The flash visual evoked potential-P2 and the detection of amnestic mild cognitive impairment: A review of empirical literature

Impaired Visual Inhibition in Amnestic Mild Cognitive Impairment

Objective.The pathophysiology of amnestic mild cognitive impairment (aMCI) and Alzheimer disease (AD) is still a matter of debate. Visual system might be precociously altered, especially for its cholinergic connections. We thus studied patients with aMCI compared to AD with paired-pulse flash-visual evoked potentials (paired-F-VEPs), a putative marker of cholinergic function. Methods. We enrolled 12 adult patients with aMCI and 12 with AD. 14 normal age- and sex-matched subjects acted as controls (HS). Stimuli were single flashes, with interspersed random flash pairs at critical interstimulus intervals (ISIs, 16.5 to 125 ms) with closed eyes. The "single" (unconditioned) F-VEP was split into a "main complex" (50 to 200 ms after the flash) and a "late response" (200 to 400 ms). As for paired stimulation, the "test" F-VEP emerged from electronic subtraction of the "single" F-VEP from the "paired"-F-VEP. Results. In the single F-VEP, P2 latency was prolonged in patients (aMCI and AD) compared to HS (p < .05). As to the paired F-VEPs, in aMCI the "late response" normal inhibition was abolished at ISIs 50-62.5 ms (p ≤ .016), compared to AD and controls. No changes were detected for the "main complex". Conclusions. Paired-F-VEPs demonstrate a defective neural inhibition in the visual system of patients with aMCI at critical intervals. It may represent a compensatory mechanism against neuronal loss, the failure of which may be involved in AD development. Paired-F-VEPs may warrant inclusion in future preclinical/clinical studies, to evaluate its potential role in the pathophysiology and management of aMCI.

Changes in the Parameters of Visual Evoked Potentials in Media Opacities

Purpose

This study compared flash visual evoked potentials (VEPs) parameter differences between eyes with unilateral opaque media and their normal contralateral counterparts.

Patients and Methods

We included 178 patients with unilateral media opacity and normal contralateral eye in each patient. The diseased eyes had normal ultrasonographic findings and were candidates for keratoplasty or anterior segment reconstruction. The patients underwent electrophysiological testing by the flash VEPs recording with the use of 1.4Hz (transient) and 8Hz (flicker) frequencies.

Results

The medians of P2 implicit times were significantly higher in eyes with media opacity than in normal eyes, with median differences between both eyes of -6.7 ms. Furthermore, the median N2P2 amplitude was 9.70 µv with media opacity compared with 11.00 µv in the normal eyes, with a significant difference of 1.3 (p = 0.002). The flash VEPs median parameters recorded at a frequency of 8-Hz showed significant differences in medians of spectral plots of 0.6 µv between normal and abnormal eyes. The same for the signal-to-noise ratio, where the difference in medians was 3 dB. Analysis of the difference between both eyes (normal-abnormal) in each patient showed in P2 implicit time a difference range of -49 to 54.7 ms with a median difference of -3 ms. The difference in amplitudes of recorded N2P2 showed a median of 2.13 µv. There was a statistically significant but weak negative correlation between N2P2 amplitude (r spearman = -0.173, p = 0.021) and the grades of corneal opacity.

Conclusion

Preoperative flash VEPs recording is useful for evaluating visual function in patients with unilateral media opacity to determine the future benefits of keratoplasty or anterior segment reconstruction. There are no correlations between the flash VEP parameters or the difference between the 2 eyes and the grades of corneal opacity.

An exploratory study of delayed flash visual evoked potential P2 wave latency in subcortical arteriosclerotic encephalopathy

BACKGROUND

Patients with cognitive dysfunction may present with significantly prolonged the P2 wave latency of flash visual evoked potential. However, no studies have been reported on whether the P2 wave latency of flash visual evoked potential is prolonged in patients with subcortical arteriosclerotic encephalopathy (SAE).

OBJECTIVE

To examine the relationship between flash visual evoked potential P2 wave latency (FVEP-P2 wave latency) and cognitive impairment in patients with SAE.

METHODS

Overall, we recruited 38 SAE patients as the observation cohort (OC) and 34 healthy volunteers as the control cohort (CC). We measured the FVEP-P2 wave latency for both groups. The SAE patients' cognitive abilities were evaluated via mini-mental state examination (MMSE) and the association between the latency of FVEP-P2 and MMSE score was explored by Pearsons´s correlation test.

RESULTS

There is no significant difference between OC (21 males and 17 females; 68.6 ± 6.7 years of age and 9.6 ± 2.8 years of education) and CC (19 males and 15 females; 65.3 ± 5.9 years of age and 10.1 ± 2.6 years of education) in gender and age composition and education level. The FVEP-P2 wave latency of the CC group was (108.80 ± 16.70) ms and the OC FVEP-P2 wave latency was (152.31 ± 20.70) ms. The OC FVEP-P2 wave latency was significantly longer than the CC (P < 0.05). In terms of MMSE scores, the MMSE scores of CC was (28.41 ± 2.34), and that of OC was (9.08 ± 4.39). Compared to the CC, the OC MMSE score was significantly lower (P < 0.05). In addition, the FVEP-P2 wave latency was inversely related to the MMSE (r = -0.4465, P < 0.05) in SAE patients.

CONCLUSION

The FVEP-P2 wave latency wave latency was significantly prolonged in SAE patients and strongly associated with the degree of cognitive dysfunction.

Standardization and Validation of the Flash Visual Evoked Potential-P2 Conversion Scores in the Diagnosis of Amnestic Mild Cognitive Impairment and Alzheimer's Dementia

Amnestic mild cognitive impairment (aMCI), which is characterized by normal daily activity, but a significant decline in episodic memory, is now widely accepted as a risk factor for the development of Alzheimer's dementia (AD). Research suggests that many of the same neuropathological changes associated with AD also occur in patients diagnosed with aMCI. A recent review of the literature revealed that the latency of the flash visual-evoked potential-P2 (FVEP-P2) may possess pathognomonic information that may assist in the early detection of aMCI. While standards exist for the recording of FVEP-P2, individual clinics often use recording parameters that may differ, resulting in latencies that may not generalize beyond the clinic that produced them. The present article illustrates the process by which the FVEP-P2 latency can be standardized across clinics using FVEP-P2 Conversion Scores. We then demonstrate the diagnostic accuracy of the newly developed scores. Method: In the present investigation, we used the previously unpublished data containing the FVEP-P2 latencies of 45 AD and 60 controls. Result: We were able to demonstrate the process by which individual clinics may first standardize FVEP-P2 latencies and then examine patient performance using FVEP-P2 Conversion Scores, providing clinicians with a richer context from which to examine the patient performance. Conclusion: Consistent with the findings of previous research, the findings of the present investigation support the use of the FVEP-P2 Conversion Scores in the diagnosis of AD. Future directions, including the modification of recording parameters associated with the FVEP-P2, are also discussed.

Research on Voxel-Based Features Detection and Analysis of Alzheimer’s Disease Using Random Survey Support Vector Machine

Alzheimer’s disease (AD) is a degenerative disease of the central nervous system characterized by memory and cognitive dysfunction, as well as abnormal changes in behavior and personality. The research focused on how machine learning classified AD became a recent hotspot. In this study, we proposed a novel voxel-based feature detection framework for AD. Specifically, using 649 voxel-based morphometry (VBM) methods obtained from MRI in Alzheimer’s Disease Neuroimaging Initiative (ADNI), we proposed a feature detection method according to the Random Survey Support Vector Machines (RS-SVM) and combined the research process based on image-, gene-, and pathway-level analysis for AD prediction. Particularly, we constructed 136, 141, and 113 novel voxel-based features for EMCI (early mild cognitive impairment)-HC (healthy control), LMCI (late mild cognitive impairment)-HC, and AD-HC groups, respectively. We applied linear regression model, least absolute shrinkage and selection operator (Lasso), partial least squares (PLS), SVM, and RS-SVM five methods to test and compare the accuracy of these features in these three groups. The prediction accuracy of the AD-HC group using the RS-SVM method was higher than 90%. In addition, we performed functional analysis of the features to explain the biological significance. The experimental results using five machine learning indicate that the identified features are effective for AD and HC classification, the RS-SVM framework has the best classification accuracy, and our strategy can identify important brain regions for AD.

The effect of wavelength on the variability of the flash visual evoked potential P2: A potential biomarker for mild cognitive impairment and Alzheimer's dementia

As the number of individuals diagnosed with amnestic mild cognitive impairment (aMCI) and Alzheimer's dementia (AD) increases, a need exists for early detection and treatment of the disorders. A recent review of the literature conducted by Arruda et al. (2020) revealed that the latency of the flash visual-evoked potential-P2 (FVEP-P2) may possess pathognomic information that may assist in the early detection and treatment of each disease. Unfortunately, while group differences in latency are robust, the ability to discriminate between individuals remains difficult due to the natural variability associated with the FVEP-P2 latency. In the current investigation, we examine the role of wavelength of light in the production of the FVEP-P2, with the goal of reducing the variability associated with the FVEP-P2 latency and improving the diagnostic accuracy of the FVEP-P2 evaluation.

METHOD

Twenty-four healthy individuals (11 males and 13 females), ages 18 to 36 years (M = 25.00, SD = 5.60), participated in this investigation. Each participant experienced five blocks of 100 strobe flashes (or trials) under two different light conditions (blue filtered light and polychromatic white light) with their eyes closed. The FVEP-P2 associated with each trial was identified and the latency and amplitude of each component was calculated.

RESULT

The results of several repeated measures analysis of variance revealed no statistically significant differences in intra- and inter-individual variability associated with the P2 latency or amplitude. However, there was a significant difference in the amplitude of the P2 produced by the two lights, with blue filtered light producing significantly lower amplitudes than the polychromatic white light.

CONCLUSION

The results of the present investigation suggest that while imperfect, the current practice of employing polychromatic white light in the production of the FVEP-P2 remains the gold standard and that additional methods of reducing the natural variability of the P2 need to be developed if the FVEP-P2 latency is to be used as a biomarker.