Dopaminergic Agents

Patients were investigated in a practical medication-off state, i.e., on the morning after overnight withdrawal (>12 h) of all dopaminergic drugs (meds-off). Kinematic data were recorded using two IMUs (Opal, APDM), at a sampling rate of 128 Hz, placed bilaterally on the outer anklebones. Each sensor was placed with its vertical axis aligned with the tibial anatomic axis. Surface leg muscle activity as measured by 10 EMG probes (FREEEMG 1000, BTS) was recorded bilaterally on tibialis anterior (Ta), soleus (S), gastrocnemius medialis (Gm), gastrocnemius lateralis (Gl), and vastus lateralis (Vl) at a sampling rate of 1000 Hz. Two transistor–transistor logic signals (TTL) were provided at the beginning and end of each trial to both EMG and IMU devices to make data synchronization possible. Patients started walking barefoot after a verbal signal at their self-selected speed along a large ellipsoidal path of about 60 m in length (Figure 1). We recorded between three and six trials (243 ± 71 s in duration) of unperturbed, steady-state, overground walking according to the clinical condition of each subject. Overall, 26 walking trials with a total duration of 105 min were obtained.

The online and offline recruitment advertisements for eligible participants (who are Chinese adults aged ≥ 18 years) were posted in the corresponding author’s university, centers of the local non-governmental organizations for social services, and general communities. Moreover, the referral of participants by Sheng Kung Hui Macau Social Services Coordination Office, a non-governmental organization which particularly provided counseling services for gamblers and families, was also adopted in the recruitment procedure. Individuals interested in this project would contact with the trained research assistant, who then arranged each participant’s schedule for participation in this study (i.e., clinical interview, self-reported questionnaire survey, and MRI scan).
Before taking the MRI scan, all the participants were interviewed by a psychiatrist, who had more than 5 years of experience on diagnostic interview of mental disorders at the psychiatric department of a public hospital in China. In this study, exclusion criteria included any self-reported physical disease, psychosis resulting from general medical conditions, mental illnesses (e.g., major depression, bipolar disorder, manic episode, and anxiety disorder), other severe medical conditions (especially taking dopaminergic medications and substance abuse), and/or family history of psychosis. According to the psychiatrist’s diagnostic assessment for participants’ past-year gambling experience, 32 participants were classified into the disordered gambler group and 57 participants were assigned to the healthy control group. All these participants were right-handed, but the data of one of them was removed from further analyses due to severe head motion during the MRI scan.
All participants were also asked to asked to fill out a questionnaire with the items regarding their demographics (e.g., sex and age) and GD symptoms (i.e., nine items listed in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders) (1 , 52 (link), 53 ). With a yes-no response scale, they reported whether they had experienced any of the nine symptoms (e.g., “Has made repeated unsuccessful efforts to control, cut back, or stop gambling.”) during the past year. Finally, our valid sample for data analyses consisted of 32 disordered gamblers (28 males/4 females) and 56 healthy controls (46 males/10 females). The average age of the gamblers was 38.27 (±12.68) years, whereas the average age of the healthy controls was 24.50 (±4.72) years (Table 1); moreover, the effects of sex and age were controlled for in all analyses. In addition, the average score of GD symptoms of the disordered gamblers was 5.63 (±2.61), while that of the healthy controls was 0.98 (±1.69), as shown in Table 1. The study acquired ethics approval from the Panel on Research Ethics (Sub-panel on Biomedical Science and Engineering) of the corresponding author’s university (reference number: BSERE20-APP014-ICI-01). Every participant gave their written consent before taking part in the study.