Dispersion Pattern of Visual Evoked Responses in Epilepsy

Abstract

The averaged visual evoked responses (AVER), the dispersion pattern (DP) resulting from their variability at each time point locked to the stimulus onset (D=f(t)), were studied in epileptics in comparison with controls of the same age range. In epileptics the AVERs, especially the last components, were higher in amplitude than in controls. The DPs were also generally ampler than in controls; in epileptic patients without mental disorders the pattern of DP was as in normals, except that the third period was higher than the first one, while in epileptics with interictal mental disorders the second period disappeared, and the peak of the DP occurred at the middle third or at the end of the period analysed.

Visual Evoked Responses and Their Dispersion Pattern in Frontal Lobe Tumours

“…Investigations performed on patients with parietal lobe tumour (results not yet published) and also with raised intracranial pressure, noted that the DP alterations were other than those above reported, which additionally suggest a relationship with frontal lobe involvement. In the cases in which appeared epileptic seizures before and/or after operation the DPs of VER were very ample (over 900 //V2) and showed an ascending pattern, data which confirm those reported in another paper [11].…”

“…Nine of the ten control subjects investigated concomitantly with the patients with frontal lobe tumours, showed, as mentioned also in other papers [8,10,11], the normal DP of VER: a first period of high ampli tude (higher than the dispersion of the background electrical activity), a second period of low amplitude and in some cases also a third one of high amplitude (less ample than the first one) ( fig. 2).…”

“…These results differ from those found after lesions of the occipital lobe [5][6][7]13]. The DPs were abnormal in all the cases and in a few of them only the DPs showed a rudiment of normal pat tern, denoting, as pointed out elsewhere [8,9,11] that the functional al teration of visual neocortical areas involves the integration mechanisms of afferent impulses. Before operation, because of the raised intracranial pressure, the DP desorganization may have been caused by a general neural alteration secondary to the intracranial hypertension.…”

“…Between DP and averaged visual evoked responses (AVER) or back ground EEG no correlation was found. Important DP changes, offering a statistically significant correlation, were found in pathological and in some special physiological conditions [8,9,11]. These results pointed to the conclusion that the DP of VER is a more reliable index to the func tional capacity of an investigated structure than the AVER is.…”

“…Previous investigations in normal subjects [8,10] and in patients with cerebrovascular strokes [9] or with epilepsy [11] showed the im portance of studying the dispersion pattern of VER (DP). In these pap ers we stated that in healthy adult subjects the VER of a series of stimu li showed an independent variability at each time point locked to the sti mulus onset, resulting in a typical dispersion pattern [D = f(t)]; the nor mal DP, investigated along 400-600 msec after the stimulus onset and on 15 samples, is characterized by an initial period of high dispersion, followed by a very constant small dispersion and then there appeared a third period, inconstant along the 400-600 msec analysis time, of high dispersion, but of smaller amplitude of dispersion than the first period.…”