Kate E. Hoy

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.

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 Cabezas (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.

Motor overflow in Huntington’s disease

We investigated both motor overflow and ability to control voluntary movement in patients with Huntington’s disease (HD). We hypothesised that, compared with controls, overflow would be significantly greater in HD participants and that they would exhibit poorer control of voluntary movement. In a finger flexion task, participants had to maintain target forces representing 25, 50, or 75% of the maximum strength capacity for whichever finger was performing the task; overflow was measured in the corresponding finger of the non-responding hand. HD participants exhibited significantly greater motor overflow than controls, and more difficulty controlling the target force with the active hand. In addition, the degree of overflow in HD participants positively correlated with overall UHDRS motor symptom severity.The presence of exacerbated motor overflow in HD, and its correlation with symptom severity, is an important finding worthy of further investigation.

Using transcranial magnetic stimulation to investigate the cortical origins of motor overflow: a study in schizophrenia and healthy controls

BACKGROUNDnPrevious research has confirmed the presence of increased motor overflow in schizophrenia. There are essentially two theories regarding the cortical origins of overflow. Recent research suggests that both may be correct, and that the cortical origin of overflow is highly dependent upon the population in which it presents. Motor overflow, due to an abnormally active ipsilateral corticospinal tract, may indicate a potentially severe brain abnormality arising in early development. In contrast, bilaterally active corticospinal tracts accounting for overflow probably represent a naturally occurring response during fatiguing contractions.nnnMETHODnThe cortical origins of motor overflow in 20 participants with schizophrenia and 20 normal controls were investigated through the use of a number of transcranial magnetic stimulation (TMS) protocols.nnnRESULTSnEach of the experimental protocols employed independently supported the contention that overflow was originating in the hemisphere contralateral to the involuntary movement.nnnCONCLUSIONSnResults indicated that the origins of overflow in schizophrenia are the same as those seen in the normal control group, i.e. motor overflow seems to be due to the presence of bilaterally active corticospinal tracts. Potential explanations for greater motor overflow seen in schizophrenia are discussed.

Motor overflow in schizophrenia

The occurrence of motor dysfunction as a sign of schizophrenia, in addition to being a side effect of medication, has received considerable support in recent years. The current study aimed to systematically investigate both the presence and pattern of one such motor dysfunction, motor overflow. It was hypothesised that patients with schizophrenia would show significantly greater motor overflow than controls, and that the pattern of motor overflow occurrence would also vary significantly between the groups. A finger flexion task was used to examine the presence and pattern of motor overflow. Subjects were asked to maintain target forces, using either their index or small finger, representing 25, 50 or 75% of the maximum strength capacity for whichever finger was performing the task. Patients were found to exhibit significantly greater motor overflow than controls. There were also significant findings with respect to the patterns of motor overflow produced, specifically in regards to fine motor control and performance variability. In summary, patients differed significantly from controls in both the degree and pattern of overflow exhibited.

The mirror neuron system in schizophrenia

Introduction: Longitudinal studies of women with eating disorders report variable outcomes and there are few consistent predictors of outcome. Aim: The study aims were to describe the course and putative predictors of outcome of community women with disordered eating. Method: One hundred and twenty-two young women (mean age 28.596.3 years) identified in a general population based survey (1) with eating disorder symptoms of clinical severity agreed to participate in a follow-up study. The present paper reports on results at two years. Eating disorder symptoms, health related quality of life, general psychological function, help-seeking, and defence style were assessed at baseline, and two years by questionnaire. Results: Eighty-seven women (71%) completed the two year followup. Multiple linear regression analyses were used to identify demographic and other characteristics related to the EDEQ global score and to the SF12 mental score at the two year follow-up. At two years of follow-up the mean EDEQ global score was 3.1, 59.8% of women had experienced at least one day out of role during the past four weeks, and the mean SF12 mental component score was 38.0. In the multivariate model, a higher level of immature defence style and baseline binge eating severity, significantly predicted higher levels of eating disorder symptom severity at two years. A higher level of immature defence style, higher general psychological disturbance, lower BMI, and not reporting home duties as main work, were associated with poorer quality of life. Conclusions: The relevance of defence style to personality structure and as a main predictor of outcome in women with eating disorders will be discussed. Reference 1. Mond JM, Hay PJ, Rodgers B, Owen, C. Self-recognition of disordered eating among women with bulimic-type eating disorders: a community-based study. Int J Eat Disord in press.

A meta-analytic study of changes in brain activation in depression.

Objective:A large number of studies with considerably variable methods have been per- formed to investigate brain regions involved in the pathophysiology of major depressive disorder. The aim of this study was to use a quantitative meta-analytic technique to synthesise the results of much of this research.Methods:Three separate quantitative meta-analytical studies were conducted using the Activation Likelihood Estimation technique. Analysis was performed on three types of studies: (1) those conducted at rest comparing brain activation in patients with depression and controls; (2) those involving brain changes following antidepressant treatment; and (3) those comparing brain activation patterns induced by the induction of positive or negative emotion in patients with depression com- pared with controls.Results:There appears to be a complex series of areas of the brain implicated in the pathophysiology of depression although limited overlap was found across imaging paradigms. This included a network of regions including frontal and temporal cortex as well as the insula and cer- ebellum that are hypoactive in depressed subjects and in which there is increase in activity with treat- ment. There was a corresponding set of subcortical and limbic regions in which opposite changes were found.Conclusions:There is limited overlap between the brain regions identified using differing imaging methods. The most consistently identified regions include areas of the anterior cingulate, dorsolateral, medial and inferior prefrontal cortex, insula, superior temporal gyrus, basal ganglia and cerebellum. Further research is required to identify if different imaging methods are identifying complementary networks that are equally involved in the disorder.Hum Brain Mapp 29:683-695, 2008. V C 2007Wiley-Liss,Inc.