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Biomedical subjects

M S Marx

Publications and source records attributed to M S Marx.

35 records · Page 2Linked to original sources
PubMed1989

Agitation and touch in the nursing home.

The relationship between manifestations of agitated behaviors and interpersonal distance was examined in 24 nursing home residents with high agitation and severe cognitive impairment. Analysis indicated that agitated residents displayed divergent responses to touch: touch was related to an increase in aggressive behaviors and to a decrease in physically nonaggressive behaviors (e.g., strange movements). The positive relationship between aggressiveness and touching suggests that residents may interpret touching as a violation of their personal space. The finding that residents exhibited fewer strange movements when touched suggests that touching can act as a quieting and comforting form of communication. The implications of these findings for caregivers are discussed.

Aged↗
PubMed1988

Signs of early damage in glaucomatous monkey eyes: low spatial frequency losses in the pattern ERG and VEP.

Experimental glaucoma was created in one eye of three cynomolgus monkeys by argon laser application to the mid-trabecular meshwork. Simultaneous pattern electroretinograms (PERG) and pattern visual evoked potentials (PVEP) were measured in both control and glaucoma eyes to spatial frequencies of 0.5, 1.25, 2.5, and 3.5 cpd which were counterphase modulated at 6 Hz. The transient flash electroretinogram was also measured. While normal flash electroretinograms were recorded in all eyes both before and after the unilateral production of elevated intraocular pressure (IOP), reductions in PERG and PVEP amplitude were seen in the eyes with glaucoma as early as two weeks following a sustained increase of IOP, despite the absence of cupping of the optic nervehead judged by ophthalmoscopic examination and analysis of photograph by two observers. Optic nervehead abnormalities occurred subsequently. In glaucomatous monkey eyes, the earliest PERG and PVEP changes were most evident with lower spatial frequencies of stimulation. Our data suggest that the optimal stimulus parameters for the detection of early glaucoma are low spatial frequency patterns presented at a rapid rate of temporal modulation.

Animals↗
PubMed1988

Spatial frequency-dependent abnormalities of the pattern electroretinogram and visual evoked potentials in a parkinsonian monkey model.

The pattern visual evoked potential (PVEP) and pattern electroretinogram (PERG) were studied in 5 cynomolgus monkeys before and during the development of a parkinsonian syndrome induced by MPTP. The stimuli were vertical bars of four spatial frequencies (0.5, 1.2, 2.5 and 3.5 cycles/degree (cpd) modulated at temporal rates of 1, 4, 6, and 8 Hz. Following MPTP administration, all monkeys developed parkinsonian signs accompanied by changes in the amplitude and latency of the PVEP and PERG. Sinemet L-dopat carbi olopa administration produced temporary recovery of both PVEP and PERG. Two of the monkeys were followed for a prolonged period: 30-40 days after MPTP, the parkinsonian signs showed partial recovery; the PVEP latency and amplitude to 2.5 and 3.5 cpd stimuli and the latency to 1.2 cpd showed improvement but remained abnormal. The latencies of PERGs were normal, but the amplitudes were significantly reduced when stimuli of 2.5 and 3.5 cpd were used. Both PVEP and PERG to 0.5 cpd stimuli returned to normal. No further modifications were seen in the recordings performed 6 months and 1 year later. This study demonstrates (1) that spatial frequency-dependent electrophysiological abnormalities occur in the MPTP-treated monkey, a result previously found in human Parkinson's disease, and (2) that dopamine has a specific function in neurotransmission in the visual system of primates.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1988

Cortical contrast gain control in human spatial vision.

1. We evaluated human visual cortical contrast gain using visual evoked potential (VEP) measurements. The steady-state VEP was elicited by 7.5 Hz contrast modulation of a 6 cycles/deg sinusoidal grating. The stimulus may be regarded as the sum of a steady grating (C) and a counterphase grating of the same spatial frequency (delta C). The counterphase grating is modulated sinusoidally in time. 2. The VEP was measured to combinations of different modulation contrasts (delta C) and different mean levels of grating contrast (C) which produced stimuli with contrast modulation depths (delta C/C) ranging from 0.0625 to 1.0 ('on-off'). 3. The VEP signals were Fourier analysed and the amplitude and phase of the first (7.5 Hz) and second (15 Hz) harmonic frequency components were examined. The monocular VEP to a contrast-modulated grating contains significant first and second harmonic frequency components. 4. The amplitude and phase of the monocular VEP was plotted as a function of delta C for each mean level of contrast explored. The amplitudes of both the first and second harmonic frequency components grow with increasing delta C. However, the slope of each function depends on the mean contrast (C): with higher levels of C, the slope of the function is more shallow. Furthermore, at each level of C the amplitude of the first harmonic frequency saturates at a lower delta C than does the second harmonic frequency component. VEP amplitude is therefore not determined by the absolute contrast change (delta C) alone. The VEP phase of the first harmonic frequency shows less dependence on either modulation or on mean contrast; the phase of the second harmonic frequency component is strongly dependent on mean contrast (C) but not on delta C. 5. When the second harmonic amplitude component of the VEP response (R) is expressed as Ractual/Rmax, where Rmax is the response to C = delta C (i.e. 'on-off'), all second harmonic VEP functions can be well fitted with a power function. This is not the case for the function of the first harmonic amplitude data. 6. A dichoptic VEP was obtained by presenting the steady and counterphase gratings to opposite eyes. The dichoptic VEP, in distinction to the monocular VEP, contains only a second harmonic frequency component. The amplitude of the second harmonic frequency component grows with increasing delta C, similar to the function seen for the monocular VEP.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1988

Relationship between depression and agitation in nursing home residents.

Nursing staff and social workers independently rated the manifestations of agitation and depression in 408 nursing home residents. The role of dementia was also investigated. The relationship between agitation (3 factors: aggressive, physically nonaggressive, and verbally agitated) and depression (2 factors: social functioning and depressed affect) was examined. While residents who manifested either aggressive behavior (e.g., hitting, cursing) or physically nonaggressive behaviors (e.g., general restlessness, pacing) tended to be more cognitively impaired, aggressive behaviors were negatively related to the social functioning aspect of depression, and physically nonaggressive behaviors were not related to either aspect of depression. Verbally agitated individuals were more cognitively intact and displayed depressed affects. It is conceivable that depressed affect was perceived only in verbally agitated residents since these persons were able to communicate their depression to caregivers. This result raises questions concerning the meaningfulness of depression measurements in noncommunicative residents.

Aged↗
PubMed1987

Electrophysiological evidence that early glaucoma affects foveal vision.

The pattern electroretinogram (PERG) and visual evoked potential (PVEP) were recorded simultaneously using a 1.1 cpd pattern which was counterphase modulated at 1 Hz. The responses of ocular hypertensive (OHT) eyes (with normal visual fields) and eyes with early glaucoma (with early visual field defects and/or early cupping of the optic nervehead) were compared to age-matched normal observers. All patients (26 eyes) and normal observers (14 eyes) had normal transient flash electroretinograms. Delays were seen in mean PERG latency in both OHT and early glaucoma eyes, while mean PERG amplitude was significantly reduced only in the early glaucoma eyes. The PVEP responses were 'unmeasurable' in 11/26 patient eyes because the waveforms were grossly abnormal in shape, making it impossible to identify the N- and P-components. The data were categorized in this manner: a patient response was considered abnormal if latency or amplitude exceeded normal limits (PERG or PVEP) or if the waveform was 'unmeasurable' due to its shape (PVEP only). Of the 26 patient eyes, we found that 8 eyes had normal PERG and PVEP, 11 eyes had abnormal PERG and PVEP, one eye had an abnormal PERG and a normal PVEP, and 6 eyes (3 patients) had a normal PERG and an abnormal PVEP. These data support the proposition that foveal vision (as assessed by the PVEP) may be affected by early glaucomatous damage. The relationship between the PERG and PVEP also was evaluated using a new measurement which we call the 'latency window'. Using this measurement, 15/26 patient eyes were abnormal-9 of these had 'unmeasurable' PVEPs. This measurement could be useful in classifying 'W'-shaped PVEPs as normal or abnormal.

Adult↗
PubMed1987

Scalp distribution of pattern visual evoked potentials in normal and hemianopic monkeys.

We examined the hemispheric distribution of the pattern visual evoked potential in 3 Cynomolgus monkeys, before and after right optic tractotomy or left occipital lobectomy. The stimuli were vertical gratings of 4 spatial frequencies, presented using counterphase and on-off modulation at 1 and 8 Hz. In the normal monkey, the amplitude and latency of the PVEPs elicited by 1 Hz stimulation were similar across all electrode sites. While no differences were found in the phase of the PVEP elicited by 8 Hz stimulation across the different derivations, PVEP amplitude generally decreased over the lateral electrodes. Once experimental hemianopia was created, PVEPs recorded over the midline and the intact hemisphere were normal. However, partially polarity-inverted PVEPs of smaller amplitude were recorded over the deafferented hemisphere. In addition, the interhemispheric phase difference became more prominent in the PVEP recorded over the deafferented hemisphere as the spatial frequency was increased.

Animals↗
PubMed1987

Visual dysfunction in Parkinson's disease. Loss in spatiotemporal contrast sensitivity.

Flicker sensitivity and spatial contrast sensitivity (CS) were examined in a total of 99 patients with Parkinson's disease (PD). All patients were undergoing treatment with dopaminergic agents. Specific losses in sensitivity observed in PD were (1) a loss in flicker sensitivity which was most pronounced around the peak of the function (8 Hz) and (2) a loss near the peak of the spatial CS curve, often with no noticeable low frequency attenuation. Several PD patients affected by the 'on-off' syndrome were tested in both 'on' and 'off' phases, and the results show that the CS function switches in parallel with motor symptoms of the disease. These data suggest that not only is the visual system affected in PD, but that dopamine may have an essential role in receptive field organization in human vision.

Adult↗
PubMed1986

The effect of refractive error on pattern electroretinograms in primates.

The effect of optical blur on the steady-state (6, 8, 10 Hz) counterphase pattern electroretinogram (PERG) was measured in three normal cynomolgus monkeys. Blur was induced using lenses of -8.00 to +12.00 diopters, and monocular PERGs were recorded at a viewing distance of 0.32 meters. A substantial decrease in PERG amplitude occurred with a 0.51 cpd grating when +4.00 diopters of blur or greater were used. PERG amplitude to a 1.25 cpd grating decreased with lenses greater than +2.00 diopters. Minus lenses caused a steep decline in PERG amplitude of both spatial frequency gratings. These results indicate that refractive state has a significant effect upon the PERG and should be carefully considered in electrophysiologic testing of the primate visual system.

Accommodation, Ocular↗
PubMed1986

Flash and pattern electroretinograms in normal and laser-induced glaucomatous primate eyes.

Experimental glaucoma was produced in one eye of five cynomolgus monkeys with the argon laser delivering 100-200 50-mu spots at 1200-1500 mW power and 0.5 sec to 360 degrees of the mid-trabecular meshwork. Monocular electroretinograms (ERGs) were recorded prior to and 2, 3, and 4 mo following the laser treatment. In the laser-treated (glaucoma) eyes, normal flash ERGs were observed using 1-Hz stimulation; however, pattern ERGs (PERGs) elicited using steady-state counterphase modulation of a 0.51 cpd square wave grating showed statistically significant reductions of amplitude. Only small reductions of PERG amplitude were seen with a 1.25 cpd grating. In three animals, abnormalities of the PERG occurred prior to clinically significant cupping of the optic nervehead. Moreover, reductions of PERG amplitude were progressive and associated with the magnitude of cupping of the optic nervehead and elevation of intraocular pressure. PERG amplitude did not change following acute reductions in intraocular pressure in the glaucoma eyes. Several control experiments were conducted to insure that results were not due to alterations in pupil size, refractive state, or accommodation in the glaucoma eyes. The authors believe they now have a monkey model for the electrophysiologic study of glaucoma.

Animals↗
PubMed1984

Spatio-temporal processing in multiple sclerosis.

The processing of spatial and temporal detail was investigated in patients with multiple sclerosis. Normal observers and 13 patients with optic neuritis secondary to multiple sclerosis performed a battery of visual tests that included contrast sensitivity, temporal integration, evoked potentials, and visual masking. The multiple sclerosis patients exhibited losses of pattern processing, and these deficits became more noticeable when the patterns were presented briefly. Moreover, these patients exhibited diverse response patterns for the different visual tests. For some, temporal integration functions appeared severely attenuated, while evoked potential latency was within normal limits. Others displayed poor performance in the visual masking test, yet contrast sensitivity functions were comparable to those of the control group. We suggest that a battery of tests that incorporates spatial as well as temporal stimuli is necessary for the detection of visual dysfunction in multiple sclerosis.

Adult↗
PubMed1984

Spatial frequency tuning in the visual evoked potential elicited by sine-wave gratings.

This investigation examined the onset response of the transient visually evoked potential elicited by the appearance-disappearance of sine-wave gratings at various levels of spatial frequency, suprathreshold contrast, and stimulus duration. The response was most easily characterized by two negative-positive complexes that were differentially tuned to spatial frequency. The earlier complex peaked at high spatial frequencies while the later complex peaked at low spatial frequencies. For both complexes, amplitude showed only slight variations across three-octave ranges of contrast and duration. Latency was curvilinearly related to spatial frequency, decreased with increasing contrast, and showed no apparent change as a function of duration.

Adult↗
PubMed1983

The relationship between temporal integration and persistence.

We measured the persistence for gratings of three different spatial frequencies after they had been equated for visibility by manipulating: (1) the contrast of the stimulus, (2) the duration of the stimulus, or (3) both contrast and duration. When we presented gratings of equal apparent contrast and equal duration, persistence increased with increasing spatial frequency. This effect occurred when apparent contrast was equated in terms of extended-duration or brief duration contrast sensitivity. However, when we examined persistence using gratings equated for temporal integration (i.e. equal apparent contrast but unequal durations), no differences in persistence as a function of spatial frequency were observed. Thus, the increase in persistence which is typically found with higher spatial frequencies can be accounted for by knowledge of the spatio-temporal characteristics of the visual system. Our findings are discussed in terms of the notion of different filter time-constants for different spatial channels.

Afterimage↗
PubMedDate not supplied

Outcomes of cataract surgery in nursing home residents.

A prospective study of vision-related outcomes of cataract surgery as well as cognitive functioning, activities of daily living (ADL) functioning, and depressed affect was conducted with 19 nursing home residents scheduled for cataract surgery. Also studied were 22 candidates for cataract surgery who decided against it. Comparison of both groups at baseline revealed that residents who chose cataract surgery were less cognitively and ADL impaired. Analysis after cataract surgery showed that visual acuity improved significantly at 4 months and was maintained at 1 year after surgery.

Activities of Daily Living↗