Some characteristics of average steady-state and transient responses evoked by modulated light.

The form of the average evoked response to clicks is highly correlated with the background electroencephalogram. However, the response during the emergent low-voltage "dreaming" stage is different from that seen during the low-voltage phase at the beginning of sleep. The results provide additional evidence that the emergent low-voltage stage is a neurophysiologically unique phase.

https://science.sciencemag.org/content/sci/138/3541/685.full.pdf

Evoked responses to clicks and electroencephalographic stages of sleep in man.

Physiological experiments and the exploitation of clinical conditions have provided compelling evidence that retinal ganglion cells and other inner retinal structures generate the pattern ERG (PERG). As an increasing number of clinical reports have been published some contradictory findings have been reported. These may be ascribed to variation in recording and measuring techniques. The PERG consists of two major portions, the early positive and the following negative component which can be investigated separately if the stimulus conditions allow isolated (or "transient") responses to be recorded. Care has to be taken in positioning the reference electrode, maintaining accurate refraction, and the influence of pupil size must be considered. Furthermore the PERG is contaminated by a luminance component which may be generated in the outer retina. The size of this increases with low spatial frequency (large check-sizes) and high mean luminance. The PERG permits the examination of an additional level of the retina and helps the understanding of pathophysiology of various eye diseases, and is of clinical importance in routine diagnosis and assessment. In glaucoma the PERG amplitude is often reduced before it is possible to detect a scotoma and it is therefore an important prognostic indicator in patients with ocular hypertension. In diabetic retinopathy, retinal ischaemia sufficient to lead to the pre-proliferative state can be demonstrated. The PERG also has a major clinical role in examining localised retinal pathology. If combined with VECP recording, it greatly extends the interpretations possible, since not only can damage to the optic nerve be detected by both tests, but the normal PERG in the presence of an abnormal PVECP implies that the losses are confined to the central pathway.

/pdf/the-pattern-electroretinogram-2reg13ppw7.pdf

The pattern electroretinogram

When the local electroretinogram (l.e.r.g.) is recorded by an intraretinal micro-electrode, the electrode tip penetrates the retinal region from which the recorded response is generated. Changes in amplitude should therefore occur as the origin of a given component is passed, and changes in polarity should also occur if the component is generated as a radial dipole; such results provide information concerning the origin of any given component. Responses from distant retinal areas may also be recorded, however, between an intraretinal electrode and a reference electrode behind the eye (Brown & Wiesel, 1961a). These responses have no significance for analysing or localizing components, but they introduce undesirable complexities superimposed upon the l.e.r.g. The vitreous humour acts as a lowresistance shunt which permits current generated in distant regions to flow through the retina at the intra-retinal electrode (Brown & Wiesel, 1961 a). Thus the problem of obtaining strictly local responses is to prevent current from flowing through the vitreous humour or from being recorded. This problem has been solved in mammals by placing the reference electrode in the vitreous humour (Brown & Wiesel, 1961 a). The efficacy of the method has been explained on the assumption that the radial resistance of the retina is so small, in relation to that of the R-membrane, that no voltage drop could be recorded through the retina itself in response to activity generated at distant sites. It follows that the l.e.r.g. will also be attenuated, particularly when the micro-electrode is in the superficial layers of the retina. An alternative method was therefore desired for recording the mammalian l.e.r.g. In the experiments of this paper, the vitreous humour was replaced by a heavy oil. This abolished the low-resistance pathway for current flow to reach the electrode from distant retinal sites. L.e.r.g.'s could then be recorded from the retinal surface, or by an intraretinal micro-electrode,

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1965.sp007560

Some properties of components of the cat electroretinogram revealed by local recording under oil.

Cortical responses to stimulation of the human fovea.

The operation of a computer which averages low-amplitude electroretinograms is described. The computer has been used to detect electroretinograms which were recorded in an investigation of area-luminance and stray-light effects within the eye. Large test stimuli were found to be more effective than small for producing responses of fixed size. Although the observers reported that the stimulus spread over much of the retina larger photopic responses appeared when the stimulus was centered on the fovea than on neighboring areas. The waveform of the response was found to depend on both the color and the position of the stimulus on the retina.

Werner H. Hengst

Papers

Summation of Retinal Potentials