Time processing is fundamental to survival and goal reaching in humans. Different time scales (seconds, minutes, and beyond) are processed through specific cognitive processes involving different neural representations. It is generally agreed that time scale in seconds-to-minutes range named "interval timing" would be anatomically linked to the striatum. Indeed, it is possible to demonstrate a deficit of interval timing processes in patients suffering from striatal damage (Huntington's disease). However, recent findings show involvement of a second brain structure, the hippocampus, in interval timing processing in the minutes range, suggesting an interaction between the striatum and hippocampus. Presumably, patients with hippocampal damage (Alzheimer's disease) would specifically show a decrease in performance for this minutes-range time scale. This study aims to provide a better understanding of the role of the striatum in the treatment of time and its interactions with other brain structures such as the hippocampus. More specifically, it is unclear whether the striatum plays a platform role that would always be involved regardless of the time scale, as suggested by the unified model of time or whether different brain structures is solicited according to the time scale, as suggested by the modular system model. In order to elucidate these issues, a potential double dissociation between brain structures and time scales will be tested.

In that aim, we will evaluate patients with Huntington's disease and patients with Alzheimer's disease by developing and using time processing paradigms comparing short and long time scales.

Inclusion Criteria:

• Huntington's disease gene carriers

  • Patient included in the BioHD protocol

  • Age from 18 to 90 years old

  • Symptomatic patient

  • TFC ≥ 11

  • UHDRS motor> 5

  • Native language: French

  • Affiliation to a social security or to another social protection

  • Signature of informed consent

    • Patients with Alzheimer's disease

  • MMS from 20 to 26 (included)

  • Age: from 60 to 90 years old

  • Native language: French

  • Progressive deterioration of memory reported by patient or caregiver for more than 6 months

  • Profile at RL /RI 16: no significant improvement with indexing

  • Episodic memory disorder isolated or associated with other cognitive disorders

  • MRI: Atrophy of the median temporal lobe

  • Affiliation to a social security or to another social protection

  • Signature of informed consent

    • Healthy subjects

  • Healthy subject included in the BioHD protocol

  • MMS ≥ 26

  • Age from 18 to 90 years old

  • Native language: French

  • Affiliation to a social security or to another social protection

  • Signature of informed consent

Exclusion Criteria:

• Huntington's disease gene carriers

  • Intellectual deterioration preventing understanding of the protocol
  • Other dementia than Huntington's disease
  • Patient living alone at home
  • Major depression
  • Patient under legal protection
  • Patient deprived of liberty
  • Pregnant or breastfeeding woman, situation known to the investigator
  • Inability to handle an electronic tablet

• Patients with Alzheimer's disease

  • Intellectual deterioration preventing understanding of the protocol
  • Patient living alone at home
  • Sudden onset of memory impairment
  • Early onset of the following symptoms: difficulty in walking, convulsions, changes in behavior
  • Focal neurological characteristics including hemiparesis, sensory loss, visual field deficit
  • Early extrapyramidal sign
  • Other dementia than Alzheimer's disease
  • Major depression
  • Cerebrovascular disease
  • Toxic, metabolic or infectious anomaly
  • Patient under legal protection
  • Patient deprived of liberty
  • Pregnant or breastfeeding woman, situation known to the investigator
  • Inability to handle an electronic tablet

• Healthy subjects

  • Intellectual deterioration preventing understanding of the protocol
  • Known neurological or psychiatric illness
  • Patient under legal protection
  • Subject deprived of liberty
  • Pregnant or breastfeeding woman, situation known to the investigator
  • Inability to handle an electronic tablet