Just Noticeable Difference Threshold of Passive Limb Motion Sense in Patients with Parkinson's Disease

Kinaesthesia, the perception of one’s body and limbs, is essential for intact motor control. Impairments in kinaesthesia commonly arise after peripheral nerve damage, and recent research indicates that kinaesthetic acuity is reduced in patients a dysfunction of the cerebro-basal ganglia loop (Maschke et al., 2003). Although the basic neurophysiology of limb perception is understood today, there is a paucity of psychophysical data on the kinaesthetic sensitivity of humans across the lifespan. This psychophysical study will systematically investigate the ability of humans to discriminate between two movement speeds of a limb. Specifically, the experiment will determine the just noticeable difference threshold (JNDT) for passive forearm motion in healthy adults and patients with Parkinson’s disease. We plan to recruit 32 healthy young adults with age 18~30, 32 elder adults with age 55~70 and 32 mild to moderate Parkinson’s disease patients. We will employ a custom-built passive motion apparatus and use established psychophysical methods to determine the just noticeable difference thresholds of passive forearm motion. The apparatus will not produce any audible noise or vibrations to be used as cues by the subject to detect the onset of motion. Without vision, participants will rest their arms on a padded splint, which will be passively moved by a torque motor causing either elbow flexion or extension. We will use the adaptive algorithm to generate speeds. Each trial presented a pair of angular velocities separated by a 2 second inter-stimulus interval. Each pair of stimuli consists of one standard velocity and one comparison velocity. We will test two standard velocities (1.5 /s - fast condition; 1.0 /s - slow condition).Using a forced-choice paradigm subjects indicated at the end of the trial, whether the angular velocities of the two stimuli were the “same” or “different The dependent variable is Δ stim, which is the difference of angular velocity between standard and comparison velocity in each trial. The independent variables are groups (young vs. old vs. patients with Parkinson’s disease), standard velocities (fast vs. slow) and testing hand (dominant hand vs. non dominant hand). A total of 240 trials will be administered (60 trials for each condition). The range of comparison velocities was 1.0~2.85 deg/s for the slow condition and 1.5 ~2.85 deg/s for the fast condition. Four JNDTs will be determined and they are the difference between the standard and a comparison velocity (Δ stim) when a probability of 75% or 50% correct response was achieved. Repeated measured ANOVA will be used to examined the group difference. This study will address the following questions: a) What is the just noticeable difference threshold of passive limb motion in healthy adults and patients with Parkinson’s disease? b) Is the sensitivity different between fast and slow standard speeds? and c) Does dominant hand affect the sensitivity to discriminate two different velocities? d) Is sensitivity different between affected and unaffected hand in patients with Parkinson’s disease?

Project ID:PB10007-7232
External Project ID:NSC100-2410-H182-015-MY2