Rapid contrast sweeping of steady-state visual evoked potentials: a new method for investigation of the visual system.

Rapid sweeping of contrast modulates the steady-state visual evoked potentials (VEP) obtained by sinusoidal gratings reversing at 16 Hz. The modulation results in a null interval of which the width measures the contrast threshold and of which the delay measures the apparent latency of the steady-state VEP, provided that the dynamic contrast sensitivity is symmetric. Data from 25 normal subjects and 27 patients with head injury show that this requirement is met in normal subjects but is often not verified in pathologic conditions. By measuring three aspects of the response to contrast changes (latency and static and dynamic contrast sensitivity) at five different spatial frequencies, one obtains a very sensitive method for investigation of the visual system.

Acute prolonged ictal confusion (resembling petit mal status) presenting "de novo" in later life.

Two female patients, aged respectively 52 and 70 years, with no past history of epilepsy, presented an acute prolonged confusional state. The electroencephalograms showed generalized slow spike and wave discharges with frontal emphasis. No structural neurological lesion nor progressive neurological disorder was found. Both patients responded to intravenous administration of clonazepam and were placed on regular anti-epileptic treatment. On follow-up both remained well. These cases do not fit in the classical category of petit mal status but appear to belong to a distinct entity.

[Occurrence of triphasic waves in two cases of thyrotoxic crisis (author's transl)]. / Ondes lentes triphasiques dans deux cas d'encéphalopathie thyréotoxique

An electroencephalogram taken on two patients suffering from a thyrotoxic crisis, showed the presence of typical triphasic waves. This pattern was first described in 1950 by Foley et al., who believed that it occurred specifically in patients with hepatic encephalopathy. Since then, however, it has been shown that triphasic waves can be identified in other (e.g. renal) metabolic brain diseases and, less commonly, in a variety of either organic or functional cerebral disorders.

Periodic electroencephalographic compleses and subacute sclerosing panencephalitis. A case report and a survey of literature.

The authors report the case of a child with a presumable diagnosis of subacute sclerosing panencephalitis (SSPE). But pathological examination of the brain showed only a moderate neuronal loss in the cortical and subcortical grey matter. From this case and from the data in the literature it is concluded that the electroencephalogram in stage II of SSPE is characterized by the appearance of paroxysmal wave complexes which recur pseudo-periodically against a disorganized basic activity. The criteria for these complexes are not as strict and the periodicity is not as regular as formerly believed. Such a tracing is not pathognomonic of SSPE and may also occur-although rarely-in other brain diseases. The theory that the periodic discharges originate from a diffuse alteration of cortical and subcortical grey matter seems the most plausible.