Functional magnetic resonance imaging (fMRI) studies have shown decreased activation in many locomotor areas of the brain in people with Parkinson's disease. This decreased activation impairs the ability to change the pace of walking. The use of external signals reduces the pressure on the internal regulation of walking timing.
The use of rhythmic auditory signals improves gait parameters in people with Parkinson's disease. Rhythmic auditory signals presumably serve as an external stimulus and alleviate the alteration of internal synchronization in Parkinson's disease.
It is important to note that the literature is closely focused on the use of faster tempo. This is probably due to the fact that most investigators seek to increase the speed of walking in order to increase the motor capacity of the sick. In addition, it has been suggested that the use of slower frequencies increases the risk of falls.
The walking speed is a function of both the cadence and the length of the step. Thus, when walking on the floor, the cadence changes induced by the auditory signals can increase the speed of walking, but without requiring a patient to increase the length of his steps.
The authors hypothesize that on a treadmill, people with Parkinson's disease will increase the step length with a slow-tempo metronome signal (85% of normal tempo) due to the fixed speed of the treadmill, and will keep this length of their step on the ground with a fast-tempo metronome signal (which increases the perception of their speed).
Indeed, the authors observed that the stride lengths were longer when walking with slow time signals on the treadmill only, while the stride length was unchanged during walking on the floor.
These results probably come from a mixture of biomechanical and neuroanatomical mechanisms. The combined use of treadmill learning and rhythmic auditory signals can therefore improve the mechanics of walking on the floor, in a way that the patient could not have achieved independently.