and earlier latencies). The schizophrenic group on the other hand, showed relatively similar fast versus slow subaverages (no differences in P200 amplitude and N200 latency). In addition, between-group (within-trial) analyses highlighted significant differences in earlier stages of processing (compared with across-trial averages) in both fast and slow subaverages (increased N100 amplitude in controls). The complementary within-trial (compared with across-trial) data are interpreted with respect to a possible disturbance in inhibitory function in patients with schizophrenia.

Adult↗
PubMed1997

Single trial variability within the P300 (250-500 ms) processing window in adolescents with attention deficit hyperactivity disorder.

The traditional averaging process used to derive event related potential components (ERPs) is a soundly based method of determining the underlying ERP. Averaging, however, ignores the variability due to the single-trial ERPs that constitute the traditional average ERP. This variability may reflect complementary functional information to the average measure. Our group applied a simple procedure, the response variance curve (RVC), which measures single-trial ERP variability relative to their average. In this study, the average ERP and RVC measures (generated from the same single-trial task-relevant target ERPs) were assessed in an auditory oddball paradigm, in 17 unmedicated male adolescents with attention deficit hyperactivity disorder (ADHD) and in 17 age- and sex-matched normal controls. P300 amplitude, latency and point of maximum variability of the RVC were measured within the P300 processing window (250-500 ms post-stimulus). There were no significant differences in P300 amplitude or latency between the groups. Unmedicated ADHD patients, however, showed significantly increased single-trial variability within the P300 window compared with controls. This variability was significantly reduced with stimulant medication.

Acoustic Stimulation↗
PubMed1997

Evoked related potentials associated with and without an orienting reflex.

Late component event related potentials (ERP) and concomitant electrodermal activity (EDA) measures of the orienting reflex (OR) were undertaken in 50 normal subjects. Our group recently developed a model to quantify electrodermal activity in conventional ERP paradigms (auditory oddball) with short interstimulus intervals (ISI). The method was used to classify the presence or absence of skin conductance response following each auditory target stimulus. Using a conventional paradigm in which data is traditionally averaged, single-trial target ERPs were sorted into those with a skin conductance response OR (ERP[+OR]) and those without (ERP[-OR]) an OR, and ERP sub-averages of the two groups were derived. The ERP(+OR) showed significantly larger P300 amplitudes and relatively earlier N200 and P300 latency than those of the ERP(-OR). These findings suggest that using concomitant SCR-ERP measures, separate ERP related processes can be determined, that are complementary to the traditional average measure.

Adolescent↗
PubMed1997

Serious brain injury from traffic-related causes: priorities for primary prevention.

This study evaluated the incidence and outcome of serious brain injury from traffic-related causes in 695 patients admitted to the Department of Neurosurgery at Karolinska Hospital during 1981-1992. A total of 37.3% of patients were car occupants, 28.1% pedestrians, 12.9% bicyclists, 12.2% car-bicycle/car-moped and 9.5% motorcycle riders. The dominating injury was brain contusion (61.6%) verified with computerized tomography. The level of consciousness was evaluated by the Glasgow Coma Scale (GCS) and outcome by the Glasgow Outcome Scale (GOS) at discharge and 6-36 months thereafter. The final outcome was 67.5% good recovery (GOS 4-5), 11.5% severely disabled (GOS 2-3) and 21.0% GOS 1 or brain dead. Patients with GOS < 4 (32.5%) were severely disabled and motivate priorities for injury prevention. Car occupants represent 40.7% of the total, followed by pedestrians at 33.6% and bicyclists at 18.2%. Much remains to be done in the primary prevention of disabling brain injury to car occupants and pedestrians. In order to achieve a more-effective primary prevention, future research should be directed toward biomechanical aspects of brain contusion as a dominating brain injury.

Accidents, Traffic↗
PubMed1997

To scale or not to scale: McCarthy and Wood revisited.

We dispute McCarthy and Wood's (1985) claim that some form of scaling should be applied routinely to ERP data before determining differences in scalp distributions between conditions (or groups). Their simulation study involved assumptions about the nature of the variability within each condition, most significantly that the standard deviations are identical at all electrodes, irrespective of the means. Alternative plausible assumptions may be proposed for which scaling is unnecessary. Furthermore, we show that the two main forms of scaling they proposed may distort or even completely eliminate real differences in scalp topography reflecting genuinely different underlying sources.

Electrodes↗
PubMed1997

Decomposing skin conductance into tonic and phasic components.

Overlapping phasic skin conductance responses (SCRs) obtained using short interstimulus interval (ISI) paradigms such as those employed in cognitive research, confound measurement of each discrete phasic SCR as well as the tonic skin conductance level (SCL). We report a method of resolving this problem using a modelling technique that takes advantage of the stereotyped nature of the within-subject SCR waveform. A four-parameter sigmoid-exponential SCR model that describes the entire response, was developed and extended to five-, six- and eight-parameter skin conductance (SC) models. These SC models were successfully curve-fitted to more than 60 SC segments, each containing one SCR or two overlapping SCRs on a sloping baseline obtained from 20 normal subjects. The SC segments were consequently decomposed into their components: the tail of the previous response, one or two SCRs and the SCL. The SCRs free of the complication of overlap were then quantified. The raw SCRs of the same data set were also measured using a standard method. The standard measurement showed a significant reduction of 15% in amplitude and 140 ms in peak latency compared to our method. The basic four SCR model parameters--onset time, rise time, decay time constant and gain--showed increasing inter-subject variability in that order. These SCR model parameters may be studied as variables in normal and patient groups and as indices of treatment response. This quantitative method also provides a means to assess the relationships between central and autonomic psychophysiologic measures.

Adult↗
PubMed1997

Hiding worries from One's spouse: associations between coping via protective buffering and distress in male post-myocardial infarction patients and their wives.

The relationship between protective buffering, a style of coping in which the individual hides his/her concerns from spouse, and level of distress was studied among post-myocardial infarction (MI) patients and their spouses. Forty-three male married MI survivors and their wives completed measures of psychological distress and protective buffering at 4 weeks and 6 months post-hospital discharge. At both time periods, a greater propensity for protective buffering by the patient was related to higher levels of patient distress. Protective buffering by wife was also associated with higher levels of wife distress. In addition, patient buffering at 4 weeks predicted increased patient distress at 6 months. The results suggest that male MI patients who conceal their worries from their spouses adjust more poorly over time.

Adaptation, Psychological↗