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Biomedical subjects

C H Brunia

Publications and source records attributed to C H Brunia.

At least 55 records · Page 3Linked to original sources
PubMed1988

Distribution of slow brain potentials related to motor preparation and stimulus anticipation in a time estimation task.

Subjects had to press a button at regular intervals of 20 sec. Two seconds after each button press a stimulus was presented indicating the length of the past interval. EEG was analysed from 2500 msec preceding the button press until the presentation of the stimulus. Preceding the button press a readiness potential (RP) was recorded with amplitudes that were larger over the hemisphere contralateral to the movement side. Preceding the stimulus negative waves were recorded which were larger over the right hemisphere, irrespective of the movement side. In a warned reaction time experiment, the CNV late wave represents both motor preparation and stimulus anticipation. In the present study motor preparation and stimulus anticipation are no longer confounded factors. Thus, it is shown that stimulus anticipation is indeed reflected by negative activity, as is motor preparation. The potential distribution of the RP, however, is different from the stimulus-preceding negativity (SPN), a pointing to a different electrophysiological source. The potential distribution of the SPN has been investigated and a right hemisphere preponderance of the SPN has been found.

Adolescent↗
PubMed1988

Movement and stimulus preceding negativity.

After a short description of the different premovement potentials it is suggested that readiness potentials (RPs) recorded over different cortical motor areas reflect different functions. Then it is proposed that the late wave of the contingent negative variation (CNV) is a composite of a RP and a stimulus preceding negativity (SPN). Arguments for the existence of a non-motoric SPN are given, based upon our recent experiments. Next, it is suggested that a SPN is found preceding at least three different kinds of stimuli. Finally, it is stated that motor preparation and stimulus anticipation are different processes, reflected in a different distribution of the accompanying Slow Waves and an all or none accompanying change in reflex amplitudes.

Animals↗
PubMed1986

Motor preparation and the Achilles tendon reflex: the role of background muscle tension.

The effects of instructed tension or relaxation of the soleus muscles on the amplitude of the Achilles tendon reflex were investigated. Reflexes were evoked during the foreperiod of a warned reaction time experiment with a plantar flexion of the right foot serving as the response, and during isometric contractions of the right soleus muscle at different low levels of tension. The tension levels were related to the subject's maximal voluntary contraction force. The results were comparable in the two tasks. When background muscle tension was present in the right leg the reflexes in that leg were depressed, whereas in the contralateral leg reflexes were increased. This difference in amplitude was roughly proportional to the amount of tension and independent of whether the antagonist muscle was also activated during the contraction. It was argued that the differential reflex effect found in the two soleus muscles during motor preparation need not be a reflection of a selective neural inhibition. It could also be explained by a reduced effectiveness of the tendon tap in stretching the muscle, due to stiffening of the muscle during contraction. It was concluded that during motor preparation, only reflex changes recorded in the absence of muscle tension can be considered reflections of subliminal changes in spinal reactivity.

Achilles Tendon↗
PubMed1985

Movement related slow potentials. II. A contrast between finger and foot movements in left-handed subjects.

Finger and foot movement related potentials (MRPs) were recorded over the frontal, central and parietal areas of both hemispheres in 20 left-handed subjects. A unilateral flexion of the index finger and a plantar flexion of the foot were studied on either side. MRPs were larger preceding foot movements than preceding finger movements, their onset being earlier also. Prior to a finger flexion amplitudes were larger over the hemisphere contralateral to the movement than over the ipsilateral hemisphere. Preceding a foot movement, however, amplitudes were larger over the ipsilateral hemisphere. These results indicate differently localized sources of the MRPs in the two kinds of movement, in accordance with data obtained in right-handed subjects. No indication of a hemisphere effect, possibly related to motor dominance, was found in left-handers. This is in contrast to a slight hemisphere effect found with foot movements in right-handed subjects in the former study.

Adolescent↗
PubMed1985

Anticipatory response-relevant muscle activity, CNV amplitude and simple reaction time.

The present experiment was aimed at whether subjects, performing a forewarned simple reaction time (RT) task, do voluntarily tense agonist and antagonist muscles during the foreperiod; if so, would such muscle tension co-vary with CNV amplitude or RT? Although excessive eye movements caused 30% of the subjects to be removed from the analysis, it was still possible after the experiment to differentiate between subjects who gradually tensed their agonist during the foreperiod and subjects who did not. The former group showed higher CNV early and late wave amplitudes as compared with the latter group. A similar effect was found on the N1 amplitude of the potential evoked by the warning stimulus. The increased EMG in the agonist muscle at the end of the foreperiod was not concomitant with faster RTs. In addition, fast RTs were preceded by higher CNV late wave amplitudes at pre- and postcentral electrode positions. The observed relationships between CNV, EMG, and RT were discussed in terms of specific and general motor preparation.

Adolescent↗
PubMed1985

Achilles tendon reflexes and surface EMG activity during anticipation of a significant event and preparation for a voluntary movement.

Achilles tendon reflexes were evoked bilaterally during and shortly after an interstimulus-interval (ISI) of 4 s and expressed as percentages of an averaged control reflex. Surface EMG of the soleus muscles were recorded continuously during the ISI, and expressed as percentages of a control EMG level. Three types of tasks were introduced, according to a between subjects design. Condition I consisted of a guessing task, involving anticipation of the second stimulus (S2) and not requiring a motor response. Conditions II and III were a warned choice and simple RT task respectively, the motor response to S2 being a plantar flexion of either the left or right foot in Condition II, and a plantar flexion of the right foot in Condition III. The results can be stated as follows: 1. Anticipation of a stimulus is not sufficient for a reflex increase to occur during an ISI. Preparation for a movement seems to be a necessary condition. 2. The reflex increase during preparation is rather independent of the amount of selectivity in the preparatory process; simple and choice RT tasks yield similar results, although the mean RTs do differ. 3. A difference between the involved and non-involved legs in the simple RT task is not found in the present experiment, as opposed to other studies. The particular instruction given to the subjects could be of importance in producing this difference. 4. Reflex changes cannot simply be accounted for by changes in background EMG of the agonist, as the EMG time course shows no changes over time in either condition.

Journal Article↗
PubMed1984

Movement-related slow potentials. I. A contrast between finger and foot movements in right-handed subjects.

Movement-related potentials ( MRPs ) preceding a finger flexion and a plantar flexion of the foot on either side were compared over the frontal, central and parietal areas of both hemispheres. MRP amplitudes were larger preceding foot than preceding finger movements. In the first case their onset was earlier and their presence in the frontal area was more marked. Prior to a finger flexion amplitudes over the hemisphere contralateral to the movement side were larger than those recorded over the ipsilateral hemisphere. On the contrary, prior to a plantar flexion of the foot, amplitudes were larger over the hemisphere ipsilateral to the movement. These findings point to differently localized sources of the MRPs in the two cases. In other experiments larger amplitudes preceding foot movements were found near the midline. It is suggested that the ipsilateral preponderance prior to foot movements is caused by a contralateral source in the depth near the longitudinal fissure. The dipoles are presumably directed obliquely to the median plane. The ipsilateral preponderance is present both prior to and following the plantar flexion. This suggests comparable directions of the dipoles in the motor and somatosensory areas.

Adolescent↗
PubMed1983

Changes of human blink reflex magnitude during a three second fixed foreperiod.

Blink reflexes were evoked at distinct times during a 3 sec foreperiod (FP) between a warning stimulus (WS) and a reaction signal (RS). Sixteen well-trained, right-handed subjects participated in the experiment. Following RS, they reacted instantaneously with a blink of the right eye. In the electrically evoked blink reflex, an early ipsilateral component (R1) with a latency of +/- 10 msec and a late bilateral component (R2) with a latency of +/- 25-40 msec could be distinguished. The peak-to-peak amplitude of R1 and the integral of R2 were computed. In the beginning of FP, R1 was enlarged as compared to control values. Toward the end of FP, a continuous rise of R1 amplitudes was seen. This increment was most pronounced in the muscle involved in the reaction following RS. R2 was inhibited immediately after WS, while no significant inhibition could be seen near the end of FP. The conclusion is that the facilitation of R1 and the disinhibition of R2 towards the end of FP reflect the preparation on the reaction after RS. The extra increment of R1 might be due to a selective extra preparation of the motoneurons of the involved muscle, although an effect of motor dominance cannot be excluded.

Adult↗
PubMed1982

Effects of stimulus and task factors on Achilles tendon reflexes evoked early during a preparatory period.

The effects of intensity, duration and modality of a warning signal on tendon (T) reflexes evoked during the initial phase of a preparatory period of 4 sec were investigated. Reflexes were evoked simultaneously in both legs, from 0 to 350 msec after warning signal onset in steps of 50 msec. The required response was a planter flexion of the right foot. A facilitation of reflexes was seen within 150 msec after warning signal onset, showing a somewhat longer latency for visual as compared to auditory signals. An effect of intensity was found in the auditory modality only, where the louder of two warning signals yielded a clear peak at 100 msec while the softer stimulus caused no significant departure of Achilles tendon reflexes from baseline. The time course of facilitation in the auditory modality was influenced by warning signal duration as well, although this effect was only marginally significant. There were no effects of physical warning signal parameters on reaction time. A comparison with an experiment in which non-signal stimuli were presented alone, pointed to aspects of the preparatory process which were manifest at the spinal level as early as 200 msec after warning signal onset.

Achilles Tendon↗