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Biomedical subjects

Koen B E Böcker

Publications and source records attributed to Koen B E Böcker.

14 recordsLinked to original sources
PubMed2006

Electrocortical correlates of control of selective attention to spatial frequency.

In the present study, we investigated control of selective attention to spatial frequency patterns, using a cueing paradigm. Subjects either used the instruction embedded in a word cue to prepare for the upcoming test stimulus (transient attention condition) or used the instruction they received before a block of trials (sustained reference condition), under completely similar stimulus conditions. The pattern of differential cue responses between these two conditions, reflecting top-down attentional control processes, was different between two groups of subjects, effectively canceling each other out. Despite comparable behavioral performance on both cues and targets, one group (n = 4) elicited a fronto-central-parietal positivity, starting 500 ms postcue over frontal and prefrontal areas, later including more central and posterior scalp sites, whereas another group (n = 8) started 400 ms postcue over central sites with a negativity, growing in strength over time and stabilizing over fronto-central sites. Only the group of eight subjects showed some evidence of occipital pretarget biasing activity. Independent of group, source modeling of the attentional control activity showed that attentional control was initiated in anterior, not posterior, parts of the brain. Furthermore, different underlying sources were found for both groups, in addition to signs of differential processing of target stimuli. Possible individual differences in attentional control ability and its relation to usage of different brain areas to deal with the task demands are discussed in more detail.

Adult↗
PubMed2006

Hypothesis testing in distributed source models for EEG and MEG data.

Hypothesis testing in distributed source models for the electro- or magnetoencephalogram is generally performed for each voxel separately. Derived from the analysis of functional magnetic resonance imaging data, such a statistical parametric map (SPM) ignores the spatial smoothing in hypothesis testing with distributed source models. For example, when intending to test a single voxel, actually an entire region of voxels is tested simultaneously. Because there are more parameters than observations, typically constraints are employed to arrive at a solution which spatially smooths the solution. If ignored, it can be concluded from the hypothesis test that there is activity at some location where there is none. In addition, an SPM on distributed source models gives the illusion of very high resolution. As an alternative, a multivariate approach is suggested in which a region of interest is tested that is spatially smooth. In simulations with MEG and EEG it is shown that clear hypothesis testing in distributed source models is possible, provided that there is high correspondence between what is intended to be tested and what is actually tested. The approach is also illustrated by an application to data from an experiment measuring visual evoked fields when presenting checkerboard patterns.

Brain↗
PubMed2005

Chronic effects of social drinking in a card-sorting task: an event related potential study.

OBJECTIVE: The Wisconsin Card Sorting Task (WCST) is one of the most widely used neuropsychological tests of frontal lobe function, which is thought to be affected by regular alcohol use. The present study used a computer-adapted version of the WCST to assess the effects of chronic alcohol consumption on the brain. METHODS: Participants (N=59) sorted cards according to an initially unknown sorting rule, which referred to shape, number, or color. The correctness of the chosen sorting rule was indicated by a feedback stimulus. This correct sorting rule had to be followed for a number of stimuli, and when it changed participants had to find out which rule had to be followed next. A distinction was made between early (correct sorting rule is unknown) and late trials (correct sorting rule is known and applied). To measure brain activity related during the task event related potentials (ERPs) were recorded to the target and feedback stimulus in light (N=14), moderate (N=16) and heavy (N=19) social drinkers and excessive alcohol users (N=10). RESULTS: No differences in number of series completed or the reaction time in each trial, were found between the four groups. In contrast, a mid-frontal N1 component in reaction to the feedback stimuli did reveal differences between the four groups. In the light and moderate drinkers, on early feedback trials the N1 was larger relative to late feedback trials, but this effect was absent in the heavy social drinkers and excessive drinkers. CONCLUSIONS: The reduced N1 effect with increasing alcohol intake could reflect abnormal allocation of attention or impaired conflict monitoring, possibly based on activity in the anterior cingulate cortex. SIGNIFICANCE: Heavy social drinking and excessive drinking leads to changes in the mid-frontal N1 during feedback trials of the WCST.

Adult↗
PubMed2005

Associations between alcohol intake and brain volumes in male and female moderate drinkers.

BACKGROUND: Alcohol-dependent individuals have brain volume loss. Possibly, moderate drinkers who are not alcohol dependent have similar but less prominent brain damage. The authors investigated whether current or lifetime alcohol intake is related to volumes of total brain, cerebellum, ventricles, peripheral cerebrospinal fluid, and cerebral gray and white matter in moderate drinkers. METHODS: The relation between current or lifetime alcohol intake and brain volumes of 47 male moderate drinkers (current alcohol intake 20 drinks per week, lifetime alcohol intake 240 kg) and 44 female moderate drinkers (current alcohol intake 15 drinks per week, lifetime alcohol intake 170 kg), all without a personal or family history of alcohol dependence, was determined using high-resolution magnetic resonance images, corrected for intracranial volume, age, and sex. RESULTS: In males, mean lifetime alcohol intake was positively associated with cerebral white matter volume, particularly in the frontal region. In females, mean lifetime alcohol intake was not associated with brain volumes. Current alcohol intake was unrelated to brain volumes in either males or females. CONCLUSIONS: Neither current nor lifetime alcohol intake is associated with decreases in brain volumes in male or female moderate drinkers. Because all participants had a negative personal and family history of alcohol dependence, the current results relatively purely concern the effects of moderate alcohol intake on brain volumes.

Adult↗
PubMed2004

Sources of auditory selective attention and the effects of methylphenidate in children with attention-deficit/hyperactivity disorder.

BACKGROUND: The aim of this study was to determine 1) whether abnormal auditory selective attention in children with attention-deficit/hyperactivity disorder (ADHD), as reflected in the processing negativity (PN) of the event-related potential, is related to impaired frontal functioning; and 2) how methylphenidate (MPh) affects attentional functioning in ADHD. METHODS: Sources of electrical brain activity were estimated in healthy control children, in ADHD children without medication, and in children with ADHD during a placebo-controlled medication trial involving MPh. RESULTS: The source models showed that the PN is generated in the auditory cortex. Children with ADHD showed less activity related to selective attention in this brain region. Administration of MPh resulted in more frontally located sources. CONCLUSIONS: The results showed no evidence for an important role of the frontal cortex in abnormalities in selective attention in children with ADHD. Also, the data did not indicate that MPh normalizes brain activity in these children.

Attention↗
PubMed2004

Differences in startle modulation during instructed threat and selective attention.

This study investigated whether attentional processes contribute to fear-potentiated startle. Ten subjects participated in a threat of shock experiment and an attentional control condition. In the threat of shock experiment, visual cues indicated whether or not an aversive shock might occur. In the attentional control, the shocks were replaced by faint vibrotactile stimuli that had to be counted. The P300 amplitudes of the ERP evoked by the visual cues did not differ under threat and counting, which suggested that both conditions engaged attention to the same extent. In contrast, startle potentiation in the threat condition was an order of magnitude larger than the marginally significant attentional startle facilitation in the counting condition. These results indicate that an attentional contribution to fear-potentiated startle under the present experimental conditions is small. In addition, contextual effects of threat of shock became manifest as baseline startle was facilitated relative to the attention condition. This may reflect a more sustained state of anxiety on which cue-specific fear responses are superimposed.

Acoustic Stimulation↗
PubMed2004

Abnormal EEG synchronisation in heavily drinking students.

OBJECTIVE: In alcoholics, grey and white brain matter is damaged. In addition, functional brain connectivity as measured by EEG coherence is abnormal. We investigated whether heavily drinking students, although drinking for a shorter period than alcoholics, already show differences in functional connectivity compared to light-drinking controls. METHODS: EEG was recorded in 11 light and 11 heavy male student drinkers during eyes closed, and eyes closed plus mental rehearsal of pictures. Functional connectivity was assessed with the Synchronisation Likelihood method. RESULTS: Heavily drinking students had more synchronisation in the theta (4-8 Hz) and gamma (30-45 Hz) band than lightly drinking students during eyes closed, both with and without a mental-rehearsal task. CONCLUSIONS: Heavy student drinkers have increases in EEG synchronisation that are indicative of changes in hippocampal-neocortical connectivity. SIGNIFICANCE: Heavy student drinkers show differences in functional connectivity as compared to their lightly drinking counterparts, even though they have a relatively short drinking history.

Adult↗
PubMed2004

The coupled dipole model: an integrated model for multiple MEG/EEG data sets.

Often MEG/EEG is measured in a few slightly different conditions to investigate the functionality of the human brain. This kind of data sets show similarities, though are different for each condition. When solving the inverse problem (IP), performing the source localization, one encounters the problem that this IP is ill-posed: constraints are necessary to solve and stabilize the solution to the IP. Moreover, a substantial amount of data is needed to avoid a signal to noise ratio (SNR) that is too poor for source localizations. In the case of similar conditions, this common information can be exploited by analyzing the data sets simultaneously. The here proposed coupled dipole model (CDM) provides an integrated method in which these similarities between conditions are used to solve and stabilize the inverse problem. The coupled dipole model is applicable when data sets contain common sources or common source time functions. The coupled dipole model uses a set of common sources and a set of common source time functions (STFs) to model all conditions in one single model. The data of each condition are mathematically described as a linear combination of these common spatial and common temporal components. This linear combination is specified in a coupling matrix for each data set. The coupled dipole model was applied in two simulation studies and in one experimental study. The simulations show that the errors in the estimated spatial and temporal parameters decrease compared to the standard separate analyses. A decrease in position error of a factor of 10 was shown for the localization of two nearby sources. In the experimental application, the coupled dipole model was shown to be necessary to obtain a plausible solution in at least 3 of 15 conditions investigated. Moreover, using the CDM, a direct comparison between parameters in different conditions is possible, whereas in separate models, the scaling of the amplitude parameters varies in general from data set to data set.

Algorithms↗
PubMed2004

Frequency domain simultaneous source and source coherence estimation with an application to MEG.

Interactions between cortical areas are crucial for cognitive functioning. Methods currently in use to assess such interactions are not well suited for this task because they lack timing precision, localization precision, or both. We present a method for simultaneous estimation of source location and orientation parameters and cross-spectral parameters to overcome these problems. Different estimators are evaluated for their performance. From a simulation study, we conclude that the estimators derived from the maximum-likelihood procedure have good statistical properties with moderate sample sizes, whereas those obtained from the generalized least squares procedure are biased and give poor-quality standard errors. The method is illustrated with visually evoked field data, with inconclusive results.

Adult↗
PubMed2003

Cognitive basis of hallucinations in schizophrenia: role of top-down information processing.

Hallucinations in schizophrenia have been regarded to result from the erroneous attribution of internally generated information to an external source. Distortions in mental imagery may underlie such confusions. We investigated performance of 77 subjects on multiple behavioral measures of auditory and visual mental imagery and perception, and a measure of reality monitoring. Comparisons were made between performance of schizophrenia patients with (N=22) and without (N=35) hallucinations and matched normal comparison subjects (N=20), after controlling for attentional factors. No differences emerged on any of the mental imagery measures, nor on reality monitoring accuracy. This suggests that there is no stable disposition towards abnormal mental imagery associated with hallucinations. However, for patients with active hallucinations (N=12), hallucination severity correlated positively with a measure of imagery-perception interaction in the auditory modality, r=0.70, p=0.01. Although preliminary, this finding is consistent with recent theoretical proposals in which hallucinations have been suggested to result from an increased influence of top-down sensory expectations on conscious perception.

Adult↗
PubMed2002

Benzodiazepines have no effect on fear-potentiated startle in humans.

RATIONALE: Pre-clinical and clinical investigations have provided a great deal of evidence that the fear-potentiated startle paradigm represents a valid model for the objective assessment of emotional states of anxiety and fear. OBJECTIVE: The four studies presented in this report sought to further validate the "threat of shock" paradigm as a human analogue to fear-potentiated startle in rats, by examining the effect of benzodiazepine administration on both baseline and fear-potentiated startle. METHODS: Three studies, conducted at Utrecht University, evaluated the effects of oxazepam and of diazepam on baseline and fear-potentiated startle, whereas a fourth study, conducted at Yale University, evaluated the effect of diazepam on baseline, contextual and cue-specific fear-potentiated startle. The threat of shock paradigm consisted of verbal instruction about two visual cues (the threat cue predicted the possible administration of electric shock, the other predicted a safe period), followed by a series of presentations of these cues. During these conditions, acoustic startle stimuli were presented in order to elicit startle responses. The magnitude of the startle response was used to index the degree of fear or alarm experienced during the periods of threat and safety. The fourth study examined the effect of IV administration of diazepam in a similar threat of shock paradigm except that there were two additional context manipulations: electrode placement and darkness. RESULTS: None of the drug manipulations affected specific threat-cue potentiation of startle. However, reductions in baseline startle were observed. Further, startle potentiation by darkness was inhibited by diazepam. CONCLUSIONS: At least one type of fear-potentiated startle, i.e. potentiation by a cue-specific fear manipulation, is not susceptible to benzodiazepine treatment. In contrast, effects of manipulations more akin to anxiety (darkness, context) appear sensitive to benzodiazepines. Human experimental models differentiating between these cue specific and contextual responses are needed to shed more light on differences in the anatomy and pharmacology of anxiety disorders.

Adolescent↗
PubMed2002

ERD as an index of anticipatory attention? Effects of stimulus degradation.

Previous research has suggested that the stimulus-preceding negativity (SPN) is largely independent of stimulus modality. In contrast, the scalp topography of the event-related desynchronization (ERD) related to the anticipation of stimuli providing knowledge of results (KR) is modality dependent. These findings, combined with functional SPN research, lead to the hypothesis that anticipatory ERD reflects anticipatory attention, whereas the SPN mainly depends on the affective-motivational properties of the anticipated stimulus. To further investigate the prestimulus ERD, and compare this measure with the SPN, 12 participants performed a time-estimation task, and were informed about the quality of their time estimation by an auditory or a visual stimulus providing KR. The KR stimuli could be either intact or degraded. Auditory degraded KR stimuli were less effective than other KR stimuli in guiding subsequent behavior, and were preceded by a larger SPN. There were no effects of degradation on the SPN in the visual modality. Preceding auditory KR stimuli no ERD was present, whereas preceding visual stimuli an occipital ERD was found. However, contrary to expectation, the latter was larger preceding intact than preceding degraded stimuli. It is concluded that the data largely agree with an interpretation of the pre-KR SPN as a reflection of the anticipation of the affective-motivational value of KR stimuli, and of the prestimulus ERD as a perceptual anticipatory attention process.

Acoustic Stimulation↗
PubMed2002

Model selection in electromagnetic source analysis with an application to VEFs.

In electromagnetic source analysis, it is necessary to determine how many sources are required to describe the electroencephalogram or magnetoencephalogram adequately. Model selection procedures (MSPs) or goodness of fit procedures give an estimate of the required number of sources. Existing and new MSPs are evaluated in different source and noise settings: two sources which are close or distant and noise which is uncorrelated or correlated. The commonly used MSP residual variance is seen to be ineffective, that is it often selects too many sources. Alternatives like the adjusted Hotelling's test, Bayes information criterion and the Wald test on source amplitudes are seen to be effective. The adjusted Hotelling's test is recommended if a conservative approach is taken and MSPs such as Bayes information criterion or the Wald test on source amplitudes are recommended if a more liberal approach is desirable. The MSPs are applied to empirical data (visual evoked fields).

Algorithms↗