Visual evoked potentials to pattern, motion and cognitive stimuli in Alzheimer’s disease

Abstract

The aim of our study was to verify reported visual dysfunctions of patients with Alzheimer disease with the use of several variants of VEPs and visual ERPs and to learn whether these methods can be useful in diagnostics of AD. We tested 15 patients (6 women and 9 men, aged from 58 to 87) with mild to moderate Alzheimer disease (12-23 points of Mini Mental State Examination) and 15 age, gender and education level matched controls. The examination consisted of VEPs to pattern-reversal and motion-onset stimulation (to translational and radial movement) and of visual ERPs recorded during an odd-ball test. The subjects were instructed to signalize target stimuli by pressing of a button, which enabled to evaluate also the reaction time. While pattern-reversal VEPs were comparable in patients and controls, there were significantly smaller N2 peak amplitudes of motion-onset VEPs in patients with AD (in particular in radial moving stimuli outside the central 20 deg of the visual field), which suggests a dysfunction of the motion-processing (magnocellular) system or the dorsal cortical stream. ERPs, having significantly longer latencies in patients than in controls, distinguished well both groups. However, the individual AD diagnostics based on ERPs seems to be limited by rather high inter-individual variability of the ERP latencies. The ERPs might, however, be useful in disease progress and therapy effect estimation. Electrophysiological parameters did not correlate with neuropsychological ADAS cog test (Alzheimer Disease Assessment Scale--cognitive part).

Different trajectories of decline for global form and global motion processing in aging, mild cognitive impairment and Alzheimer's disease

“…Thus, motion processing deficits in AD do not reflect broad declines across global visual processing mechanisms. This reinforces previous reports suggesting more disruption to classic dorsal stream functioning than ventral stream in AD (Nguyen et al, 2003;Sartucci et al, 2010;Kubová et al, 2010), and explains why many more studies claim complex motion-related deficits than form-related deficits in these patients. The patterns reported here for AD are similar to those found in developmental disorders in childhood using the same methodology (Spencer et al, 2000;Atkinson et al, 2006), and they allow us to extend the concept of "dorsal stream vulnerability" (Braddick et al, 2003) into disorders of old age.…”

“…Bokde et al (2010) used fMRI to show that, compared with controls, AD patients recruit additional brain areas when performing location-matching but not face-matching tasks. Similarly, Kubová et al (2010) and Sartucci et al (2010) report a reduced amplitude of EEG response in AD patients versus controls to radial optic flow, and high contrast luminance gratings reversed at high temporal frequency ("dorsal stream"), but not stimuli thought to represent ventral stream processing. Overall, while form-based impairments may occur in AD, the evidence is of lesser magnitude and consistency than the evidence for decline in motion systems.…”

“…People with AD are less able than healthy controls to identify shape from motion (Rizzo & Nawrot, 1998;Rizzo et al, 2000;Kim 2012), to discriminate optic flow (Tetewsky & Duffy, 1999;Mapstone et al, 2008, Kavcic et al 2011 and to process objects moving incongruently with their own apparent motion (Mapstone & Duffy, 2010). Imaging with fMRI shows less activation of motion-processing areas in AD patients than controls when viewing moving 3D stimuli (Thiyagesh et al, 2009), and with EEG, a reduced amplitude of response to motion onset (Kubová et al, 2010) or changing optic flow stimuli (Fernandez & Duffy, 2012;Fernandez et al, 2013). Nevertheless, patients' performance of simple motionrelated tasks such as discriminating the direction of horizontal motion is typically more comparable to healthy controls' (Rizzo & Nawrot, 1998;Tetewsky & Duffy, 1999;Rizzo et al 2000;Mapstone et al, 2008).…”

Visual Motion Event Related Potentials Distinguish Aging and Alzheimer's Disease

“…Thus, our findings link age-related delays in a behavioral tasks [42] to prolonged ERP latencies [43], and AD related perceptual impairments [44] to reductions in ERP amplitudes [45]. As a result, we must conclude that aging and AD are distinguishable processes.…”

Neuropsychological Parameters as Potential Biomarkers for Alzheimer’s Disease

“…In contrast, the AD patients showed greater activation in the inferior parietal lobule and recruitment of additional regions. Moreover, recent EEG studies have used visual [86] and auditory [87•] oddball tests to elicit event-related potentials (ERPs) with AD and MCI patients. Both of these studies revealed that the latencies of ERPs in AD and MCI patients were significantly more prolonged than that of normal individuals.…”