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

Abstract

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.

Mirror movements in healthy humans across the lifespan: effects of development and ageing

“…Several studies support the theory of an immature central nervous system that is most probably responsible, at the very least, for the exaggerated mirroring in children until the age of 10 3,4,23,24 . Our results additionally confirm previous data on the persistence of mirror movements during adulthood in healthy volunteers and the recurrent increase during later adulthood 7–9,25 . Greater motor overflow in the elderly has often been discussed as the result of compensatory mechanisms of impaired brain function and consecutive uninhibited bilateral cortical activation 8–10 .…”

“…Subtle mirroring of the upper extremities, however, can be observed in healthy adults. The intensity of this mirror activity is known to increase with more demanding motor tasks, muscle fatigue, decrease in attention, and advancing age 6–10 …”

Electromyographic analysis of joint-dependent global synkinesis in the upper limb of healthy adults: Laterality of intensity and symmetry of spatial representation

“…Consistent with previous studies based on occurrence frequency of mirror movement [6,25,30], our EMG finding accounting for non-homologous irradiation agreed with laterality of GS intensity during strenuous motor tasks. Moreover, laterality of GS intensity was directionally sensitive so that the difference in the amount of contralateral irradiation became marked specifically during flexion/abduction of the shoulder, flexion/extension of the elbow, and extension of the wrist (Fig.…”

Relative or Absolute? Implications and Consequences of the Measures Adopted to Investigate Motor Overflow

“…Overflow relative to target or achieved voluntary force acknowledges that this bimanual movement phenomenon is influenced by the capabilities of the active hand and the specific voluntary movement performed (Addamo et al, 2009b;Armatas & Summers, 2001;Armatas et al, 1994;Parlow, 1990;Post, Bayrak, Kernell, & Zijdewind, 2008;Todor & Lazarus, 1986a;Vardy, Daffertshofer, Ridderikhoff, & Beek, 2007). Nelles et al (1998) had stroke patients and controls perform unimanual repetitive and sustained squeezing tasks (see Table 1).…”