Scientific background and rationale: Motor sequence learning (MSL) is composed of three phases: initial acquisition or rapid learning occurs during the first practice session, characterized by a rapid increase in motor performance; consolidation comes next, in the following hours, with a stabilization or even an increase in performance without additional practice; finally, slow learning allows long-term memorization of the skills acquired after several practice sessions. Motor sequence learning is an essential ability at any age but is altered with aging. Furthermore, the repetition of movements required for MSL may be tiring for the most vulnerable individuals. There is thus a need to develop the use of alternative and effective methods of MSL in the elderly. Mental practice (MP) based on motor imagery (MI) and anodal transcranial direct current stimulation (a-tDCS) are such innovative methods that have shown a positive impact on MSL in older adults. On the one hand, motor imagery training relates to mentally practicing movements without actual execution. This method has been shown to advantageously complement or even replace physical practice. Nevertheless, for fine and gross motor skills, the association MP/physical practice (PP) has been little studied in healthy elderly subjects. On the other hand, tDCS is a safe and noninvasive brain stimulation method used to modulate cortical excitability and enhance neuroplasticity. It has been shown that an anodal stimulation of the primary motor cortex (M1) immediately after the acquisition of a sequence of finger movements (manual task) enhanced consolidation in healthy elderly people. These effects have, however, never been tested for more ecological sequential tasks involving the whole body (body task).

Aim: The main aim of this study is to investigate the effects of a-tDCS on the consolidation of complex manual and body tasks, after MP alone, PP alone, and MP + PP in older adults.

A secondary aim is to test the effects of MP alone, PP alone and MP + PP in the acquisition of these complex manual and body tasks, in older adults.

A third aim is to test the evolution of electroencephalographic (EEG) activity between rest and motor imagery of these tasks, and, for motor imagery, before and after training.

Inclusion Criteria:

• Male or female
• Aged between 65 and 80.
• Mastery of the French language.
• Available for the entire study.
• Right-handedness of the upper limbs with a score > 0.5 on the Edinburgh laterality test (Oldfield, 1971).
• Right-handedness of the lower limbs with a score of ≥ -6 on the Waterloo laterality test (Waterloo, 1980).
• Cognitively preserved with an MMSE score ≥ 25 (Mini Mental State Examination, GRECO version, 2003).

Exclusion Criteria:

• A refusal to participate in the study or to sign the consent.
• No coverage by a Social Security plan.
• A deprivation of civil rights (guardianship, tutorship, protection of justice).
• A Body Mass Index (BMI) > 25kg/m2.
• A nap every afternoon.
• A psychiatric, neurological or motor disorder.
• A visuospatial empan < 3 on the Corsi block test (Corsi, 1972).
• A depression score > 5 on the Yesavage Geriatric Depression Scale (Yesavage et al., 1982).
• A walking aid (cane, walker).
• A fall during the last 12 months.
• A risk of falling, with a score > 14s on the Timed Up and GO (TUG, Podsiadlo & Richardson, 1991).
• A difficulty in standing or moving, grasping or manipulating objects.
• A disabling pain in the upper and/or lower limbs.
• The presence of osteoarthritis or arthritis in the fingers of the left hand and lower limbs.
• A chronic disease (rheumatoid arthritis, fibromyalgia, multiple sclerosis...).
• An injury to the left hand and/or lower limbs that is less than 3 months old.
• A surgery on a joint that is less than 6 months old.
• Current or past practice of an activity involving strong manual dexterity (piano, guitar, typing, etc.) or coordination of the lower limbs (dance, rhythmic gymnastics, English boxing, etc.) for more than 3 hours per week.
• An inability to perform motor imagery with a score of 10 on the Kinesthetic and Visual Imagery Questionnaire (KVIQ, Malouin et al., 2007) as well as an imagined time/actual execution time ratio > 1.5s on the mental chronometric test.

Common exclusion criteria applied for the safe use of tDCS:

• No significant neurological history (e.g., history of migraines, traumatic brain injury resulting in a loss of consciousness, epilepsy or history of epilepsy);
• No history of alcohol and/or substance abuse;
• No psychiatric illness;
• No metallic implants (intracranial electrodes, surgical clips, pacemaker)
• No wound scalp or skin condition (psoriasis, eczema).

This is a double-blind study for the tDCS part. Participant will be blind to the type of stimulation (sham or real tDCS). The experimenter will be also blind to the type of stimulation using the "study mode" implemented in the stimulator device that encodes sham and real stimulation mode using predefined numeric codes.