The mental repetition of movements - or motor imagery (MI) practice - facilitates motor learning. It allows avoiding fatigue that occurs during physical practice; this method is thus particularly interesting for elderly people. Transcranial direct current stimulation (tDCS) is a noninvasive method of neurostimulation during which a low direct current is applied to the brain via electrodes placed on the scalp. This method has been successfully used to enhance motor learning in both young and elderly subjects.

The main aim of this study is to assess the impact of MI practice combined with tDCS on the learning of a complex finger sequence, in young and elderly subjects.

For that purpose, young and elderly healthy subjects will be randomly assigned to Stimulation and Sham groups. There will thus be a total of four groups: Young Stim, Young Sham, Elderly Stim, and Elderly Sham.

All subjects will participate to three training sessions spread over five days, and a retention test one week after the third training session.

During training they will mentally repeat a complex finger sequence with the left hand, for 13 min:

• Subjects of the Stimulation groups (Young Stim and Elderly Stim) will receive in parallel an anodal tDCS of the primary motor cortex.
• Subjects of the Sham groups (Young Sham and Elderly Sham) will receive in parallel a sham tDCS of the primary motor cortex.

Immediately before (pretest) and after (posttest) each training session, as well as during the retention test, subjects will repeat the sequence as many times of possible, for 1 min. During these tests (pretests, posttests and retention test) electroencephalographic activity will be recorded to assess the Mu rhythm power.

Inclusion Criteria:

• Being aged between 20 and 35 years for the young subjects / between 65 and 80 years for the elderly subjects
• For elderly subjects: Mini Mental State Examination (MMSE) ≥ 24
• Being a male or a female
• Being right handed
• Taking an effective method of contraception for the women of childbearing age
• Having signed the consent form
• Being registered with a social security scheme

Exclusion Criteria:

• Presenting a neurologic, psychiatric or motor trouble

• Practicing or having practiced at least 5 hours by week an activity involving a high manual dexterity (e.g. piano)

• Showing any contraindication to tDCS:

  • History of epilepsy
  • head trauma with loss of consciousness
  • Implanted material (pacemaker, surgical clips, metal specks in the skull, etc.)
  • Past neurosurgical intervention
  • Open sore on the scalp
  • Consumption of more than three glasses of alcohol daily
  • Use of drugs
  • Pregnancy (positive pregnancy test)