CCNi

Centre for Cognitive Neuroimaging

   Functional MRI (fMRI) allows the non-invasive measurement of neuronal activity in normal participants. It is based on the 'BOLD effect', which consists of measuring local magnetic changes caused by increases in blood oxygenation that accompany neuronal activity. The resulting images of cerebral activity have a very good spatial resolution - a few millimetres - although the temporal resolution is far from excellent (changes in blood oxygenation are typically delayed by 3-5 seconds after the onset of neuronal activity because of the sluggishness of the vascular response).

   fMRI is a recent technique: the first cognitive neuroscience application of fMRI was published in 1991. However, it has rapidly become one of the most extensively used techniques in cognitive neuroimaging mainly because of two main advantages. First, fMRI yields statistically robust maps of cerebral activity in single subjects after a one-hour session - in contrast to older techniques such as positron emission tomography that require averaging measures from a large group of subjects. Second, it does not require any injection: subjects are simply put in a strong magnet that allows the detection of slight changes in local magnetic fields caused by changes in blood oxygenation. There are no known side effects associated with this technique. 


Image1.jpgfMRI subject preparation: a participant, ready to be entered in the scanner, is equipped with  MRI-compatible sound transmitters and a 45°-tilted mirror above the eyes for visual  stimulation via projection on a screen at the back of the scanner.

Image2.jpgfMRI acquisition and analysis: a series of T2* cerebral images is acquired at regular intervals, while the participant is placed in different cognitive conditions. Analysis consists of measuring BOLD signal changes between the different conditions for each cerebral voxel. The resulting information can be viewed as a statistical map showing cortical regions in which activity is significantly different during the different conditions (courtesy of J. Culham).

CCNi includes a ultra-high field scanner (3 Tesla) and state-of-the-art equipment for sensory stimulation, measure of eye movements and physiological signals such as heart rate, skin conductance, etc. An fMRI-compatible EEG system will also allow joint recording of fMRI and EEG signals. Experiments, conducted in normal adult volunteers, will investigate issues related to ongoing research within the Department such as auditory cognition, high-level vision and cognition, perception and action.

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 Example of auditory fMRI experiment: contrasting conditions of auditory stimulation with vocal vs. non-vocal sounds (above) highlights "voice-selective" regions in human auditory cortex.



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Example of visual fMRI experiment: Cortical activity in primary visual cortex (V1) representing the illusory motion trace (green) of an apparent motion illusion.

 

 



Selected References
Belin P, Zatorre RJ, Lafaille P, Ahad P, Pike B. 
Voice-selective areas in human auditory cortex. (2000) Nature, 403:309-12.

Belliveau J, Kennedy D, McKinstry R, Buchbinder B, Weisskoff R, Cohen M, Vevea J, Brady T, Rosen B (1991).
Functional mapping of the human visual cortex by magnetic resonance imaging Science, 254: 716-719.

Culham, J. “fMRI for dummies”
ttp://defiant.ssc.uwo.ca/Jody_web/fmri4dummies.htm

Grosbras MH, PausT. (2005) Brain Networks Involved in Viewing Angry Hands or Faces Cerebral Cortex.

Huettel, SA, Song, AW, McCarthy, G. (2004)  Functional Magnetic Resonance Imaging Sinauer Associates, Inc., Sunderland, Massachussets, USA.

Muckli, L., A. Kohler, N. Kriegeskorte & W. Singer.
Primary visual cortex activity along the apparent-motion trace reflects illusory perception (2005). PLoS Biol. Jul 19;3(8):e265-275
Facilities Overview Facilities Labs functional Magnetic Resonance Imaging (fMRI)