**3. Visual Evoked Potentials (VEPs)**

PD and parkinsonism are associated with a variety of visual signs and symptoms summarized in table 2.


Table 2. Abnormal visual symptoms in PD

presentation in a tertiary clinic, not later than 1 year from the onset of dementia [5]. Supportive elements for the diagnosis came from Clinical Assessment of Fluctuations (CAF) scale, polysomnography (PSG) and Mayo Sleep Questionnaire for the assessment of REM sleep Behaviour Disorder (RBD). CAF is a neuropsychological test [6] able to evidence, on the basis of patient and caregivers interviews, the presence of fluctuating consciousness. The questionnaires are able to discriminate 85% of DLB patients, as confirmed by autopsy [7]. Cognitive fluctuations are considered a clinical feature typical of DLB, described in 70-80%

PD and parkinsonism are associated with a variety of visual signs and symptoms

of these patients, only in 14-20% of AD patients and in 15-30% of VaD subjects [8].

**OCULAR ASPECT CHANGE IN PD REFERENCES** 

VISION BLURRED FOR COLOURED STIMULI/PROGRESSIVE DETERIORATION

SLOWER THAN NORMAL

FIELD DEFECTS

HYPOMETRIA

REDUCED NOT OBSERVED

REDUCED

LONGER LATENCY

WITH L-DOPA

AMPLITUDE

IMPAIRED

Table 2. Abnormal visual symptoms in PD

SEVERE IMPAIRMENT

POOR, ESPECIALLY AT LOW CONTRAST INCREASE IN GLAUCOMATOSE VISUAL

AFFECTED EARLY IN DISEASE PROCESS ABNORMAL IN SOME PATIENTS

REDUCED AMPLITUDE OF b WAVE with

INCREASED LATENCY AND REDUCED

CHRONIC IN 30-60% TREATED CASES

PHOTIC E SCOTOPIC STIMULI REDUCED AMPLITUDE, DELAYED P50 DELAYED P100, CHANGING TO NORMAL Repka et al., 1996 Bayer et al., 2002 Price at al., 1992/ Diederich et al., 2002

Shibasaki et al., 1999 Crawford et al., 1989 Bares et al., 2003 Shibasaki et al., 1999

Garland et al., 1952 Garland et al., 1952

Biousse et al., 2004 Miceli et al., 1991

Gottlob et al., 1987 Gottlob et al., 1987 Bodis-Wallner et al.,

Sartucci et al., 2006

Davidsdottir et al., 2005 Trick et al., 1994 Diederich et al., 2005

1982

**3. Visual Evoked Potentials (VEPs)** 

summarized in table 2.

**EYE MOVEMENTS**  SACCADIC GAZE SACCADIC EYE MOVEMENT SMOOTH PURSUIT OPTOKINETIC NYSTAGMUS

**BLINK REFLEX**  FREQUENCY HABITUATION

**VEP**  FLASH ERG PATTERN ERG CORTICAL VEP CHROMATIC VEP

PUPIL REACTIVITY CONTRACTION AMPLITUDE LIGHT REFLEX

**COMPLEX VISUAL FUNCTION**  VISUO-SPATIAL ORIENTATION VISUAL

HALLUCINATIONS

**PRIMARY FUNCTION**  VISUAL ACUITY VISUAL FIELD COLOR VISION

Recent epidemiological studies have shown an association between visual impairments and visual hallucinations in patients with PD [9]. Neuropsychological studies have revealed visuoperceptual impairments in PDD and DLB patients with visual hallucinations [10]. Additionally, recent radiological studies have demonstrated decreased blood flow in the posterior temporal and occipital regions in hallucinatory PD and DLB patients [11]. Taking these findings together, it is possible to speculate that visual information processing functions are selectively impaired in DLB and PDD.

Impairment of achromatic as well as chromatic vision in PD has been extensively proven using clinical, psychophysiological and electrophysiological methods (ERGs and VEPs) and attributed to dopaminergic deficiency at the retina level.

Some studies demonstrated a significant difference between PD patients and well matched control subjects in the amplitude of VEP, of flash (ERG) and pattern electroretinogram (PERG: retinal response evoked by viewing an alternating checkerboard or grating) [12]. The VEP, PERG and flash ERG originate from different parts of the retina and central nervous system and reflect different physiological processes. The changes in these potentials in PD may reflect the widespread nature of the biochemical disorder affecting both retina and central nervous system. Indeed PD patients have also been shown to have abnormal auditory evoked potentials [13]. Abnormal VEPs were described in patients with PD: the percentage of VEP delays and the amount of latency increments detected in PD patients are dependent on the spatial frequency (that is a parameter of the stimulating pattern). The VEP latency increases as a function of increasing spatial frequency [14] in normal subjects, and our results [15] show that this latency increase is enhanced in PD and also when dopamine blockers are administered. Delayed responses, consisting of increased latencies of the P100 component evoked by patterned stimuli of degree to 7.5' elements (spatial frequency of 0.5 to 4 cycles per degree) were observed in PD patients and the delays disappeared together with clinical symptoms when L-Dopa was administered [15,16,17]. The evidence of VEP delays in PD were concomitant with the identification of dopaminergic cells (amacrine and horizontal cells) in the retina, both evidences reciprocally supporting the idea that the cause of delays was dependent on retinal dopamine cell deficiencies. In these studies retinal and occipital visual evoked potentials and event-related potentials (P300) have been recorded in normal human subjects before and after the administration of the dopaminergic receptor antagonist, haloperidol, and/or the dopaminergic precursor L-DOPA. The data show that either retinal or occipital visual potentials and P300 are delayed by haloperidol. These findings are consistent with the hypothesis that haloperidol in healthy subjects mimics the electrophysiological abnormalities observed in PD. On the other hand, L-Dopa does not generally modify these latencies in controls, while it is known to decrease the same parameters in PD patients. This is in accord with the involvement of a specific mechanism in the recovery observed in PD patients during L-Dopa therapy. Data confirm that the alterations of visual and cognitive potentials observed in PD are closely related to the impairment of dopaminergic transmission. The results of our study [15] on haloperidol administration in non-PD patients showed that this dopamine receptor blocking drug increased the latency of VEPs obtained with 2 and 4 cpd stimuli, while the effect on 0.5 cpd and 1 cpd VEPs was less consistent. This finding supports the hypothesis that dopamine modifies the processing of VEPs by acting at the synaptic level. The specific sensitivity of VEP changes to the spatial frequency of stimulation in PD and haloperidol treated subjects, which is evident in our results, might suggest that the VEP abnormalities found in our study

Is There a Place for Clinical Neurophysiology Assessments in Synucleinopathies? 305

In an event related potential (ERP) the P300 is a positive deflection peaking at approximately 300 ms after a stimulus. It is supposed to be an endogenous response, mainly depending on the processing of stimulus context, involving registration, evaluation and memory of stimuli, and categorization (decision/closure) and impinging on attention and arousal [28]. P300 can reliably be elicited with relatively simple paradigms, such as the "oddball paradigm", which requires the detection of a rare ("target") stimulus within a train of frequent irrelevant "non target" stimuli. Other complex paradigms include the administration of multiple stimuli, dichotic stimuli, multisensory modalities, in order to evaluate responses evoked from anterior brain regions. We recently performed a P300 study on patients with DLB in comparisons with patients with AD matched for dementia severity and age and with age matched control subjects [29] to look for differences of P300 responses in the two dementia subtypes and for possible correlations between P300 recordings and

P300 responses were recorded with Ag/AgCl electrodes from 19 derivations corresponding to Fp1, Fp2, F3, F4, C3, C4, P3, P4, O1, O2, F7, F8, T3, T4, T5, T6, Cz, Fz, Pz positions of the 10-20 International System with supplementary A1 and A2 derivations. Care was taken to avoid recordings if variations of body temperature, recent food ingestion, or previous-night sleep disturbances were present [30]. A classical auditory "oddball" paradigm was used. The stimuli were 500 Hz and 1000 Hz tones, designated as the "non-target" and "target" stimuli, respectively, and delivered by STIM System Headphones. Patients were instructed to count only "target" stimuli, aloud in a preliminary trial and mentally in subsequent trials. The presentation ratio of "non target/target" tones for training was 4/1-8/1 and during recording purposes 5/1. The intensity of the tone was 75 dBnHL, the duration of the stimulus was 150 ms (rise-fall and the plateau times 5 and 140 ms, respectively). The presentation rate was random with a minimum inter-stimulus interval of 1.1 seconds and a maximum interval of 4 seconds. Digital filters was set at 0.15 Hz and 100 Hz, and averaged with a dwell time of 0.5 ms, 2000 Hz sampling rate, 100 ms of pre-stimulus baseline recording. An artifact rejection system was calibrated on four supplementary derivations placed on eyebrows and inferior orbital ridges; the rejection system blocked the acquisition when eye movement exceeded 100 uV. As the mean reference is known to distort P300 distribution one earlobe was used as online reference, with offline averaging with the other

In each recording session, the correspondence between the counted and delivered stimuli was checked as described in previous studies [32] and stored on the hard disk. Sets where two or more targets had not been recognized or sets impaired by attention defects or false

In each patient and control 120 responses to non-target and target stimuli were averaged in a single Final Average (FA). Four Sub-Averages (SA) of only 30 responses to target stimuli were preliminarily obtained in order to assess reliability of P300 among the recording sessions. Finally, inter-subject Grand Averages (GA) were obtained in DLB, AD and control groups. N100, N200, and P200 were detected at the Fz, Cz and Pz electrode for each subject separately. Peak latencies of each component were measured from stimulus onset to the point of maximum voltage in the range of 50-150 ms and 150-250 ms respectively. P300 was identified, in a time window of 300-500 ms, according to the operating definition based on

EEG, as abnormal EEG variability was described in DLB [5].

**4. P 300 abnormalities** 

earlobe [31].

recognitions were discarded from analysis.

are dependent on the impairment of dopaminergic neural structures which regulate spatial frequency sensitivity. VEP findings were robustly confirmed in studies performed in animal models of PD [18, 19]. Despite the interest for the finding, only few confirmative studies were provided [15-17], most studies come from few laboratories devoted to this experimental approach. Guidelines for the use of VEPs in clinical practice only rarely suggested a role of VEPs in PD studies and VEPs were finally confined to the assessment of Multiple Sclerosis. Although the increased latency of the VEP in multiple sclerosis has in general been attributed to demyelination in the visual pathways, other mechanisms such as humoral factors, synaptic malfunction or changes in dendritic potentials may play a part. Such mechanisms may also be relevant to central nervous system disorders other than multiple sclerosis which have abnormal VEPs. Although the major clinical manifestations of PD involve the motor systems and the responsible pathology is located in the basal ganglia, there is evidence of more widespread disease, both pathologically, electrophysiologically and clinically. Only two studies explored the possible use of VEPs for the assessment of DLB [20,21] yet no comparison were presented with other forms of dementia. In MSA the visual system is believed to be spared and dopamine deficiency has been hypothesized to be less pronounced than in PD [22], even though the data in the literature are scarce and not unanimous and nothing on retinal dopamine content has been reported. Little information is available on VEPs and PERGs in MSA patients [22]. The main interest for studying responses elicited by patterns with pure chromatic contrast is that they allow recording of specific responses from colour-opponent pathways, anatomically and physiologically distinct from the achromatic ones at the retinal as well as the geniculate and cortical levels. A more recent study [23] showed that PERGs are virtually unaffected in MSA, whereas in early PD they are clearly impaired, suggesting different pathogenic retinal mechanisms and a useful simple tool for distinguishing MSA from PD. The strongest objection against the use of VEPs for the assessment of synucleinopathies derived from the technical constraints of VEP recordings: VEPs are altered by abnormalities of optic nerve and visual pathways, VEPs recordings require the adequate collaboration of patients who must focus attention on stimuli [24-26], VEP variable (amplitude, latency) are dependent on laboratories settings and must be adjusted according to each laboratory statistics of distribution.

The characteristic of VEP cannot be simply shared by different laboratories and differences in equipments might sustain variability which are far wider than variability observed in patient and control populations.

With the introduction of digital and led stimulating screen this condition worsened rather than improving [27].

In the age range of AD, DLB and PDD optic and visual abnormalities (cataracts, maculopathies, retinopathies, ischemic lesions) are frequent and might mislead possible diagnoses. In DLB, fluctuations of cognition (i.e. defective attention and collaboration to the task) are common and might impair the diagnostic yield of VEP recordings. It has been suggested that the discrepancies between different reports on VEP in Parkinson's disease may be due to the greater sensitivity of grating patterns compared to checkerboard patterns and, if so, this might in part account for our normal PD VEP latencies. The grating subtense used is about one third of that for the checkerboard, and the retinal field stimulated is predominantly foveal for the grating whereas for the checkerboard it extends beyond the perimacula. This could explain the observed differences rather than the pattern form, per se. We suggest that VEP recordings might still represent a "niche" research tool, but do not provide sufficient robustness in order to constitute a biomarker.
