Christine Armatas

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.

Mirror movements in normal adult subjects

Intensity of mirror movements occurring under specific task conditions in normal adults was investigated using a finger flexion task. Subjects were asked to sustain target pressures using different fingers. Greater pressures of mirror movement were recorded when the weaker, small finger of either hand performed the task. The target pressure which subjects were asked to sustain did not influence the amount of mirror movement exhibited by either males or females, even though higher target forces required a significantly greater percentage of total finger strength. On average, males exhibited the same quantity of mirror movements as female subjects, despite the force requirements of the task representing for them a significantly smaller percentage of total finger strength. Moreover, when the right hand performed the experimental tasks, less mirror movement was exhibited than when the left hand was active. Thus, the left hand showed stronger mirror movements. The findings were consistent with previous research using children as subjects, although the nonsignificant effects of gender and pressure were unexpected and need to be examined further. It appears that, while the force requirement of the task does influence the magnitude of mirror movement, it is not the principle determinant.

Surfing: an avenue for socially acceptable risk-taking, satisfying needs for sensation seeking and experience seeking

Abstract Whether the personality characteristics of sensation seeking and openness to experience and participation motives differ between participants in the high-risk sport of surfing (n=41) and participants in a low-risk sport (golf; n=44) was investigated. Multivariate analysis indicated that surfers are characterised by higher levels of sensation seeking, as measured by the Sensation Seeking Scale-V (Zuckerman, 1983) and Openness to Experience, as measured by the NEO-Personality Inventory Revised (Costa & McCrae, 1992). Surfers also demonstrated higher levels of Intrinsic Motivation, measured by the Sports Motivation Scale (Pelletier et al., 1995) than golfers, while both groups demonstrated similar levels of Extrinsic Motivation. These results suggest that personality factors, together with types of participation motives, may be useful in discriminating between participants in low- and high-risk sports, which in turn could be used to promote surfing as a positive risk-taking pursuit.

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.

Handedness and performance variability as factors influencing mirror movement occurrence.

A finger flexion task was used to investigate the effect of hand preference and performance variability on intensity of mirror movement. Right- and left-handed subjects were asked to maintain target forces, with either their index or small finger, that represented 25, 50, or 75% of their maximum strength capacity for the active finger. Greater mirror movement occurred when the small finger was active, and where there was greater variability in task performance, while mirror movement intensity was less when the dominant hand and the index finger were active. These findings were consistent with the cortical activation explanation of motor overflow (Todor & Lazarus, 1986a), and suggest that task variability is an important factor influencing motor overflow production. It was concluded that, if performance variability reflects the efficiency of cortical activation underlying control of a voluntary task, then refined cortical control decreases the potential for motor overflow to occur. However, it is necessary to clarify the relationship between hand preference, performance variability, and motor overflow, perhaps by examining the neural pathways involved in motor overflow production.

Impacts of an Online-Supported, Resource-Based Learning Environment: Does One Size Fit All?

This paper reports on the use of an online, resource-based learning (RBL) approach in first year psychology at Deakin University. Differences between on- and off-campus students that emerged are examined in the context of the learning goals and study approaches of the two student groups and their attitudes to using computers. Unlike the on-campus students who were less positive about working with computers and reported confusion about how and what to study for the unit, the off-campus students reported feeling confident they had a good study strategy and were more positive about computers. The off-campus students also reported that they spent more time working with electronic resources and attached greater value to them. While all students valued the prescribed resources, the off-campus students found some of the optional, electronic resources valuable because they added to the learning experience. These students also reported greater use of the computer-mediated communication available as part of the online learning environment, and valued this functionality more highly than did the on-campus students. These findings highlight the need to take into account learner characteristics when designing learning environments that cater for individual differences and preferences. While online-supported RBL approaches have the potential to cater to the diverse needs of students, learning environments need to be designed, structured and delivered so the learning experience can be customized to the needs of different student cohorts, while preserving the overarching, pedagogical goals.

Strength as a factor influencing mirror movements

Abstract A finger flexion task was used to investigate intensity of mirror movement. Subjects were asked to maintain target forces, with either their index or small finger, that represented 25, 50 or 75 percent of their maximum strength capacity for the finger performing the task. Relative to the force produced, males and females exhibited the same amount of mirror movement. However, mirror movement relative to force exerted was greater when the left hand performed the task, a finding consistent with previous research. Greater amounts of mirror movement were recorded for movements of the small finger compared to the index finger, consistent with the cortical activation explanation (Todor and Lazarus, 1986). These results suggest that strength differences are not the principal determinant of intensity of mirror movement. Rather, differing functional roles of the hands and fingers, reflecting differences in cortical activation and organisation, appear to mediate the intensity of mirror movement occurrence.

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.

The Influence of Task Characteristics on the Intermanual Asymmetry of Motor Overflow

The two studies reported here were designed to test the proposition that greater motor overflow occurs when movements are performed by the non-dominant hand. Unlike previous studies using normal adults, the task in these studies did not require force production. In the first study, a group of 19 right-handed participants performed unweighted finger lifting. That the frequency of motor overflow occurrence was the same regardless of which hand performed the task, did not support findings from other studies where tasks involving force production resulted in more overflow when performed by the non-dominant hand. To investigate further the influence of task characteristics on motor overflow occurrence, in the second study participants were required to remember and reproduce a prescribed sequence of four finger lifts. Left- and right-handed participants (N =30) performed both single and sequenced finger lifting. The relative frequency of motor overflow (unintended lifts of fingers of the passive hand) was compared between hand preference groups, active hand and task type (single/sequenced). Contrary to the expectation that motor overflow would be greater for the sequenced finger lifting task, overflow was exhibited with a significantly greater frequency on single finger lifting. This finding indicates that task characteristics influence the pattern of overflow occurrence in normal adults. The task used in this study did not involve force production and did not result in an intermanual asymmetry of motor overflow. This contrasts with findings from other studies requiring adults to exert forces where greater overflow occurred when the non-dominant hand was active. However, this study confirms previous findings which show that left-handers produce greater overflow compared to right-handers regardless of the task being performed and the hand performing the task.

Measurement of Body Image Satisfaction Using Computer Manipulation of a Digital Image

The authors investigated a method for assessing body image satisfaction based on computer manipulation of a digitized image of self using a sample of 56 female students aged 17 to 22 years. The total percentage change when re-sizing the actual image to the ideal by the computer adjustment method was significantly correlated with the figural/silhouette discrepancy method. Both of these measures were correlated significantly with body part satisfaction and body mass index but not with social physique anxiety. Although for this sample the 2 methods yielded similar results, the computer adjustment method addresses several limitations of the figural/silhouette method, such as scale coarseness and the accuracy of proportional change between figural/silhouettes. Furthermore, by using the individuals actual image, potential confounds associated with stylized figure drawings that are typically based on Caucasian physical features are removed. Finally, this method also takes into account the importance of various body parts for determining body image satisfaction.