Determination of Cerebellar Dominance from Muscle Tone 
of the Limbs

Summary

Objective:
Is the more pronounced physiological passivity of the left upper and lower extremities (UE, LE) in right-handed individuals equally present in the right limbs of left-handed subjects? May we define cerebellar dominance from this information?

Methods:
Muscle tone of the limbs was investigated in healthy 18–57 years old individuals (n = 69) considered right-handed (n = 26) or left-handed (n = 35) as assessed by the Edinburgh Inventory. Impaired ambidextrous (n = 8) were excluded. Muscle tone was ascertained: a) by conventional clinical examination of passivity in the shoulder, elbow, wrist, knee and instep; b) by 10 times repeated and registered number of UE swings fallowing a fall from forward arm raise, the number of shank swings following a fall from extension in sitting individuals, forearms falling from extension in prone position and after patellar and tricipital reflexes. The data were analysed using the chi-squared test of independence in 2 × 2 contingency tables; graphical presentations are based on statistical significance of percent predictive values. Number of swings was evaluated using the 2-way ANOVA model.

Results:
Right-handed females (n = 13) and right-handed males (n = 13) had a reduced muscle tone in 90% of left UEs and 65% of left LEs. Unlike right-handed, only 50% of left-handed females (n = 21) and left-handed males (n = 14) had an increased muscle tone on both extremities. The lateral difference in muscle tone, more manifested on UE, was not as evident in left-handers as in right-handers. The different pendular responses were significant in falling of forearms (p = 0.026) and in patellar reflex (p = 0.030).

Conclusions:
Right-handers represent a more homogeneous group. The asymmetry of muscle tone in left-handed does not correspond to the simple traditional concept of cerebellar dominance contralateral to the dominant hemisphere of the brain.

Key words:
muscle tone – cerebellar dominance – dextrals – left-handed – ambidextrous