Biomedical subjects
C H Brunia
Publications and source records attributed to C H Brunia.
Central effects of baroreceptor activation in humans: attenuation of skeletal reflexes and pain perception.
Activating the arterial baroreceptors blunts pain sensation and produces other forms of central nervous system inhibition in animals. These effects may be important to blood pressure regulation but have not been rigorously verified in humans. We describe (i) a noninvasive behaviorally unbiased method for baroreceptor stimulation and (ii) the application of this method to measurement of baroreceptor-mediated attenuation of pain perception and of the Achilles tendon reflex. The findings are relevant to basic mechanisms of blood pressure stabilization and cardiovascular reactivity and may also have implications for noncompliance with antihypertensive medications and for the pathophysiology of essential hypertension.
A spatiotemporal dipole model of the stimulus preceding negativity (SPN) prior to feedback stimuli.
Ten subjects performed a time production task, in which they were instructed to press a button four seconds after the presentation of an auditory stimulus. Two seconds after the button press they received either auditory or visual feedback on the temporal accuracy of their response. In such a paradigm negative slow brain potentials can be recorded preceding the response (Movement Preceding Negativity, MPN) as well as preceding the feedback stimulus (Stimulus Preceding Negativity, SPN). Spatiotemporal dipole modelling is used to gain insight in the possible generators of MPN and SPN. From the models it follows that the MPN can be described by one contralateral radial dipole and a bilateral pair of tangential dipoles. All three dipoles are located near central electrode positions, so the generators of the MPN probably reside within the motor cortex. The SPN is modelled by a bilateral frontotemporal pair of dipoles, hypothetically representing activation of the Insulae Reili. The insular cortex is involved in the processing of affective-motivational input, such as carried by the feedback in the present paradigm. However, processing of the information content of the feedback stimulus might by itself also activate the frontal cortex. Both the response and the feedback stimulus are followed by a positive peak, which can be described by the same deep posterior dipole. Both peaks probably represent a P3, which is related to context updating.
A spatio-temporal dipole model of the readiness potential in humans. I. Finger movement.
Preceding unilateral finger movements readiness potentials (RPs) were recorded in 9 right-handed subjects. The data are presented as time series, potential maps and spatio-temporal dipole models. The latter are interpreted with respect to the underlying generators of the RP. Explicit hypotheses about the unilateral or bilateral activation of particular sensorimotor areas preceding unilateral movements are addressed. The choice for the best spatio-temporal dipole model was guided by a test on the orthogonality of the individual residuals and by a priori neurophysiological evidence. From the final model it is concluded that the initial bilateral symmetrical part of the RP is generated in the posterior walls of the precentral gyrus bilaterally, whereas the later lateralized components originate from the crown of that same gyrus contralaterally. This confirms and extends data from subdural recording, magnetoencephalography (MEG) and EEG.
A spatio-temporal dipole model of the readiness potential in humans. II. Foot movement.
Readiness potentials (RP) have been recorded in 9 subjects who performed voluntary unilateral plantar flexions with the right or left foot. These show a paradoxical ipsilateral dominance. Spatio-temporal dipole models were obtained for these data, by iterative parameter estimation. The non-uniqueness of the inverse problem leads to several models which describe the data almost equally well, and which all pass orthogonality tests for the individual residuals and source waves. In these dipole models the ipsilateral preponderance is attributed to generators in the contralateral hemisphere, which agrees with results from MEG recording. According to these models the main generators of the RP are in the primary motor cortex, one bilaterally in its posterior wall and the other in the contralateral crown. This agrees with earlier results for finger RPs. However, for foot RPs, it was difficult to distinguish individual sub-components in both the observed scalp potentials and the estimated temporal activation patterns of the dipoles. Some of the presented models include a fronto-central dipole which possibly represents activity of the supplementary motor area. It is concluded that this finding is at best suggestive and needs further investigation.
Motor and non-motor components of the Contingent Negative Variation.
To study the contribution of the Stimulus-Preceding Negativity (SPN) to the late wave of the Contingent Negative Variation (CNV), negativity was recorded preceding an instruction stimulus (S1), an instruction stimulus to which a motor response was required (S2) and a stimulus that transmitted Knowledge of Results (KR). All recorded negativities showed a centro-parietal maximum. The pre-instruction negativities tended to be larger over the left hemisphere, while a right hemisphere preponderance was found for the pre-KR negativity. Unlike the pre-S1 negativity, the pre-KR negativity may depend on affective-motivational processes. The pre-S1 negativity was small and influenced by factors other than the instruction at S1. It is concluded that the SPN contributes to the late CNV, but that this contribution was relatively small.
Motor and non-motor aspects of slow brain potentials.
In order to study motor and non-motor aspects of the contingent negative variation (CNV), fifteen right-handed subjects were asked to perform tightly controlled responses in a WS-S1-S2 paradigm. WS was a non-informative warning signal; S1 and S2 provided information about the response required at S2. This information was either delivered before a block of trials (Simple), at S1 (Precued), or at S2 (Choice). Negativity was larger prior to the informative than to the non-informative stimulus, suggesting the presence of a component called stimulus-preceding negativity (SPN). This finding supported the hypothesis that the late CNV consists of a readiness potential and an SPN. The scalp distribution of the SPN was different before S1 and before S2. The significance of these components is discussed in terms of motor preparation, stimulus anticipation and energetical processes.
Is a stimulus conveying task-relevant information a sufficient condition to elicit a stimulus-preceding negativity?
Movement-preceding and stimulus-preceding negativities were recorded when a movement was followed by one of three informative visual stimuli. The meaning of the visual stimulus alternated between (a) conveying a task-relevant instruction about a subsequent time production task and (b) providing feedback (knowledge of results) about performance on the current time production task. In a control condition, premovement and postmovement scalp potentials were recorded when subjects made the same movements but in a voluntary, self-paced manner. Under all conditions, movements were preceded by a movement-preceding negativity, and neither the amplitude nor the lateral asymmetry of this negativity was affected by the subsequent presentation of either kind of informative stimulus. When the movement was followed by a stimulus conveying knowledge of results, the negativity in the postmovement epoch was enhanced, but this enhancement was not evident in epochs preceding instruction stimuli. We conclude that not all task relevant stimuli elicit a stimulus-preceding negativity, and we provide a functional interpretation of this negativity in terms of emotional anticipation and the contingency of the stimulus on a previous event.
Sensory effects of baroreceptor activation and perceived stress together predict long-term blood pressure elevations.
Activating the arterial baroreceptors in animals has been shown to blunt pain sensation and provide other forms of central nervous system inhibition. This study tested the hypothesis that, among human subjects, a tonic increase in blood pressure (BP) could be a learned response to environmental stressors among subjects in whom the baroreceptor inhibitory mechanism is active. In a sample of 96 healthy, normotensive men and women, amount of pain-reduction produced by baroreceptor stimulation predicted an increase in resting BP 20 months later: the increase was proportional to self-assessed daily life stress. Among the subjects reporting the greatest amount of stress, the pain inhibition effect accounted for more than 80% of the BP variance. These results support the hypothesis that the reduction in perceived stress produced by baroreceptor stimulation may reward learned increases in BP.
Activation of carotid baroreceptors inhibits spinal reflexes in man.
The present study was designed to investigate the effect of baroreceptors on a spinal reflex. The Achilles tendon reflex (T reflex), a monosynaptic spinal reflex, was chosen as an indicator of descending influences of central activation. The baroreceptors are stretch receptors which respond to extensions of the arterial wall. Carotid sinus baroreceptors can be manipulated non-invasively by means of a cuff around the neck. In this study, the phase-related external suction (PRES) neck cuff technique was used. PRES applies short changes in cuff pressure as a function of heart cycle phase, controlling for non-specific effects found in other baroreceptor manipulation methods. The T reflex was reduced when elicited during the highest levels of baroreceptor activation. Reflex amplitude was largest when elicited during the lowest levels of baroreceptor activation. These results are consistent with previous findings that baroreceptor activation reduces CNS excitability.
Disturbed frontal regulation of attention in Parkinson's disease.
Parkinson's disease is characterized not only by tremor, akinesia and rigidity, but also by frontal cognitive dysfunction, that can be understood as a disturbance in the 'Supervisory Attentional System' (SAS). This concept refers to a system, located in the frontal cortex, that regulates attentional processes under novel, non-routine conditions. The hypothesis that cognitive dysfunction in Parkinson's disease results from a disturbance in the SAS was investigated by recording 'processing negativity' in 33 parkinsonian patients and 17 controls. Processing negativity is an event-related potential that reflects neuronal activity during selective attention. The contribution of the frontal cortex to selective attention can be studied directly using processing negativity. Parkinsonian patients were also scored for clinical symptoms and subjected to a neuropsychological test battery. Processing negativity was clearly disturbed in the parkinsonian patients. Moreover, parkinsonian patients with the lowest scores on 'frontal' neuropsychological tests such as Stroop, Trail Making and Word Fluency, also had the lowest processing negativity. Our results support the hypothesis that cognitive dysfunction in Parkinson's disease might be understood as a disturbance in the frontal regulation of attentional processes. Degeneration of the dopaminergic mesocortical innervation of the frontal cortex in Parkinson's disease is a possible neurochemical substrate of these frontal attentional disturbances.
Waiting in readiness: gating in attention and motor preparation.
In this paper the similarities in the structural and functional organization of motor preparation and attention are discussed. A crucial structure in this organization is the thalamus, a complex of sensory and motor nuclei that transmits information from subcortical origins to the cortex. For the most part, the thalamus is overlapped by the nucleus reticularis, which has a local inhibitory influence on the underlying nuclei. This serves as a gating mechanism for the transmission of sensory information to the cortex. Skinner and Yingling (1977) have provided arguments in favor of a frontal control in the gating of sensory information. The present paper extends their suggestions to the motor system: a similar gating mechanism for the transmission of subcortical motor information to the cortex is hypothesized, also under frontal control. Slow potentials recorded during motor preparation and attention for an upcoming stimulus show a different distribution over the scalp. These distributions are interpreted as an indication of which thalamic gates are open to transmit information to the cortex. Probe responses (spinal reflexes, evoked potentials, and the startle reflex) can also be used to investigate which thalamocortical gates are open under certain experimental conditions. It is concluded that the sensory and motor input to the cortex are subjected to a similar control mechanism.
Detection of EMG onset in ERP research.
Many researchers have used off-line techniques for the automatic detection of electromyogram (EMG) onset. However, very little is known about the accuracy of these methods. In the present study, five such methods are evaluated and their accuracy is reported. Five subjects were asked to produce fast (ballistic) and slow (ramp) contractions with thumb and index finger of the right hand in a simple reaction time task. EMG was recorded from the first dorsal interosseus muscle, and onsets were visually determined in the raw EMG. These onsets were compared with the onsets produced by the automated methods on the rectified and low-pass filtered EMG. Four of the automated methods produced very reliable estimates of the visually determined onsets, at least when additional constraints upon the initial estimates were made. Studies using automated methods for EMG onset detection should report findings about their accuracy.
Event-related potentials to different feedback stimuli.
Event-related potentials (ERPs) were recorded in a time estimation task under different feedback conditions, in which the informative value of the feedback signals (true versus false) was manipulated. A control condition was added in which no signal was presented. Fifteen subjects pressed a button 3 seconds after presentation of a warning signal. Two seconds after the response, a visual feedback signal was presented, indicating whether the preceding interval was estimated correctly. Two different slow waves were observed: the response was preceded by a readiness potential and the feedback stimulus was preceded by a negative slow wave called the stimulus-preceding negativity. The readiness potential was not influenced by the different feedback conditions. The stimulus-preceding negativity was larger in the true feedback condition compared to the false feedback and no feedback conditions. The P300 to the feedback signal was also larger following a true as compared to a false feedback signal. The conclusion is that the stimulus-preceding negativity is an anticipatory component contingent upon the presentation of an informative feedback signal.
The effect of an acoustic warning stimulus upon the electrically elicited blink reflex in humans.
In a warned Go/No-Go reaction time experiment blink reflexes were elicited electrically immediately before, at, and shortly after the onset of a low intensity acoustic warning stimulus. This provided the opportunity to study the mutual effects of two stimuli of different modalities arriving at the facial nucleus. The warning stimulus was followed after 3 s by an acoustic response stimulus. Sixteen subjects participated in the experiment. They were informed by the response stimulus if a response (a voluntary blink of the right eye) was required. R1 magnitude was increased from 10 ms to 100 ms after warning stimulus onset, with a pronounced peak at 50 ms. The bilateral late component R2 was enhanced when the reflex eliciting stimulus preceded the warning stimulus. Between 20 ms and 30 ms after warning stimulus onset, R2 returned to control level, whereas an eliciting stimulus presented 40 ms or later after warning stimulus onset produced a pronounced inhibition. R2 latency was facilitated immediately after warning stimulus onset. It was concluded that the mutual effects of stimuli of different modalities can be interpreted only if the moment of arrival at the motor nucleus is taken into consideration.
Contingent Negative Variation in migraine.
The Contingent Negative Variation (CNV) is an event-related slow potential. It was recorded in healthy volunteers (n = 8) and in patients suffering from migraine without (n = 12) or with (n = 5) aura, during one (CNV1) and three second (CNV3) foreperiods in a forewarned reaction time task. CNV1 was recorded at the vertex while CNV3 was recorded at multiple electrode sites to assess topographical differences. Seven out of twelve migraine patients without aura had increased CNV1 amplitudes. CNV3 amplitudes were increased as well, but only at electrode positions C3 and C4 and not at Fz. CNV3, which allows for analysis of both an early and a late CNV component, could improve the discrimination of migraine without aura beyond that of CNV1. In migraine with aura all CNV parameters were at control levels, confirming previous results. The data obtained are discussed in terms of arousal, activation and stress and the "biobehavioral model of migraine" (Welch, 1986).
Correction of ocular artifacts in EEGs using an autoregressive model to describe the EEG; a pilot study.
The basic idea in eye movement (EM) artifact corrections is that the actual recording is the summation of brain potentials (true EEG) and artifact. Often a regression analysis is performed, using simultaneous EEG and EOG data, to find the parameters describing the relationship between artifact and EOG derivations (EOGs). Our method uses a maximum likelihood parameter estimation and considers data from preceding sample moments as well, since there may be a delay in the artifact transferring over the scalp. For the error term (true EEG) an autoregressive function is used. Results from estimations on data from one volunteer indicate that a delay need not be considered and that 3 autoregressive parameters are sufficient. For F3 4 EOGs give only somewhat better results than 2 EOGs. For C3 and C4 2 EOGs are sufficient. For practical reasons for each of these 3 EEG recordings, 2 EOGs were used to perform corrections. Corrections were performed using either the parameters estimated for EMs and blinks together, or the parameters estimated for EMs only (used for EMs), or the parameters estimated for blinks only (used for blinks). For EMs the differences between these corrections are very small. For blinks the differences are much larger. Parameters estimated for one trial may be used to correct other trials, recorded within a period of about 15 min preceding or following that trial.