1. Un potentiel évoqué (PE) désigne la modification du potentiel électrique produite par le système nerveux en réponse à une stimulation externe, notamment sensorielle (un son, une image, etc.) mais aussi à un événement interne, notamment une activité cognitive (attention, préparation motrice, etc.). In English, this is called an Event-‐Related Potential (ERP). The ERP is the measured electrophysiological response to a sensory, cognitive, or motor stimulus. An ERP occurs when a large number of neurons fire at the same time while processing information. Le potentiel évoqué visuel (PEV) et le potentiel évoqué auditif (PEA) sont deux types des PE exogènes. Pour PEV, L'intérêt est de tester les voies optiques, soit par visualisation de motifs alternés types "damiers", soit par Flash lumineux. Pour PEA, L'intérêt est de vérifier les voies auditives à l'aide d'une stimulation monoaurale. In English, the PEV is the visual ERP and the PEA is the auditory ERP. They are the ERPs measured in response to a visual stimulus or an auditory stimulus. Sensory ERPs, like PEV and PEA, often occur within 100 ms after the stimulus. NIRS (la spectroscopie proche infrarouge) est une méthode spectroscopique utilisée dans la gamme infrarouge du spectre électromagnétique. In English, NIRS (near-‐ infrared spectroscopy) is a spectroscopic method that uses the near-‐infrared region of the electromagnetic spectrum (800 nm to 2500 nm). NIRS can be used to non-‐ invasively measure brain activity by detecting changes in blood hemoglobin concentration. If there is more hemoglobin in a particular brain region, it means there is more blood flow and therefore more brain activity. NIRS can only be used to measure activity in the cortex (outermost layer of the brain). 2. Goal: To use NIRS to study PEV and PEA. 3. Introduction: Please use information from 1. In addition, PEV and PEA are usually measured with EEG (electroencephalography), which non-‐invasively measures electrical activity of the brain over time using electrodes placed on the scalp. Here, we will use NIRS instead. We can also use EEG at the same time to see if the results match. EEG is good at measuring the timing of brain responses, but it is not good at measuring where the brain response is. If the results match, we should see that NIRS and EEG measure brain activation at the same time. 4. Materials: NIRS equipment, EEG equipment, visual and auditory stimuli
5. Schema: NIRS: Here is a picture of NIRS. The subject is wearing a cap with probes, and the scientist can see which parts of the brain are activated on the screen.
EEG: Here is a picture of how PEA is measured with EEG.
Researchers have also been able to combine the NIRS and EEG caps into one cap, so they can measure NIRS and EEG at the same time.
6. Procedure: Are you doing this experiment in class, or are you asked to come up with your own procedure? If you are creating your own procedure, I think you should measure NIRS and EEG at the same time with the NIRS-‐EEG cap. You can give the patient visual and auditory stimuli to evoke PEV and PEA, and measure the responses with NIRS and EEG. 7 and 8. Measures and Results: Are you doing this experiment and getting results in class, or are you asked to create theoretical results? If you are creating your own results, the NIRS results for a visual stimulus (PEV) should be brain activation in the visual cortex (green in the picture). The NIRS results for auditory stimulus (PEA) should be brain activation in the auditory cortex (purple in the picture).
The EEG results for PEV and PEA should look something like this (picture). It shows brain activation (in terms of voltage) over time.
9. Discussion: The theoretical prediction is that NIRS and EEG should show brain activation at the same time, in response to a visual or auditory stimulus. We also predict that NIRS should show brain activation in the correct brain regions (visual cortex for PEV, auditory cortex for PEA).
