Can fMRI probe fast dynamics of neural system-interaction
occurring at milliseconds time scale?

Seiji Ogawa

Biological Computation Research
Bell Laboratories, Lucent Technologies

Room 3L 407
700 Mountain Ave.
Murray Hill, New Jersey 07974

Phone:908 582 3477 or 3216,
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Functional MRI is known to have a very slow response time of many seconds in contrast to the neuronal event that occurs within tens of milliseconds. Therefore, to follow the dynamics of neural events, fMRI is only useful to detect temporal changes slower than several tenth of a second at best. On the other hand, the signal strength is well coupled to the neuronal activation rather quantitatively. When there is a change in the level of neural system activation, the change should appear in the fMRI signal intensity. Such neural events may occur at a very fast neural time scale, but their temporal aspect may be tractable by fMRI. In order to show that an approach to probe some fast interaction between neural systems is possible, firstly we checked that fMRI signal is highly coupled to the electrical event of neural system activation. We have used a rat model with simultaneous measurements of ERP and fMRI to compare the two phenomena. Furthermore, when a neural system is perturbed by another neural event, the activation of the system is modulated by the perturbation and the ERP as well as fMRI signals can reflect such modulation The temporal information of such system-system interaction can be obtained by varying the temporal relation of event-inducing tasks in the fMRI paradigm so that one can modify the extent of the interaction. Examples of such cases, including a refractory process of neural origin, cross hemisphere inhibitory interaction, are shown. An application in the human brain has also been tested.