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

Pattern-VEP findings in individuals with mild cognitive impairment

BACKGROUND

Visual evoked potential (VEP) is a technique used to evaluate the electrical response of the brain to visual stimuli. This study aimed to examine neural transmission in the visual pathway by VEP test in individuals with mild cognitive impairment (MCI) and compare it with age-appropriate controls and also investigate for a correlation between VEP parameters and cognitive test domains.

METHODS

The groups consisted of 56 MCI and 50 healthy volunteers, aged 60-80 years, matched for age and education. Mini-Mental State Examination (MMSE) was applied to the participants for cognitive assessment. Patients were also subjected to other dementia screening tests and other treatable causes were excluded. In addition, groups were formed from those who completed the test. The pattern-reversal VEP method was used in this study.

RESULTS

The mean MMSE score in the MCI group was 21.42 ± 1.55 points. Our findings showed that individuals with MCI had a longer left P100 latency compared to controls (p = 0.027). In addition, right N75-P100 and right P100-N145 amplitudes of VEP parameters were found to be positively correlated with the recall test, which is one of the MMSE domains (p < 0.05, rho: 0.399,0.314).

CONCLUSION

The evidence provided by this study supports the possibility of using pattern VEP with clinical parameters to evaluate MCI patients. In addition, a positive correlation between interpeak amplitudes and the recall test highlights the importance of the VEP test in these patients.

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.

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.