Biomedical subjects

J G Van Dijk

Publications and source records attributed to J G Van Dijk.

8 recordsLinked to original sources

PubMed1992

Background EEG reactivity in auditory event-related potentials.

Mental activity has influences on auditory event-related potentials (AERP) as well as on some EEG rhythms, notably the alpha rhythm. In this study, background reactivity (BR) of the EEG was investigated in the context of AERPs. Single responses of 14 healthy subjects were analysed in 3 reaction time AERP experiments of increasing difficulty: the first involved one type of tone delivered at random intervals, the second offered two types of tone (an "oddball" design), and the third offered 3 types of tone. Averages were formed and subtracted from the separate responses to reduce their contribution to the EEG. The 1526 msec EEG epoch was divided in 9 overlapping periods, and averaged power spectra were calculated for these periods. Changes in area of the delta, theta, alpha and beta bands in the course of the epoch were calculated. Background alpha and beta activity decreased following infrequent but not following frequent tones. The decrease was larger for more difficult tasks and reached a maximum in the period in which the AERP P3 and N3 peaks fell. Delta and theta powers showed increases rather than decreases; these could be attributed to the contribution of AERP activity to total EEG power. No clear relationships were found between the amount of background reactivity and peak latencies or reaction times. The occurrence of background reactivity, not apparent in an average, shows that the averaged AERP reveals only part of the EEG changes related to mental activity. Background reactivity proved to be more sensitive to task difficulty than P300 latency. The results are discussed in the context of the additive model of evoked potentials.

Acoustic Stimulation↗

PubMed1992

Altered postural reflexes in Parkinson's disease: a reverse hypothesis.

In subjects standing on a movable platform, sudden dorsiflexion of the ankle joint elicits a set of reflexes in leg muscles. These responses include a short latency (SL) and medium latency (ML) stretch reflex in the gastrocnemius muscle and a distal to proximal innervation sequence of long latency (LL) reflexes in the shortened tibialis anterior and vastus lateralis muscles. Because of their role in maintaining upright stance these responses have been termed postural reflexes. In patients with Parkinson's disease (PD), the following abnormalities have been described: 1) enhanced ML-amplitudes; 2) a reversed LL innervation sequence; and 3) delayed onset latencies. These abnormalities are thought to be due to defective motor programming and disturbed control of spinal and supraspinal reflex centers by basal ganglia circuits. The altered reflexes have been held responsible for some of the clinical features of PD, including balance impairment and rigidity. In this paper, we argue the reverse hypothesis that postural reflexes are essentially normal in PD, and that the observed alterations are at least in part consequence rather than cause of balance impairment, the stooped parkinsonian posture and rigidity of PD patients.

Humans↗

PubMed1992

Korsakoff minus Wernicke syndrome.

It is commonly believed that Korsakoff's amnesic state in alcoholics is characteristically the sequel to Wernicke's disease. However, in a study of 44 Korsakoff patients it was found that 33 had developed serious memory impairment without having had alarming neurological symptoms. This insidious nature of the onset of the disease indicates that all alcohol-dependent patients should be treated with vitamin B.

Alcohol Amnestic Disorder↗

PubMed1991

Long-term EEG monitoring in the early premature: developmental and chronobiological aspects.

Long-term cassette EEG monitoring in the neonatal intensive care unit has established prognostic criteria regarding the developmental outcome by quantifying seizure activity. The clinical significance of the organization of continuous and discontinuous EEG patterns in the early premature is still an open question. This report presents quantified EEG data from repeated 24 h records during the first week of life in premature infants (conceptional age less than 32 weeks) with and without ultrasound evidence of intracerebral hemorrhage. The repartition and evolution of EEG background activity is not a reliable parameter regarding pathology. The continuity index is rather a maturational variable and its ultradian fluctuation is an early expression of the "basic rest activity cycle" (BRAC) rhythm.

Aging↗

PubMed1991

Long latency postural responses are functionally modified by cognitive set.

We examined how cognitive set influences the long latency components of normal postural responses in the legs. We disturbed the postural stability of standing human subjects with sudden toe-up ankle rotations. To influence the subjects' cognitive set, we varied the rotation amplitude either predictably (serial 4 degrees versus serial 10 degrees) or unpredictably (random mixture of 4 degrees and 10 degrees). The subjects' responses to these ankle rotations were assessed from the EMG activity of the tibialis anterior, the medial gastrocnemius, and the vastus lateralis muscles of the left leg. The results indicate that, when the rotation amplitude is predictable, only the amplitude of the long latency (LL) response in tibialis anterior and vastus lateralis varied directly with perturbation size. Furthermore, when the rotation amplitude is unpredictable, the central nervous system selects a default amplitude for the LL response in the tibialis anterior. When normal subjects are exposed to 2 perturbation amplitudes which include the potential risk of falling, the default LL response in tibialis anterior appropriately anticipates the larger amplitude perturbation rather than the smaller or an intermediate one.

Adult↗

PubMed1990

Habituation of K-complexes or event-related potentials during sleep.

We examined habituation and dishabituation of evoked K-complexes (equivalent to auditory event-related potentials) during sleep. Habituation is investigated by presenting trains of stimuli with a 5 sec inter-stimulus interval and a 4 min inter-train interval. Habituation is complete by the third identical stimulus in a train and dishabituation occurs after deviant stimuli and after the inter-train interval. Although there are morphological differences between K-complexes in sleep and auditory event-related potentials in wakefulness, they share the phenomenon of habituation to repetitive events.

Acoustic Stimulation↗

PubMed1990

Trigeminal neuralgia-like pain in an aged woman with fibrous dysplasia of the skull base.

A 72 year old woman with attacks of severe lancinating pain in the right frontotemporal region of her face had, on CT scan of the skull base, fibrous dysplasia of the right sphenoid bone, involving the areas traversed by the trigeminal nerve. Her pain ceased following treatment with methysergide. In patients with hemifacial pain but no evident facial or skull deformities, CT scan of the skull base may be helpful in elucidating the diagnosis.

Aged↗

PubMed1988

Respiration during sleep in Huntington's chorea.

In view of recent reports on lower brainstem dysfunction in Huntington's chorea, we studied respiration during sleep in 12 patients with Huntington's chorea (HC) and in controls. There were no statistically significant differences between patients and controls with respect to apnea periods, respiratory frequency and time elapsed between minimal and maximal value of the respiratory curve. No statistically significant differences in respiratory variability were observed between patients and controls. In the present study, no indication was found for dysfunction of lower brainstem structures involved in respiration in HC.

Adult↗