EEG investigation of gait and balance in Parkinson*s disease using immersive virtual reality

Alterations in balance, posture and gait are among the most important motor
symptoms of Parkinson*s disease (PD). With progress of the disease, they may
lead to serious impairments of walking mobility, ultimately in the form of
freezing of gait and falls. The physiological mechanisms behind the occurrence
of FOG are still not clear, but there is compelling evidence for a disturbance
in visuomotor processing.
EEG has become an important research tool for the investigation of the
motor pathophysiology of PD. This is due to the observation of increased
synchronization of brain oscillations in the beta frequency range (13-30 Hz).
Since the beta rhythm, recorded from scalp regions overlying the motor cortex,
shows strong task-related modulations in motor tasks, it also provides a means
to evaluate the effect of experimental interventions on the cortical control of
movement in PD, complementing behavioural measures.
The current state of incomplete understanding of parkinsonian gait problems
may be improved upon with research methods that allow the study of brain
activation patterns during locomotion with high temporal resolution. Recent EEG
studies of treadmill walking have demonstrated the feasibility of obtaining EEG
data of sufficient quality to assess intra-stride patterns of cortical
activation and deactivation, but to date EEG analysis during externally cued
gait performance has not been applied in PD. The limitations of treadmill
walking with regard to realistic optical patterns of movement, as opposed to
walking in a natural environment, can be compensated with virtual reality (VR)
methods. VR methods also afford an opportunity for systematically manipulating
the walking environment so as to investigate relevant factors affecting gait
and gait control.

For a more extensive background, we refer to pp 8-9 of the protocol.

The project aim is to optimize existing EEG methods for recording and analyzing
EEG data acquired during walking in combination with advanced VR methods for
the investigation and rehabilitation of gait and balance impairments. The
project aims to deliver a methodological contribution to their combined use.
The combined use will be directed at the investigation of visual information
processing in the service of gait control. Specifically, the project aims (i)
to clarify the effect, and possible benefit of visual cues on gait in PD, and
(ii) to elucidate the increased sensitivity of PD patients* gait to visual
information.

Primary Objective:
Assess and describe oscillatory EEG characteristics of supraspinal mechanisms
for gait control in Parkinson*s disease

Secondary Objectives:
- Assess the responsiveness of EEG rhythms involved in gait control to visual
information provided by visual cues
- Identify EEG correlates of visuospatial and visuomotor processes contributing
to visually induced gait impairment

The design is an observational study investigating electroencephalographic
brain activity during walking in patients with PD and healthy controls. EEG
activity is measured during walking on a treadmill, whilst the visual
environment is manipulated to compare groups under different conditions.
Two experiments are planned. The first experiment examines EEG activity during
walking with and without external visual cues projected on the ground. The
second experiment manipulates optic flow information, projected using a 180
degrees projections screen.

Experiment 1: Effect of visual cues on beta oscillatory activity during walking
Aim: Assess whether beneficial effects of visual cues are mediated by increased
reactivity of beta power
PD patients are known to have a reduced reactivity of beta oscillatory
activity, with an enhanced beta power that does not attenuate before and during
movement in the same way as in healthy controls. That is, the attenuation is
delayed in time and of lower amplitude. The experiment will test whether this
*sluggishness* of beta activity in PD is partly reverted by visual cues. Such a
result would (i) further underpin the pathophysiological significance of
abnormal beta activity in PD, and (ii) contribute to the explanation of cueing
benefits.

Experiment 2: Effect of optic flow information on oscillatory activity during
walking
Aim: Assess whether detrimental effects of visual information on walking are
mediated by changes in beta activity
Visual information can help (Experiment 1) as well as hinder movement
(Experiment 2). It is known that changing the direction and speed of optic flow
has a greater effect on walking velocity in PD patients than in healthy
subjects. Here we investigate whether this is expressed in changes in beta
reactivity. Of interest is further whether visuomotor processes mediating such
effects have an identifiable EEG signature.

For further details, we refer to pp 11-12 of the protocol.

There are no risks associated with the EEG measurements. Time burden is ~3 hrs
for the actual experiment (including preparation and debriefing). There is no
direct benefit for a patient or healthy subject in participating.