Exogenous Effects of Standard Medical Care (Dopamine) on Motor Learning of an Upper Limb Task in Parkinson Disease

Exogenous Effects of Standard Medical Care (Dopamine) on Motor Learning of an Upper Limb Task in Parkinson Disease

Exogenous Effects of Standard Medical Care (Dopamine) on Motor Learning of an Upper Limb Task in Parkinson Disease

The study determines whether standard medical care (dopamine) affects learning and retention of an upper limb feeding task in people with Parkinson's disease (PD) and whether training on the feeding task generalises to performance on an untrained upper limb buttoning task. Half the participants will train on the feeding task after they have taken their first dose of dopamine for the day (i.e. "on" medication state), while the other half will train on the same feeding task before taking their first daily dose of dopamine (i.e. "off" medication state).

Parkinson disease (PD) is an age related neurodegenerative disorder with symptomatic declines in motor function due to a loss of dopaminergic neurons within the basal ganglia. Ironically, treatment with exogenous dopamine-replacement medication (e.g. levodopa) may have positive effects on existing motor skills such as handwriting or walking, but may have detrimental effects on the learning of motor skills necessary for effective rehabilitation. Although dopamine medications are routinely prescribed to replace lost dopamine in the sensorimotor areas of the striatum, they may actually be "overdosing" the associative striatum, a candidate neuroanatomical correlate for motor learning. To date, however, this 'overdose' hypothesis has not been widely tested, given that few studies of motor learning in PD have reported or controlled for whether individuals were tested "on" or "off" their dopamine replacement medication.

Participants will train on the upper limb feeding task before taking their first daily dose of standard dopamine medication for Parkinson's disease, i.e. while "off" dopamine replacement medication

Participants will train on the upper limb feeding task after taking their first daily dose of standard dopamine medication for Parkinson's disease, i.e. while "on" dopamine replacement medication

Participants will spoon two raw kidney beans at a time from a center proximal "start" cup to three distal "target" cups positioned 16 cm away at 45°, 90° and 135° around the start cup as fast as possible using their non-dominant hand. Spooning two beans between the start cup and a target cup is considered one repetition; each trial will consist of 15 repetitions. Participants will perform 50 trials per day for 3 consecutive days.

Task performance (response time) at initial retention, adjusted for baseline (first trial of acquisition on Day 3)

Immediate decrement (difference in response time between initial retention and the last trial of acquisition) in task performance, adjusted for baseline (first trial of acquisition)

Delayed decrement (difference in response time between delayed retention and the last trial of acquisition) in task performance, adjusted for baseline (first trial of acquisition)

Rate of improvement (c) modelled on the exponential decay function: y = a + be(exp[-x/c]), where a is the final trial time value that the exponential decay function approaches (ie, asymptote), b is the scale of the learning from the first trial time to the value a, x is the trial number, 1/c is the number of trials needed to obtain asymptote (ie, 1 - e-1).

Time taken to complete the Nine Hole Peg Test at delayed retention, adjusted for baseline (Nine Hole Peg Test score at baseline, i.e. 3 days prior to the first block of training)

Time taken to complete the Buttoning task at delayed retention, adjusted for baseline (Buttoning task score at baseline, i.e. 3 days prior to the first block of training)

Inclusion Criteria: Idiopathic Parkinson's disease confirmed by neurologist Hoehn and Yahr stages 1 to 3 On a stable dose of antiparkinsonian medication for the past month and will continue on this regime for at least another subsequent month Walks unaided Exclusion Criteria: Not taking dopamine replacement therapy With prior surgical management for PD (e.g. deep brain stimulation) With medication-resistant freezing of gait Significant cognitive impairment (Montreal Cognitive Assessment score <18) Unstable medical conditions Other neurological conditions Unable to follow instructions or safely complete the training tasks