Dispersion pattern of visual evoked responses: Normative data

The Role of the Thalamus in the Organization of Photic-Evoked Responses in Man

“…The APER components which can be defined here as neither primary nor secondary will be referred to conventionally as 'early' and 'late', meaning thereby the first negative-positive wave and the subsequent ones respectively. In previous studies [6,7] we showed that the APERs and their DP were two complementary aspects of the reaction to flashes and that they behaved independently of one another under pathological conditions. In the thal amic syndromes with hemianopsia, whether or not APERs were present, the DP was atypical in every case; in subthalamic lesions DP was typical independent of any APER amplitude and latency difference to that re corded in controls.…”

“…According also to our previous investiga tions the resultant R at each 't' moment subsequent to the 't0' stimulus on set moment in a sum of the amplitude of three components: R(t) = F(t) + S(t) + N(t), F being the fixed component, S the stochastic component according to the above-mentioned conditions and N the 'noise', considered as nonrelated to the stimulus [6]. The first period of DP represents the predominance of the S component, while the second one, with the smallest dispersion am plitude, represents a maximum synchronizing activity of the neural com plexes, with predominance of the F component; in the third period the N component is overwhelming [7]. Thalamic syndromes with hemianopsia, pointing to lesions involving the specific visual pathways, lacked the first period, i.e., that of prevalence of the stochastic mechanisms.…”

“…The DP of PER showed two or three periods, as stated in our previous papers [6,7]: a first period characterized by a high amplitude dispersion (378 /uV2 mean value) occurring 20-40 msec after the stimulus onset and lasting up to the 180-240th msec from the stimulus onset; a second period (the most constant of all) characterized by a small-ampli tude dispersion (170 /¿V2 mean value), which in 50% of the cases exceed ed the 400 msec analysis time of our investigation method and in the re maining 50% lasted to the 340-380th msec after the stimulus onset; a third period which appeared in 50% of the cases only, with a dispersion of the same amplitude as that of the background electrical activity ( fig. 1).…”

“…The bulb of the photostimulator was situated 50 cm in front of the patient's eyes. The APER [M = f(t)] and DP of PER [D = f(t)] and of background activity were computed by a digital computer according to the method described in previous papers [6,7].…”

“…In previous investigations we showed that the DP was an important parameter for estimating the capacity of neural structures to respond to afferent impulses [6,7].…”