Action Observation for Neurorehabilitation in Apraxia

Abstract

Neurorehabilitation and brain stimulation studies of post-stroke patients suggest that action-observation effects can lead to rapid improvements in the recovery of motor functions and long-term motor cortical reorganization. Apraxia is a clinically important disorder characterized by marked impairment in representing and performing skillful movements [gestures], which limits many daily activities and impedes independent functioning. Recent clinical research has revealed errors of visuo-motor integration in patients with apraxia. This paper presents a rehabilitative perspective focusing on the possibility of action observation as a therapeutic treatment for patients with apraxia. This perspective also outlines impacts on neurorehabilitation and brain repair following the reinforcement of the perceptual-motor coupling. To date, interventions based primarily on action observation in apraxia have not been undertaken.

Full text

PERSPECTIVE
published: 03 April 2019
doi: 10.3389/fneur.2019.00309
Frontiers in Neurology | www.frontiersin.org 1April 2019 | Volume 10 | Article 309
Edited by:
Giorgio Sandrini,
University of Pavia, Italy
Reviewed by:
Marianna Capecci,
Polytechnical University of Marche,
Italy
Marialuisa Gandolfi,
University of Verona, Italy
*Correspondence:
Mariella Pazzaglia
mariella.pazzaglia@uniroma1.it
Specialty section:
This article was submitted to
Neurorehabilitation,
a section of the journal
Frontiers in Neurology
Received: 30 August 2018
Accepted: 11 March 2019
Published: 03 April 2019
Citation:
Pazzaglia M and Galli G (2019) Action
Observation for Neurorehabilitation in
Apraxia. Front. Neurol. 10:309.
doi: 10.3389/fneur.2019.00309
Action Observation for
Neurorehabilitation in Apraxia
Mariella Pazzaglia 1,2
*and Giulia Galli 2
1Department of Psychology, University of Rome “La Sapienza,” Rome, Italy, 2IRCCS Fondazione Santa Lucia, Rome, Italy
Neurorehabilitation and brain stimulation studies of post-stroke patients suggest that
action-observation effects can lead to rapid improvements in the recovery of motor
functions and long-term motor cortical reorganization. Apraxia is a clinically important
disorder characterized by marked impairment in representing and performing skillful
movements [gestures], which limits many daily activities and impedes independent
functioning. Recent clinical research has revealed errors of visuo-motor integration in
patients with apraxia. This paper presents a rehabilitative perspective focusing on the
possibility of action observation as a therapeutic treatment for patients with apraxia. This
perspective also outlines impacts on neurorehabilitation and brain repair following the
reinforcement of the perceptual-motor coupling. To date, interventions based primarily
on action observation in apraxia have not been undertaken.
Keywords: apraxia, action recognition, action execution, mirror activity, neurorehabilitation
INTRODUCTION
Apraxia encompasses a broad spectrum of higher-order purposeful movement disorders (1) and
is most often associated with neurological damage to left-hemisphere (2). The accepted definition
of apraxia includes deficits in performing, imitating, and recognizing skilled actions involved in
the intentional movements, colloquially referred to as gestures (3). Pathological conditions such as
apraxia result from an inability to evince the concept of specific actions (4) or to execute related
motor programs (5). Classically, apraxia is diagnosed when a patient presents with an inability
to execute gestures in response to verbal commands or imitate with different effectors (mouth,
hand, or foot) (4), including movements involving the non-paretic limb ipsilateral to the lesion[s].
Although apraxia primarily affects motor activities, studies report that higher impairment levels
may be related to visuo-motor integration (6). Recent evidence supports the notion that apraxia
influences skilled acts in the environment, interferes with independent functioning, impedes daily
activities, and affects the performance of routine self-care (7,8); that is, persons may have difficulty
brushing their teeth (9), eating (7), preparing food (10), and getting dressed (11). As a consequence,
patients with apraxia can develop severe anxiety and reductions in the spontaneous use of social
gestures (12), leading to isolation and depression (13) and consequent delays in returning to
work (14).
Almost 50% of patients with left-hemispheric stroke (15) and ∼35% of patients with Alzheimer’s
disease and corticobasal degeneration (16–18) develop apraxia that persists after illness onset
and affects functional abilities. Research to aid in the development and optimization of apraxia
neurorehabilitation is crucial. Several approaches for the treatment of apraxia deficits are currently
in practice [for a review see (19,20)], including verbal (21) or pictorial (22) facilitation and the
use of physical cues based on repetitive behavioral-training programs with gesture-production
exercises. The errorless completion method represents another recent approach (23). Autonomy in

Pazzaglia and Galli Neurorehabilitation and Apraxia
activities of daily living tends to be underestimated (24),
and rehabilitation studies remain limited due to the nature
of disturbances to automatic/voluntary dissociations (i.e., an
ability to execute actions only in natural settings). To date,
no rehabilitation treatment or therapeutic possibilities based
primary on action observation has been studied in apraxia.
THE VALUE OF ACTION OBSERVATION IN
TREATING APRAXIA
Language disorders among patients with apraxia who suffer from
concomitant aphasia suggest that defects in gesture imitation,
rather than gestures in response to verbal commands, are more
sensitive indicators of apraxia (25). Goldenberg has proposed
that imitation apraxia could be primarily considered a deficit of
perceptual analysis (26). Evidence from several studies indicates
that perceptual and motor codes are closely associated (27,
28) and that patients with apraxia may be defective both in
performing motor acts and in the perceptual code necessary to
represent the appropriate gesture. Sunderland and Sluman have
shown, for example, that problems orienting a spoon in a bean-
spooning task suggest an inability to remember the correct action
and to judge the correctness of the perceived action (29).
Although apraxia is commonly considered a motor
impairment, deficits in intact gestural perception are not
uncommon, occurring in 33% of one sample (30). Such
patients, who exhibit deficits in the execution of actions,
also commit errors when judging between correctly and
incorrectly performed acts (30–32), understanding the meaning
of pantomimes (33,34), discriminating among action-related
sounds (35,36), matching photographs of gestures (26), engaging
visuo-motor temporal integration (6), and predicting incoming
observed movements (37,38).
Movement-execution effects in apraxia thus are not purely
motor processes and visual representations of given actions may
influence the actions’ execution by visuo-motor transfer (39). The
integrity of gesture representations has important implications
for rehabilitation strategies (40). The spatial and temporal use
of a body part for the planning of a tool-related action and
the imitation of others’ actions involve an inherent perceptual
component, which can be disturbed following apraxia onset. As
a result, modern assessments of apraxia include evaluations of
gesture understanding (32,41).
VISUAL-MOTOR STRATEGIES IN THE
REHABILITATION OF PATIENTS WITH
LIMB APRAXIA
The notion of common representations for both executed and
observed actions is of considerable interest in the applied field
of stroke neurorehabilitation (42,43). Despite the use of state-
of-the-art apraxia-evaluation batteries (44) to explore perceptual
deficits in the understanding of actions in patients with apraxia,
few studies have proposed new rehabilitation programs that
include elements of both observation and execution of actions.
Smania et al.’s (45) clinical examinations of 43 left brain-
damaged patients with apraxia revealed defective performances
in gesture execution and imitation, as well as in the recognition
and identification of transitive and intransitive gestures. For their
study, approximately half of the patients received training in
ecological action production and comprehension; the other half
underwent conventional language rehabilitation for the same
number of treatment hours. The training, which combined the
observation and execution of observed actions, consisted of three
progressive phases, each characterized by increasing degrees of
difficulty, obtained by phased reductions of facilitation cues as
performance improved. After ∼30 sessions, therapists recorded
significant improvements: approximately 50% improvement in
the ADL scale and an average of 40% in the praxis test (22). When
only considering apraxia patients with cortical lesions primarily
in the fronto-parietal network, the improvement was even greater
(45). No significant performance changes were observed in the
outcome measures of control patients who did not undergo
specific programs of gesture production/observation exercises.
Interestingly, authors reported a significant improvement in
gesture recognition performance after the apraxia treatment,
and a correlation was found between gesture comprehension
tests and the ADL questionnaire (ADL-gesture comprehension:
R=0.37, p=0.034) (22). These results suggest that the positive
effects of this rehabilitative approach in apraxia require parity
in the treatment of both the motor and the perceptual aspects
of action processing (45). Of note, beneficial effects persisted
for at least 2 months and extended to the daily living activities
even of untreated actions, helping patients attain functional
independence from their caregivers (22).
Goldenberg and Hagmann (9) developed a particularly
successful restorative method in which training comprised two
different methods. The first aimed at helping patients to learn and
correctly execute complete activities, with therapists providing
different support at all clinical steps (e.g., by demonstrating
gesture execution and asking patients to imitate them), and
reducing the support only when patients were able to perform
these steps on their own. The second aimed at directing patients’
attention to the functional meaning of objects’ individual features
and details, critical for various actions. This two-step procedure
ensured a double reinforcement of the action’s perceptual-
motor code: the first online within the simultaneity of the
demonstration and the second off-line as a delayed imitation.
The combination of these two methods led to significant
improvements in trained ADL, but virtually no generalization of
training effects was observed between trained and non-trained
activities. The therapy’s success was preserved among those
patients who performed the activities at home but not among
those who did not. In a subsequent study (46), the authors
developed a slightly different variant to previous approaches
in which patients carried out entire activities with a minimum
of errors. In this approach, the functional commonalities
between different objects were emphasized by providing verbal
instructions and visual and gestural support. Effects of these
treatments lasted up to 3 months after the treatment ended.
Compensatory treatment indicate that the patients showed
large improvements in ADL functioning after rehabilitative
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Pazzaglia and Galli Neurorehabilitation and Apraxia
programs aiming at teaching visual strategies to overcome the
apraxic impairments during execution of everyday activities (47).
Patients were taught strategies to compensate internally (e.g.,
self-verbalization or imagination) or externally (e.g., observation
of pictorial cues) the distinct phases of a complex action, while
performing the daily activities (47–50).
All described interventions included elements of visuo-motor
integration and seemed to indicate that motor and visual
relearning in these patients was inextricably intertwined (see
Table 1).
Perceptual approach has been successfully applied to a
different rehabilitative intervention showing how action
observation has a positive effect on the performance of a specific
motor skill [for a review see (41,52,53)]. Patients watch a specific
motor act presented in a video clip or in a real demonstration,
and simultaneously (or thereafter) performed the same action.
A match (or mismatch) between visual signals and the gesture
performed drive re-learning about how the limb should move
in order to perform the motor act accurately (see Figure 1
for a hypothetical model on apraxia). Correctly reproducing
temporal (56,57), spatial (58), and body coding (59) helps
characterize movements, facilitate the motor patterns that
patients have to execute, and stimulate a rapid online correction
of movement (58,60,61). Observation combined with physical
practice in a congruent mode leads to increased motor cortex
excitability, and synaptic and cortical map plasticity strengthens
the memory trace of the motor act (62). Differently, rehabilitative
training based on physical practice alone (300–1,000 daily
repetitions) elicits only minimal neural reorganization (63). This
combined visual-motor therapy has been shown to improve
motor performance in patients that suffered a chronic stroke
(64–86), patients with Parkinson’s disease (87–92), children
with cerebral palsy (93–97) and elderly individuals with reduced
cognitive abilities (98). Electrophysiological studies have also
reported positive effects of action observation on the recovery
of motor functions after acute and chronic stroke (71,99).
This non-invasive, inexpensive, user-friendly approach works
more quickly on biological effectors (mouth, limbs, and trunk),
promoting better and faster recovery.
A NEURAL SUBSTRATE FOR ACTION
OBSERVATION AND EXECUTION IN
APRAXIA REHABILITATION
The inextricable link between action perception and execution
was first posited in the ideomotor theory, which has been
validated through delineation of the brain network, known as
the mirror neuron system (MNS). Inspired by single-cell (“mirror
neuron”) recordings in monkeys (100,101), many neuroimaging
and neurophysiological studies have suggested that the adult
human brain is equipped with neural systems and mechanisms
that represent both the visual perception and execution of actions
in a common format (102). Action deficits among the patients
with apraxia may be described at multiple levels. While these
levels partially overlap, four levels of hierarchical modeling at
which an MNS mechanism can support an observed action
(42,103) are as follows:
(i) kinematic: Patients with apraxia frequently present with
abnormalities in kinematic movements in the form of motor
patterns that are slower, shorter, and less vertical than those
of individuals without apraxia (104);
(ii) motor: Limb apraxia interferes with the selection and
control of the hand-muscle activity (105). Moreover,
it interferes with the formation of appropriate hand
configurations for using objects (106);
(iii) goal: Understanding the immediate purpose of an action is
impeded; for example, patients with apraxia are impaired
access to mental representation of tool use (33);
(iv) intention: Patients present with an altered ability to monitor
the early planning phases of their own actions (107).
The cortical areas have been shown to contain mirror neurons
that are often described as a part of an integrated sensorimotor
information system underpinned by neural activity in the frontal
(103), parietal (108), and superior temporal sulcus areas. This
system is called the action observation network (AON) (109).
In humans, these cortical regions mediate the observation of
actions that form a part of the observer’s motor repertoire (41).
They also contribute to the imitation (110) and comprehension
(111) of these movements, and are involved in skill acquisition
(112). Lesion symptom mapping studies have reported gestural
deficits in patients with apraxia, which are most frequently
apparent following lesions in the inferior frontal lobe (30,113–
116), and in supramarginal and angular gyrus (37,113,115,
117) of the left hemisphere. However, apraxia has also been
observed in patients with damage in posterior middle temporal
lobe, anterior temporal lobe (37,113,115,117), occipital, and
subcortical regions (6,118,119). Despite the damaged neural
substrate was not constant across all the studies, it includes the
areas that are considered crucial for the AON. Undoubtedly, the
mirror neurons just provide a part of the complex information
for achieving action comprehension while action recognition
and production occur simultaneously by accessing the same
neural representations. However, as posited by the influential
cognitive neuropsychological models of apraxia (120,121) and
demonstrated by various clinical studies (121–124), the range
of possible dissociations between action execution and action
understanding that can occur in patients with apraxia is quite
multifaceted and cannot be explained by a mere action mirroring
mechanism nor by a single lesion locus. Impairments in the
visual recognition of action paralleled deficits in performing
these actions could depend on both common and distinct
neural localization, most of which could be external to mirror
regions. Failures in imitating or in recognizing gestures may
occur because of damage at any level in the process between
perceiving (input lexicon) and performing (output lexicon) an
action (120,121). Indeed, some apraxic patients show deficits
in the recognition/discrimination of the gestures, some do not
[for a review (125)]. Theoretical and empirical studies suggest
that complementary routes to action understanding taking place
on the dorso-dorsal and ventro-dorsal stream (126,127). Lesion
in ventral-dorsal stream may impede the top-down activation
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Pazzaglia and Galli Neurorehabilitation and Apraxia
TABLE 1 | Apraxia intervention studies.
References Number of participants Treatment
duration
Type of
action
Control Intervention Perceptual aspects
of training
Improvements in
experimental group
No effect
Experimental
group
Control
group
van Heugten
et al. (47)
33 30 min for 12
weeks
Everyday
activities
Strategy training Observation of picture
sequences Imagination
ADL Barthel Index
Apraxia Test Motor
functioning
Goldenberg and
Hagmann (9)
15 5 weeks Three
activities from
the domains
eating,
dressing, and
grooming
Direct training of
the activity:
errorless
completion of the
activity
The patients perform
action immediately after
observing the
therapist’s
demonstration
10 patients improved
on all three trained
activities
6 months later,
improvement is
not maintained
without practice
Smania et al. (45) 6 7 35 sessions,
three per
week
Transitive
action
Intransitive
action
Imitation
Aphasia
therapy
Gesture
recognition
Gesture execution
Observation of picture
(context, object)
Gesture recognition
Imitation
Apraxia Test Gesture
recognition
Verbal
comprehension
Oral apraxia
Donkervoort et al.
(48)
42 48 8 weeks Everyday
activities
Occupational
therapy
Strategy training Observation of picture
sequences Imagination
ADL Barthel Index Apraxia Test ADL
untrained
Goldenberg et al.
(46)
6 4 weeks Four everyday
activities
Explorative training
vs. Direct training
of the activity
The patients perform
action immediately after
observing the
therapist’s
demonstration
Direct training of activity
reduced errors and
amount of assistance
Exploration
training had no
effect on
performance
Smania et al. (22) 18 15 30 sessions,
three per
week
Transitive
action
Intransitive
action
Imitation
Aphasia
therapy
Gesture
recognition
Gesture execution
Observation of picture
(context, object)
Gesture recognition
Imitation
Apraxia Test Gesture
recognition ADL
Verbal
comprehension
Oral apraxia
Geusgens et al.
(50)
56 57 25 sessions,
8 weeks
Action of daily
living
Occupational
therapy
Strategy training Observation of picture
sequences
ADL untrained
Geusgens et al.
(49)
29 25 sessions,
8 weeks
Action of daily
living
Strategy training Observation of picture
sequences
Apraxia Test ADL
trained ADL untrained
Barthel Index
Functional Motor
Test
Bolognini et al.
(51)
6 6 3 sessions,
10 min
Limb gesture
imitation
Sham
stimulation
Anodal tDCS on
the left parietal
cortex
Imitation (observation
+execution)
Imitation execution tDCS on the motor
cortex
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Pazzaglia and Galli Neurorehabilitation and Apraxia
FIGURE 1 | Hypothetical model for performing and recognizing a transitive action [adapted from (54) and (55)]. Failures in performing or recognizing gestures may
occur because of damage at any stage in the directional flow between perceiving (input) and performing (output) the action. The observation of a video clip or a real
demonstration of action can have a positive effect on the selection and retrieval of the correct movement. In figure the example of grasping a cup of coffee. After the
correct visual identification of the object as a cup, patients with apraxia have a difficult retrieval of the correct action associated with that object. When an incorrect
movement is performed, a discrepancy occurs between the (correct) action observed on the model and the perception of own (incorrect) performed gesture.
Combining motor training and action observation may enhance the relearning of daily actions and strengthen the visuo-motor coupling.
of motor engrams. It may produce disturbances in the on-
line selection and integration of distinctive and relevant motor
acts that ensure a high recognizability of the gesture (117).
This can be responsible for the disordered motor planning,
imitation, and motor-memory recall of gesture movements found
in patients with apraxia (126,127). As has been briefly shown,
many questions remain, and there may be more than one
mechanism leading to apraxia disturb. Given the complexity
of the impairment and the separate neural substrates that
are typically affected in apraxia, treatments related to action
observation to support action execution or relearning of gestures
of daily living, can be planned.
NEUROREHABILITATION AND BRAIN
REPAIR AFTER APRAXIA
The behavioral success of rehabilitation methods based on the
principle of action observation should promote reorganization
by adaptive plasticity at the neural level (128,129). Functional
reorganization clearly depends on the residual neural integrity
of efferent (motor) and afferent (sensory) information, which
leads to improved treatment outcomes among some apraxia
patients but not for others. In this perspective, we considered
three possible sources of informational content for how
neurorehabilitation and brain repair after apraxia works: injury
site, elapsed time after apraxia onset, and lesion size.
The first factor to consider is the location of the infarct,
which can ultimately determine the outcome of rehabilitation
treatment. Whereas, lesions of the frontal and parietal cortices
in the left hemisphere have been shown to primarily disrupt
gesture production in patients with apraxia (2), no clear
correlation has been found between lesion location and
impairment in visual gesture representation. Apraxic patients
with cortical lesions—but not those with subcortical lesions—
cannot comprehend the meaning of gestures (130). In rare
cases, a lesion in the left occipito-temporal cortex may also
critically hamper the ability to recognize gestures in patients
with apraxia (120,131). Patients with parietal lesions have also
been reported to exhibit significant impairments in executing
gestures but only slight impairments in understanding those
performed by others (132). The neural specificity of this
disturbed typology may explain why certain patients with
apraxia are able to comprehend the meaning of gestures
despite being unable to perform them themselves. Accordingly,
single-case and group studies report dissociations between
action execution and representation and the underpinning
damaged neural substrate (121–124). Efficiency and speed of
the therapeutic means of action observation depend partly
on the different roles that intact and damaged brain regions
play in both action production and recognition (125,133).
Neural damage to a functional system can be partial, and
studies in monkeys seem to suggest that the frontal and
parietal cortices are neurally equipped for such divisions of
labor (134).
Several studies have documented that neurorehabilitation
techniques involving observation strategies among brain-
damaged patients induce long-lasting neural changes in the
motor cortex, potentiating activity in the affected areas. In
brain-damaged patients, TMS studies have found direct evidence
of increased motor-cortex excitability (84), and synaptic and
cortical map plasticity have been documented using fMRI (75).
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Pazzaglia and Galli Neurorehabilitation and Apraxia
TMS studies have also indicated that action observation alone
is able to drive reorganization in the primary motor cortex,
strengthening the motor memory of observed actions among
young (135) and elderly subjects (mean ages: 34 and 65 years,
respectively) (98) and among chronically brain-damaged patients
(84). Additionally, a study reported positive effects on gesture
imitation of anodal transcranial direct current stimulation
(tDCS) on the left parietal compared to sham tDCS, supporting
the view that apraxia disorders in Parkinson (136) and in brain
left damaged patients (51) can be improved by stimulating
distinct structures.
A second factor to consider is the temporal stage of the illness.
The neural substrates of action production and comprehension
could be associated with different physiological mechanisms at
different temporal stages of apraxia. Frontal and parietal areas
may become temporarily inactive because of cerebral edema
and intracranial hypertension, hemodynamic signs of ischemic
penumbra, or local inflammatory effects in acute but not chronic
stages of apraxia (137). Different studies report that during
early periods (including an acute four-week, post-onset phase),
impaired gesture recognition may be associated with left frontal–
lobe and basal-ganglia lesions (138), whereas in the chronic stages
of the illness, these deficits can be associated with left-parietal
lesions (32,37).
In practice, transitory effects such as the inability to mimic
actions from visual cues are often observed in apraxia’s early
stages. If so, an observation intervention in early therapy may
be inefficacy.
During later apraxia stages, a close overlap of the networks
underlying observation and execution, as indicated by advanced
neuroimaging and the lesion locations studies in patients, are
helpful in identifying patient in which observative approach
is potentially useful. Observation therapy associated with
adaptive neurophysiological and neurometabolic changes can be
conducted even several years after stroke onset. A session of 4
weeks of active, 18 days-cycle visual/motor training has been
found to significantly enhance motor function, with increases
in the activity of specific motor areas that possess mirror
properties (75). Massed, high-frequency rehabilitative training
(300–1,000 daily repetitions) is needed to elicit minimal neural
reorganization (63). These increases in cortical activity during
both action observation and execution also tend to be present
in the hemispheres (139,140) close to and far from the
lesion site.
A third possible factor to consider is that the failure to link
perceptual and motor representations in apraxia treatment may
be an effect of infarct size; larger lesions are more likely to include
front parietal injury and may not benefit from observation
treatment. Indeed, improvements in imitation (reproduction
off-line of the observed gesture) in patients with apraxia are
influenced by the size of the parietal lesion (51): the larger
the left parietal damage, the smaller the tDCS treatment-related
improvement. When a functional system is completely damaged,
however, recovery is achieved largely by process of substitution
and may depend on the implicit engagement of neural systems to
take over the functions of the damaged areas (141).
Whereas, some systems may constitute the sites of gesture
performance, others may reduce the impact of deficits (142)
by stimulating coupled visual knowledge mechanisms (98). The
integrity of both the frontal and parietal cortices might be crucial
for re-learning as a result of motor mirroring. Nonetheless, non-
injured cortical areas could also trigger additional, independent
internal mechanisms that support but are not necessary for
guiding the motor system to match vision with motor routines
(143,144). Studies on the neural representations of motor skills
based on observations of the motor cortex of macaque monkeys
(145) and humans (146) provide empirical support for such
an alternative system. These studies suggest that congruent
activity during action execution/observation occurs even outside
the canonical “mirror area,” representing a potential general
property of the motor system. Targeting interventions on the
basis of specific brain structures intact and damaged that could
mediate the effects of training is an important future challenge in
cognitive neurorehabilitation.
CONCLUSION
While research on the relationship between observed and
executed actions in apraxia neurorehabilitation has a short
history, it has already provided insights about the positive effect
of a visual-motor training. The observation of actions through
a process of visual retrieval may help in the selection of the
most probable action, providing a powerful tool for overcoming
intentional motor-gestural difficulties (55). Moreover, tailored
interventions based on individual’s ability to acquire new (or
relearn old) motor-memory traces through multisensory [i.e.,
auditory (35,147), olfactory (148,149), and tactile (150–
155)] feedback may be the most promising approach for a
normal temporal integration action (156,157). Multisensory
stimulation can activate multiple cortical brain structures,
inducing cortical reorganization and modulating motor cortical
excitability for the stimulated afferents (158,159). Results
are encouraging, but it is important to emphasize that this
hypothesis does not imply that all deficits in apraxia can
be treated by action observation therapy. Rather, we believe
that action observation might be a therapeutic option for
improving praxis function among certain specific typologies
of patients.
AUTHOR CONTRIBUTIONS
MP: study concept and design, manuscript development, and
writing. GG: contributed to the writing of the manuscript.
FUNDING
This work was supported by the Italian Ministry of Health
(RF-2018-12365682 to MP).
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Pazzaglia and Galli Neurorehabilitation and Apraxia
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Conflict of Interest Statement: The authors declare that the research was
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Frontiers in Neurology | www.frontiersin.org 10 April 2019 | Volume 10 | Article 309