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Biomedical subjects

M Brigell

Publications and source records attributed to M Brigell.

10 recordsLinked to original sources
PubMed1992

Spatial frequency evoked visuograms in multiple sclerosis.

We obtained steady-state visual evoked potentials (VEPs) to sinusoidal gratings alternating at 4 Hz with spatial frequencies varying from 0.5 to 8 cpd in 21 normal controls and 21 patients with multiple sclerosis (MS), and analyzed responses by fast Fourier transform. Amplitude- and phase-spatial frequency functions were obtained and referred to as amplitude and phase "visuograms." We observed two types of abnormalities in the phase visuograms of MS patients: (1) abnormal responses at all spatial frequencies tested (37%), and (2) abnormal responses only at selective spatial frequencies (52%). Some patients had phase lag limited to low, middle, or high spatial frequencies. Steady-state and transient VEPs to 2 and 4 cpd showed a similar percent of abnormalities. The use of more than one spatial frequency stimulus increased the diagnostic yield by 17%. Our data confirm that MS may selectively affect specific neuronal channels within the visual pathways.

Adolescent↗
PubMed1992

Event-related potentials.

Event-related potentials (ERPs) are scalp recorded electrophysiological responses that are related to an internal cognitive event. This review summarizes recent findings on the effects of neurologic disease and the origin of ERPs obtained in expectancy, attention, memory, and linguistic tasks. Cognitive ERPs allow the physiologic activity of the brain to be analyzed with exquisite temporal resolution. Our understanding of these potentials is incomplete at present. Advances in cognitive psychology and source localization of these surface potentials, however, may result in an increased understanding of both the organization of cognitive processing in the brain and cognitive deficits that result from neurologic disease.

Arousal↗
PubMed1990

Optic neuritis: a prospective study.

We studied 20 patients with acute optic neuritis prospectively for 12 months. Visual fields, color vision, and VEPs to 15' checks were initially abnormal in all patients. Visual acuity was abnormal in 90% and contrast sensitivity in 95% of patients. We devised a graded visual impairment scale (GVIS) to include all visual functions tested. Complete recovery of visual function occurred in 65% of cases. Recovery in the majority of patients was rapid and complete within the first 2 months. In some patients, improvement continued over 6 months. The initial classification on the GVIS was significantly correlated with the final outcome. Patients initially classified as having moderate visual impairment recovered completely or improved to near normal vision. Sixty percent of patients initially classified as total or severe blindness had permanent visual impairment. VEP latency remained prolonged in 19 patients, even when their vision had returned to normal, and is a reliable indicator of resolved optic neuritis.

Adult↗
PubMed1990

Olivopontocerebellar atrophy presenting with hemiparkinsonian ocular motor signs.

A patient with olivopontocerebellar atrophy presented with an asymmetric parkinsonian syndrome consisting of right limb rigidity, bradykinesia, masked facies, and a hypophonic, monotonous voice. Right limb clumsiness suggested corticospinal tract involvement. Gait was slightly wide based, but no other cerebellar or brainstem signs were present. Eye movements were characteristic of parkinsonism with low-gain pursuit and hypometric rightward saccades. Saccadic velocity and the vestibular ocular reflex were within normal limits. There was no pathologic nystagmus or saccadic dysmetria. Magnetic resonance imaging showed cerebellar and lower brainstem atrophy virtually diagnostic of olivopontocerebellar atrophy. Olivopontocerebellar atrophy may present uncommonly with asymmetric parkinsonian features, including parkinsonian eye movement abnormalities.

Humans↗
PubMed1989

Hemi-field pattern visual evoked potentials: a comparison of display and analysis techniques.

Three methods for analyzing the spatial organization of visual evoked potentials were compared. Pattern reversal visual evoked potentials were obtained from a single subject under three viewing conditions: stimulation of the left, right, and both visual fields. The scalp distribution of the VEP to 1 deg checks was displayed using three recording and analysis techniques: a conventional horizontal occipital array of electrodes, topographic mapping, and 3-dimensional evoked potentials. All three techniques revealed "paradoxical" lateralization of P100. The relative merits of each technique are discussed.

Brain Mapping↗
PubMed1988

Visual evoked potentials to multiple temporal frequencies. Use in the differential diagnosis of optic neuropathy.

The usefulness of the visual evoked potential (VEP) in differential diagnosis increases when stimulus parameters such as check size and grating orientation are varied. In this study we varied the stimulation frequency. Temporal frequency-specific abnormalities were compared in three patient categories, including retrobulbar optic neuritis (eight patients), pseudotumor cerebri (11 patients), and thyroid eye disease (seven patients). All patients had minimal clinical evidence of optic nerve damage when tested. A 2.3 cycle-per-degree sinusoidal grating of 55% contrast was phase reversed at either 1 or 4 Hz. The P1 latency of the 1-Hz data and the phase at 8 Hz, the second harmonic of the 4-Hz input frequency, were measured. In retrobulbar neuritis, latency (phase) was severely abnormal at both temporal frequencies. In thyroid eye disease, VEP phase was abnormal at 8 Hz while the P1 latency was normal at 1 Hz. The P1 latency and phase were normal in most cases of pseudotumor cerebri. The results suggest differing mechanisms for damage in compressive vs primary demyelinating neuropathies.

Adolescent↗
PubMed1984

Hypometric saccades and low-gain pursuit resulting from a thalamic hemorrhage.

Saccadic and pursuit eye movements were measured in a patient with a right thalamic hemorrhage using an infrared reflection technique. Saccades were hypometric when directed away from the side of the lesion, and pursuit was low in gain, with many interposed saccades, when directed toward the side of the lesion. This eye movement pattern is similar to that observed in hemidecorticate patients. We postulate that the ocular abnormalities observed in our patients were secondary to an interruption of the efferent pathways from the right cerebral areas mediating saccadic and smooth-pursuit eye movements.

Eye Movements↗
PubMed1979

The relational determination of length illusions and length aftereffects.

When two lines were presented simultaneously, in an illusion paradigm, the judged length of one of the lines (the focal line) assimilated toward the length of the contextual line. When the lines were presented sequentially, in an aftereffect paradigm, the apparent length of the focal line was displaced away from the length of a previously presented contextual line (i.e. contrast). The largest effects obtained at inverse contextual-to-focal length ratios: 1.67:1 for contextual lines longer than the focal line and 0.60:1 for contextual lines shorter than the focal line. Overestimation of focal length was larger than underestimation for both illusions and aftereffects despite the fact that identical stimuli produced effects in opposite directions in the two paradigms. Results were discussed in terms of a neural length-coding model and were related to visual size constancy.

Figural Aftereffect↗
PubMed1977

Contextual influences on judgments of linear extent.

A series of experiments was performed to test the predictions of adaptation level, efferent readiness, and framing explanations of illusions of extent. The framing notion, that the ratio of total figure length to shaft length (i.e., the framing ratio) determines the magnitude of illusions, was supported for the Müller-Lyer, Baldwin, and divided line illusions. Peak overestimation of shaft length obtained when the framing ratio was 3:2. Variation of proximal figure size, achieved by altering either viewing distance or distal figure size, was found to be directly related to the magnitude of the illusions. A model was proposed to account for the effects of both the framing ratio and proximal shaft length on judgments of focal length.

Cues↗