Is backward disequilibrium in the elderly caused by an abnormal perception of verticality? A pilot study.

OBJECTIVE

We hypothesised that backward disequilibrium (BD), defined by a posterior position of the centre of mass with respect to the base of support, could be caused by a backward tilt in the perception of verticality.

METHODS

The relationship between BD, the perception of verticality, and the history of falls in 25 subjects aged 84.5+/-7.4 years was analysed. An original ordinal scale, the BD scale (BDS), was used to quantify BD. Postural (PV) and haptic verticals (HV) were measured in sagittal plane.

RESULTS

BDS scores closely correlated with the number of falls (r = 0.81, p =10(-5)). The more the PV was tilted backward, the greater the BDS scores (r = -0.95, p<10(-6)), with a huge backward tilt of about 15 degrees in 4 subjects with severe BD. In these subjects, the tilt in perception of verticality was transmodal since a severe backward HV tilt was also found.

CONCLUSIONS

This transmodality suggested high-order cognitive disruption in the construction of the subjective vertical used in postural control by subjects showing BD, which confirmed our hypothesis.

SIGNIFICANCE

This study clearly shows that perception and action with respect to gravity are closely related and brings a new insight about fall mechanisms in the elderly.