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Biomedical subjects

R T Pivik

Publications and source records attributed to R T Pivik.

At least 55 records · Page 3Linked to original sources
PubMed1983

Abnormal visual--vestibular interactions in psychosis.

Vestibular reactivity and suppression of caloric nystagmus by visual fixation were examined in 40 psychiatric patients (36 schizophrenics and 4 manic-depressives) and 20 normal control subjects. Indices of reactivity commonly considered to reflect vestibular integrity, namely, slow-phase velocity and bilateral symmetry of response, did not discriminate patients from controls. However, response irregularities in the form of dysrhythmia and slower velocity of the nystagmus fast (saccadic) component were present to a significant degree in patients. Visual fixation effectively suppressed caloric nystagmus in normal controls, but not in hospitalized patients. This failure of fixation suppression was most marked in patients showing active symptomatology. These results indicate a central regulatory dysfunction of visual-vestibular interaction in psychiatric patients which varies with intensity of psychotic symptomatology and which does not seem attributable to medication or attentional factors.

Adult↗
PubMed1982

EEG and behavioral effects of gamma-hydroxybutyrate in the rabbit.

The effects of gamma-hydroxybutyrate (GHB) upon sleep wakefulness patterns and quantified nuchal muscle activity were examined in the rabbit in a dose-response paradigm (25-1,000 mg/kg). Relative to control (saline) values, there was no facilitation of sleep onset or epileptogenic activity at any of the dosages studied. However, at the higher GHB concentrations, slow wave sleep and tonic muscle activity were enhanced and a high amplitude, slow activity was superimposed on background EEG patterns. The highest concentration of GHB (1,000 mg/kg) was associated with depression of motor activity. An enhancement of paradoxical sleep observed at lower GHB levels in other species occurred in attenuated form in the rabbit. The results indicate dose-related effects on both sleep and motor activation in the rabbit, but the absence of seizure activity for the concentrations of GHB studied.

Animals↗
PubMed1981

Effects of locus coeruleus lesions upon sleeping and waking in the rabbit.

The effects of radiofrequency lesions in the region of the locus coeruleus (LC) upon sleep--waking states and behaviors were investigated in chronically implanted New Zealand White rabbits. Polygraphic recordings were taken prior to and at 5- and 14-day intervals following lesioning. In animals exhibiting absence of paradoxical sleep and the presence of bizarre motor behavior, additional recordings were taken 30 days postlesion. Prelesion sleep-wakefulness pattern data were comparable to those previously observed in intact rabbits, including the recently reported absence of sustained PS-related nuchal muscle atonia. Lesions histologically localized to the area of the locus coeruleus were of two types, i.e., those effecting bilateral destruction of greater than or equal to 80% (n = 11) or 30-50% (n = 11) of the LC. A transient period of inactivity was present immediately following lesioning, but by two weeks postlesion animals had generally regained normal waking behavioral and physiological functioning, e.g., eating, drinking and grooming behaviors had returned and respiration, micturition and general urological functioning were normal. The more extensive LC lesions were followed by increases in the proportion of total recording time spent in wakefulness, but primarily in quiet rather than active wakefulness. Sleep was fragmented by phasic muscular activation in proportion to the amount of LC destroyed. In animals with the most extensive lesions, slow wave sleep was interrupted by brief, abrupt episodes of twitching, and episodes of marked phasic muscular activation, often violent in nature, occurred following periods of slow wave sleep. The postlesion occurrence of PS was inversely related to the degree of LC destruction and, accordingly, to the presence of episodes of phasic motor activation. These results did not confirm earlier reports in other species implicating the LC in urogenital functioning and respiration, but do corroborate previous findings indicating that neural elements in the LC regions are essential to the integrity of sleep and are especially important to the control of motor mechanisms during sleep.

Animals↗
PubMed1981

Spinal motoneuronal excitability in hyperkinesis: H-reflex recovery function and homosynaptic depression during wakefulness.

Variations in amplitude of the spinal monosynaptic H-reflex were examined during relaxed wakefulness in three unmedicated groups of subjects, hyperactive children (n=5), an age-matched group of control children (n=5), and a group of young adults (n=10), using techniques involving equal intensity percutaneous stimuli delivered in pairs or trains at varying rates. The paired-stimuli procedure generates a recovery function, the outstanding features of which are early depression, a peak of facilitation occurring between 100-300 msec, and complete recovery by 2-5 sec. Trains of stimuli delivered at rates greater than or equal to 1/sec effect a reduction in reflex amplitude which is termed homosynaptic depression. Both procedures revealed differences between hyperkinetic children and comparison groups. The paired-stimulus technique revealed a generalized reduction in excitability for hyperkinetic children for intervals extending up to 800 msec. In particular, hyperkinetic children were characterized by a significantly increased variability at the longer stimulus intervals. Hyperkinetic children also showed a more rapid reduction in reflex amplitude to initial stimuli in stimulus trains delivered at rates greater than or equal to 1/sec. Trains of stimuli at rates effecting facilitation in terms of the paired stimulus technique, i.e., 3,4 and 5/sec, revealed sustained amplitude enhancement for control subjects only. The recovery function data are consonant with spinal motoneuronal hypoexcitability in hyperkinetic children. Possible neruophysiological and neurochemical mechanisms underlying the reduced capability of hyperkinetic children to respond to rapidly delivered, repetitive stimuli are discussed.

Adult↗
PubMed1981

Sleep patterns in hyperkinetic and normal children.

Sleep patterns in nonmedicated hyperkinetic (n = 11) and normal control (n = 11) male children (8-12 years old) were compared to document possible sleep disturbance in hyperkinetic children. Electroencephalographic, electro-oculographic, electromyographic, and autonomic measures were monitored continuously for five consecutive nights. Analysis of sleep pattern variables revealed a significantly longer rapid eye movement onset latency (p less than 0.05) and marginally significant greater absolute and relative amounts of movement time (p less than 0.07) for the hyperkinetic group relative to controls. No other sleep parameters differentiated the groups. It was concluded that baseline tonic sleep parameters do not indicate marked sleep disturbance in hyperkinesis. The results are discussed within the context of hypothesized arousal dysfunction underlying this disorder. Key Words: Hyperkinetic children--Hyperkinesis--NREM and REM sleep cycles--Spontaneous skin potential responses.

Arousal↗
PubMed1979

Target velocity and smooth pursuit eye movements in psychiatric patients.

Smooth pursuit tracking performance of psychiatric patients and non-hospitalized normal controls was compared for targets oscillating at 0.45 Hz and 0.31 Hz. Psychiatric inpatients exhibited significantly more velocity arrests than psychiatric outpatients or normals under both conditions. Tracking performance of all groups at 0.31 Hz was improved relative to that at 0.45 Hz, but significant improvement occurred only for outpatients and normals. The role of attentional and stimulus factors in the tracking performance or psychiatric patients is discussed.

Adult↗
PubMed1979

Motoneuronal excitability during wakefulness and non-REM sleep: H-reflex recovery function in man.

Comparisons were made in 13 normal young adults of alpha motoneuronal excitability during non-rapid-eye-movement (NREM) sleep (stages 2--4) and wakefulness based on a study of the recovery cycle of the H-reflex after a conditioning stimulus. During sleep, excitability was generally decreased and a peak of secondary facilitation, which characteristically occurs 100--300 msec after the conditioning stimulus during wakefulness, was reduced or absent. A variety of mechanisms, including long-loop reflexes and afferent discharges from reflex muscle contraction and cutaneous fibers, has been proposed to account for this phase of facilitation in the waking recovery curve. However, since studies to date indicate the absence of tonic presynaptic or postsynpatic inhibitory influences acting on the monosynatpic reflex pathway during NREM sleep, but report tonic reduction in fusimotor activity at this time, it is suggested that a primary factor underlying the absence of facilitation during sleep is a reduction in central excitability deriving from depressed fusimotor activity.

Adolescent↗
PubMed1979

Smooth pursuit eye movements and attention in psychiatric patients.

The effects of two putative attention-engaging maneuvers on tracking performance were studied in three groups of subjects: inpatients (n = 19), outpatients (n = 19), and controls (n = 20). One method involved realerting subjects during tracking by repeating instructions to track carefully. The second method, a signal detection task incorporated into the tracking stimulus, required that subjects signal their perception of brief interruptions of the tracking light by pressing a hand-held button. The tracking performance of inpatients was significantly inferior to that of both outpatients and controls, whereas tracking performance of these two latter groups did not differ. Verbal realerting did not significantly improve tracking performance in any group; moreover, during the administration of these instructions there was an increase in tracking errors in inpatients. Inpatients also made more tracking errors than comparison groups during signal detection trials. Other subject factors of possible relevance to tracking performance, e.g., age, gender, and level of arousal, were found not to covary with tracking accuracy in a manner which would explain the observed group differences. It is unlikely that voluntary inattention is the basis for the observed impaired tracking in hospitalized psychiatric patients; the data are more consistent with an interpretation based on heightened distractibility or information overload in these patients.

Adolescent↗
PubMed1977

Eye movement-associated discharge in brain stem neurons during desynchronized sleep.

The relationship between isolated eye movement during desynchronized sleep and unit discharge in the pontine brain stem was investigated during spontaneously occurring desynchronized sleep episodes in cats. Units histologically localized to the gigantocellular tegmental field (FTG) showed the earliest and most prominent discharge rate increases relative to eye movement onset. Inflection points for discharge rate increases of these reticular elements peaked 150-100 msec before eye movement onset and discharge maxima occurred in the time period 50 msec before and 50 msec after eye movement onset. Within the FTG there was a correlation between giant cell density and intensity of discharge rate increases relative to eye movement onset, indicating that the giant cells are the neurons that show this pattern most strongly. The exponential form of the curves of FTG inflection points and discharge maxima is compatible with self-excitation as a mechanism for recruitment in the FTG pool. Units in the central, lateral, and paralemniscal tegmental reticular fields had activity curves qualitatively similar to those of the FTG, but with less intensity of discharge rate change and shorter lead-times. The discharge pattern was quite different in the two other cell groups studied. Many units in the tegmental reticular nucleus had bursts of discharges tightly locked to eye movement onset, while pontine grey units had an irregular pattern and a low degree of phase-locking to eye movement onset. Of the neurons studied, the giant cells of the FTG best satisfy correlational criteria for eye movement generation during desynchronized sleep. These findings support the hypothesis that the FTG is part of a generator system for desynchronized sleep and may contribute directly to the elaboration of the phasic events characterizing that state.

Action Potentials↗