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PubMed1992

Analysis of striate activity underlying the pattern onset EP of children.

The checkerboard onset Evoked Potential (EP) does not obtain its adult form before puberty. To determine the site of origin of these processes we studied the origin of the checkerboard onset EP in a group of 10 children between the ages of 6 and 16 years. Since the development of the waveform of the pattern onset EP varies with check size we also studied the dependence of these EPs on check size. The child checkerboard onset EPs described in this paper are dominated by a single source. Following an equivalent dipole source localization approach, the position, orientation and variation in strength of the equivalent dipole is estimated. The position and orientation of this dipole indicates an origin in the primary visual cortex (area 17). The variation in strength of the dipole changes from a single positive deflection, specific for children of 8 years and younger, into a negative-positive complex for the children studied between the age of 9 and 16 years. These changes in waveform must be due to changes in the activity pattern of the striate cortex.

Adolescent↗
PubMed1984

Spatio-temporal mapping of evoked cerebral activity.

A technique is described for the colour-coded display of averaged scalp electrical activity at 40 instants in time. An application of this technique to the pattern reversal visual evoked potential is discussed, showing the value of spatio-temporal mapping in the interpretation of multichannel evoked potential recordings.

Brain↗
PubMed1986

Methods for the identification of evoked response components in the frequency and combined time/frequency domains.

Two prominent frequency components designated f1 and f2 have been identified in the visual evoked response to the transient presentation of sinusoidal luminance gratings in the range of 0.5-8 c/deg. The components occur at temporal frequencies below the alpha band, with the f1 frequency being roughly half that of the f2 frequency. The f1 component is largest at low spatial frequencies with f2 becoming progressively dominant as spatial frequency is increased. The frequency and amplitude of f1 and f2 change substantially over the time course of the response. This has been studied by calculating the temporal frequency spectrum of the transient evoked potential over successive short-time epochs running through the response. Using this technique, the response is shown to consist of narrow-band frequency peaks or 'formants' emerging at different times after stimulus onset. These formants occur at frequencies other than those of the spontaneous EEG and undergo changes in frequency and amplitude over the time course of the response. Two spectrum analysis techniques were employed: the Discrete Fourier Transform and Linear Predictive Coding. Frequency components were successfully identified in single-trial responses using the LPC technique.

Electroencephalography↗
PubMedDate not supplied

Neuronal generators of the visual evoked potentials: intracerebral recording in awake humans.

Flash and pattern reversal visual evoked potentials were recorded in awake patients undergoing stereotactic procedures for severe dyskinetic disorders resistant to medical treatment. The nucleus ventralis lateralis thalami was reached via an occipital approach. VEPs were recorded on the scalp at the entrance of the intracerebral electrode, and serially from sites at different depths. A polarity reversal of the surface recorded wave form took place as the intracerebral electrode was advanced beneath the surface cortical layers. As concerns F-VEPs, most of the scalp activity mirrored the potentials recorded down to the depth of 70-65 mm from the thalamus. The largest amplitude of intracerebral F-VEPs was obtained from recording sites at 50-70 mm from the thalamus, i.e., in the depth of the calcarine fissure. A negative wave, peaking around 47-50 msec, became evident in recording sites at 30-40 mm from the thalamus but vanished as the electrode was advanced farther. In only one patient could we record a small negative wave, peaking at 33 msec, in the vicinity of the corpus geniculatum externum. Furthermore, the oscillatory activity recorded from the scalp appeared to be generated in the cortical layers. PR-VEPs also underwent polarity reversal as the electrode traversed the cortex. PR-VEPs disappeared more superficially than F-VEPs. No PR-evoked activity could be recorded in the vicinity of the corpus geniculatum externum. We conclude that slow and fast components of VEPs recorded from the scalp are entirely generated in cortical layers.

Brain Mapping↗
PubMedDate not supplied

The influence of pattern size on amplitude, latency and wave form of retinal and cortical potentials elicited by checkerboard pattern reversal and stimulus onset-offset.

Transient pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) were recorded with checkerboard pattern reversal and equiluminance stimulus onset-offset, elicited by a high quality moving mirror stimulator. Different sized checkerboard patterns (0.35-4.2 c/deg) were used as stimulus patterns. The wave forms of the equiluminance stimulus onset responses were similar to ERGs evoked with luminance decrease and the stimulus offset PERGs were like ERGs elicited by luminance increase. The PERG c wave and the VEP showed spatial frequency tuning with pattern reversal and stimulus offset. Spatial frequency tuning was not detectable with PERG a and b waves. Pattern reversal and stimulus onset evoked PERGs had no major spectral components above 40 Hz; stimulus offset evoked PERGs contained components up to 55.3 Hz. Retino-cortical time--measured as a latency difference of the PERG b wave to VEP P100--was identical with pattern reversal and stimulus onset and about 12 msec longer with stimulus offset. Our results suggest that the 3 stimulation modes, reversal, onset and offset induce different types of processing at the retinal and cortical levels. PERG a and b waves to our high luminance/contrast stimuli contain no pattern specific information and the c waves are the sum of luminance and pattern specific responses.

Cerebral Cortex↗
PubMed1992

Alterations in rat flash and pattern reversal evoked potentials after acute or repeated administration of carbon disulfide (CS2).

Because solvents may selectively alter portions of visual evoked potentials, we examined the effects of carbon disulfide (CS2) on flash (FEPs) and pattern reversal (PREPs) evoked potentials. Long-Evans rats were administered ip carbon disulfide either acutely or for 30 days. FEPs or PREPs were recorded prior to and 1, 2, 4, 8, or 24 hr after a single dose of CS2 (0, 100, 200, 400, or 500 mg/kg). Flash evoked potentials were also recorded 1, 2, 6, and 24 hr after the last of 30 doses of 200 mg CS2/kg/day. Acute exposure to CS2 consistently decreased the amplitude of FEP peak N160 at 1 hr, depressed peak N30 amplitude over 2-4 hr, and increased the latency of peaks P21, N30, P46, N56, and N160 for up to 4 hr after treatment. Carbon disulfide decreased the amplitude of PREP peaks P65, N83, P88, and N122 4 hr after treatment. Colonic temperature was depressed up to 8 hr after treatment. Administration of 200 mg CS2/kg/day decreased the amplitude of FEP peak N30 and increased the latencies of peaks P21, N30, P46, N56, and N160 up to 24 hr after the last dose. The differential effects of CS2 on portions of FEPs indicate that FEP peaks can be independently modulated. Changes in PREPs were temporally correlated with alterations in early FEP peaks, but FEP peak N160 was depressed at an earlier time point. Repeated CS2 exposure affected FEPs at lower doses and for a longer time than an acute exposure, similar to the reported greater severity of neurological disturbances following repeated CS2 exposures in humans.

Animals↗
PubMed1981

[Determination of visual acuity by the visually evoked cortical potential (author's transl)].

Monocularly evoked cortical potentials were recorded monopolarly (3 cm above Prot. occ. ext. sup.) to steady-state checkerboard stimuli (check sizes 1.4 to 26 min, rev. freq. 7/s, mean luminance 10.8 cd/m2, field diameter 4.5 deg., centr. fix.). For a number of visual acuities (obtained by inserting plus lenses up to 3.0 dpt) the smallest check size evoking reliable VECPs was related to the visual acuities obtained at a visual test chart. The use of 20 instead of 100 per cent contrast stimuli provided a significant decrease of slope of threshold check size versus visual acuity, resulting in a three-fold increase in the resolution of data. The method permits the evaluation of visual acuities between 0.1 and 1.0 in normals and patients within limits of +/- log 0.1 (1 sigma) and +/- log 0.2 visual acuity (2 sigma).

Adult↗
PubMed1992

A developmental event-related potential study of picture matching in children, adolescents, and young adults: a replication and extension.

Event-related potentials were recorded in a developmental study of picture matching using an adaptation of Posner's (1978) letter-matching tasks. Subjects ranging in age from 6-39 were asked to decide whether two line drawings, presented sequentially, were the same or different on the basis of physical (physical identity), nominal (name identity), or categorical (category identity) criteria. The amplitude of a negativity at 400 ms (Neg400) increased as the number of dimensions on which the two line drawings differed increased. This effect held for all age groups, and was interpreted as reflecting the degree of semantic and/or physical relationship between the two pictures. However, one finding for Neg400 did suggest a qualitative difference in processing mode between the younger and older subjects. Both Neg400 and P3b latencies showed highly significant linear age trends, decreasing with increasing age. These age-related changes were interpreted as demonstrating quantitative speed of processing differences among age groups. The latencies of both Neg400 and P3b increased as the matching criteria became more complex. Moreover, P3b latency increased as the number of dimensions on which the two pictures differed increased, and this did not interact with age. Although both Neg400 and P3b showed age-related changes in scalp distribution, the fact that each was related to the experimental variables in similar fashion in all age groups suggested that they were homologous components across the age range studied. Taken as a whole, the data support continuity of information processing during these tasks across a wide age range.

Adolescent↗
PubMed1983

Abnormal evoked potential latencies in amblyopia.

The latency of the first (P1) and second (P2) major positive waves of the pattern reversal visual evoked potential (VEP) for small checks (15 minutes of arc) was measured in 68 visually normal children and 32 amblyopic children with mild to moderate visual acuity losses. In the normal children there were no P1 and P2 interocular latency differences. The amblyopic children showed longer P1 latencies and shorter P2 latencies in their amblyopic eye than their normal fellow eye. These findings can be accounted for by a selective loss of the contrast-specific evoked potential mechanisms in amblyopia. The 'shorter' P2 latency obtained from amblyopic eyes for small checks is a reflection of the luminance responses that are normally elicited by larger (60 minute) checks.

Amblyopia↗
PubMed1989

Pattern-reversal visual evoked potentials in normal 7- to 15-year-old twins: a correlation analysis.

Pattern-reversal visual evoked potentials (PRVEPs) were tested in 11 sets of monozygotic (MZ) twins and 22 sets of dizygotic (DZ) twins matched on age, sex and educational level. They ranged in age from 7 to 15 years. The PRVEPs of MZ twins exhibited a significantly greater degree of similarity than those of DZ twins. The peak latencies and amplitudes of PRVEP components obtained from MZ twin pairs were significantly correlated. The correlation coefficients for the peak latencies of the P2 (or P100) component were the only ones to differ significantly between the DZ twins of the same sex and DZ twins of opposite sexes. These coefficients, obtained using PRVEPs, were much greater than those obtained with flash visual evoked potentials.

Adolescent↗
PubMed1988

Visual evoked potentials in elderly patients with primary or multi-infarct dementia.

Flash and pattern-reversal visual evoked potentials (VEP) were recorded in 35 elderly patients with dementia, and 19 controls of equivalent age. Dementia produced a slowing of the major positive (P2) component of the flash VEP but did not affect the latency of the flash P1 component or the P100 pattern-reversal component. This unusual type of abnormality was found in both primary and multi-infarct types of dementia, and has previously been found in primary presenile dementia. The results show that the VEP can be used for the diagnosis of multi-infarct, and primary presenile and senile dementias.

Aged↗
PubMed1991

Quantitative analysis of the cross-correlation between pattern ERG and pattern VEP.

The cross-correlation between PVEPs and PERG was investigated. (1) There were high correlations between PVEPs recorded from the inion and those from points Oz, Pz, Cz, and Fz in the range of 75-150 msec following pattern visual stimulation to the eyes although no correlation was found in the range 0-75 msec. (2) PVEPs recorded from the inion highly correlated with PERG in the 75-150 msec range but not in the 0-75 msec range. It suggests that the late negative component included in the PERG reflected the electrotonically spread at the eye level of PVEP. (3) Intra-individual reproducibility was studied. PVEPs showed a high reproducibility in the 75-150 msec range, but not in the 0-75 msec range. The reproducibility of PERG was high in the 0-75 msec range but also in the 75-150 msec range, where PERG reflected PVEPs. These results suggest that the early positive component of PERG was specific to the cell activities in the retina to the pattern visual stimulus, and had an origin different from the brain activity for PVEPs.

Adult↗
PubMed1990

[State and complexity-dependent symmetry identification of 2-dimensional patterns and evoked potentials].

To analyse the influence of structural complexity of visual patterns and of an operationally defined cognitive state on evoked potentials some on--line closed--loop experiments were carried out. Symmetrical checkerboard patterns generated by means of Walsh functions were used as stimuli. The inherent symmetry should be recognized by the subjects. The state was defined on the basis of the spectral power density distribution of the EEG measured in the time interval of one second before the stimulus onset. The two state values were labeled by the state of alpha wave dominance and the state of non alpha wave dominance. According to the definition for the state of alpha wave dominance 70% of the whole spectral power must be contained in the frequency range from 8 Hz until 13 Hz at least. Otherwise the prestimulus EEG are labeled by the concept of non alpha wave state. The influence of the cognitive state and of the structural complexity on the evoked potentials has been verified experimentally. Significantly higher amplitudes of the evoked potentials in the time range of 140 ms until 200 ms after stimulus onset are due to higher complexity of the stimuli. The state of alpha wave dominance led to significantly stronger negativity of the evoked potentials in the range of 280 ms until 400 ms after stimulus onset.

Arousal↗
PubMed1988

Anatomy and physiology of visual evoked potentials and electroretinograms.

ERGs are electrical potentials originating in the retina and recorded directly from the corneal surface of the eyes. Flash ERGs are elicited by high intensity flashes either on scotopic or photopic conditions. The origin of the A and B waves of ERG are a combination of photoreceptor potentials, K+ mediated current flow and DC potentials within Müller cells, whereas the C waves are altered K+ fluxes induced by light in the pigment epithelia. Oscillatory potentials are probably related to feedback circuits of the inner layer of the retina. Electroretinograms evoked by pattern are mostly originated in ganglion cells. The use of various visual stimuli allow the selective activation of different retinal structures. Flashes selectively activate retina luminance and color detectors, whereas small pattern stimuli preferentially activate contrast and edge detectors. Visual evoked potentials recorded from the scalp probably originate from multiple cortical visual areas. P-100 response of the visual evoked potential to pattern stimulation is a cortically originated wave either produced exclusively by area 17 or 18 or by a multiplicity of cortical neuronal pools. Visual evoked potentials have important application for the diagnosis of optic nerve disease, assessment in conjunction with pattern ERG of the prognosis of recovery of visual function, and the evaluation of visual physiology and physiopathology.

Animals↗