• 50-85 years of age, male or female

• Able to give informed consent

• Adequate visual and auditory acuity to complete the neuropsychological testing

• No presence or history of significant neurological or psychiatric disorders

• BDI ≥ 20, moderate depression

• No presence or history of inflammatory or autoimmune disorders

• Negative family history for neurodegenerative diseases

• Cognitively healthy (i.e., education-adjusted MoCA total score ≥ 26 points at screening)

• Female subjects must either be documented by medical records or physician's note to be either surgically sterile (by means of hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or post-menopausal for at least 1 year (no menses for 12 months without an alternative medical cause) or if they are of childbearing potential, they must commit to use of a highly effective contraceptive measure for the duration of the study and a minimum of six months following the PET scan (including combined \[estrogen and progestogen containing\] hormonal contraception associated with inhibition of ovulation \[oral, intravaginal, or transdermal\], progestogen-only hormonal contraception associated with inhibition of ovulation \[oral, injectable, or implantable\], intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, vasectomised partner or sexual abstinence).

• Male subjects and their partners of childbearing potential must commit to the use of a highly effective method of contraception during the study and for a minimum of three months following each PET scan (including, for female partners of childbearing potential, combined \[estrogen and progestogen containing\] hormonal contraception associated with inhibition of ovulation \[oral, intravaginal, or transdermal\], progestogen-only hormonal contraception associated with inhibition of ovulation \[oral, injectable, or implantable\], intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, male subjects with vasectomy or sexual abstinence).

• Male subjects must commit to not donate sperm during the study and for a minimum of three months after the last PET scan.

• Individuals must commit to refrain from drinking alcohol for 48 hours before each visit, refrain from drinking any caffeinated substance for 12 hours before the PET-MR visits, and to refrain from smoking or using any nicotine-containing products on the day of the PET-MR scans.

• Individuals must commit to not donating blood up to three months after the last PET scan.

• Individuals must commit to come to the screening and Day 1 visits in a fasting state (i.e., minimum of 8 hours since last meal/food intake).

• Individuals must commit to not to take any over-the-counter non-steroidal anti-inflammatory drugs or drink alcohol for 48h before screening visit.

• 50-85 years of age, male or female

• Able to give informed consent

• Adequate visual and auditory acuity to complete the neuropsychological testing

• No presence or history of other significant neurological or psychiatric disorders

• Diagnosis of PD according to the Movement Disorder Society Clinical Diagnostic Criteria (Postuma et al., Mov Disord 2015)

• Drug-naïve participants with PD must have a diagnosis of PD but must be therapy-free at the time of enrolment

• For participants with PD-MCI: diagnosis of MCI according the diagnostic criteria for MCI-PD (Level I; Litvan et al., Mov Disord 2012) and/or MoCA \< 23

• For participants with PD taking dopaminergic therapy: must be in stable therapy (i.e. not have changed therapy in the last 60 days)

• Female subjects must either be documented by medical records or physician's note to be either surgically sterile (by means of hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or post-menopausal for at least 1 year (no menses for 12 months without an alternative medical cause) or if they are of childbearing potential, they must commit to use of a highly effective contraceptive measure for the duration of the study and a minimum of six months following the PET scan (including combined \[estrogen and progestogen containing\] hormonal contraception associated with inhibition of ovulation \[oral, intravaginal, or transdermal\], progestogen-only hormonal contraception associated with inhibition of ovulation \[oral, injectable, or implantable\], intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, vasectomised partner or sexual abstinence).

• Male subjects and their partners of childbearing potential must commit to the use of a highly effective method of contraception during the study and for a minimum of three months following each PET scan (including, for female partners of childbearing potential, combined \[estrogen and progestogen containing\] hormonal contraception associated with inhibition of ovulation \[oral, intravaginal, or transdermal\], progestogen-only hormonal contraception associated with inhibition of ovulation \[oral, injectable, or implantable\], intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, male subjects with vasectomy or sexual abstinence).

• Male subjects must commit to not donate sperm during the study and for a minimum of three months after the last PET scan.

• Individuals must commit to refrain from drinking alcohol for 48 hours before each visit, refrain from drinking any caffeinated substance for 12 hours before the PET-MR visits, and to refrain from smoking or using any nicotine-containing products on the day of the PET-MR scans.

• Individuals must commit to not donating blood up to three months after the last PET scan.

• Individuals must commit to come to the screening and Day 1 visits in a fasting state (i.e., minimum of 8 hours since last meal/food intake).

• Individuals must commit to not to take any over-the-counter non-steroidal anti-inflammatory drugs or drink alcohol for 48h before screening visit.

⁃ For participants with iRBD:

• 40-85 years of age, male or female

• Able to give informed consent

• Adequate visual and auditory acuity to complete the neuropsychological testing

• No presence or history of significant neurological or psychiatric disorders

• BDI-II ≥ 20, moderate depression

• No presence or history of inflammatory or autoimmune disorders

• Negative family history for neurodegenerative diseases

• Cognitively healthy (i.e., education-adjusted MoCA total score ≥ 26 points at screening)

• Female subjects must either be documented by medical records or physician's note to be either surgically sterile (by means of hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or post-menopausal for at least 1 year (no menses for 12 months without an alternative medical cause) or if they are of childbearing potential, they must commit to use of a highly effective contraceptive measure for the duration of the study and a minimum of six months following the PET scan (including combined \[estrogen and progestogen containing\] hormonal contraception associated with inhibition of ovulation \[oral, intravaginal, or transdermal\], progestogen-only hormonal contraception associated with inhibition of ovulation \[oral, injectable, or implantable\], intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, vasectomised partner or sexual abstinence).

• Male subjects and their partners of childbearing potential must commit to the use of a highly effective method of contraception during the study and for a minimum of three months following each PET scan (including, for female partners of childbearing potential, combined \[estrogen and progestogen containing\] hormonal contraception associated with inhibition of ovulation \[oral, intravaginal, or transdermal\], progestogen-only hormonal contraception associated with inhibition of ovulation \[oral, injectable, or implantable\], intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, male subjects with vasectomy or sexual abstinence).

• Male subjects must commit to not donate sperm during the study and for a minimum of three months after the last PET scan.

• Individuals must commit to refrain from drinking alcohol for 48 hours before each visit, refrain from drinking any caffeinated substance for 12 hours before the PET-MR visits, and to refrain from smoking or using any nicotine-containing products on the day of the PET-MR scans.

• Individuals must commit to not donating blood up to three months after the last PET scan.

• Individuals must commit to come to the screening and Day 1 visits in a fasting state (i.e., minimum of 8 hours since last meal/food intake).

• Individuals must commit to not to take any over-the-counter non-steroidal anti-inflammatory drugs or drink alcohol for 48h before screening visit.