Biomedical subjects

E Chronicle

Publications and source records attributed to E Chronicle.

3 recordsLinked to original sources

PubMed1996

Gratings that induce perceptual distortions mask superimposed targets.

Masking is known to depend upon the relationship between the spatial-frequency content of target and mask. This relationship has been held constant in three experiments in order to investigate the separate contribution of the spatial parameters of the mask, in this case a grating with square-wave luminance profile. Thresholds for the detection of a probe target were highest when the background grating upon which the probe was superimposed had a spatial frequency of about 4 cycles deg-1 (experiment 1) and a duty cycle of 50% (experiment 3). In experiment 2, the thresholds were strongly affected by the size of the background grating even though the size of the target was small in proportion to the grating and remained constant. The increase in threshold was linearly related to the area of visual cortex to which the grating projected. The spatial parameters of gratings that maximise masking are therefore the same as those that have been shown to be optimal for the induction of perceptual distortions, suggesting a possible physiological mechanism for both the masking and the distortions.

Adult↗

PubMed1994

Might migraine damage the brain?

Recent debate concerning the interpretation of studies of regional cerebral blood flow in migraine has re-emphasized that cerebral ischaemia may occur during attacks of migraine with aura. In this article we suggest that the presence of ischaemia during attacks makes it possible that migraine with aura causes neuronal damage in the long term. We argue that damage is likely to occur in the primary visual cortex, given that a recent high-resolution rCBF study has found flow reductions confined to this area. Furthermore, we hypothesize that the extent to which rCBF is reduced in migraine with aura is sufficient to cause damage only to GABA-ergic inhibitory interneurons in layer IV of this cortex. In animal models, similar cells are known to be selectively vulnerable to damage as a result of hypoxic conditions. Evidence consistent with our hypothesis is provided by recent studies of visual function in migraine. Some clinical and pathophysiological implications of this hypothesis are discussed.

Animals↗

PubMed1994

Precortical dysfunction of spatial and temporal visual processing in migraine.

This paper examines spatial and temporal processing in migraineurs (diagnosed according to International Headache Society criteria, 1988), using psychophysical tests that measure spatial and temporal responses. These tests are considered to specifically assess precortical mechanisms. Results suggest precortical dysfunction for processing of spatial and temporal visual stimuli in 11 migraineurs with visual aura and 13 migraineurs without aura; the two groups could not be distinguished. As precortical dysfunction seems to be common to both groups of patients, it is suggested that symptoms that are experienced by both groups, such as blurring of vision and photophobia, may have their basis at a precortical level.

Adult↗