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.     

Follow-up studies of visual potentials in multiple sclerosis evoked by checkerboard and foveal stimulation

Visual cortical potentials were evoked by reversal of a checkerboard pattern and a small quadrangular foveal stimulus. Examination of 68 patients with MS showed the highest detection rate for abnormality of VEPs with a combination of both methods. Follow-up studies revealed changes (improvement or impairment) of VEP amplitudes or latencies in nearly half of the patients. Most of the changes were correlated with a history of acute optic neuritis. For the detection of changes the foveal stimulus is preferable to the checkerboard pattern.     

Visual evoked cortical responses and electroretinograms following implantation of human fetal mesencephalon to the right caudate nucleus in Parkinson's disease.

Pattern electroretinograms and visual evoked cortical responses following flash and checkerboard pattern reversal stimulation were performed in 7 patients with advanced Parkinson's disease before and after implantation of human fetal ventral mesencephalon to the head of the right caudate nucleus. Six to nine months following surgery there was bilateral enhancement of flash-evoked response amplitudes. Electroretinogram measurements were unchanged. Individual increases in amplitude and decreases in latency were seen following pattern stimulation which were not statistically significant. A relationship between change in dyskinesia, and change in checkerboard pattern stimulation amplitude at 2.4 cycles per degree suggests that amplitude effects at this stimulus frequency are mediated via altered dopaminergic receptor status in the grafted hemisphere. This may be relevant to the mechanisms leading to generalised clinical improvements following this grafting technique.     

Vector analysis of visual evoked potentials elicited by pattern reversal and photic stimuli.

OBJECTIVE: The 2D VEPs to pattern reversal (PR) and LED goggle were studied in order to obtain a stable parameter for the functional assessing of posterior visual pathways regardless of the stimulus type used. DESIGN AND METHODS: Apex c latency, bc segment amplitude (V), and bc vector orientation angle (theta) in voltage space were computed from VEPs recorded in 50 normal human beings and two patients with left posterior brain lesions, in an orthogonal Fpz-Oz and T3-T4 montage and displayed as a two channel Lissajous' trajectory. The effects of stimulus type and stimulated eye were analyzed in the normal group by a two-way ANOVA. RESULTS: The stimulated eye had no effect on any parameter. Apex c latency was slightly longer, and V was greater and more variable in the responses to goggle stimuli, but there was no significant difference in theta, oriented to mid-occipital scalp with very low variability for both stimulus types. The patients showed significant deviations of theta towards the affected hemisphere. CONCLUSIONS: The bc vector orientation (theta) is a stable parameter for the evaluation of the posterior visual pathways using both pattern reversal and LED stimuli, specially the latter, useful in unconscious or uncooperative patients.     

Normal checkerboard pattern reversal evoked potentials in parkinsonism

The utility of checkerboard pattern reversal visual evoked potentials in the evaluation of Parkinson disease (Pd) was studied in 25 patients and controls without eye pathology. The results did not reveal differences in potential latency but the amplitude appeared slightly larger in PD than controls. Major intraocular differences were observed only in Pd patients with glaucoma, cataracts or retinal degeneration. The commonly employed high contrast and luminance, checkerboard pattern reversal technique did not appear useful in the evaluation of Pd. Selection of proper stimulus parameters may be critical in detecting VEP abnormality in Pd.     

棋盘格翻转的视野刺激区域对硬脑膜上皮质脑电的影响

To explore the effect of the location of a visual stimulus on neural responses in the primary visual cortex (V1), a micro-electromechanical system-based microelectrode array with nine channels was implanted on the cerebral dura mater of V1 in adult cats. 2 Hz pattern reversal checkerboard stimuli were used to stimulate the four visual quadrants (i.e., upper left, upper right, lower left, and lower right fields). The results showed that there was a N75 component of the visual evoked potential around 50-80 ms after the onset of a checkerboard stimulus, and the onset of these N75 peaks varied with different stimulus locations. The checkerboard stimuli induced shorter latencies in the contralateral V1 than in the ipsilateral V1, while the checkerboard stimulus in the upper half visual field induced shorter latencies for N75. These results suggested that the pattern-reversal stimuli induced neural activities in V1 that can be recorded with multichannel microelectrodes, and more detailed temporal and spatial properties can be measured.     

Visual evoked potentials and attention processes in depression

The study of the attention process during depression has been realized with the recording of visual evoked potential (VEP) by simple pattern reversal checkerboard and in sequences where a rare stimulus appears randomly, with or without task. The recordings obtained on fifty patients have been compared to the VEP obtained on fifteen reference subjects. The results indicate that some perturbations, characteristic of the depressive state, should happen at the both levels of attentional selection, early (P1 and N1 components) and late (P3 component). The responses of the depressive patients appear to reflect rather an intervention of automatic attention process.     

A sequential technique for half-field pattern visual evoked potential testing

A stimulus technique is described where left and right half fields of a video checkerboard pattern reverse sequentially at a 245 msec interval. The pattern VEPs are recorded on a 512 msce timebase. This allows VEPs to left and right half-field reversal to be obtained on the same sweep, cutting total stimulus time required for testing in half. Normal values for absolute and relative latency and amplitude are given.     

Latency of luminance and contrast evoked potentials in multiple sclerosis patients.

Luminance and contrast visual evoked potentials (VEPs), were studied in 18 multiple sclerosis (MS) patients and 11 healthy subjects. Luminance EPs were recorded to stimulation with noise modulated light (0--60 Hz); contrast EPs were obtained to appearance-disappearance or reversal of a checkerboard pattern with various check sizes and repetition periods. Our results indicate that the apparent latency of luminance EPs to noise modulated light can hardly be used for diagnosis of MS, since the range of normal values scatters widely and greatly overlaps the range of latency values in MS patients (detection rate of 3/13). Our data confirm, on the other hand, that the latency of contrast EPs can be used to discriminate between MS patients and healthy subjects (detection rate of 12/18). We recommend for diagnostic purposes to determine the apparent latency from the phase spectrum of the responses to checkerboard reversal at repetition rates between 5 and 20 Hz, since in this frequency range the failure rate was found to be minimal. The specificity of the apparent latency data can be improved if the wave form of the transient reversal EP at a lower repetition rate (around 2 Hz) is also inspected. We suggest that an increased latency can be ascribed to several causes, only one of these being an increased conduction time due to demyelination. Indirectly this confirms that an increased EP latency is not specific for MS.     

Effects of selective attention on visual evoked potentials in depressed patients and healthy controls

The study of the attention process during depression has been realized with the recording of visual evoked potentials (VEP) by simple pattern reversal checkerboard, and in sequences where a rare stimulus appears randomly, with of without task. The recordings obtained on fifty patients before antidepressive treatment (D0) have been compared to the VEP obtained on the same patients at the end of the treatment (D28) and to those obtained on fifteen reference subjects. The results indicate that some perturbations, characteristic of the depressive state, should happen at both levels of attentional selection, early (components P1 and N1) and late (component P3). The responses of the depressive patient appear to reflect rather the intervention of automatic attention process. Electrophysiological and behavioral data seem to indicate a positive effect of the psychotropic treatment.     

Responses to paired onset stimuli: implications for the delayed evoked potentials in multiple sclerosis

In multiple sclerosis (MS), demyelination is reported to be patchy and randomly distributed across the optic nerve, and a double peaked or broadened shape of the peaks of the pattern evoked potential would be expected. We tested quantitatively this hypothesis for our routinely recorded responses of MS patients. There was no significant broadening of the peak shape in the 75 prolonged latency responses. In order to simulate the patchy character of the affection of the optic nerve in MS, we tested 2 healthy subjects with a stimulus consisting of 2 presentations of a checkerboard pattern to different parts of the visual field, but with an adjustable onset asynchrony. It was found that, when the asynchrony was small (less than 40 msec) the second of the two stimuli did not contribute to the response. This suppression of the second response could be observed even when the second stimulus, by increasing its contrast, was made to evoke a much larger response than the first stimulus, when presented separately. Inhibition of the second response seems to explain the lack of wave shape alteration in the responses of MS patients, which would be expected on the basis of the patchy character of the demyelination. The responses from the fastest conducting fibres seem to determine the response, and inhibit the responses of the demyelinated fibres. From this, it can be concluded that a delayed response would be expected only in patients in whom a considerable number of the fibres of the optic nerve is affected by the demyelination. This seriously limits the sensitivity of the method for early diagnosis.     

Different influence of backward masking on visual pattern recognition in the early stages of presenile dementia and normal ageing

The effect of backward masking with illumination of all fields or with a checkerboard pattern, respectively, on the recognition of pattern + or T was measured on four groups of subjects: 21 presenile onset DAT patients, 16 patients with a questionable vascular dementia of the same age (CVD group), 15 age-matched control subjects (EC group) and 16 younger control subjects (YC group, mean age 22 years). The pattern stimulus had a duration of 20 ms and was followed by the masking stimulus pattern (20 ms duration) with increasing intervals in steps of 5 ms. The mean recognition threshold (RT) for each of the four possible pattern–mask combinations was measured in five trials. The RTs decreased within the five trials in all groups. DAT patients and CVD patients adapted with different speeds during the five trials. We found a small significant RT difference between elder and younger control subjects, whereas patients had increased RTs in the first trial and differences in the four variants in the further trials compared with age-matched controls. The test contributes to a set of data for diagnosis and differential diagnosis in the early stages of presenile dementia.     

Sequential spatial maps of visual potentials evoked by checkerboard-pattern reversal: effect of the retinal field stimulated on response topography

Sequential color maps of visual potentials evoked by the reversal of various checkerboard patterns were recorded in 10 young adults using a 16 channel montage. It was found that each of the components of the N75-P100-N145 occipital complex had a specific spatial distribution on the scalp and was selectively influenced by the size, the spatial frequency, the luminance and possibly the wave length of the stimulus. Component N75 was found to be elicited by the more peripheral area of the TV stimulus (12 degrees X 16 degrees). Component P100 was associated with a frontal negativity of similar latency favoring the hypothesis of a dipolar occipital generator. With half-field stimulations the dipole orientation was modified, leading to a 'paradoxical' lateralization of P100 in most cases. However the reverse situation (P100 contralateral to the stimulated half-field) was observed in 4 and 3 subjects out of 10 with left and right half-field stimulations respectively. Thus VEP to full-field TV pattern reversal cannot be recommended to investigate hemianopic patients. Component N145 was of maximal amplitude when elicited by the reversal of small foveal patterns (2.18 degrees), especially red light emitting diodes.     

Visual evoked cortical potentials (V.E.C.P.) by television presentation of different patterned stimuli to patients with multiple sclerosis

Visual pattern reversal evoked potentials constitute a test that can reveal early pathological changes in multiple sclerosis Sixty nine subjects (52 controls, and 17 patients) were studied with this technique.The transient potentials evoked by checkerboard pattern reversal reveal an increase in the CII peak latency (significantly different from the controls) in M.S., with single elements of 15 and 30 min of arc and 20%–50% of contrast depth.The steady state potentials are absent or show phase lags in some patients with transient responses within the normal limits.The delayed evoked responses are detectable in a high percentage of patients with M.S., even when ocular symptoms are not seen in the clinical observation.Transient and steady-state E.Ps can furnish early tools for evaluation of funcionality of visual pathways related to retinal form- and movement-analyzers, the former being sensitive to high spatial frequencies but conducting more slowly than the latter.     

Diagnosis of demyelination processes based on the visual evoked potential test using a checkerboard reversal pattern

Visual evoked potentials in response to checkerboard reversal pattern were evaluated in 160 patients: 24 with isolated retrobulbar optic neuritis, 100 with unquestionable and probable multiple sclerosis, 36 with paraparesis or with disseminated changes of unestablished aetiology (degenerative or inflammatory) and in 80 healthy controls. Normal visual evoked potentials were obtained in all controls. In all cases of present or past optic neuritis abnormal potentials were observed, usually unilateral. In multiple sclerosis patients with unquestionable diagnosis abnormal potentials were present in 92% of cases, and in patients with probable multiple sclerosis they were found in 58%, and in cases without retrobulbar neuritis they were present in 71% and 48% of cases respectively. The abnormalities were found most frequently in both optic nerves. It was tried to find out other correlations making possible partial differentiation of the axonal and demyelinating type of damage to the anterior part of the visual pathways.     

Efficient acquisition of human retinotopic maps

A bifield stimulation method for rapidly obtaining retinotopic maps in human occipital cortex using functional MRI was compared to conventional unifield stimulation. While maintaining central fixation, each participant viewed the conventional display, consisting of a single rotating checkerboard wedge and, in a separate run, the bifield display, consisting of two symmetrically placed rotating checkerboard wedges (a "propeller" configuration). Both stimulus configurations used wedges with 30 degree polar angle width, 6.8 degrees visual angle extension from fixation, and 8.3 Hz contrast polarity reversal rate. Retinotopic maps in each condition were projected onto a distortion corrected computationally flattened cortical surface representation obtained from a high-resolution structural MRI. An automated procedure to localize borders between early visual areas revealed, as expected, that map precision increased with duration of data acquisition for both conditions. Bifield stimulation required 40% less time to yield maps with similar precision to those obtained using conventional unifield stimulation.     

Steady-state visual evoked potentials and travelling waves.

OBJECTIVE: The amplitude and phase of the steady-state visual evoked potential (SSVEP) is sensitive to cognition and attention but the underlying mechanism is not well understood. This study examines stimulus evoked changes in the SSVEP phase topography and the putative role of travelling waves. METHODS: Eighteen subjects viewed a central-field checkerboard and full-field flicker stimulus temporally modulated at the peak alpha rhythm frequency. EEG was recorded from 10 midline scalp sites and the bipolar SSVEP obtained from differences between adjacent electrodes. RESULTS: The SSVEP phase comprised either progressive variations consistent with travelling waves or a phase reversal consistent with standing waves. The checkerboard pattern elicited travelling wave patterns in 14 subjects with estimated phase velocities ranging from 7 to 11 m/s after correcting for folded cortex. The flicker stimulus elicited phase reversals in 9 subjects, suggesting standing waves. Six subjects demonstrated a phase topography specific to the stimulus with travelling wave patterns associated with the checkerboard and standing wave patterns associated with the flicker. CONCLUSIONS: These differences suggest the emergence of travelling and standing waves under different spatial configurations of visual input to the cortex and that wave phenomena contribute to the spatiotemporal dynamics of the SSVEP.     

A case of reflex epilepsy with binasal visual field defects attack induced by family computer game

A 12-year-old male case of reflex epilepsy with visual field defects attack induced by a family computer game was reported. This patient showed binasal visual field defects attack when he was playing a family computer game. Neurological findings and ophthalmological examinations were normal. EEG showed spike and slow wave complex distributed on right occipital region. These paroxysmal waves were activated by checkerboard pattern reversal stimuli. Stimulus intensity was closely related with these activations, but not stimulus ratio was. Examinations of brain CT and brain MRI were normal. This patient complained of discomfort without visual symptoms when he suffered checkerboard pattern stimuli. A family computer game needs mental concentration, recognition, decision, alert state of consciousness and complex finger movement. Integration of these factors may have induced visual field defects attack. It is interesting that a family computer game is the inducer of reflex epilepsy with visual symptoms. The number of reflex epilepsy is thought to increase because of prevalence of family computer games.     

Persistent visual hallucinations secondary to chronic solvent encephalopathy: case report and review of the literature

A case of solvent encephalopathy presenting with persistent visual hallucinations, and characterised by a diffusely abnormal EEG and delayed visually evoked responses to checkerboard pattern reversal (VERs), is described. Abnormalities in the EEG and VERs showed minimal improvement over many months of abstinence from glue sniffing. The literature on the neurological sequelae of solvent abuse is reviewed.     

Differences between the occipital distribution of upper and lower field pattern-evoked responses in man

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The consistent reversal in the polarity of the occipital response to a reversing checkerboard stimulus in the upper and lower visual field, previously reported by the authors, has been investigated further in 9 healthy subjects, using a variety of reference electrodes, to decide between two possible explanations put forward in the earlier paper, viz., that the upper and lower field generators were situated on the lower and upper surfaces of the occipital lobe respectively, or alternatively that both responses, although of opposite surface polarity, came from the same general area of convergent information on the upper convexity.