fMRI & GABA Spectroscopy D. G. Norris

Our work falls into three main categories:

1. Methods development for neuroimaging

In this category we have mainly concentrated our efforts on simultaneous multislice imaging techniques, which make it possible to substantially accelerate data acquisition and also in some situations to also reduce the power deposited during an examination. One example is the turbo spin-echo (TSE) technique that is widely used at standard field strengths, but was hitherto restricted at 7T by high power deposition. The image shows a TSE image obtained at 7T in two minutes at 80% of the maximum allowed power compared to 6.5 minutes for the same data obtained with standard techniques at 100% power deposition.

2. Laminar resolution functional MRI

Improving the spatial resolution of fMRI to better than 1mm isotropic makes it possible to explore activation not only at the level of brain regions, but also to look at the activation as a function of depth within grey matter. There are six histological layers within grey matter, having different functions and connectivity patterns. As an example we explored primary visual cortex in two conditions: seeing an illusionary triangle and not seeing it. In both cases the visual input is identical, but when the illusion is seen there is increased activity in the lower layers corresponding to input from higher visual regions.

3. GABA spectroscopy

Gamma-amino butyric acid (GABA) is the main inhibitory neurotransmitter in the brain, and is detectable with proton magnetic resonance spectroscopy. The signal is however weak, and masked by the signal of other metabolites. It can be detected by using editing techniques, which we have implemented at 7T. We have been able to show that the tonic level of GABA in brain regions associated with memory formation is a predictor of memory performance.

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