Neuropsychological deficits are recognized as primary
symptoms of psychotic disorders, since they are detected even in the early
stages, with some of them showing a more significant decline (e.g. executive
functions, memory, attention) and others a smaller but significant one (e.g.
language , movement perception, psychomotor). A wealth of neuropsychological
research over the past decade has contributed to elucidating the nature and
significance of cognitive dysfunction in schizophrenia. Today we know that patients
with schizophrenia show lower performance in all known neuropsychological tests
compared to healthy controls.
Schizophrenic deficits
in psychomotor speed
We know that schizophrenia is governed by deficits in
psychomotor speed [1,2]. Psychomotor speed refers to the time to process a
stimulus, prepare the response to that stimulus, and execute the response. It
has been shown that patients with schizophrenia are disadvantaged compared to
healthy individuals in tests of psychomotor speed [3]. However, this difference
does not always reach the significance level [4]. Of interest is the result of
the research by Riley and his colleagues (2000) that deficits in psychomotor
speed in schizophrenia appear as early as the first episode, reinforcing the
view that this area is greatly damaged by the presence of psychotic symptoms
[5]. Sweeney et al.'s (1991) study found improvement in psychomotor speed in
both first-episode schizophrenia patients and patients with a previous history
of psychosis, which is consistent with the view that neurocognitive deficits in
patients with schizophrenia remain relatively stable across the lifespan [6].
The depiction of
movement
Movement imagery is a mental process in which a
specific movement is internally simulated without actually performing the
movement. According to simulation theory, mental movements are essentially
movements that do not take place [7]. Much research has highlighted the
relationship between real movement and its corresponding mental representation
as well as common brain areas that are activated during planning and execution
in both cases, while both mental and real movement follow the same rules (e
.e.g. speed-accuracy, speed-curvature relationship) and maintain the same
temporal structure [8-12]. In addition, mental training improves motor
performance and enhances muscle strength [13-19]. Neuroimaging studies have
revealed a common activation of specific brain regions during both motor and
mental execution of a movement (parietal and prefrontal cortex, primary cortex,
basal ganglia and cerebellum) [20-24]. Research using movement imagery tests is
a useful and sensitive method of investigating the unconscious process of
representation [25]. Movement imagery has been widely used to investigate the
movement system in both healthy and clinical populations. The advantage of
investigating kinesthetic imaging is that the internal processes of real
movement that involve planning and planning can be studied. This element is
very important for the study of the production and execution of the movement
and the related deficits shown by patients of various categories such as
patients with psychiatric or neurological syndromes. In these patient cases the
ability or inability to produce or perform a movement can indicate whether the
relevant brain function has begun to be affected, to what extent it is
deficient, and the degree of progressive impairment. Deficits in mental imagery
of movement have been assessed in Parkinson's disease, prefrontal cortex
syndrome, motor - sensory cortex, and in multiple sclerosis [26-31].
Investigating the mental imagery of movement also helps psychomotor retardation
(Psychomotor retardation -PMR-) which is a central factor in the assessment of
clinical and therapeutic effects and can seriously affect the psychosocial
functioning of patients. Psychomotor rehabilitation modifies all of the
person's actions, including mobility, mental activity, and speech [32].
Schizophrenics' deficits
in motor mental imagery
Kinetic imagery is about being able to create
internal/mental images before they are executed. Patients with schizophrenia
have difficulty accurately tracking mental images of movement, and are unable
to produce accurate mental images of their own movements. Research has shown
that many of the first-order symptoms of schizophrenia, for example delusions
of control in which the patient believes that external forces are controlling
their thoughts or actions, can be characterized as deficits in reality
monitoring or self-monitoring of internally generated thoughts. For the
schizophrenic patient a self-control deficit, which manifests as an inability
to recognize his thoughts or actions as his own, is also auditory
hallucinations when these manifest as an inability to recognize inner speech as
self-generated. However, patients with schizophrenia are a heterogeneous group
of patients with deficits in attention, memory, and executive functions. Thus,
a difficulty to examine the hypothesis that they present difficulties and
deficits in motor mental imagery, is the use of neuropsychological tests that
usually concern cognitive abilities (such as attention and memory) that in one
way or another are presented as deficits in this group of patients. From a
neuropsychological point of view the parietal cerebral cortex is an interesting
area for research in patients with schizophrenia, since it receives information
from multiple sensory inputs, is crucial for the control of directed limb and
eye movements, and plays an important role in proprioception (somatotopographic
recognition). The two brain regions of the parietal cortex are involved in
different cognitive functions with the left region involved in speech and
movement processes, and the right region involved in processing spatial
representations and focusing attention on specific environmental stimuli.
Previous research has shown deficits in eye movement control and visual
attention in patients with schizophrenia, suggesting deficits in parietal lobe
function [33]. Frontal and parietal brain structures play an important role not
only in the control and execution of goal-directed movements but also in the
ability to recognize movements as individual. Neuroimaging studies
investigating the recognition of self-generated movements versus other
movements have shown increased activation in regions of the parietal and
frontal cortex that are critical for the control of goal-directed movements.
Interestingly, when hallucinating schizophrenics are asked to discriminate
between self-made hand movements and movements of a "foreign" hand,
they mistake the foreign movements as their own in 80% of trials. Also, the
conscious control of certain movements for patients with schizophrenia presents
particular difficulties. However, the question that has not been sufficiently
answered to date is whether these difficulties are exclusively related to
visual feedback of information or are related to a central deficiency in the
ability to visually motor coordination for the execution of goal-directed
movements of patients with schizophrenia. Motor mental imagery presupposes the
creation of an internal mental image of a movement and its mental projection
with successive individual images of the intended action. Tasks requiring motor
imagery are a good means of studying goal-directed movement for patients with
schizophrenia as well. Typically, when subjects are asked to imagine a movement
at a mental level the time required to mentally perform that movement will be
the same as the time to actually perform the movement.
