Superior Colliculus Activity in Parkinson Disease: a Potential Marker?
Condition: Parkinson's Disease
MeSH terms: Parkinson Disease
Study type: Observational

Summary: 
      The ultimate goal of this project is to evaluate a possible new strategy to diagnose earlier
      Parkinson's disease, using the superior colliculus as a biomarker.

      Preliminary data from the investigator's group in a rat model of Parkinson's disease suggest
      that the superior colliculus, a sensory structure, show an early deficit in visual
      processing. The investigator's data also suggests that with the evolution of the disease,
      this structure presents a neuronal re-organisation leading which causes a sensory rebound
      after the introduction of the treatment. The light responses in the superior colliculus were
      faster, bigger in amplitude and lasted longer (Rolland et al., 2012). Those results raise an
      important question about the superior colliculus functional state in Parkinson's patients. If
      this structure have a similar neuroplasticity, the investigators could hypothesize that the
      superior colliculus may also present a sensory rebound when introducing the treatment. If
      this hypothesis is true, the accelerated and amplified light responses of this structure may
      explain the difficulties felt by the patients to inhibit reflexive saccades induced by the
      appearance of unexpected visual stimuli. Indeed, the superior colliculus is involved in the
      orientation of the head and eye toward any sudden changes in our environment (Wurtz and
      Albano, 1980) and the light responses of this structure are strongly correlated with the
      speed of the saccade (Marino et al., 2012).

      Therefore, the investigators want to test if a similar deficit could be observed in the
      superior colliculus of newly diagnosed PD patients. Data will be compared to matching
      controls.
    

Detailed description: 
      This project aims at better understanding the physiopathology of Parkinson's disease and the
      effect of the administration of the classical medical treatment. The main aim of this project
      is to evaluate the possibility of an early detection using a new original strategy. The
      investigators want to demonstrate the predictive value of the superior colliculus light
      responses as an early biomarker.

      The investigators will perform functional magnetic resonance imagery (fMRI) to measure the
      BOLD light responses of the superior colliculus at different key stages of the normal medical
      follow up of Parkinson's patients by the neurologist (when diagnosed, when introducing the
      first treatment and when the treatment is stabilised).

      Two groups of participants will be tested: a) a group of de novo patients, which have just
      been diagnosed and haven't started their treatment; b) a group of matching controls.

      A first fMRI session (S1) will be performed to compare the light induced BOLD response of the
      superior colliculus between de novo patients and their matching controls. This session will
      evaluate a possible visual processing dysfunction in the superior colliculus of newly
      diagnosed patients.

      Parkinson's patients will then start their treatment and a second session (S2) will be done
      on this group shortly after the introduction of the treatment to measure its acute effect. If
      the superior colliculus of those patients presents a sensory rebound, the investigators
      should observe a bigger light-induced BOLD response after the treatment compared to before
      the treatment.

      A third session (S3) will be performed after the optimal adjustment of the treatment on motor
      symptoms which would be around six month after the start of the treatment. This adjustment is
      long and difficult, realized by the neurologist according to its effect on the motor
      symptoms. Those two last fMRI will allow the investigators to compare the effect of the
      introduction of the treatment on the motor symptoms, known to not improve correctly at this
      stage, and on non-motor symptoms (visual processing deficits in this project) from which no
      information are available to the investigators knowledge.
    

Intervention name(s): fMRI; Ophthalmologic evaluation; visual psychophysics test
Intervention type(s): Other; Other; Other
Intervention description(s): The investigators will use a non invasive fMRI technique centred on the superior colliculus during the presentation of flickered check-boards with varying contrast (1, 3, 5 and 9 %).; The aim of this experiment is the evaluate the functional state of a visual structure. Therefore, with this ophthalmologic test, the investigators will control if the participant does not present major visual deficits. This examination will evaluate the visual acuity and the visual field. A funduscopic examination will also be performed to check the retina.; This test will allow to control the sensitivity of the participant to our contrast. The participant will be asked to look at screen on which three static check-boards will be presented. The participant will have to choose the two check-boards with the closest contrast.
Observational model: Case-Control
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Groups of de novo Parkinson's patients and their age matching controls.
      
Keywords: Parkinson's disease; Non-motor symptoms; Visual deficits; Superior colliculus; fMRI