Motor overflow in schizophrenia

Behavioural and cerebral asymmetries of mirror movements are specific to rhythmic task and related to higher attentional and executive control

Mirror movements (MM) refer to the involuntary movements or contractions occurring in homologous muscles contralateral to the unilateral voluntary movements. This behavioural manifestation increases in elderly. In right-handed adults, some studies report asymmetry in MM production, with greater MM in the right dominant hand during voluntary movements of the left non-dominant hand than the opposite. However, other studies report contradictory results, suggesting that MM asymmetry could depend on the characteristics of the task. The present study investigates the behavioural asymmetry of MM and its associated cerebral correlates during a rhythmic task and a non-rhythmic task using low-force contractions (i.e., 25 % MVC). We determined the quantity and the intensity of MM using electromyography (EMG) and cerebral correlates through electroencephalography (EEG) in right-handed healthy young and middle-aged adults during unimanual rhythmic vs. non-rhythmic tasks. Overall, results revealed (1) behavioural asymmetry of MM specific to the rhythmic task and irrespective of age, (2) cerebral asymmetry of motor activations specific to the rhythmic task and irrespective of age and (3) greater attentional and executive activations in the rhythmic task compared to the non-rhythmic task. In line with our hypotheses, behavioural and cerebral motor asymmetries of MM seem to be specific to the rhythmic task. Results are discussed in terms of cognitive-motor interactions: greater attentional and executive control required in the rhythmic tasks could contribute to the increased occurrence of involuntary movements in both young and middle-aged adults.

Excessive motor overflow reveals abnormal inter-hemispheric connectivity in Friedreich ataxia

This study sought to characterise force variability and motor overflow in 12 individuals with Friedreich ataxia (FRDA) and 12 age- and gender-matched controls. Participants performed a finger-pressing task by exerting 30 and 70 % of their maximum finger force using the index finger of the right and left hand. Control of force production was measured as force variability, while any involuntary movements occurring on the finger of the other, passive hand, was measured as motor overflow. Significantly greater force variability in individuals with FRDA compared with controls is indicative of cortico-cerebellar disruption affecting motor control. Meanwhile, significantly greater motor overflow in this group provides the first evidence of possible abnormal inter-hemispheric activity that may be attributable to asymmetrical neuronal loss in the dentate nucleus. Overall, this study demonstrated a differential engagement in the underlying default processes of the motor system in FRDA.

Neuroleptic treatments and overflow movements in schizophrenia: are they independent?

Neurological soft signs (NSS) are minor neurological abnormalities that can be revealed by a clinical examination focused on sensory and motor information processing. NSS include overflow movements (OMs), which are defined as involuntary movements that may accompany the production of voluntary movements. OM is generally considered to be a characteristic feature of schizophrenia. White matter abnormalities might be involved in the pathogenesis of OMs. Dopamine receptors play a role in oligodendrocytes development. There is a direct link between antipsychotic agents that bind to dopamine receptors on oligodendrocytes and the development of oligodendrocytes and myelin formation. In this paper, we review the current knowledge of the effects of antipsychotic agents on NSS in schizophrenic patients. As a result of this critical review we hypothesize that the neuroleptic actions described in this paper could explain why antipsychotic agents have no effect on the resolution of NSS in patients with schizophrenia.

Interhemispheric control of unilateral movement

To perform strictly unilateral movements, the brain relies on a large cortical and subcortical network. This network enables healthy adults to perform complex unimanual motor tasks without the activation of contralateral muscles. However, mirror movements (involuntary movements in ipsilateral muscles that can accompany intended movement) can be seen in healthy individuals if a task is complex or fatiguing, in childhood, and with increasing age. Lateralization of movement depends on complex interhemispheric communication between cortical (i.e., dorsal premotor cortex, supplementary motor area) and subcortical (i.e., basal ganglia) areas, probably coursing through the corpus callosum (CC). Here, we will focus on transcallosal interhemispheric inhibition (IHI), which facilitates complex unilateral movements and appears to play an important role in handedness, pathological conditions such as Parkinson's disease, and stroke recovery.

Excessive contralateral motor overflow in schizophrenia measured by fMRI

Schizophrenia is characterized by significant problems in control of behavior; however, the disturbances in neural systems that control movement remain poorly characterized. We used functional magnetic resonance imaging (fMRI) to evaluate the origin of motor overflow in schizophrenia. Twenty-seven clinically stable medicated outpatients with Diagnostic and Statistical Manual, 4th edition, text revision (DSM-IV-TR)-defined schizophrenia (SZ), and 18 healthy control (HC) subjects, all right-handed, performed a dominant-handed, single-choice visual sensorimotor reaction time paradigm during fMRI. Voxel-wise analyses were conducted within sensorimotor cortical and striatal regions on general linear model (GLM)-derived measures of blood oxygen level-dependent (BOLD) signal change. The SZ group was not different from the HC group in reaction time, activation in somatosensory or motor cortices ipsilateral to the active (intended) descending corticospinal tract, nor visual cortex. However, in the right hemisphere (contralateral to the active M1), the SZ group showed significantly higher activation in primary motor cortex and adjacent premotor and somatosensory cortices (right Brodmann areas (BA) 1 through 4, and 6), and significantly lower activation in bilateral basal ganglia. Right BA 4 activation was strongly related to disorganization and poverty symptoms (and unrelated to medications) in the patient group. This study provides evidence in SZ of excessive neural activity in motor cortex contralateral to the intended primary motor cortex, which may form the basis for altered motor laterality and motor overflow previously observed, and disorganized behavior. This pathological motor overflow may be partly due to altered modulation of intended movement within the basal ganglia and premotor cortex.

Relative or absolute? Implications and consequences of the measures adopted to investigate motor overflow

Motor overflow is involuntary overt movement or covert muscle activity that cooccurs with voluntary movement. Overflow is present in several pathological conditions, as well as in neurologically healthy children and older adults, and can be induced in healthy young adults under effortful conditions. This motor phenomenon may provide insight into the underlying mechanisms and kinetic characteristics of voluntary and involuntary motor control in various populations. Although often measured behaviorally using force transduction techniques, different methods of calculating and presenting such overflow data have resulted in seemingly contradictory findings, with limited discussion of the advantages and limitations of different approaches. In this article, the authors examined the relevant literature to highlight significant methodological considerations for authors and readers conducting or appraising this type of research. Issues regarding the interpretation and reporting of findings are also discussed. Researchers are encouraged to continue using behavioral measures to create well-defined variables that enable the study of the kinematic characteristics of overflow, as these may offer promising new ways forward in better characterizing and understanding this intriguing movement phenomenon.

Finger muscle control in children with dystonia

BACKGROUND

Childhood dystonia is a disorder that involves inappropriate muscle activation during attempts at voluntary movement. Few studies have investigated the muscle activity associated with dystonia in children, and none have done so in the hands.

METHODS

In this study, we measured surface electromyographic activity in four intrinsic hand muscles while participants attempted to perform an isometric tracking task using one of the muscles.

RESULTS

Children with dystonia had greater tracking error with the task-related muscle and greater overflow to non-task muscles. Both tracking error and overflow correlated with the Barry-Albright Dystonia scale of the respective upper limb. Overflow also decreased when participants received visual feedback of non-task muscle activity.

DISCUSSION

We conclude that two of the motor deficits in childhood dystonia--motor overflow and difficulties in actively controlling muscles--can be seen in the surface electromyographic activity of individual muscles during an isometric task. As expected from results in adults, overflow is an important feature of childhood dystonia. However, overflow may be at least partially dependent on an individual's level of awareness of their muscle activity. Most importantly, poor single-muscle tracking shows that children with dystonia have deficits of individual muscle control in addition to overflow or co-contraction. These results provide the first quantitative measures of the muscle activity associated with hand dystonia in children, and they suggest possible directions for control of dystonic symptoms.

Neurological soft signs in schizophrenia: investigating motor overflow

Investigation of neurological soft signs (NSSs) in schizophrenia may allow for a greater understanding of its underlying pathology. Motor overflow, involuntary movement occurring during voluntary movement, is a NSS thought to occur to a greater degree in schizophrenia. The aim of the current study was to replicate the only objective investigation which found enhanced motor overflow in schizophrenia and to further characterise its properties in a more systematic manner than previous research. The current study involved examining motor overflow production in 30 participants (15 with schizophrenia, 15 controls). Participants exerted 25 and 75% of their maximal force output, while overflow was monitored in the passive hand using linear variable differential transformer (LVDT) units. Patients with schizophrenia not only exhibited a significantly greater degree of motor overflow, compared to controls, they also exhibited a differential pattern of overflow production. Direct investigation of the cortical processes leading to motor overflow may provide a more complete understanding of the pathological relevance of motor overflow, and by extension NSSs, in schizophrenia.

Transcranial Magnetic Stimulation at M1 disrupts cognitive networks in schizophrenia

Transcranial Magnetic Stimulation (TMS) is rapidly gaining acceptance as a non-invasive probe into brain functionality. We utilize TMS to study the connectivity of a simple motor network in patients of schizophrenia (N=19), and in healthy control subjects (N=9). TMS was used in an externally paced finger tapping task, perturbing the internal network oscillations invoked by the finger motion as it keeps pace with a metronome. TMS perturbations were synchronized to the metronome and applied to the network at the level of the primary motor cortex (M1). Contrary to initial expectations, TMS did not affect the sensorimotor synchronization of subjects with schizophrenia or their tapping accuracy. TMS did cause extreme deviations in the finger's trajectory, and altered the timing perceptions of subjects with schizophrenia. Additionally, it invoked high-level deficiencies related to attention and volition in the form of lapses, implying that the connectivity between modules in the brain that underlie motor control, sensorimotor synchronization, timing perception and awareness of action, can be disrupted by TMS in subjects with schizophrenia, but not in healthy subjects. The ability to disrupt high level network functions with perturbations to the lower level of M1 supports models describing deficits in connectivity of distributed networks in the brains of schizophrenia patients. It also demonstrates the use of TMS to probe connectivity between components of such networks.

The effects of age and attention on motor overflow production—A review

Motor overflow refers to overt involuntary movement, or covert muscle activity, that sometimes co-occurs with voluntary movement. Various clinical populations exhibit overflow. Motor overflow is also present in healthy children and the elderly, although in young adults, overt overflow is considered abnormal unless elicited under conditions of extreme force or muscle fatigue. Current theories of overflow imply that the corpus callosum may mediate production of this phenomenon. However, given that the corpus callosum is a conduit enabling the transfer of cortical information, surprisingly few studies have considered the cortical or subcortical structures underlying overflow. This review considers the developmental trend of motor overflow production, specifically in the upper-limbs, and the mechanisms thought to underlie this age-related phenomenon. Potential neurological correlates of motor overflow will be discussed in conjunction with higher order attentional processes which also regulate motor overflow production. Future research investigating the impact of attentional processes on overflow production may be particularly valuable for designing rehabilitation strategies for patients experiencing induced pathological overflow or conversely, to develop techniques to encourage the recovery of movement function in individuals with paretic limbs.

The influence of attention and age on the occurrence of mirror movements

This study utilised a finger force task to investigate the influence of attention and age on the occurrence of motor overflow in the form of mirror movements in neurologically intact adults. Forty right-handed participants were recruited from three age groups: 20-30 years, 40-50 years, and 60-70 years. Participants were required to maintain a target force using both their index and middle fingers, representing 50% of their maximum strength capacity for that hand. Attention was directed to a hand by activating a bone conduction vibrator attached to the small finger of that hand. Based on Cabeza's (2002) model of hemispheric asymmetry reduction in older adults, it was hypothesised that mirror movements would increase with age. Furthermore, it was expected that when the attentional demands of the task were increased, motor overflow occurrence would be exacerbated for the older adult group. The results obtained provide support for the model, and qualified support for the hypothesis that increasing the attentional demands of a task results in greater motor overflow. It is proposed that the association between mirror movements and age observed in this study may result from an age-related increase in bihemispheric activation that occurs in older adults, who, unlike younger adults, benefit from bihemispheric processing for task performance.

Investigating the cortical origins of motor overflow

Motor overflow refers to the involuntary movements which may accompany the production of voluntary movements. While overflow is not usually seen in the normal population, it does present in children and the elderly, as well as those suffering certain neurological dysfunctions. Advancements in methodology over the last decade have allowed for more convincing conclusions regarding the cortical origins of motor overflow. However, despite significant research, the exact mechanism underlying the production of motor overflow is still unclear. This review presents a more comprehensive conceptualization of the theories of motor overflow, which have often been only vaguely defined. Further, the major findings are explored in an attempt to differentiate the competing theories of motor overflow production. This exploration is done in the context of a range of neurological and psychiatric disorders, in order to elucidate the possible underlying mechanisms of overflow.