ABSTRACT
An alternating checkerboard pattern subtending a visual angle of 25 min arc is capable of eliciting remarkably high amplitudes of visually evoked potentials (VEP) outside a visual angle of 2.5 degree. These contributions cannot be neglected when evaluating a VEP response obtained with a larger field of stimulation. When the retina is consecutively stimulated by concentric frame-shaped stimuli, the algebraic sum of all single cortical responses augmented the cortical response obtained when stimulating the whole field simultaneously by approximately 30%. This finding may be explained by the inhibiting interactions within the receptive field organisation of the retina.
Subject(s)
Macula Lutea/physiology , Retina/physiology , Visual Cortex/physiology , Evoked Potentials , Humans , Photic Stimulation/methodsABSTRACT
Visual evoked potentials were recorded sequentially, using permanent epidurally implanted electrodes, before and after accelerating the heads of rabbits. The amplitude of VEP, recorded after lesioning, was diminished and recovery time was prolonged depending on the amount of acceleration and the extent of brain lesions found later in histological examinations. VEP reflected damage to the brain more precisely than EEG or somatosensory evoked potentials, thus giving values for judging the extent of lesions in patients with brain injuries.
Subject(s)
Brain Injuries/physiopathology , Visual Cortex/physiopathology , Animals , Disease Models, Animal , Electroencephalography , Evoked Potentials , Photic Stimulation , Physical Stimulation , RabbitsABSTRACT
In a patient with superior oblique myokymia, the causative pathological motor unit was found by electromyography in the superior oblique eye muscle. Firing of this unit was somewhat irregular, but often assumed a nearly constant frequency around 35/s, so that the mechanical effect was mainly a tonic deviation rather than a tremor. Single discharges, analysed by computer averaging, showed a peculiar shape, prolonged duration, and high voltage, supranuclear control of the pathological unit was defective, although not completely lacking.
Subject(s)
Oculomotor Muscles/physiopathology , Tremor/physiopathology , Action Potentials , Adult , Electromyography , Female , HumansABSTRACT
Enucleated bull's eyes were perfused with blood and ERG recorded, with special attention paid to the slow components. When the blood flow was interrupted, the ERG components vanished in the following order: b wave, c wave, off-effect (d wave), and a wave. When the perfusion was continued afterward, we saw a variation in the standing potential that hinted at the biochemical activities causing slow electrical potentials of the retina.
