Investigation And Assessment Of Mirror Neuron Activity For Rehabilitation Purposes
Özet
Mirror neurons, discovered on prefrontal cortex and subsequently on
inferior parietal lobule of macaque monkey, are a class of neurons that
become activated with both performing an action and observing the same
action. A similar system of neurons also exists in humans. On the basis
of features of the putative mirror neuron system (MNS) and its role in
action understanding and internal rehearsal (motor imagery) of actions,
this action observation-execution matching system has been proposed as
a new approach for training in the rehabilitation of patients with motor
impairment of the upper limb after stroke.
This thesis investigates the mu and/or beta frequency band suppression as
an index of the human mirror neuron system (MNS) in
Electroencephalography (EEG). Several experimental design and control
procedures were applied with the primary objective that the study might
be beneficial to motor rehabilitation programs of upper extremities for
stroke patients.
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In the first experiment, subjects observed different types of objectdirected
hand actions in order to explore whether observation of any of
these actions may have a relatively strong effect on MNS activity. Here,
EEG was recorded at electrode locations C3, C4, P3, P4, F7 and F8. The
results showed that all conditions were associated with a significant mu
band (8-12 Hz) desynchronization over the somatosensory cortex.
Further investigation of the effect of the visual stimuli on MNS revealed
the main effect of video stimuli of hand squeezing soft and hard springs,
at the frontal channels nearly corresponding to ventral premotor cortex
(vPMC) area of the brain. The activation of mirror neurons in this area
during action observation plays a crucial role in observational learning.
Based on these results, it was proposed that specific type of visual stimuli
may be implemented in the action observation-based treatment of stroke
patients to have a positive additional impact.
Recent evidence suggests that motor imagery might be beneficial to
recovery of motor functions after stroke. The implemented strategy in
imagery-based rehabilitation may have a crucial role to optimize the
imagery performance. In the second experiment, it has been explored if
prior execution facilitates the subsequent imagery performance when the
motor task to be imagined was associated with a symbolic cue. 10 healthy
participants were divided into two groups and performed the execution
and imagery of a sequential pinch grip task: one group started the
experiment by execution of the task (group named GEF) and the other
group performed the imagery session at first stage (group named GIM).
Event Related Spectral Perturbations (ERSPs) at mu (8-12 Hz) and beta
(15-25 Hz) frequency bands from EEG data were extracted for imagery
and execution conditions of 10 subjects over central, parietal and frontal
brain regions. The results showed that both simple execution and imagery
conditions were associated with a significant (p<0.05) mu and beta band
desynchronization over the somatosensory cortex. A significant main
effect of frequency was found during imagery condition of 10 subjects
and over all relevant channels. This supplies evidence that mu and beta
rhythms might have different functional properties for mental rehearsal
of actions. ERSP data from two experimentally manipulated groups
showed that brain activity (desynchronization) for imagery condition was
slightly higher for group GEF. Significant differences between two groups
were found at contralateral parietal and bilateral frontal sides. It was
concluded that for a cue-based simple motor task, a prior execution of
the motor task might facilitate the subsequent imagery task and frontal
regions appears to reflect the motor imagery performance. The results
will have further implications in imagery-based rehabilitation of patients
with stroke.
In the last experimental study of this thesis, a fully actuated finger
exoskeloton robot ExoPinch was utilized to investigate the anticipatory
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effect of execution on observation. The results showed that the
observational condition (with or without anticipation) interacted with
hemisphere at central channels near somatosensory cortex. Additionally,
the response of MNS was explored on the kinetics features of visual
stimuli. The results revealed an interaction effect of kinetics features and
hemisphere at frontal channels corresponding nearly to the ventral
premotor cortex area of the brain. The activation of mirror neurons in
this area plays a crucial role in observational learning. Based on the
results, it was proposed that specific type of visual stimuli can be
combined with the functional abilities of the MNS in the action
observation based treatment of hand motor dysfunction of stroke
patients to have positive functional motor responses.
